text
stringlengths 2
132k
| source
dict |
|---|---|
The molecular formula C19H28N4O2 (molar mass: 344.459 g/mol) may refer to: ADB-PINACA ADB-P7AICA
|
{
"page_id": 43254635,
"source": null,
"title": "C19H28N4O2"
}
|
Emulsified fuels are a type of emulsion that combines water with a combustible liquid, such as oil or fuel. An emulsion is a specialized form of dispersion that contains both a continuous phase and a dispersed phase. The most commonly utilized emulsified fuel is a water-in-diesel emulsion (also known as hydrodiesel). In these emulsions, the two phases are immiscible liquids—water and oil. Emulsified fuels can be categorized as either microemulsions or conventional emulsions (sometimes called macroemulsions to distinguish them from microemulsions). The main differences between these types are related to stability and particle size. Microemulsions are thermodynamically stable, forming spontaneously with particle sizes of 10 to 200 nm. In contrast, macroemulsions are kinetically stabilized, created through a shearing process, with particle sizes ranging from 100 nm to over 1 micrometer. While microemulsions are isotropic, macroemulsions may undergo settling (or creaming) over time and experience changes in particle size. Both types use surfactants (also known as emulsifiers) and can be water-in-oil (inverted emulsions), oil-in-water (regular emulsions), or bicontinuous (also called multiple or complex emulsions). == Applications == Oil-in-water emulsified fuels, such as the Orimulsion system and bitumen emulsions, are examples of water-continuous systems. These emulsions are often considered high internal phase emulsions (HIPE) because the continuous phase makes up about 30% of the fuel composition, whereas the dispersed phase is usually the minor component. Emulsions of heavy crude oils and bitumen are easier to pump than their original forms, which typically require heating or dilution with light oils like kerosene to facilitate handling. Emulsions of residual fuels, including heavy fuel oils used in industrial applications, can also be created to reduce the reliance on cutter fluids and improve combustion emissions from lower-quality fuels. Water-in-oil emulsified fuels, such as diesel and biodiesel-water emulsions, are widely used in Europe, with standards established by
|
{
"page_id": 32310124,
"source": null,
"title": "Emulsified fuel"
}
|
the CEN workshop (CWA 15145:2004). These emulsions usually contain between 5% and 30% water by mass. Water-in-diesel emulsions can serve as alternative fuels, offering lower emissions and improved brake thermal efficiency. Since 2006, Nonox Ltd. has offered on-demand water-in-fuel emulsions for heavy fuel oil (HFO) and diesel, used in shipping and stationary boilers. This approach, known as Emulsion to Combustion (E2C), allows for mixing without chemical surfactants, the adjustment of the water-to-fuel ratio based on load, and prevents separation during storage. This system has demonstrated reductions in soot emissions of up to 90% and NOx emissions by 40%, while also delivering fuel savings depending on baseline efficiency. Microemulsions of fuels have been prepared using specific types of surfactants, which differentiate them from other commercial emulsion fuels. These microemulsions are often utilized in contexts where safety (e.g., fire prevention;) or enhanced commercial returns (e.g., improved oil recovery using surfactant flooding;) justify the additional costs. == Theory == The main benefits of using emulsified fuels instead of conventional fuels include environmental and economic advantages. Introducing water into the combustion process reduces temperatures and NOx emissions. Research comparing water injection and emulsified fuels in diesel engines (both marine and stationary) has shown that emulsified fuels are particularly effective at simultaneously decreasing NOx and particulate matter emissions. Additional studies have investigated the impact of exhaust gas recirculation (EGR) and emulsion fuels on diesel engines. == See also == Emulsions – Mixture of two or more immiscible liquidsPages displaying short descriptions of redirect targets Emulsion dispersion – Thermoplastics or elastomers suspended in a liquid state by means of emulsifiers Microemulsion – Thermodynamically stable, isotropic mixture of oil, water, and surfactant Miniemulsion – Particular type of emulsion Pickering emulsion – Type of emulsion Water-in-water emulsion == References == 'Experimental investigation of a Diesel engine power, torque
|
{
"page_id": 32310124,
"source": null,
"title": "Emulsified fuel"
}
|
and noise emission using Water-Diesel emulsions', Mohammad Reza Seifi et al. http://doi.org/10.1016/j.fuel.2015.10.122 == External links == Serdyuk, Vasily (2008). "In search of the fuel of the future: In the near future, usual types of motor fuel will be replaced by water-fuel emulsions". Oil of Russia. No. 3. Lukoil. OCLC 74330613.
|
{
"page_id": 32310124,
"source": null,
"title": "Emulsified fuel"
}
|
The switching Kalman filtering (SKF) method is a variant of the Kalman filter. In its generalised form, it is often attributed to Kevin P. Murphy, but related switching state-space models have been in use. == Applications == Applications of the switching Kalman filter include: Brain–computer interfaces and neural decoding, real-time decoding for continuous neural-prosthetic control, and sensorimotor learning in humans. It also has application in econometrics, signal processing, tracking, computer vision, etc. It is an alternative to the Kalman filter when the system's state has a discrete component. The additional error when using a Kalman filter instead of a Switching Kalman filter may be quantified in terms of the switching system's parameters. For example, when an industrial plant has "multiple discrete modes of behaviour, each of which having a linear (Gaussian) dynamics". == Model == There are several variants of SKF discussed in. === Special case === In the simpler case, switching state-space models are defined based on a switching variable which evolves independent of the hidden variable. The probabilistic model of such variant of SKF is as the following: [This section is badly written: It does not explain the notation used below.] Pr ( { S t , X t ( 1 ) , … , X t ( M ) , Y t } ) = Pr ( S 1 ) ∏ t = 2 T Pr ( S t ∣ S t − 1 ) × ∏ m = 1 M Pr ( X 1 ( m ) ) ∏ t = 2 T Pr ( X t ( m ) ∣ X t − 1 ( m ) ) × ∏ t = 1 T Pr ( Y t ∣ X t ( 1 ) , … , X t ( M ) , S t
|
{
"page_id": 53543792,
"source": null,
"title": "Switching Kalman filter"
}
|
) . {\displaystyle {\begin{aligned}&\Pr(\{S_{t},X_{t}^{(1)},\ldots ,X_{t}^{(M)},Y_{t}\})\\={}&\Pr(S_{1})\prod _{t=2}^{T}\Pr(S_{t}\mid S_{t-1})\times \prod _{m=1}^{M}\Pr(X_{1}^{(m)})\prod _{t=2}^{T}\Pr(X_{t}^{(m)}\mid X_{t-1}^{(m)})\times \prod _{t=1}^{T}\Pr(Y_{t}\mid X_{t}^{(1)},\ldots ,X_{t}^{(M)},S_{t}).\end{aligned}}} The hidden variables include not only the continuous X {\displaystyle X} , but also a discrete *switch* (or switching) variable S t {\displaystyle S_{t}} . The dynamics of the switch variable are defined by the term Pr ( S t ∣ S t − 1 ) {\displaystyle \Pr(S_{t}\mid S_{t-1})} . The probability model of X {\displaystyle X} and Y {\displaystyle Y} can depend on S t {\displaystyle S_{t}} . The switch variable can take its values from a set S t ∈ { 1 , 2 , … , M } {\displaystyle S_{t}\in \{1,2,\ldots ,M\}} . This changes the joint distribution ( X t , Y t ) {\displaystyle (X_{t},Y_{t})} which is a separate multivariate Gaussian distribution in case of each value of S t {\displaystyle S_{t}} . === General case === In more generalised variants, the switch variable affects the dynamics of X t {\displaystyle X_{t}} , e.g. through Pr ( X t ∣ X t − 1 , S t ) {\displaystyle \Pr(X_{t}\mid X_{t-1},S_{t})} . The filtering and smoothing procedure for general cases is discussed in. == References ==
|
{
"page_id": 53543792,
"source": null,
"title": "Switching Kalman filter"
}
|
Cytoplasm-to-vacuole targeting (CVT) is an autophagy-related pathway which occurs in fungi and specifically yeasts. This is a mechanism occurs under starvation conditions and moves molecules from the cytoplasm to vacuoles. This pathway is a production of complex molecules resulting in the digestion of cytoplasm components. Cell cytoplasm and vacuoles play key roles in this pathway and are primarily responsible for its function. The acronym CVT stands for Cytoplasm Vacuole Targeting. This pathway consists of components from the cytoplasm which are targeted for transport to cell vacuoles and digested. == CVT pathway == The CVT pathway targets the enzymes alpha-mannosidase and aminopeptidase I (Ape I). These hydrolases are present within the cytoplasm of cells, hence why they are selected and targeted for vacuole delivery and digestion. During this process cells digest components of their own cytoplasm. This is done with through the use of enzymes, specifically hydrolases. These are enzymes specifically designated for catalyzing molecule breakdown through the addition of water. Under vegetative conditions it delivers the hydrolase aminopeptidase 1 (Ape1), to the vacuole. Hydrolases are a class of enzymes which serve as catalysts for biochemical reactions; speeding up reaction rates. The main function of Hydrolases is to break down nutrients into smaller components to be easily digested, through the use of water to break bonds. These components make the CVT pathway the only known biosynthetic pathway to utilize the machinery of autophagy for operation. == Organelles == The cytoplasm and vacuole of cells are two very important organelles, designed to carry out many biological cell functions. The cytoplasm of a cell fills the interior spaces of a cell and is responsible for holding organelles in place, protecting the cell and is where many biochemical interactions occur-including transport, and protein folding. Vacuoles are membrane bound organelles and is responsible for holding
|
{
"page_id": 34276211,
"source": null,
"title": "Cytoplasm-to-vacuole targeting"
}
|
of excess water and removal of waste. Understanding the functions of these organelles is imperative for understanding their complex relationship that occurs in the Cytoplasm to Vacuole Targeting Pathway (CVT). == In yeast == One of the main organisms in which the CVT pathway occurs is in fungi- in the form of yeasts. Saccharomyces cerevisiae (S. cerevisiae) is a main source of nutritional yeast, where this pathway is common. In yeasts CVT pathway uses selective targeting for hydrolases alpha-mannosidase and aminopeptidase I (Ape I). These are present in yeast cytoplasm and are selected for transport to the cells vacuole where they are digested. == References ==
|
{
"page_id": 34276211,
"source": null,
"title": "Cytoplasm-to-vacuole targeting"
}
|
The Thorpe reaction is a chemical reaction described as a self-condensation of aliphatic nitriles catalyzed by base to form enamines. The reaction was discovered by Jocelyn Field Thorpe. == Thorpe–Ziegler reaction == The Thorpe–Ziegler reaction (named after Jocelyn Field Thorpe and Karl Ziegler), or Ziegler method, is the intramolecular modification with a dinitrile as a reactant and a cyclic ketone as the final reaction product after acidic hydrolysis. The reaction is conceptually related to the Dieckmann condensation. == References == == External links == Thorpe-Ziegler reaction: 4-Phosphorinanone, 1-phenyl- Organic Syntheses, Coll. Vol. 6, p. 932 (1988); Vol. 53, p. 98 (1973) Link
|
{
"page_id": 7340915,
"source": null,
"title": "Thorpe reaction"
}
|
Modern spectroscopy in the Western world started in the 17th century. New designs in optics, specifically prisms, enabled systematic observations of the solar spectrum. Isaac Newton first applied the word spectrum to describe the rainbow of colors that combine to form white light. During the early 1800s, Joseph von Fraunhofer conducted experiments with dispersive spectrometers that enabled spectroscopy to become a more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics and astronomy. Fraunhofer observed and measured dark lines in the Sun's spectrum, which now bear his name although several of them were observed earlier by Wollaston. == Origins and experimental development == The Romans were already familiar with the ability of a prism to generate a rainbow of colors. Newton is traditionally regarded as the founder of spectroscopy, but he was not the first scientist who studied and reported on the solar spectrum. The works of Athanasius Kircher (1646), Jan Marek Marci (1648), Robert Boyle (1664), and Francesco Maria Grimaldi (1665), predate Newton's optics experiments (1666–1672). Newton published his experiments and theoretical explanations of dispersion of light in his Opticks. His experiments demonstrated that white light could be split up into component colors by means of a prism and that these components could be recombined to generate white light. He demonstrated that the prism is not imparting or creating the colors but rather separating constituent parts of the white light. Newton's corpuscular theory of light was gradually succeeded by the wave theory. It was not until the 19th century that the quantitative measurement of dispersed light was recognized and standardized. As with many subsequent spectroscopy experiments, Newton's sources of white light included flames and stars, including the Sun. Subsequent studies of the nature of light include those of
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
Hooke, Huygens, Young. Subsequent experiments with prisms provided the first indications that spectra were associated uniquely with chemical constituents. Scientists observed the emission of distinct patterns of colour when salts were added to alcohol flames. === Early 19th century (1800–1829) === In 1802, William Hyde Wollaston built a spectrometer, improving on Newton's model, that included a lens to focus the Sun's spectrum on a screen. Upon use, Wollaston realized that the colors were not spread uniformly, but instead had missing patches of colors, which appeared as dark bands in the sun's spectrum. At the time, Wollaston believed these lines to be natural boundaries between the colors, but this hypothesis was later ruled out in 1815 by Fraunhofer's work. Joseph von Fraunhofer made a significant experimental leap forward by replacing a prism with a diffraction grating as the source of wavelength dispersion. Fraunhofer built off the theories of light interference developed by Thomas Young, François Arago and Augustin-Jean Fresnel. He conducted his own experiments to demonstrate the effect of passing light through a single rectangular slit, two slits, and so forth, eventually developing a means of closely spacing thousands of slits to form a diffraction grating. The interference achieved by a diffraction grating both improves the spectral resolution over a prism and allows for the dispersed wavelengths to be quantified. Fraunhofer's establishment of a quantified wavelength scale paved the way for matching spectra observed in multiple laboratories, from multiple sources (flames and the sun) and with different instruments. Fraunhofer made and published systematic observations of the solar spectrum, and the dark bands he observed and specified the wavelengths of are still known as Fraunhofer lines. Throughout the early 1800s, a number of scientists pushed the techniques and understanding of spectroscopy forward. In the 1820s, both John Herschel and William H. F.
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
Talbot made systematic observations of salts using flame spectroscopy. === Mid-19th century (1830–1869) === In 1835, Charles Wheatstone reported that different metals could be easily distinguished by the different bright lines in the emission spectra of their sparks, thereby introducing an alternative mechanism to flame spectroscopy. In 1849, J. B. L. Foucault experimentally demonstrated that absorption and emission lines appearing at the same wavelength are both due to the same material, with the difference between the two originating from the temperature of the light source. In 1853, the Swedish physicist Anders Jonas Ångström presented observations and theories about gas spectra in his work Optiska Undersökningar (Optical investigations) to the Royal Swedish Academy of Sciences. Ångström postulated that an incandescent gas emits luminous rays of the same wavelength as those it can absorb. Ångström was unaware of Foucalt's experimental results. At the same time George Stokes and William Thomson (Kelvin) were discussing similar postulates. Ångström also measured the emission spectrum from hydrogen later labeled the Balmer lines. In 1854 and 1855, David Alter published observations on the spectra of metals and gases, including an independent observation of the Balmer lines of hydrogen. The systematic attribution of spectra to chemical elements began in the 1860s with the work of German physicists Robert Bunsen and Gustav Kirchhoff, who found that Fraunhofer lines correspond to emission spectral lines observed in laboratory light sources. This laid way for spectrochemical analysis in laboratory and astrophysical science. Bunsen and Kirchhoff applied the optical techniques of Fraunhofer, Bunsen's improved flame source and a highly systematic experimental procedure to a detailed examination of the spectra of chemical compounds. They established the linkage between chemical elements and their unique spectral patterns. In the process, they established the technique of analytical spectroscopy. In 1860, they published their findings on the spectra
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
of eight elements and identified these elements' presence in several natural compounds. They demonstrated that spectroscopy could be used for trace chemical analysis and several of the chemical elements they discovered were previously unknown. Kirchhoff and Bunsen also definitively established the link between absorption and emission lines, including attributing solar absorption lines to particular elements based on their corresponding spectra. Kirchhoff went on to contribute fundamental research on the nature of spectral absorption and emission, including what is now known as Kirchhoff's law of thermal radiation. Kirchhoff's applications of this law to spectroscopy are captured in three laws of spectroscopy: An incandescent solid, liquid or gas under high pressure emits a continuous spectrum. A hot gas under low pressure emits a "bright-line" or emission-line spectrum. A continuous spectrum source viewed through a cool, low-density gas produces an absorption-line spectrum. In the 1860s the husband-and-wife team of William and Margaret Huggins used spectroscopy to determine that the stars were composed of the same elements as found on earth. They also used the non-relativistic Doppler shift (redshift) equation on the spectrum of the star Sirius in 1868 to determine its axial speed. They were the first to take a spectrum of a planetary nebula when the Cat's Eye Nebula (NGC 6543) was analyzed. Using spectral techniques, they were able to distinguish nebulae from stars. August Beer observed a relationship between light absorption and concentration and created the color comparator which was later replaced by a more accurate device called the spectrophotometer. === Late 19th century (1870–1899) === In the 19th century new developments such as the discovery of photography, Rowland's invention of the concave diffraction grating, and Schumann's works on discovery of vacuum ultraviolet (fluorite for prisms and lenses, low-gelatin photographic plates and absorption of UV in air below 185 nm) made
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
advance to shorter wavelengths very fast. In 1871, Stoney suggested using a wavenumber scale for spectra and Hartley followed up, finding constant wave-number differences in the triplets of zinc. : I:375 Liveing and Dewar observed that alkali spectra appeared to form a series and Alfred Cornu found similar structure in the spectra of thallium and aluminum, setting the stage for Balmer to discover a relation connecting wavelengths in the visible hydrogen spectrum.: 376 In 1890, Kayser and Runge organized the series reported by Liveing and Dewar using names like 'Principal', 'diffuse', and 'sharp' series. Rydberg gave a formula for wave-numbers of all spectral series of all the alkalis and hydrogen.: 376 In 1895, the German physicist Wilhelm Conrad Röntgen discovered and extensively studied X-rays, which were later used in X-ray spectroscopy. One year later, in 1896, French physicist Antoine Henri Becquerel discovered radioactivity, and Dutch physicist Pieter Zeeman observed spectral lines being split by a magnetic field. In 1897, theoretical physicist, Joseph Larmor explained the splitting of the spectral lines in a magnetic field by the oscillation of electrons. Physicist, Joseph Larmor, created the first solar system model of the atom in 1897. He also postulated the proton, calling it a “positive electron.” He said the destruction of this type of atom making up matter “is an occurrence of infinitely small probability.” === Early 20th century (1900–1950) === The first decade of the 20th century brought the basics of quantum theory (Planck, Einstein) and interpretation of spectral series of hydrogen by Lyman in VUV and by Paschen in infrared. Ritz formulated the combination principle. John William Nicholson had created an atomic model in 1912, a year before Niels Bohr, that was both nuclear and quantum in which he showed that electron oscillations in his atom matched the solar and nebular
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
spectral lines. Bohr had been working on his atom during this period, but Bohr's model had only a single ground state and no spectra until he incorporated the Nicholson model and referenced the Nicholson papers in his model of the atom. In 1913, Bohr formulated his quantum mechanical model of atom. This stimulated empirical term analysis.: 83 Bohr published a theory of the hydrogen-like atoms that could explain the observed wavelengths of spectral lines due to electrons transitioning from different energy states. In 1937 "E. Lehrer created the first fully-automated spectrometer" to help more accurately measure spectral lines. With the development of more advanced instruments such as photo-detectors scientists were then able to more accurately measure specific wavelength absorption of substances. == Development of quantum mechanics == Between 1920 and 1930 fundamental concepts of quantum mechanics were developed by Pauli, Heisenberg, Schrödinger, and Dirac. Understanding of the spin and exclusion principle allowed conceiving how electron shells of atoms are filled with the increasing atomic number. == Multiply ionized atoms == This branch of spectroscopy deals with radiation related to atoms that are stripped of several electrons (multiply ionized atoms (MIA), multiply charged ions, highly charged ions). These are observed in very hot plasmas (laboratory or astrophysical) or in accelerator experiments (beam-foil, electron beam ion trap (EBIT)). The lowest exited electron shells of such ions decay into stable ground states producing photons in VUV, EUV and soft X-ray spectral regions (so-called resonance transitions). === Structure studies === Further progress in studies of atomic structure was in tight connection with the advance to shorter wavelength in EUV region. Millikan, Sawyer, Bowen used electric discharges in vacuum to observe some emission spectral lines down to 13 nm they prescribed to stripped atoms. In 1927 Osgood and Hoag reported on grazing incidence concave grating
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
spectrographs and photographed lines down to 4.4 nm (Kα of carbon). Dauvillier used a fatty acid crystal of large crystal grating space to extend soft x-ray spectra up to 12.1 nm, and the gap was closed. In the same period Manne Siegbahn constructed a very sophisticated grazing incidence spectrograph that enabled Ericson and Edlén to obtain spectra of vacuum spark with high quality and to reliably identify lines of multiply ionized atoms up to O VI, with five stripped electrons. Grotrian developed his graphic presentation of energy structure of the atoms. Russel and Saunders proposed their coupling scheme for the spin-orbit interaction and their generally recognized notation for spectral terms. === Accuracy === Theoretical quantum-mechanical calculations become rather accurate to describe the energy structure of some simple electronic configurations. The results of theoretical developments were summarized by Condon and Shortley in 1935. Edlén thoroughly analyzed spectra of MIA for many chemical elements and derived regularities in energy structures of MIA for many isoelectronic sequences (ions with the same number of electrons, but different nuclear charges). Spectra of rather high ionization stages (e.g. Cu XIX) were observed. The most exciting event was in 1942, when Edlén proved the identification of some solar coronal lines on the basis of his precise analyses of spectra of MIA. This implied that the solar corona has a temperature of a million degrees, and strongly advanced understanding of solar and stellar physics. After the WW II experiments on balloons and rockets were started to observe the VUV radiation of the Sun. (See X-ray astronomy). More intense research continued since 1960 including spectrometers on satellites. In the same period the laboratory spectroscopy of MIA becomes relevant as a diagnostic tool for hot plasmas of thermonuclear devices (see Nuclear fusion) which begun with building Stellarator in 1951 by
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
Spitzer, and continued with tokamaks, z-pinches and the laser produced plasmas. Progress in ion accelerators stimulated beam-foil spectroscopy as a means to measure lifetimes of exited states of MIA. Many various data on highly exited energy levels, autoionization and inner-core ionization states were obtained. === Electron beam ion trap === Simultaneously theoretical and computational approaches provided data necessary for identification of new spectra and interpretation of observed line intensities. New laboratory and theoretical data become very useful for spectral observation in space. It was a real upheaval of works on MIA in USA, England, France, Italy, Israel, Sweden, Russia and other countries A new page in the spectroscopy of MIA may be dated as 1986 with development of EBIT (Levine and Marrs, LLNL) due to a favorable composition of modern high technologies such as cryogenics, ultra-high vacuum, superconducting magnets, powerful electron beams and semiconductor detectors. Very quickly EBIT sources were created in many countries (see NIST summary for many details as well as reviews.) A wide field of spectroscopic research with EBIT is enabled including achievement of highest grades of ionization (U92+), wavelength measurement, hyperfine structure of energy levels, quantum electrodynamic studies, ionization cross-sections (CS) measurements, electron-impact excitation CS, X-ray polarization, relative line intensities, dielectronic recombination CS, magnetic octupole decay, lifetimes of forbidden transitions, charge-exchange recombination, etc. == Infrared and Raman spectroscopy == Many early scientists who studied the IR spectra of compounds had to develop and build their own instruments to be able to record their measurements making it very difficult to get accurate measurements. During World War II, the U.S. government contracted different companies to develop a method for the polymerization of butadiene to create rubber, but this could only be done through analysis of C4 hydrocarbon isomers. These contracted companies started developing optical instruments and eventually created
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
the first infrared spectrometers. With the development of these commercial spectrometers, Infrared Spectroscopy became a more popular method to determine the "fingerprint" for any molecule. Raman spectroscopy was first observed in 1928 by Sir Chandrasekhara Venkata Raman in liquid substances and also by "Grigory Landsberg and Leonid Mandelstam in crystals". Raman spectroscopy is based on the observation of the raman effect which is defined as "The intensity of the scattered light is dependent on the amount of the polarization potential change". The raman spectrum records light intensity vs. light frequency (wavenumber) and the wavenumber shift is characteristic to each individual compound. == Laser spectroscopy == Laser spectroscopy is a spectroscopic technique that uses lasers to be able determine the emitted frequencies of matter. The laser was invented because spectroscopists took the concept of its predecessor, the maser, and applied it to the visible and infrared ranges of light. The maser was invented by Charles Townes and other spectroscopists to stimulate matter to determine the radiative frequencies that specific atoms and molecules emitted. While working on the maser, Townes realized that more accurate detections were possible as the frequency of the microwave emitted increased. This led to an idea a few years later to use the visible and eventually the infrared ranges of light for spectroscopy that became a reality with the help of Arthur Schawlow. Since then, lasers have gone on to significantly advance experimental spectroscopy. The laser light allowed for much higher precision experiments specifically in the uses of studying collisional effects of light as well as being able to accurately detect specific wavelengths and frequencies of light, allowing for the invention of devices such as laser atomic clocks. Lasers also made spectroscopy that used time methods more accurate by using speeds or decay times of photons at specific
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
wavelengths and frequencies to keep time. Laser spectroscopic techniques have been used for many different applications. One example is using laser spectroscopy to detect compounds in materials. One specific method is called Laser-induced Fluorescence Spectroscopy, and uses spectroscopic methods to be able to detect what materials are in a solid, liquid, or gas, in situ. This allows for direct testing of materials, instead of having to take the material to a lab to figure out what the solid, liquid, or gas is made of. == See also == List of spectroscopists Mass spectrometry History of quantum mechanics == References == == External links == MIT Spectroscopy Lab's History of Spectroscopy Spectroscopy Magazine's "A Timeline of Atomic Spectroscopy" Archived 2014-08-09 at the Wayback Machine
|
{
"page_id": 35980148,
"source": null,
"title": "History of spectroscopy"
}
|
Simonellite (1,1-dimethyl-1,2,3,4-tetrahydro-7-isopropyl phenanthrene) is a polycyclic aromatic hydrocarbon with a chemical formula C19H24. It is similar to retene. Simonellite occurs naturally as an organic mineral derived from diterpenes present in conifer resins. It is named after its discoverer, Vittorio Simonelli (1860–1929), an Italian geologist. It forms colorless to white orthorhombic crystals. It occurs in Fognano, Tuscany, Italy. Simonellite, together with cadalene, retene and ip-iHMN, is a biomarker of higher plants, which makes it useful for paleobotanic analysis of rock sediments. == See also == Fichtelite Retene == References ==
|
{
"page_id": 7013240,
"source": null,
"title": "Simonellite"
}
|
The National Standard Examination in Chemistry or NSEC is an examination in chemistry for higher secondary school students in India, usually conducted in the end of November. The examination is organized by the Indian Association of Chemistry Teachers. Over 30,000 students, mainly from Standard 12, sit for this examination. == Eligibility == The examination is intended for students in 12th standard, though 11th standard students are also allowed to take the examination. == Importance == The top 1% students from this examination are selected to sit for the Indian National Chemistry Olympiad. The theory part of the examination is held in the last week of January. The top 30 among all students are selected for the Orientation-Cum-Selection-Camp (OCSC), Chemistry. == Format == The NSEC contains only multiple choice questions. The questions include physical chemistry, organic chemistry, and inorganic chemistry. The stress on biochemistry is more in the NSEC than in the typical school syllabi. == Fee == As per the new revised norms the fee for the NSEC is about Rs. 150. Application for this examination is typically handled through the school/college to which the student is affiliated. == References == == See also == Indian National Chemistry Olympiad India at the IPhO
|
{
"page_id": 8651640,
"source": null,
"title": "National Standard Examination in Chemistry"
}
|
The Poisson–Boltzmann equation describes the distribution of the electric potential in solution in the direction normal to a charged surface. This distribution is important to determine how the electrostatic interactions will affect the molecules in solution. It is expressed as a differential equation of the electric potential ψ {\displaystyle \psi } , which depends on the solvent permitivity ε {\displaystyle \varepsilon } , the solution temperature T {\displaystyle T} , and the mean concentration of each ion species c i 0 {\displaystyle c_{i}^{0}} : ∇ 2 ψ = − 1 ε ∑ i c i 0 q i exp ( − q i ψ ( x , y , z ) k B T ) {\displaystyle \nabla ^{2}\psi =-{\frac {1}{\varepsilon }}\sum _{i}c_{i}^{0}q_{i}\exp \left({\frac {-q_{i}\psi (x,y,z)}{k_{B}T}}\right)} The Poisson–Boltzmann equation is derived via mean-field assumptions. From the Poisson–Boltzmann equation many other equations have been derived with a number of different assumptions. == Origins == === Background and derivation === The Poisson–Boltzmann equation describes a model proposed independently by Louis Georges Gouy and David Leonard Chapman in 1910 and 1913, respectively. In the Gouy-Chapman model, a charged solid comes into contact with an ionic solution, creating a layer of surface charges and counter-ions or double layer. Due to thermal motion of ions, the layer of counter-ions is a diffuse layer and is more extended than a single molecular layer, as previously proposed by Hermann Helmholtz in the Helmholtz model. The Stern Layer model goes a step further and takes into account the finite ion size. The Gouy–Chapman model explains the capacitance-like qualities of the electric double layer. A simple planar case with a negatively charged surface can be seen in the figure below. As expected, the concentration of counter-ions is higher near the surface than in the bulk solution. The Poisson–Boltzmann equation
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
describes the electrochemical potential of ions in the diffuse layer. The three-dimensional potential distribution can be described by the Poisson equation ∇ 2 ψ = ∂ 2 ψ ∂ x 2 + ∂ 2 ψ ∂ y 2 + ∂ 2 ψ ∂ z 2 = − ρ e ε , {\displaystyle \nabla ^{2}\psi ={\frac {\partial ^{2}\psi }{\partial x^{2}}}+{\frac {\partial ^{2}\psi }{\partial y^{2}}}+{\frac {\partial ^{2}\psi }{\partial z^{2}}}=-{\frac {\rho _{e}}{\varepsilon }},} where ρ e {\displaystyle \rho _{e}} is the local electric charge density in C/m3, ε {\displaystyle \varepsilon } is the permittivity of the solvent, ψ is the electric potential. The freedom of movement of ions in solution can be accounted for by Boltzmann statistics. The Boltzmann equation is used to calculate the local ion density such that c i = c i 0 ⋅ exp ( − W i k B T ) , {\displaystyle c_{i}=c_{i}^{0}\cdot \exp \left({\frac {-W_{i}}{k_{\mathrm {B} }T}}\right),} where c i 0 {\displaystyle c_{i}^{0}} is the ion concentration at the bulk, W i {\displaystyle W_{i}} is the work required to move an ion closer to the surface from an infinitely far distance, k B {\displaystyle k_{\mathrm {B} }} is the Boltzmann constant, T {\displaystyle T} is the temperature in kelvins. The equation for local ion density can be substituted into the Poisson equation under the assumptions that the work being done is only electric work, and that the concentration of salt is much higher than the concentration of ions. The electric work to bring an ion of charge q i {\displaystyle q_{i}} to a surface with potential ψ can be represented by W i = q i ψ {\displaystyle W_{i}=q_{i}\psi } . These work equations can be substituted into the Boltzmann equation, producing an expression for the concentration of each ion species c i = c
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
i 0 exp ( − q i ψ ( x , y , z ) k B T ) {\displaystyle c_{i}=c_{i}^{0}\exp \left(-{\frac {q_{i}\psi (x,y,z)}{k_{B}T}}\right)} . Substituting this Boltzmann relation into the local electric charge density expression, the following expression can be obtained ρ e = ∑ i c i q i = ∑ i c i 0 q i exp ( − q i ψ ( x , y , z ) k B T ) . {\displaystyle \rho _{e}=\sum _{i}c_{i}q_{i}=\sum _{i}c_{i}^{0}q_{i}\exp \left({\frac {-q_{i}\psi (x,y,z)}{k_{B}T}}\right).} Finally the charge density can be substituted into the Poisson equation to produce the Poisson–Boltzmann equation: When distance is measured as multiples of Bjerrum length l b {\displaystyle l_{b}} and potential is measured in multiples of k B T / e {\displaystyle k_{B}T/e} then the equation can be rearranged to dimensionless form ∇ 2 ψ = 2 c 0 ( l b ) 3 sinh ( ψ ) . {\displaystyle \nabla ^{2}\psi =2c_{0}(l_{b})^{3}\sinh \left(\psi \right).} === Related theories === The Poisson–Boltzmann equation can take many forms throughout various scientific fields. In biophysics and certain surface chemistry applications, it is known simply as the Poisson–Boltzmann equation. It is also known in electrochemistry as Gouy-Chapman theory; in solution chemistry as Debye–Huckel theory; in colloid chemistry as Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Only minor modifications are necessary to apply the Poisson–Boltzmann equation to various interfacial models, making it a highly useful tool in determining electrostatic potential at surfaces. == Solving analytically == Because the Poisson–Boltzmann equation is a partial differential of the second order, it is commonly solved numerically; however, with certain geometries, it can be solved analytically. === Geometries === The geometry that most easily facilitates this is a planar surface. In the case of an infinitely extended planar surface, there are two dimensions in which
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
the potential cannot change because of symmetry. Assuming these dimensions are the y and z dimensions, only the x dimension is left. Below is the Poisson–Boltzmann equation solved analytically in terms of a second order derivative with respect to x. d 2 ψ d x 2 = c 0 e ε ⋅ [ e e ψ ( x ) k B T − e − e ψ ( x ) k B T ] {\displaystyle {\frac {d^{2}\psi }{dx^{2}}}={\frac {c_{0}e}{\varepsilon }}\cdot \left[e^{\frac {e\psi (x)}{k_{\mathrm {B} }T}}-e^{\frac {-e\psi (x)}{k_{\mathrm {B} }T}}\right]} Analytical solutions have also been found for axial and spherical cases in a particular study. The equation is in the form of a logarithm of a power series and it is as follows: d 2 ψ d r 2 + L r d ψ d r = e ψ − δ e − ψ {\displaystyle {\frac {d^{2}\psi }{dr^{2}}}+{\frac {L}{r}}{\frac {d\psi }{dr}}=e^{\psi }-\delta e^{-\psi }} It uses a dimensionless potential ψ = e Φ k T {\displaystyle \psi ={\frac {e\Phi }{kT}}} and the lengths are measured in units of the Debye electron radius in the region of zero potential R e D = k T 4 π e 2 n e 0 {\displaystyle R_{eD}={\sqrt {\frac {kT}{4\pi e^{2}n_{e0}}}}} (where n e 0 {\displaystyle n_{e0}} denotes the number density of negative ions in the zero potential region). For the spherical case, L=2, the axial case, L=1, and the planar case, L=0. === Low-potential vs high-potential cases === When using the Poisson–Boltzmann equation, it is important to determine if the specific case is low or high potential. The high-potential case becomes more complex so if applicable, use the low-potential equation. In the low-potential condition, the linearized version of the Poisson–Boltzmann equation (shown below) is valid, and it is commonly used as it is more simple
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
and spans a wide variety of cases. ψ = ψ 0 e − K x {\displaystyle \psi =\psi _{0}e^{-\mathrm {K} x}} ==== Low-potential case conditions ==== Strictly, low potential means that e | ψ | ≪ k B T {\displaystyle e\left\vert \psi \right\vert \ll k_{\mathrm {B} }T} ; however, the results that the equations yields are valid for a wider range of potentials, from 50–80mV. Nevertheless, at room temperature, ψ ≤ 25 m V {\displaystyle \psi \leq \mathrm {25mV} } and that is generally the standard. Some boundary conditions that apply in low potential cases are that: at the surface, the potential must be equal to the surface potential and at large distances from the surface the potential approaches a zero value. This distance decay length is yielded by the Debye length λ D {\displaystyle \lambda _{D}} equation. K = 2 c 0 e 2 ε k B T {\displaystyle \mathrm {K} ={\sqrt {\frac {2c_{0}e^{2}}{\varepsilon k_{\mathrm {B} }T}}}} λ D = K − 1 {\displaystyle \lambda _{D}=\mathrm {K} ^{-1}} As salt concentration increases, the Debye length decreases due to the ions in solution screening the surface charge. A special instance of this equation is for the case of 25 ∘ C {\displaystyle 25^{\circ }C} water with a monovalent salt. The Debye length equation is then: λ D = 0.304 n m c 0 {\displaystyle \lambda _{D}={\frac {\mathrm {0.304nm} }{\sqrt {c_{0}}}}} where c 0 {\displaystyle c_{0}} is the salt concentration in mol/L. These equations all require 1:1 salt concentration cases, but if ions that have higher valence are present, the following case is used. K = e 2 ε k B T ∑ c i Z i 2 {\displaystyle \mathrm {K} ={\sqrt {{\frac {e^{2}}{\varepsilon k_{\mathrm {B} }T}}\sum c_{i}{Z_{i}}^{2}}}} == High-potential case == The high-potential case is referred to as the “full
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
one-dimensional case”. In order to obtain the equation, the general solution to the Poisson–Boltzmann equation is used and the case of low potentials is dropped. The equation is solved with a dimensionless parameter y ≡ e ψ k B T {\displaystyle y\equiv {\frac {e\psi }{k_{B}T}}} , which is not to be confused with the spatial coordinate symbol, y. Employing several trigonometric identities and the boundary conditions that at large distances from the surface, the dimensionless potential and its derivative are zero, the high potential equation is revealed. e − K x = ( e y / 2 − 1 ) ( e y 0 / 2 + 1 ) ( e y / 2 + 1 ) ( e y 0 / 2 − 1 ) {\displaystyle e^{-\mathrm {K} x}={\frac {(e^{y/2}-1)(e^{y_{0}/2}+1)}{(e^{y/2}+1)(e^{y_{0}/2}-1)}}} This equation solved for e y / 2 {\displaystyle e^{y/2}} is shown below. e y / 2 = e y 0 / 2 + 1 + ( e y 0 / 2 − 1 ) ⋅ e − K x e y 0 / 2 + 1 − ( e y 0 / 2 − 1 ) ⋅ e − K x {\displaystyle e^{y/2}={\frac {e^{y_{0}/2}+1+(e^{y_{0}/2}-1)\cdot e^{-\mathrm {K} x}}{e^{y_{0}/2}+1-(e^{y_{0}/2}-1)\cdot e^{-\mathrm {K} x}}}} In order to obtain a more useful equation that facilitates graphing high potential distributions, take the natural logarithm of both sides and solve for the dimensionless potential, y. y = 2 ln e y 0 / 2 + 1 + ( e y 0 / 2 − 1 ) ⋅ e − K x e y 0 / 2 + 1 − ( e y 0 / 2 − 1 ) ⋅ e − K x {\displaystyle y=2\ln {\frac {e^{y_{0}/2}+1+(e^{y_{0}/2}-1)\cdot e^{-\mathrm {K} x}}{e^{y_{0}/2}+1-(e^{y_{0}/2}-1)\cdot e^{-\mathrm {K} x}}}} Knowing that y ≡ e ψ k B T {\displaystyle y\equiv
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
{\frac {e\psi }{k_{B}T}}} , substitute this for y in the previous equation and solve for ψ {\displaystyle \psi } . The following equation is rendered. ψ = 2 k B T e ⋅ ln e y 0 / 2 + 1 + ( e y 0 / 2 − 1 ) ⋅ e − K x e y 0 / 2 + 1 − ( e y 0 / 2 − 1 ) ⋅ e − K x {\displaystyle \psi ={\frac {2k_{B}T}{e}}\cdot \ln {\frac {e^{y_{0}/2}+1+(e^{y_{0}/2}-1)\cdot e^{-\mathrm {K} x}}{e^{y_{0}/2}+1-(e^{y_{0}/2}-1)\cdot e^{-\mathrm {K} x}}}} y 0 = e ψ 0 k B T {\displaystyle y_{0}={\frac {e\psi _{0}}{k_{B}T}}} === Conditions === In low potential cases, the high potential equation may be used and will still yield accurate results. As the potential rises, the low potential, linear case overestimates the potential as a function of distance from the surface. This overestimation is visible at distances less than half the Debye length, where the decay is steeper than exponential decay. The following figure employs the linearized equation and the high potential graphing equation derived above. It is a potential-versus-distance graph for varying surface potentials of 50, 100, 150, and 200 mV. The equations employed in this figure assume an 80mM NaCl solution. == General applications == The Poisson–Boltzmann equation can be applied in a variety of fields mainly as a modeling tool to make approximations for applications such as charged biomolecular interactions, dynamics of electrons in semiconductors or plasma, etc. Most applications of this equation are used as models to gain further insight on electrostatics. === Physiological applications === The Poisson–Boltzmann equation can be applied to biomolecular systems. One example is the binding of electrolytes to biomolecules in a solution. This process is dependent upon the electrostatic field generated by the molecule, the electrostatic potential
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
on the surface of the molecule, as well as the electrostatic free energy. The linearized Poisson–Boltzmann equation can be used to calculate the electrostatic potential and free energy of highly charged molecules such as tRNA in an ionic solution with different number of bound ions at varying physiological ionic strengths. It is shown that electrostatic potential depends on the charge of the molecule, while the electrostatic free energy takes into account the net charge of the system. Another example of utilizing the Poisson–Boltzmann equation is the determination of an electric potential profile at points perpendicular to the phospholipid bilayer of an erythrocyte. This takes into account both the glycocalyx and spectrin layers of the erythrocyte membrane. This information is useful for many reasons including the study of the mechanical stability of the erythrocyte membrane. ==== Electrostatic free energy ==== The Poisson–Boltzmann equation can also be used to calculate the electrostatic free energy for hypothetically charging a sphere using the following charging integral: Δ G el = ∫ τ q U ( τ ′ ) d τ ′ {\displaystyle \Delta G^{\text{el}}=\int ^{\tau }qU(\tau ')\,d\tau '} where τ q {\displaystyle \tau q} is the final charge on the sphere The electrostatic free energy can also be expressed by taking the process of the charging system. The following expression utilizes chemical potential of solute molecules and implements the Poisson-Boltzmann Equation with the Euler-Lagrange functional: Δ G el = ∫ V ( k T ∑ i c i ∞ [ 1 − exp ( − z i q U k T ) ] + p f U − − ε ( ∇ U ) 2 8 π ) d V {\displaystyle \Delta G^{\text{el}}=\int _{V}\left(kT\sum _{i}c_{i}^{\infty }\left[1-\exp \left({\frac {-z_{i}qU}{kT}}\right)\right]+p^{f}U-{\frac {-\varepsilon ({\boldsymbol {\nabla }}U)^{2}}{8\pi }}\right)dV} Note that the free energy is independent of the charging
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
pathway [5c]. The above expression can be rewritten into separate free energy terms based on different contributions to the total free energy Δ G el = Δ G ef + Δ G em + Δ G mob + Δ G solv {\displaystyle \Delta G^{\text{el}}=\Delta G^{\text{ef}}+\Delta G^{\text{em}}+\Delta G^{\text{mob}}+\Delta G^{\text{solv}}} where Electrostatic fixed charges = Δ G ef = ∫ V p f U 2 d V {\displaystyle \Delta G^{\text{ef}}=\int _{V}{\frac {p^{f}U}{2}}dV} Electrostatic mobile charges = Δ G em = ∫ V ∑ i c i z i q U 2 d V {\displaystyle \Delta G^{\text{em}}=\int _{V}{\frac {\sum _{i}c_{i}z_{i}qU}{2}}dV} Entropic free energy of mixing of mobile species = Δ G mob = k T ∫ V c i ln c i c i ∞ d V {\displaystyle \Delta G^{\text{mob}}=kT\int _{V}c_{i}\ln {\frac {c_{i}}{c_{i}^{\infty }}}dV} Entropic free energy of mixing of solvent = Δ G solv = k T ∫ V ∑ i c i ∞ [ 1 − exp ( − z i q U k T ) ] d V {\displaystyle \Delta G^{\text{solv}}=kT\int _{V}\sum _{i}c_{i}^{\infty }\left[1-\exp \left({\frac {-z_{i}qU}{kT}}\right)\right]dV} Finally, by combining the last three term the following equation representing the outer space contribution to the free energy density integral Δ G out = Δ G em + Δ G mob + Δ G solv {\displaystyle \Delta G^{\text{out}}=\Delta G^{\text{em}}+\Delta G^{\text{mob}}+\Delta G^{\text{solv}}} These equations can act as simple geometry models for biological systems such as proteins, nucleic acids, and membranes. This involves the equations being solved with simple boundary conditions such as constant surface potential. These approximations are useful in fields such as colloid chemistry. === Materials science === An analytical solution to the Poisson–Boltzmann equation can be used to describe an electron-electron interaction in a metal-insulator semiconductor (MIS). This can be used to describe both time and position dependence of dissipative
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
systems such as a mesoscopic system. This is done by solving the Poisson–Boltzmann equation analytically in the three-dimensional case. Solving this results in expressions of the distribution function for the Boltzmann equation and self-consistent average potential for the Poisson equation. These expressions are useful for analyzing quantum transport in a mesoscopic system. In metal-insulator semiconductor tunneling junctions, the electrons can build up close to the interface between layers and as a result the quantum transport of the system will be affected by the electron-electron interactions. Certain transport properties such as electric current and electronic density can be known by solving for self-consistent Coulombic average potential from the electron-electron interactions, which is related to electronic distribution. Therefore, it is essential to analytically solve the Poisson–Boltzmann equation in order to obtain the analytical quantities in the MIS tunneling junctions. Applying the following analytical solution of the Poisson–Boltzmann equation (see section 2) to MIS tunneling junctions, the following expression can be formed to express electronic transport quantities such as electronic density and electric current f 1 f 0 − f 0 + e E z τ 0 m ∂ f 0 ∂ v z ( 1 − e − τ τ 0 ) − ∫ 0 t e m e t − τ ′ τ 0 ∇ ρ [ r − v ( t − t ′ ) ] × ∂ f 0 ∂ v d t ′ {\displaystyle f_{1}f^{0}-f_{0}+{\frac {eE_{z}\tau _{0}}{m}}{\frac {\partial f_{0}}{\partial v_{z}}}\left(1-e^{\frac {-\tau }{\tau _{0}}}\right)-\int _{0}^{t}{\frac {e}{m}}e{^{\frac {t-\tau '}{\tau _{0}}}}\nabla \rho [r-v(t-t')]\times {\frac {\partial f_{0}}{\partial v}}dt'} Applying the equation above to the MIS tunneling junction, electronic transport can be analyzed along the z-axis, which is referenced perpendicular to the plane of the layers. An n-type junction is chosen in this case with a bias V applied along the z-axis. The
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
self-consistent average potential of the system can be found using ρ ρ 1 + ρ 2 {\displaystyle \rho \rho _{1}+\rho _{2}} where ρ 1 ≈ a E z 2 λ D 1 e − λ D 1 z {\displaystyle \rho _{1}\approx {\frac {aE_{z}}{2\lambda _{D1}}}e^{-\lambda _{D1}z}} and ρ 2 ≈ n e π G ( i λ D 1 ) e − t τ 0 − λ D 1 z 3 3 ε λ D 1 ( 1 − e 1 − 2 n e 2 t 2 m ε ) {\displaystyle \rho _{2}\approx {\frac {ne{\sqrt {\pi }}G(i\lambda _{D1})e^{{\frac {-t}{\tau _{0}}}-\lambda _{D1}z}}{3{\sqrt {3}}\varepsilon \lambda _{D1}}}\left(1-e^{1-{\sqrt {\frac {2ne^{2}t^{2}}{m\varepsilon }}}}\right)} λ is called the Debye length. The electronic density and electric current can be found by manipulation to equation 16 above as functions of position z. These electronic transport quantities can be used to help understand various transport properties in the system. == Limitations == Source: As with any approximate model, the Poisson–Boltzmann equation is an approximation rather than an exact representation. Several assumptions were made to approximate the potential of the diffuse layer. The finite size of the ions was considered negligible and ions were treated as individual point charges, where ions were assumed to interact with the average electrostatic field of all their neighbors rather than each neighbor individually. In addition, non-Coulombic interactions were not considered and certain interactions were unaccounted for, such as the overlap of ion hydration spheres in an aqueous system. The permittivity of the solvent was assumed to be constant, resulting in a rough approximation as polar molecules are prevented from freely moving when they encounter the strong electric field at the solid surface. Though the model faces certain limitations, it describes electric double layers very well. The errors resulting from the previously mentioned assumptions cancel each
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
other for the most part. Accounting for non-Coulombic interactions increases the ion concentration at the surface and leads to a reduced surface potential. On the other hand, including the finite size of the ions causes the opposite effect. The Poisson–Boltzmann equation is most appropriate for approximating the electrostatic potential at the surface for aqueous solutions of univalent salts at concentrations smaller than 0.2 M and potentials not exceeding 50–80 mV. In the limit of strong electrostatic interactions, a strong coupling theory is more applicable than the weak coupling assumed in deriving the Poisson-Boltzmann theory. == See also == Double layer == References == == External links == Adaptive Poisson–Boltzmann Solver – A free, open-source Poisson-Boltzmann electrostatics and biomolecular solvation software package Zap – A Poisson–Boltzmann electrostatics solver MIBPB Matched Interface & Boundary based Poisson–Boltzmann solver CHARMM-GUI: PBEQ Solver AFMPB Adaptive Fast Multipole Poisson–Boltzmann Solver, free and open-source Global classical solutions of the Boltzmann equation with long-range interactions, Philip T. Gressman and Robert M. Strain, 2009, University of Pennsylvania, Department of Mathematics, Philadelphia, PA, USA.
|
{
"page_id": 6161274,
"source": null,
"title": "Poisson–Boltzmann equation"
}
|
In clinical trials, a surrogate endpoint (or surrogate marker) is a measure of effect of a specific treatment that may correlate with a real clinical endpoint but does not necessarily have a guaranteed relationship. The National Institutes of Health (USA) defines surrogate endpoint as "a biomarker intended to substitute for a clinical endpoint". Surrogate markers are used when the primary endpoint is undesired (e.g., death), or when the number of events is very small, thus making it impractical to conduct a clinical trial to gather a statistically significant number of endpoints. The FDA and other regulatory agencies will often accept evidence from clinical trials that show a direct clinical benefit to surrogate markers. Surrogate endpoints can be obtained from different modalities, such as, behavioural or cognitive scores, or biomarkers from Electroencephalography (qEEG), MRI, PET, or biochemical biomarkers. A correlate does not make a surrogate. It is a common misconception that if an outcome is a correlate (that is, correlated with the true clinical outcome) it can be used as a valid surrogate endpoint (that is, a replacement for the true clinical outcome). However, proper justification for such replacement requires that the effect of the intervention on the surrogate endpoint predicts the effect on the clinical outcome: a much stronger condition than correlation. In this context, the term Prentice criteria is used. The term "surrogate" should not be used in describing endpoints. Instead, descriptions of results and interpretations should be formulated in terms that designate the specific nature and category of variable assessed. A surrogate endpoint of a clinical trial is a laboratory measurement or a physical sign used as a substitute for a clinically meaningful endpoint that measures directly how a patient feels, functions or survives. Changes induced by a therapy on a surrogate endpoint are expected to reflect changes
|
{
"page_id": 1180539,
"source": null,
"title": "Surrogate endpoint"
}
|
in a clinically meaningful endpoint. == Examples == === Cardiovascular disease === A commonly used example is cholesterol. While elevated cholesterol levels increase the likelihood for heart disease, the relationship is not linear - many people with normal cholesterol develop heart disease, and many with high cholesterol do not. "Death from heart disease" is the endpoint of interest, but "cholesterol" is the surrogate marker. A clinical trial may show that a particular drug (for example, simvastatin (Zocor)) is effective in reducing cholesterol, without showing directly that simvastatin prevents death. Proof of Zocor's efficacy in reducing cardiovascular disease was only presented five years after its original introduction, and then only for secondary prevention. In another case, AstraZeneca was accused of marketing rosuvastatin (Crestor) without providing hard endpoint data, relying instead on surrogate endpoints. The company countered that rosuvastatin had been tested on larger groups of patients than any other drug in the class, and that its effects should be comparable to the other statins. === Cancer === Progression Free Survival is a prominent example in Oncology contexts. There are examples of cancer drugs approved on the basis of progression-free survival failed to show subsequent improvements in overall survival in subsequent studies. In breast cancer, Bevacizumab (Avastin) initially gained approval from the Food and Drug Administration, but subsequently had its license revoked. More patient focused surrogate endpoints may offer a more meaningful alternative such as Overall Treatment Utility. === Infectious disease === In HIV/AIDS medicine, CD4 counts and viral loads are used as surrogate markers for drug approval for clinical trials. In hepatitis C medicine, the surrogate endpoint "Sustained Virological Response" has been used for the approval of expensive drugs known as Direct Acting Antivirals. The validity of this surrogate endpoint for predicting clinical outcomes has been challenged. For several vaccines (anthrax,
|
{
"page_id": 1180539,
"source": null,
"title": "Surrogate endpoint"
}
|
hepatitis A, etc), the induction of detectable antibodies in blood is used as a surrogate marker for vaccine effectiveness, as exposure of individuals to an actual pathogen is considered unethical. === Alzheimer's disease === A recent study showed that plasma biomarkers have the potential to be used as surrogate biomarkers in Alzheimer's disease (AD) clinical trials. More specifically, this study demonstrated that plasma p-tau181 could potentially be used to monitor large-scale population interventions targeting preclinical AD individuals. == Criticism == There have been a number of instances when studies using surrogate markers have been used to show benefit from a particular treatment, but later, a repeat study looking at endpoints has not shown a benefit, or has even shown a harm. In 2021, the FDA came under heavy criticism for the approval of an alzheimer's drug called Aduhelm based on a surrogate endpoint that was later shown to be based on fraudulent data. == Reporting Guidelines == Reporting surrogate endpoints in randomized controlled trials is an emerging source of concern for clinicians and epidemiologists. This issue has been addressed in two reporting guidelines called CONSORT and SPIRIT, which will help researchers report surrogate endpoints in randomized controlled trials. == See also == FDA Accelerated Approval Program based on surrogate endpoints == References ==
|
{
"page_id": 1180539,
"source": null,
"title": "Surrogate endpoint"
}
|
Nanochemistry is an emerging sub-discipline of the chemical and material sciences that deals with the development of new methods for creating nanoscale materials. The term "nanochemistry" was first used by Ozin in 1992 as 'the uses of chemical synthesis to reproducibly afford nanomaterials from the atom "up", contrary to the nanoengineering and nanophysics approach that operates from the bulk "down"'. Nanochemistry focuses on solid-state chemistry that emphasizes synthesis of building blocks that are dependent on size, surface, shape, and defect properties, rather than the actual production of matter. Atomic and molecular properties mainly deal with the degrees of freedom of atoms in the periodic table. However, nanochemistry introduced other degrees of freedom that controls material's behaviors by transformation into solutions. Nanoscale objects exhibit novel material properties, largely as a consequence of their finite small size. Several chemical modifications on nanometer-scaled structures approve size dependent effects. Nanochemistry is used in chemical, materials and physical science as well as engineering, biological, and medical applications. Silica, gold, polydimethylsiloxane, cadmium selenide, iron oxide, and carbon are materials that show its transformative power. Nanochemistry can make the most effective contrast agent of MRI out of iron oxide (rust) which can detect cancers and kill them at their initial stages. Silica (glass) can be used to bend or stop lights in their tracks. Developing countries also use silicone to make circuits for the fluids used in pathogen detection. Nano-construct synthesis leads to the self-assembly of the building blocks into functional structures that may be useful for electronic, photonic, medical, or bioanalytical problems. Nanochemical methods can be used to create carbon nanomaterials such as carbon nanotubes, graphene, and fullerenes which have gained attention in recent years due to their remarkable mechanical and electrical properties. == History == One of the first scientific reports is the colloidal gold
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
particles synthesized by Michael Faraday as early as 1857. By the early 1940’s, precipitated and fumed silica nanoparticles were being manufactured and sold in USA and Germany as substitutes for ultrafine carbon black for rubber reinforcements. == Applications == === Medicine === ==== Magnetic Resonance Imaging (MRI) Detection ==== Over the past two decades, iron oxide nanoparticles for biomedical use had increased dramatically, largely due to its ability of non-invasive imaging, targeting and triggering drug release, or cancer therapy. Stem or immune cell could be marked with iron oxide nanoparticles to be detected by Magnetic resonance imaging (MRI). However, the concentration of iron oxide nanoparticles needs to be high enough to enable the significant detection by MRI. Due to the limited understanding of physicochemical nature of iron oxide nanoparticles in biological systems, more research is needed to ensure nanoparticles can be controlled under certain conditions for medical usage without posing harm to humans. ==== Drug delivery ==== Emerging methods of drug delivery involving nanotechnological methods can be useful by improving bodily response, specific targeting, and non-toxic metabolism. Many nanotechnological methods and materials can be functionalized for drug delivery. Ideal materials employ a controlled-activation nanomaterial to carry a drug cargo into the body. Mesoporous silica nanoparticles (MSN) have increased in research popularity due to their large surface area and flexibility for various individual modifications while maintaining high-resolution performance under imaging techniques. Activation methods greatly vary across nanoscale drug delivery molecules, but the most commonly used activation method uses specific wavelengths of light to release the cargo. Nanovalve-controlled cargo release uses low-intensity light and plasmonic heating to release the cargo in a variation of MSN containing gold molecules. The two-photon activated photo-transducer (2-NPT) uses near infrared wavelengths of light to induce the breaking of a disulfide bond to release the cargo. Recently,
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
nanodiamonds have demonstrated potential in drug delivery due to non-toxicity, spontaneous absorption through the skin, and the ability to enter the blood–brain barrier. The unique structure of carbon nanotubes also gives rise to many innovative inventions of new medical methods. As more medicine is made at the nano level to revolutionize the ways for human to detect and treat diseases, carbon nanotubes become a stronger candidate in new detection methods and therapeutic strategies. Specially, carbon nanotubes can be transformed into sophisticated biomolecule and allow its detection through changes in the carbon nanotube fluorescence spectra. Also, carbon nanotubes can be designed to match the size of small drug and endocitozed by a target cell, hence becoming a delivery agent. ==== Tissue engineering ==== Cells are very sensitive to nanotopographical features, so optimization of surfaces in tissue engineering has pushed towards implantation. Under appropriate conditions, a carefully crafted 3-dimensional scaffold is used to direct cell seeds toward artificial organ growth. The 3-D scaffold incorporates various nanoscale factors that control the environment for optimal and appropriate functionality. The scaffold is an analog of the in vivo extracellular matrix in vitro, allowing for successful artificial organ growth by providing the necessary, complex biological factors in vitro. ==== Wounds healing ==== For abrasions and wounds, nanochemistry has demonstrated applications in improving the healing process. Electrospinning is a polymerization method used biologically in tissue engineering but can also be used for wound dressing and drug delivery. This produces nanofibers that encourage cell proliferation, antibacterial properties, in controlled environment. These properties appear macroscopically, however, nanoscale versions may show improved efficiency due to nanotopographical features. Targeted interfaces between nanofibers and wounds have higher surface area interactions and are advantageous in vivo. There is evidence that certain nanoparticles of silver are useful to inhibit some viruses and bacteria. ===
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
Cosmetics === Materials in certain cosmetics such as sun cream, moisturizer, and deodorant may have potential benefits from the use of nanochemistry. Manufacturers are working to increase the effectiveness of various cosmetics by facilitating oil nanoemulsion. These particles have extended the boundaries in managing wrinkling, dehydrated, and inelastic skin associated with aging. In sunscreen, titanium dioxide and zinc oxide nanoparticles prove to be effective UV filters but can also penetrate through skin. These chemicals protect the skin against harmful UV light by absorbing or reflecting the light and prevent the skin from retaining full damage by photoexcitation of electrons in the nanoparticle. === Electrics === ==== Nanowire compositions ==== Scientists have devised a large number of nanowire compositions with controlled length, diameter, doping, and surface structure by using vapor and solution phase strategies. These oriented single crystals are being used in semiconductor nanowire devices such as diodes, transistors, logic circuits, lasers, and sensors. Since nanowires have a one-dimensional structure, meaning a large surface-to-volume ratio, the diffusion resistance decreases. In addition, their efficiency in electron transport which is due to the quantum confinement effect, makes their electrical properties be influenced by minor perturbation. Therefore, the use of these nanowires in nanosensor elements increases the sensitivity in electrode response. As mentioned above, the one-dimensionality and chemical flexibility of the semiconductor nanowires make them applicable in nanolasers. Peidong Yang and his co-workers have done some research on the room-temperature ultraviolet nanowires used in nanolasers. They have concluded that using short wavelength nanolasers has applications in different fields such as optical computing, information storage, and microanalysis. === Catalysis === ==== Nanoenzymes (or nanozymes) ==== The small size of nanoenzymes (or nanozymes) (1–100 nm) has provided them with unique optical, magnetic, electronic, and catalytic properties. Moreover, the control of surface functionality of nanoparticles and the
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
predictable nanostructure of these small-sized enzymes have allowed them to create a complex structure on their surface that can meet the needs of specific applications == Research areas == === Nanodiamonds === ==== Synthesis ==== Fluorescent nanoparticles are highly sought after. They have broad applications, but their use in macroscopic arrays allows them efficient in applications of plasmonics, photonics, and quantum communications. While there are many methods in assembling nanoparticles array, especially gold nanoparticles, they tend to be weakly bonded to their substrate so they can't be used for wet chemistry processing steps or lithography. Nanodiamonds allow for greater variability in access that can subsequently be used to couple plasmonic waveguides to realize quantum plasmonic circuitry. Nanodiamonds can be synthesized by employing nanoscale carbonaceous seeds created in a single step by using a mask-free electron beam-induced position technique to add amine groups. This assembles nanodiamonds into an array. The presence of dangling bonds at the nanodiamond surface allows them to be functionalized with a variety of ligands. The surfaces of these nanodiamonds are terminated with carboxylic acid groups, enabling their attachment to amine-terminated surfaces through carbodiimide coupling chemistry. This process affords a high yield that relies on covalent bonding between the amine and carboxyl functional groups on amorphous carbon and nanodiamond surfaces in the presence of EDC. Thus unlike gold nanoparticles, they can withstand processing and treatment, for many device applications. ==== Fluorescent (nitrogen vacancy) ==== Fluorescent properties in nanodiamonds arise from the presence of nitrogen-vacancy (NV) centers, nitrogen atoms next to a vacancy. Fluorescent nanodiamond (FND) was invented in 2005 and has since been used in various fields of study. The invention received a US patent in 2008 States7326837 B2 United States 7326837 B2, Chau-Chung Han; Huan-Cheng Chang & Shen-Chung Lee et al., "Clinical applications of crystalline diamond particles",
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
issued February 5, 2008, assigned to Academia Sinica, Taipei (TW) , and a subsequent patent in 2012 States8168413 B2 United States 8168413 B2, Huan-Cheng Chang; Wunshian Fann & Chau-Chung Han, "Luminescent Diamond Particles", issued May 1, 2012, assigned to Academia Sinica, Taipei (TW) . NV centers can be created by irradiating nanodiamonds with high-energy particles (electrons, protons, helium ions), followed by vacuum-annealing at 600–800°C. Irradiation forms vaccines in the diamond structure while vacuum-annealing migrates these vacancies, which will get trapped by nitrogen atoms within the nanodiamond. This process produces two types of NV centers. Two types of NV centers are formed—neutral (NV0) and negatively charged (NV–)—and these have different emission spectra. The NV– the center is of particular interest because it has an S = 1 spin ground state that can be spin-polarized by optical pumping and manipulated using electron paramagnetic resonance. Fluorescent nanodiamonds combine the advantages of semiconductor quantum dots (small size, high photostability, bright multicolor fluorescence) with biocompatibility, non-toxicity, and rich surface chemistry, which means that they have the potential to revolutionize Vivo imaging applications. ==== Drug-delivery and biological compatibility ==== Nanodiamonds can self-assemble and a wide range of small molecules, proteins antibodies, therapeutics, and nucleic acids can bind to its surface allowing for drug delivery, protein-mimicking, and surgical implants. Other potential biomedical applications are the use of nanodiamonds as support for solid-phase peptide synthesis and as sorbents for detoxification and separation and fluorescent nanodiamonds for biomedical imaging. Nanodiamonds are capable of biocompatibility, the ability to carry a broad range of therapeutics, dispersibility in water and scalability, and the potential for targeted therapy all properties needed for a drug delivery platform. The small size, stable core, rich surface chemistry, ability to self-assemble, and low cytotoxicity of nanodiamonds have led to suggestions that they could be used to mimic
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
globular proteins. Nanodiamonds have been mostly studied as potential injectable therapeutic agents for generalized drug delivery, but it has also been shown that films of Parylene nanodiamond composites can be used for localized sustained release of drugs over periods ranging from two days to one month. === Nanolithography === Nanolithography is the technique to pattern materials and build devices under nano-scale. Nanolithography is often used together with thin-film-deposition, self-assembly, and self-organization techniques for various nanofabrications purpose. Many practical applications make use of nanolithography, including semiconductor chips in computers. There are many types of nanolithography, which include: Photolithography Electron-beam lithography X-ray lithography Extreme ultraviolet lithography Light coupling nanolithography Scanning probe microscope Nanoimprint lithography Dip-Pen nanolithography Soft lithography Each nanolithography technique has varying factors of the resolution, time consumption, and cost. There are three basic methods used by nanolithography. One involves using a resist material that acts as a "mask", known as photoresists, to cover and protect the areas of the surface that are intended to be smooth. The uncovered portions can now be etched away, with the protective material acting as a stencil. The second method involves directly carving the desired pattern. Etching may involve using a beam of quantum particles, such as electrons or light, or chemical methods such as oxidation or Self-assembled monolayers. The third method places the desired pattern directly on the surface, producing a final product that is ultimately a few nanometers thicker than the original surface. To visualize the surface to be fabricated, the surface must be visualized by a nano-resolution microscope, which includes the scanning probe microscopy and the atomic force microscope. Both microscopes can also be engaged in processing the final product. ==== Photoresists ==== Photoresists are light-sensitive materials, composed of a polymer, a sensitizer, and a solvent. Each element has a particular function.
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
The polymer changes its structure when it is exposed to radiation. The solvent allows the photoresist to be spun and to form thin layers over the wafer surface. Finally, the sensitizer, or inhibitor, controls the photochemical reaction in the polymer phase. Photoresists can be classified as positive or negative. In positive photoresists, the photochemical reaction that occurs during exposure, weakens the polymer, making it more soluble to the developer so the positive pattern is achieved. Therefore, the masks contains an exact copy of the pattern, which is to remain on the wafer, as a stencil for subsequent processing. In the case of negative photoresists, exposure to light causes the polymerization of the photoresist so the negative resist remains on the surface of the substrate where it is exposed, and the developer solution removes only the unexposed areas. Masks used for negative photoresists contain the inverse or photographic “negative” of the pattern to be transferred. Both negative and positive photoresists have their own advantages. The advantages of negative photoresists are good adhesion to silicon, lower cost, and a shorter processing time. The advantages of positive photoresists are better resolution and thermal stability. === Nanometer-size clusters === Monodisperse, nanometer-size clusters (also known as nanoclusters) are synthetically grown crystals whose size and structure influence their properties through the effects of quantum confinement. One method of growing these crystals is through inverse micellar cages in non-aqueous solvents. Research conducted on the optical properties of MoS2 nanoclusters compared them to their bulk crystal counterparts and analyzed their absorbance spectra. The analysis reveals that size dependence of the absorbance spectrum by bulk crystals is continuous, whereas the absorbance spectrum of nanoclusters takes on discrete energy levels. This indicates a shift from solid-like to molecular-like behavior which occurs at a reported cluster the size of 4.5 –
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
3.0 nm. Interest in the magnetic properties of nanoclusters exists due to their potential use in magnetic recording, magnetic fluids, permanent magnets, and catalysis. Analysis of Fe clusters shows behavior consistent with ferromagnetic or superparamagnetic behavior due to strong magnetic interactions within clusters. Dielectric properties of nanoclusters are also a subject of interest due to their possible applications in catalysis, photocatalysis, micro capacitors, microelectronics, and nonlinear optics. === Nanothermodynamics === The idea of nanothermodynamics was initially proposed by T. L. Hill in 1960, theorizing the differences between differential and integral forms of properties due to small sizes. The size, shape, and environment of a nanoparticle affect the power law, or its proportionality, between nano and macroscopic properties. Transitioning from macro to nano changes the proportionality from exponential to power. Therefore, nanothermodynamics and the theory of statistical mechanics are related in concept. Building on these ideas, recent research has shown that, in finite nanosystems, the spatial dependence of intensive variables persists even in the thermodynamic limit. == Notable researchers == There are several researchers in nanochemistry that have been credited with the development of the field. Geoffrey A. Ozin, from the University of Toronto, is known as one of the "founding fathers of Nanochemistry" due to his four and a half decades of research on this subject. This research includes the study of matrix isolation laser Raman spectroscopy, naked metal clusters chemistry and photochemistry, nanoporous materials, hybrid nanomaterials, mesoscopic materials, and ultrathin inorganic nanowires. Another chemist who is also viewed as one of the nanochemistry's pioneers is Charles M. Lieber at Harvard University. He is known for his contributions to the development of nano-scale technologies, particularly in the field of biology and medicine. The technologies include nanowires, a new class of quasi-one-dimensional materials that have demonstrated superior electrical, optical, mechanical, and
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
thermal properties and can be used potentially as biological sensors. Research under Lieber has delved into the use of nanowires mapping brain activity. Shimon Weiss, a professor at the University of California, Los Angeles, is known for his research of fluorescent semiconductor nanocrystals, a subclass of quantum dots, for biological labeling. Paul Alivisatos, from the University of California, Berkeley, is also notable for his research on the fabrication and use of nanocrystals. This research has the potential to develop insight into the mechanisms of small-scale particles such as the process of nucleation, cation exchange, and branching. A notable application of these crystals is the development of quantum dots. Peidong Yang, another researcher from the University of California, Berkeley, is also notable for his contributions to the development of 1-dimensional nanostructures. The Yang group has active research projects in the areas of nanowire photonics, nanowire-based solar cells, nanowires for solar to fuel conversion, nanowire thermoelectrics, nanowire-cell interface, nanocrystal catalysis, nanotube nanofluidics, and plasmonics. == References == == Selected books == J.W. Steed, D.R. Turner, K. Wallace Core Concepts in Supramolecular Chemistry and Nanochemistry (Wiley, 2007) 315p. ISBN 978-0-470-85867-7 Brechignac C., Houdy P., Lahmani M. (Eds.) Nanomaterials and Nanochemistry (Springer, 2007) 748p. ISBN 978-3-540-72993-8 H. Watarai, N. Teramae, T. Sawada Interfacial Nanochemistry: Molecular Science and Engineering at Liquid-Liquid Interfaces (Nanostructure Science and Technology) 2005. 321p. ISBN 978-0-387-27541-3 Ozin G., Arsenault A.C., Cademartiri L. Nanochemistry: A Chemical Approach to Nanomaterials 2nd Eds. (Royal Society of Chemistry, 2008) 820p. ISBN 978-1847558954 Kenneth J. Klabunde; Ryan M. Richards, eds. (2009). Nanoscale Materials in Chemistry (2nd ed.). Wiley. ISBN 978-0-470-22270-6.
|
{
"page_id": 4653948,
"source": null,
"title": "Nanochemistry"
}
|
The Max Planck Institute of Microstructure Physics in Halle (Saale) is a research institute in Germany focused novel materials with useful functionalities. Active research topics includes spintronics, neuromorphic systems, nano-photonics, topological metals and insulators etc . It was founded in 1992 by Hellmut Fischmeister and is a follow-up to the German Academy of Sciences Institute of Solid State Physics and Electron Microscopy. The institute moved into new buildings from 1997 till 1999. It is one of 84 institutes in the Max Planck Society (Max-Planck-Gesellschaft). The institute has three main departments: Stuart Parkin: Nano-systems from Ions, Spins and Electrons (NISE) Joyce Poon: Nano-photonics, Integration and Neural Technology (NINT) Xinliang Feng: Synthetic Materials and Functional Devices (SMFD) Former departments include the following: The Theory Department, headed by Prof. Eberhard Gross, mainly carries out theoretical research on the electronic, magnetic, optical, and electrical properties of micro- and nanostructured solid-state systems'. The Experimental Department 1, headed by Prof. Jürgen Kirschner, mainly deals with the magnetic properties of dimensionally reduced systems and their dependence on electronic structure, crystalline structure and morphology. The Experimental Department 2, headed by Prof. Ulrich Gösele, is focussed on the scientific understanding, design and fabrication of new materials for information, communication, engineering as well as bio-technological applications. The Experimental Department 3, headed by Prof. Johannes Heydenreich, is focused on analytical methods using high-resolution electronic microscopy. == PhD program == The Max Planck Institute for Microstructure Physics, the Martin Luther University of Halle-Wittenberg, and the Fraunhofer Institute for Mechanics of Materials offer a PhD program under the "International Max-Planck Research School for Science and Technology of Nano-Systems (IMPRS-STNS)". == References == == External links == Max Planck Institute of Microstructure Physics Comprehensive list of scientific publications from the institute
|
{
"page_id": 10421112,
"source": null,
"title": "Max Planck Institute of Microstructure Physics"
}
|
Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abundant as water vapor (which averages about 4000 ppmv, but varies greatly), 23 times as abundant as carbon dioxide (400 ppmv), and more than 500 times as abundant as neon (18 ppmv). Argon is the most abundant noble gas in Earth's crust, comprising 0.00015% of the crust. Nearly all argon in Earth's atmosphere is radiogenic argon-40, derived from the decay of potassium-40 in Earth's crust. In the universe, argon-36 is by far the most common argon isotope, as it is the most easily produced by stellar nucleosynthesis in supernovas. The name "argon" is derived from the Greek word ἀργόν, neuter singular form of ἀργός meaning 'lazy' or 'inactive', as a reference to the fact that the element undergoes almost no chemical reactions. The complete octet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements. Its triple point temperature of 83.8058 K is a defining fixed point in the International Temperature Scale of 1990. Argon is extracted industrially by the fractional distillation of liquid air. It is mostly used as an inert shielding gas in welding and other high-temperature industrial processes where ordinarily unreactive substances become reactive; for example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning. It is also used in incandescent and fluorescent lighting, and other gas-discharge tubes. It makes a distinctive blue-green gas laser. It is also used in fluorescent glow starters. == Characteristics == Argon has approximately the same solubility in water as oxygen and
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
is 2.5 times more soluble in water than nitrogen. Argon is colorless, odorless, nonflammable and nontoxic as a solid, liquid or gas. Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperature. Although argon is a noble gas, it can form some compounds under various extreme conditions. Argon fluorohydride (HArF), a compound of argon with fluorine and hydrogen that is stable below 17 K (−256.1 °C; −429.1 °F), has been demonstrated. Although the neutral ground-state chemical compounds of argon are presently limited to HArF, argon can form clathrates with water when atoms of argon are trapped in a lattice of water molecules. Ions, such as ArH+, and excited-state complexes, such as ArF, have been demonstrated. Theoretical calculation predicts several more argon compounds that should be stable but have not yet been synthesized. == History == Argon (Greek ἀργόν, neuter singular form of ἀργός meaning "lazy" or "inactive") is named in reference to its chemical inactivity. This chemical property of this first noble gas to be discovered impressed the namers. An unreactive gas was suspected to be a component of air by Henry Cavendish in 1785. Argon was first isolated from air in 1894 by Lord Rayleigh and Sir William Ramsay at University College London by removing oxygen, carbon dioxide, water, and nitrogen from a sample of clean air. They first accomplished this by replicating an experiment of Henry Cavendish's. They trapped a mixture of atmospheric air with additional oxygen in a test-tube (A) upside-down over a large quantity of dilute alkali solution (B), which in Cavendish's original experiment was potassium hydroxide, and conveyed a current through wires insulated by U-shaped glass tubes (CC) which sealed around the platinum wire electrodes, leaving the ends of the wires (DD) exposed to the gas and insulated from
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
the alkali solution. The arc was powered by a battery of five Grove cells and a Ruhmkorff coil of medium size. The alkali absorbed the oxides of nitrogen produced by the arc and also carbon dioxide. They operated the arc until no more reduction of volume of the gas could be seen for at least an hour or two and the spectral lines of nitrogen disappeared when the gas was examined. The remaining oxygen was reacted with alkaline pyrogallate to leave behind an apparently non-reactive gas which they called argon. Before isolating the gas, they had determined that nitrogen produced from chemical compounds was 0.5% lighter than nitrogen from the atmosphere. The difference was slight, but it was important enough to attract their attention for many months. They concluded that there was another gas in the air mixed in with the nitrogen. Argon was also encountered in 1882 through independent research of H. F. Newall and W. N. Hartley. Each observed new lines in the emission spectrum of air that did not match known elements. Prior to 1957, the symbol for argon was "A". This was changed to Ar after the International Union of Pure and Applied Chemistry published the work Nomenclature of Inorganic Chemistry in 1957. == Occurrence == Argon constitutes 0.934% by volume and 1.288% by mass of Earth's atmosphere. Air is the primary industrial source of purified argon products. Argon is isolated from air by fractionation, most commonly by cryogenic fractional distillation, a process that also produces purified nitrogen, oxygen, neon, krypton and xenon. Earth's crust and seawater contain 1.2 ppm and 0.45 ppm of argon, respectively. == Isotopes == The main isotopes of argon found on Earth are 40Ar (99.6%), 36Ar (0.34%), and 38Ar (0.06%). Naturally occurring 40K, with a half-life of 1.25×109 years, decays to
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
stable 40Ar (11.2%) by electron capture or positron emission, and also to stable 40Ca (88.8%) by beta decay. These properties and ratios are used to determine the age of rocks by K–Ar dating. In Earth's atmosphere, 39Ar is made by cosmic ray activity, primarily by neutron capture of 40Ar followed by two-neutron emission. In the subsurface environment, it is also produced through neutron capture by 39K, followed by proton emission. 37Ar is created from the neutron capture by 40Ca followed by an alpha particle emission as a result of subsurface nuclear explosions. It has a half-life of 35 days. Between locations in the Solar System, the isotopic composition of argon varies greatly. Where the major source of argon is the decay of 40K in rocks, 40Ar will be the dominant isotope, as it is on Earth. Argon produced directly by stellar nucleosynthesis is dominated by the alpha-process nuclide 36Ar. Correspondingly, solar argon contains 84.6% 36Ar (according to solar wind measurements), and the ratio of the three isotopes 36Ar : 38Ar : 40Ar in the atmospheres of the outer planets is 8400 : 1600 : 1. This contrasts with the low abundance of primordial 36Ar in Earth's atmosphere, which is only 31.5 ppmv (= 9340 ppmv × 0.337%), comparable with that of neon (18.18 ppmv) on Earth and with interplanetary gasses, measured by probes. The atmospheres of Mars, Mercury and Titan (the largest moon of Saturn) contain argon, predominantly as 40Ar. The predominance of radiogenic 40Ar is the reason the standard atomic weight of terrestrial argon is greater than that of the next element, potassium, a fact that was puzzling when argon was discovered. Mendeleev positioned the elements on his periodic table in order of atomic weight, but the inertness of argon suggested a placement before the reactive alkali metal. Henry
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
Moseley later solved this problem by showing that the periodic table is actually arranged in order of atomic number (see History of the periodic table). == Compounds == Argon's complete octet of electrons indicates full s and p subshells. This full valence shell makes argon very stable and extremely resistant to bonding with other elements. Before 1962, argon and the other noble gases were considered to be chemically inert and unable to form compounds; however, compounds of the heavier noble gases have since been synthesized. The first argon compound with tungsten pentacarbonyl, W(CO)5Ar, was isolated in 1975. However, it was not widely recognised at that time. In August 2000, another argon compound, argon fluorohydride (HArF), was formed by researchers at the University of Helsinki, by shining ultraviolet light onto frozen argon containing a small amount of hydrogen fluoride with caesium iodide. This discovery caused the recognition that argon could form weakly bound compounds, even though it was not the first. It is stable up to 17 kelvins (−256 °C). The metastable ArCF2+2 dication, which is valence-isoelectronic with carbonyl fluoride and phosgene, was observed in 2010. Argon-36, in the form of argon hydride (argonium) ions, has been detected in interstellar medium associated with the Crab Nebula supernova; this was the first noble-gas molecule detected in outer space. Solid argon hydride (Ar(H2)2) has the same crystal structure as the MgZn2 Laves phase. It forms at pressures between 4.3 and 220 GPa, though Raman measurements suggest that the H2 molecules in Ar(H2)2 dissociate above 175 GPa. == Production == Argon is extracted industrially by the fractional distillation of liquid air in a cryogenic air separation unit; a process that separates liquid nitrogen, which boils at 77.3 K, from argon, which boils at 87.3 K, and liquid oxygen, which boils at 90.2 K. About
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
700,000 tonnes of argon are produced worldwide every year. == Applications == Argon has several desirable properties: Argon is a chemically inert gas. Argon is the cheapest alternative when nitrogen is not sufficiently inert. Argon has low thermal conductivity. Argon has electronic properties (ionization and/or the emission spectrum) desirable for some applications. Other noble gases would be equally suitable for most of these applications, but argon is by far the cheapest. It is inexpensive, since it occurs naturally in air and is readily obtained as a byproduct of cryogenic air separation in the production of liquid oxygen and liquid nitrogen: the primary constituents of air are used on a large industrial scale. The other noble gases (except helium) are produced this way as well, but argon is the most plentiful by far. The bulk of its applications arise simply because it is inert and relatively cheap. === Industrial processes === Argon is used in some high-temperature industrial processes where ordinarily non-reactive substances become reactive. For example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning. For some of these processes, the presence of nitrogen or oxygen gases might cause defects within the material. Argon is used in some types of arc welding such as gas metal arc welding and gas tungsten arc welding, as well as in the processing of titanium and other reactive elements. An argon atmosphere is also used for growing crystals of silicon and germanium. Argon is used in the poultry industry to asphyxiate birds, either for mass culling following disease outbreaks, or as a means of slaughter more humane than electric stunning. Argon is denser than air and displaces oxygen close to the ground during inert gas asphyxiation. Its non-reactive nature makes it suitable in a food product, and since
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
it replaces oxygen within the dead bird, argon also enhances shelf life. Argon is sometimes used for extinguishing fires where valuable equipment may be damaged by water or foam. === Scientific research === Liquid argon is used as the target for neutrino experiments and direct dark matter searches. The interaction between the hypothetical WIMPs and an argon nucleus produces scintillation light that is detected by photomultiplier tubes. Two-phase detectors containing argon gas are used to detect the ionized electrons produced during the WIMP–nucleus scattering. As with most other liquefied noble gases, argon has a high scintillation light yield (about 51 photons/keV), is transparent to its own scintillation light, and is relatively easy to purify. Compared to xenon, argon is cheaper and has a distinct scintillation time profile, which allows the separation of electronic recoils from nuclear recoils. On the other hand, its intrinsic beta-ray background is larger due to 39Ar contamination, unless one uses argon from underground sources, which has much less 39Ar contamination. Most of the argon in Earth's atmosphere was produced by electron capture of long-lived 40K (40K + e− → 40Ar + ν) present in natural potassium within Earth. The 39Ar activity in the atmosphere is maintained by cosmogenic production through the knockout reaction 40Ar(n,2n)39Ar and similar reactions. The half-life of 39Ar is only 269 years. As a result, the underground Ar, shielded by rock and water, has much less 39Ar contamination. Dark-matter detectors currently operating with liquid argon include DarkSide, WArP, ArDM, microCLEAN and DEAP. Neutrino experiments include ICARUS and MicroBooNE, both of which use high-purity liquid argon in a time projection chamber for fine grained three-dimensional imaging of neutrino interactions. At Linköping University, Sweden, the inert gas is being utilized in a vacuum chamber in which plasma is introduced to ionize metallic films. This process
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
results in a film usable for manufacturing computer processors. The new process would eliminate the need for chemical baths and use of expensive, dangerous and rare materials. === Preservative === Argon is used to displace oxygen- and moisture-containing air in packaging material to extend the shelf-lives of the contents (argon has the European food additive code E938). Aerial oxidation, hydrolysis, and other chemical reactions that degrade the products are retarded or prevented entirely. High-purity chemicals and pharmaceuticals are sometimes packed and sealed in argon. In winemaking, argon is used in a variety of activities to provide a barrier against oxygen at the liquid surface, which can spoil wine by fueling both microbial metabolism (as with acetic acid bacteria) and standard redox chemistry. Argon is sometimes used as the propellant in aerosol cans. Argon is also used as a preservative for such products as varnish, polyurethane, and paint, by displacing air to prepare a container for storage. Since 2002, the American National Archives stores important national documents such as the Declaration of Independence and the Constitution within argon-filled cases to inhibit their degradation. Argon is preferable to the helium that had been used in the preceding five decades, because helium gas escapes through the intermolecular pores in most containers and must be regularly replaced. === Laboratory equipment === Argon may be used as the inert gas within Schlenk lines and gloveboxes. Argon is preferred to less expensive nitrogen in cases where nitrogen may react with the reagents or apparatus. Argon may be used as the carrier gas in gas chromatography and in electrospray ionization mass spectrometry; it is the gas of choice for the plasma used in ICP spectroscopy. Argon is preferred for the sputter coating of specimens for scanning electron microscopy. Argon gas is also commonly used for sputter deposition
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
of thin films as in microelectronics and for wafer cleaning in microfabrication. === Medical use === Cryosurgery procedures such as cryoablation use liquid argon to destroy tissue such as cancer cells. It is used in a procedure called "argon-enhanced coagulation", a form of argon plasma beam electrosurgery. The procedure carries a risk of producing gas embolism and has resulted in the death of at least one patient. Blue argon lasers are used in surgery to weld arteries, destroy tumors, and correct eye defects. Argon has also been used experimentally to replace nitrogen in the breathing or decompression mix known as Argox, to speed the elimination of dissolved nitrogen from the blood. === Lighting === Incandescent lights are filled with argon, to preserve the filaments at high temperature from oxidation. It is used for the specific way it ionizes and emits light, such as in plasma globes and calorimetry in experimental particle physics. Gas-discharge lamps filled with pure argon provide lilac/violet light; with argon and some mercury, blue light. Argon is also used for blue and green argon-ion lasers. === Miscellaneous uses === Argon is used for thermal insulation in energy-efficient windows. Argon is also used in technical scuba diving to inflate a dry suit because it is inert and has low thermal conductivity. Argon is used as a propellant in the development of the Variable Specific Impulse Magnetoplasma Rocket (VASIMR). Compressed argon gas is allowed to expand, to cool the seeker heads of some versions of the AIM-9 Sidewinder missile and other missiles that use cooled thermal seeker heads. The gas is stored at high pressure. Argon-39, with a half-life of 269 years, has been used for a number of applications, primarily ice core and ground water dating. Also, potassium–argon dating and related argon-argon dating are used to date sedimentary,
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
metamorphic, and igneous rocks. Argon has been used by athletes as a doping agent to simulate hypoxic conditions. In 2014, the World Anti-Doping Agency (WADA) added argon and xenon to the list of prohibited substances and methods, although at this time there is no reliable test for abuse. == Safety == Although argon is non-toxic, it is 38% more dense than air and therefore considered a dangerous asphyxiant in closed areas. It is difficult to detect because it is colorless, odorless, and tasteless. A 1994 incident, in which a man was asphyxiated after entering an argon-filled section of oil pipe under construction in Alaska, highlights the dangers of argon tank leakage in confined spaces and emphasizes the need for proper use, storage and handling. == See also == Industrial gas Oxygen–argon ratio, a ratio of two physically similar gases, which has importance in various sectors. == References == == Further reading == Brown, T. L.; Bursten, B. E.; LeMay, H. E. (2006). J. Challice; N. Folchetti (eds.). Chemistry: The Central Science (10th ed.). Pearson Education. pp. 276& 289. ISBN 978-0-13-109686-8. Lide, D. R. (2005). "Properties of the Elements and Inorganic Compounds; Melting, boiling, triple, and critical temperatures of the elements". CRC Handbook of Chemistry and Physics (86th ed.). CRC Press. §4. ISBN 978-0-8493-0486-6. On triple point pressure at 69 kPa. Preston-Thomas, H. (1990). "The International Temperature Scale of 1990 (ITS-90)". Metrologia. 27 (1): 3–10. Bibcode:1990Metro..27....3P. doi:10.1088/0026-1394/27/1/002. S2CID 250785635. On triple point pressure at 83.8058 K. == External links == Argon at The Periodic Table of Videos (University of Nottingham) USGS Periodic Table – Argon Diving applications: Why Argon?
|
{
"page_id": 896,
"source": null,
"title": "Argon"
}
|
Arsenic is a chemical element; it has symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is notoriously toxic. It occurs naturally in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. It has various allotropes, but only the grey form, which has a metallic appearance, is important to industry. The primary use of arsenic is in alloys of lead (for example, in car batteries and ammunition). Arsenic is also a common n-type dopant in semiconductor electronic devices, and a component of the III–V compound semiconductor gallium arsenide. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. These applications are declining with the increasing recognition of the persistent toxicity of arsenic and its compounds. Arsenic has been known since ancient times to be poisonous to humans. However, a few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic have been proposed to be an essential dietary element in rats, hamsters, goats, and chickens. Research has not been conducted to determine whether small amounts of arsenic may play a role in human metabolism. However, arsenic poisoning occurs in multicellular life if quantities are larger than needed. Arsenic contamination of groundwater is a problem that affects millions of people across the world. The United States' Environmental Protection Agency states that all forms of arsenic are a serious risk to human health. The United States Agency for Toxic Substances and Disease Registry ranked arsenic number 1 in its 2001 prioritized list of hazardous substances at Superfund sites. Arsenic is classified as a group-A carcinogen. == Characteristics == ===
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
Physical characteristics === The three most common arsenic allotropes are grey, yellow, and black arsenic, with grey being the most common. Grey arsenic (α-As, space group R3m No. 166) adopts a double-layered structure consisting of many interlocked, ruffled, six-membered rings. Because of weak bonding between the layers, grey arsenic is brittle and has a relatively low Mohs hardness of 3.5. Nearest and next-nearest neighbors form a distorted octahedral complex, with the three atoms in the same double-layer being slightly closer than the three atoms in the next. This relatively close packing leads to a high density of 5.73 g/cm3. Grey arsenic is a semimetal, but becomes a semiconductor with a bandgap of 1.2–1.4 eV if amorphized. Grey arsenic is also the most stable form. Yellow arsenic is soft and waxy, and somewhat similar to tetraphosphorus (P4). Both have four atoms arranged in a tetrahedral structure in which each atom is bound to each of the other three atoms by a single bond. This unstable allotrope, being molecular, is the most volatile, least dense, and most toxic. Solid yellow arsenic is produced by rapid cooling of arsenic vapor, As4. It is rapidly transformed into grey arsenic by light. The yellow form has a density of 1.97 g/cm3. Black arsenic is similar in structure to black phosphorus. Black arsenic can also be formed by cooling vapor at around 100–220 °C and by crystallization of amorphous arsenic in the presence of mercury vapors. It is glassy and brittle. Black arsenic is also a poor electrical conductor. Arsenic sublimes upon heating at atmospheric pressure, converting directly to a gaseous form without an intervening liquid state at 887 K (614 °C). The triple point is at 3.63 MPa and 1,090 K (820 °C). === Isotopes === Arsenic occurs in nature as one stable isotope, 75As,
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
and is therefore called a monoisotopic element. As of 2024, at least 32 radioisotopes have also been synthesized, ranging in atomic mass from 64 to 95. The most stable of these is 73As with a half-life of 80.30 days. The majority of the other isotopes have half-lives of under one day, with the exceptions being Isotopes that are lighter than the stable 75As tend to decay by β+ decay, and those that are heavier tend to decay by β− decay, with some exceptions. At least 10 nuclear isomers have been described, ranging in atomic mass from 66 to 84. The most stable of arsenic's isomers is 68mAs with a half-life of 111 seconds. === Chemistry === Arsenic has a similar electronegativity and ionization energies to its lighter pnictogen congener phosphorus and therefore readily forms covalent molecules with most of the nonmetals. Though stable in dry air, arsenic forms a golden-bronze tarnish upon exposure to humidity which eventually becomes a black surface layer. When heated in air, arsenic oxidizes to arsenic trioxide; the fumes from this reaction have an odor resembling garlic. This odor can be detected on striking arsenide minerals such as arsenopyrite with a hammer. It burns in oxygen to form arsenic trioxide and arsenic pentoxide, which have the same structure as the more well-known phosphorus compounds, and in fluorine to give arsenic pentafluoride. Arsenic makes arsenic acid with concentrated nitric acid, arsenous acid with dilute nitric acid, and arsenic trioxide with concentrated sulfuric acid; however, it does not react with water, alkalis, or non-oxidising acids. Arsenic reacts with metals to form arsenides, though these are not ionic compounds containing the As3− ion as the formation of such an anion would be highly endothermic and even the group 1 arsenides have properties of intermetallic compounds. Like germanium, selenium, and
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
bromine, which like arsenic succeed the 3d transition series, arsenic is much less stable in the +5 oxidation state than its vertical neighbors phosphorus and antimony, and hence arsenic pentoxide and arsenic acid are potent oxidizers. == Compounds == Compounds of arsenic resemble, in some respects, those of phosphorus, which occupies the same group (column) of the periodic table. The most common oxidation states for arsenic are: −3 in the arsenides, which are alloy-like intermetallic compounds, +3 in the arsenites, and +5 in the arsenates and most organoarsenic compounds. Arsenic also bonds readily to itself as seen in the square As3−4 ions in the mineral skutterudite. In the +3 oxidation state, arsenic is typically pyramidal owing to the influence of the lone pair of electrons. === Inorganic compounds === One of the simplest arsenic compounds is the trihydride, the highly toxic, flammable, pyrophoric arsine (AsH3). This compound is generally regarded as stable, since at room temperature it decomposes only slowly. At temperatures of 250–300 °C decomposition to arsenic and hydrogen is rapid. Several factors, such as humidity, presence of light and certain catalysts (namely aluminium) facilitate the rate of decomposition. It oxidises readily in air to form arsenic trioxide and water, and analogous reactions take place with sulfur and selenium instead of oxygen. Arsenic forms colorless, odorless, crystalline oxides As2O3 ("white arsenic") and As2O5 which are hygroscopic and readily soluble in water to form acidic solutions. Arsenic(V) acid is a weak acid and its salts, known as arsenates, are a major source of arsenic contamination of groundwater in regions with high levels of naturally-occurring arsenic minerals. Synthetic arsenates include Scheele's Green (cupric hydrogen arsenate, acidic copper arsenate), calcium arsenate, and lead hydrogen arsenate. These three have been used as agricultural insecticides and poisons. The protonation steps between the arsenate and
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
arsenic acid are similar to those between phosphate and phosphoric acid. Unlike phosphorous acid, arsenous acid is genuinely tribasic, with the formula As(OH)3. A broad variety of sulfur compounds of arsenic are known. Orpiment (As2S3) and realgar (As4S4) are somewhat abundant and were formerly used as painting pigments. In As4S10, arsenic has a formal oxidation state of +2 in As4S4 which features As-As bonds so that the total covalency of As is still 3. Both orpiment and realgar, as well as As4S3, have selenium analogs; the analogous As2Te3 is known as the mineral kalgoorlieite, and the anion As2Te− is known as a ligand in cobalt complexes. All trihalides of arsenic(III) are well known except the astatide, which is unknown. Arsenic pentafluoride (AsF5) is the only important pentahalide, reflecting the lower stability of the +5 oxidation state; even so, it is a very strong fluorinating and oxidizing agent. (The pentachloride is stable only below −50 °C, at which temperature it decomposes to the trichloride, releasing chlorine gas.) ==== Alloys ==== Arsenic is used as the group 5 element in the III-V semiconductors gallium arsenide, indium arsenide, and aluminium arsenide. The valence electron count of GaAs is the same as a pair of Si atoms, but the band structure is completely different which results in distinct bulk properties. Other arsenic alloys include the II-V semiconductor cadmium arsenide. === Organoarsenic compounds === A large variety of organoarsenic compounds are known. Several were developed as chemical warfare agents during World War I, including vesicants such as lewisite and vomiting agents such as adamsite. Cacodylic acid, which is of historic and practical interest, arises from the methylation of arsenic trioxide, a reaction that has no analogy in phosphorus chemistry. Cacodyl was the first organometallic compound known (even though arsenic is not a true metal) and
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
was named from the Greek κακωδία "stink" for its offensive, garlic-like odor; it is very toxic. == Occurrence and production == Arsenic is the 53rd most abundant element in the Earth's crust, comprising about 1.5 parts per million (0.00015%). Typical background concentrations of arsenic do not exceed 3 ng/m3 in the atmosphere; 100 mg/kg in soil; 400 μg/kg in vegetation; 10 μg/L in freshwater and 1.5 μg/L in seawater. Arsenic is the 22nd most abundant element in seawater and ranks 41st in abundance in the universe. Minerals with the formula MAsS and MAs2 (M = Fe, Ni, Co) are the dominant commercial sources of arsenic, together with realgar (an arsenic sulfide mineral) and native (elemental) arsenic. An illustrative mineral is arsenopyrite (FeAsS), which is structurally related to iron pyrite. Many minor As-containing minerals are known. Arsenic also occurs in various organic forms in the environment. In 2014, China was the top producer of white arsenic with almost 70% world share, followed by Morocco, Russia, and Belgium, according to the British Geological Survey and the United States Geological Survey. Most arsenic refinement operations in the US and Europe have closed over environmental concerns. Arsenic is found in the smelter dust from copper, gold, and lead smelters, and is recovered primarily from copper refinement dust. Arsenic is the main impurity found in copper concentrates to enter copper smelting facilities. There has been an increase in arsenic in copper concentrates over the years since copper mining has moved into deep high-impurity ores as shallow, low-arsenic copper deposits have been progressively depleted. On roasting arsenopyrite in air, arsenic sublimes as arsenic(III) oxide leaving iron oxides, while roasting without air results in the production of gray arsenic. Further purification from sulfur and other chalcogens is achieved by sublimation in vacuum, in a hydrogen atmosphere, or
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
by distillation from molten lead-arsenic mixture. == History == The word arsenic has its origin in the Syriac word ܙܪܢܝܟܐ zarnika, from Arabic al-zarnīḵ الزرنيخ 'the orpiment', based on Persian zar ("gold") from the word زرنيخ zarnikh, meaning "yellow" (literally "gold-colored") and hence "(yellow) orpiment". It was adopted into Greek (using folk etymology) as arsenikon (ἀρσενικόν) – a neuter form of the Greek adjective arsenikos (ἀρσενικός), meaning "male", "virile". Latin-speakers adopted the Greek term as arsenicum, which in French ultimately became arsenic, whence the English word "arsenic". Arsenic sulfides (orpiment, realgar) and oxides have been known and used since ancient times. Zosimos (c. 300 AD) describes roasting sandarach (realgar) to obtain cloud of arsenic (arsenic trioxide), which he then reduces to gray arsenic. As the symptoms of arsenic poisoning are not very specific, the substance was frequently used for murder until the advent in the 1830s of the Marsh test, a sensitive chemical test for its presence. (Another less sensitive but more general test is the Reinsch test.) Owing to its use by the ruling class to murder one another and its potency and discreetness, arsenic has been called the "poison of kings" and the "king of poisons". Arsenic became known as "the inheritance powder" due to its use in killing family members in the Renaissance era. During the Bronze Age, arsenic was melted with copper to make arsenical bronze. Jabir ibn Hayyan described the isolation of arsenic before 815 AD. Albertus Magnus (Albert the Great, 1193–1280) later isolated the element from a compound in 1250, by heating soap together with arsenic trisulfide. In 1649, Johann Schröder published two ways of preparing arsenic. Crystals of elemental (native) arsenic are found in nature, although rarely. Cadet's fuming liquid (impure cacodyl), often claimed as the first synthetic organometallic compound, was synthesized in
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
1760 by Louis Claude Cadet de Gassicourt through the reaction of potassium acetate with arsenic trioxide. In the Victorian era, women would eat "arsenic" ("white arsenic" or arsenic trioxide) mixed with vinegar and chalk to improve the complexion of their faces, making their skin paler (to show they did not work in the fields). The accidental use of arsenic in the adulteration of foodstuffs led to the Bradford sweet poisoning in 1858, which resulted in 21 deaths. From the late 18th century wallpaper production began to use dyes made from arsenic, which was thought to increase the pigment's brightness. One account of the illness and 1821 death of Napoleon implicates arsenic poisoning involving wallpaper. Two arsenic pigments have been widely used since their discovery – Paris Green in 1814 and Scheele's Green in 1775. After the toxicity of arsenic became widely known, these chemicals were used less often as pigments and more often as insecticides. In the 1860s, an arsenic byproduct of dye production, London Purple, was widely used. This was a solid mixture of arsenic trioxide, aniline, lime, and ferrous oxide, insoluble in water and very toxic by inhalation or ingestion But it was later replaced with Paris Green, another arsenic-based dye. With better understanding of the toxicology mechanism, two other compounds were used starting in the 1890s. Arsenite of lime and arsenate of lead were used widely as insecticides until the discovery of DDT in 1942. In small doses, soluble arsenic compounds act as stimulants, and were once popular as medicine by people in the mid-18th to 19th centuries; this use was especially prevalent for sport animals such as race horses or work dogs and continued into the 20th century. A 2006 study of the remains of the Australian racehorse Phar Lap determined that its 1932 death was
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
caused by a massive overdose of arsenic. Sydney veterinarian Percy Sykes stated, "In those days, arsenic was quite a common tonic, usually given in the form of a solution (Fowler's Solution) ... It was so common that I'd reckon 90 per cent of the horses had arsenic in their system." == Applications == === Agricultural === The toxicity of arsenic to insects, bacteria, and fungi led to its use as a wood preservative. In the 1930s, a process of treating wood with chromated copper arsenate (also known as CCA or Tanalith) was invented, and for decades, this treatment was the most extensive industrial use of arsenic. An increased appreciation of the toxicity of arsenic led to a ban of CCA in consumer products in 2004, initiated by the European Union and United States. However, CCA remains in heavy use in other countries (such as on Malaysian rubber plantations). Arsenic was also used in various agricultural insecticides and poisons. For example, lead hydrogen arsenate was a common insecticide on fruit trees, but contact with the compound sometimes resulted in brain damage among those working the sprayers. In the second half of the 20th century, monosodium methyl arsenate (MSMA) and disodium methyl arsenate (DSMA) – less toxic organic forms of arsenic – replaced lead arsenate in agriculture. These organic arsenicals were in turn phased out in the United States by 2013 in all agricultural activities except cotton farming. The biogeochemistry of arsenic is complex and includes various adsorption and desorption processes. The toxicity of arsenic is connected to its solubility and is affected by pH. Arsenite (AsO3−3) is more soluble than arsenate (AsO3−4) and is more toxic; however, at a lower pH, arsenate becomes more mobile and toxic. It was found that addition of sulfur, phosphorus, and iron oxides to high-arsenite soils
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
greatly reduces arsenic phytotoxicity. Arsenic is used as a feed additive in poultry and swine production, in particular it was used in the U.S. until 2015 to increase weight gain, improve feed efficiency, and prevent disease. An example is roxarsone, which had been used as a broiler starter by about 70% of U.S. broiler growers. In 2011, Alpharma, a subsidiary of Pfizer Inc., which produces roxarsone, voluntarily suspended sales of the drug in response to studies showing elevated levels of inorganic arsenic, a carcinogen, in treated chickens. A successor to Alpharma, Zoetis, continued to sell nitarsone until 2015, primarily for use in turkeys. === Medical use === During the 17th, 18th, and 19th centuries, a number of arsenic compounds were used as medicines, including arsphenamine (by Paul Ehrlich) and arsenic trioxide (by Thomas Fowler), for treating diseases such as cancer or psoriasis. Arsphenamine, as well as neosalvarsan, was indicated for syphilis, but has been superseded by modern antibiotics. However, arsenicals such as melarsoprol are still used for the treatment of trypanosomiasis in spite of their severe toxicity, since the disease is almost uniformly fatal if untreated. In 2000 the US Food and Drug Administration approved arsenic trioxide for the treatment of patients with acute promyelocytic leukemia that is resistant to all-trans retinoic acid. A 2008 paper reports success in locating tumors using arsenic-74 (a positron emitter). This isotope produces clearer PET scan images than the previous radioactive agent, iodine-124, because the body tends to transport iodine to the thyroid gland producing signal noise. Nanoparticles of arsenic have shown ability to kill cancer cells with lesser cytotoxicity than other arsenic formulations. === Alloys === The main use of arsenic is in alloying with lead. Lead components in car batteries are strengthened by the presence of a very small percentage of arsenic.
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
Dezincification of brass (a copper-zinc alloy) is greatly reduced by the addition of arsenic. "Phosphorus Deoxidized Arsenical Copper" with an arsenic content of 0.3% has an increased corrosion stability in certain environments. Gallium arsenide is an important semiconductor material, used in integrated circuits. Circuits made from GaAs are much faster (but also much more expensive) than those made from silicon. Unlike silicon, GaAs has a direct bandgap, and can be used in laser diodes and LEDs to convert electrical energy directly into light. === Military === After World War I, the United States built a stockpile of 20,000 tons of weaponized lewisite (ClCH=CHAsCl2), an organoarsenic vesicant (blister agent) and lung irritant. The stockpile was neutralized with bleach and dumped into the Gulf of Mexico in the 1950s. Lewisite, the chemical warfare agent, is known for its acute toxicity to aquatic organisms. However, studies assessing the environmental impact of this disposal in the Gulf are lacking. During the Vietnam War, the United States used Agent Blue, a mixture of sodium cacodylate and its acid form, as one of the rainbow herbicides to deprive North Vietnamese soldiers of foliage cover and rice. === Other uses === Copper acetoarsenite was used as a green pigment known under many names, including Paris Green and Emerald Green. It caused numerous arsenic poisonings. Scheele's Green, a copper arsenate, was used in the 19th century as a coloring agent in sweets. Arsenic is used in bronzing. As much as 2% of produced arsenic is used in lead alloys for lead shot and bullets. Arsenic is added in small quantities to alpha-brass to make it dezincification-resistant. This grade of brass is used in plumbing fittings and other wet environments. Arsenic is also used for taxonomic sample preservation. It was also used in embalming fluids historically. Arsenic was used
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
in the taxidermy process up until the 1980s. Arsenic was used as an opacifier in ceramics, creating white glazes. Until recently, arsenic was used in optical glass. Modern glass manufacturers have ceased using both arsenic and lead. == Biological role == === Bacteria === Some species of bacteria obtain their energy in the absence of oxygen by oxidizing various fuels while reducing arsenate to arsenite. Under oxidative environmental conditions some bacteria use arsenite as fuel, which they oxidize to arsenate. The enzymes involved are known as arsenate reductases (Arr). In 2008, bacteria were discovered that employ a version of photosynthesis in the absence of oxygen with arsenites as electron donors, producing arsenates (just as ordinary photosynthesis uses water as electron donor, producing molecular oxygen). Researchers conjecture that, over the course of history, these photosynthesizing organisms produced the arsenates that allowed the arsenate-reducing bacteria to thrive. One strain, PHS-1, has been isolated and is related to the gammaproteobacterium Ectothiorhodospira shaposhnikovii. The mechanism is unknown, but an encoded Arr enzyme may function in reverse to its known homologues. In 2010, researchers reported the discovery of a strain of the bacterium Halomonas (designated GFAJ-1) that was allegedly capable of substituting arsenic for phosphorus in its biomolecules, including DNA, when grown in an arsenic-rich, phosphate-limited environment. This claim, published in Science, suggested that arsenic could potentially serve as a building block of life in place of phosphorus, challenging long-standing assumptions about biochemical requirements for life on Earth. The claim was met with widespread skepticism. Subsequent studies provided evidence contradicting the initial findings. One follow-up study published in Science in 2011 demonstrated that GFAJ-1 still requires phosphate to grow and does not incorporate arsenate into its DNA in any biologically significant way. Another independent investigation in 2012 used more sensitive techniques to purify and analyze
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
the DNA of GFAJ-1 and found no detectable arsenate incorporated into the DNA backbone. The authors concluded that the original observations were likely due to experimental contamination or insufficient purification methods. Together, these studies reaffirmed phosphorus as an essential element for all known forms of life. === Potential role in higher animals === Arsenic may be an essential trace mineral in birds, involved in the synthesis of methionine metabolites. However, the role of arsenic in bird nutrition is disputed, as other authors state that arsenic is toxic in small amounts. Some evidence indicates that arsenic is an essential trace mineral in mammals. Experimental studies in rodents and livestock have shown that arsenic deprivation can lead to impaired growth, reduced reproductive performance, and abnormal glucose metabolism, suggesting it may play a role in essential metabolic processes. Arsenic has been proposed to participate in methylation reactions, possibly influencing gene regulation and detoxification pathways. However, because the threshold between beneficial and toxic exposure is extremely narrow, arsenic is not currently classified as an essential element for humans, and its physiological role in higher animals remains uncertain. === Heredity === Arsenic has been linked to epigenetic changes, heritable changes in gene expression that occur without changes in DNA sequence. These include DNA methylation, histone modification, and RNA interference. Toxic levels of arsenic cause significant DNA hypermethylation of tumor suppressor genes p16 and p53, thus increasing risk of carcinogenesis. These epigenetic events have been studied in vitro using human kidney cells and in vivo using rat liver cells and peripheral blood leukocytes in humans. Inductively coupled plasma mass spectrometry (ICP-MS) is used to detect precise levels of intracellular arsenic and other arsenic bases involved in epigenetic modification of DNA. Studies investigating arsenic as an epigenetic factor can be used to develop precise biomarkers of exposure
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
and susceptibility. The Chinese brake fern (Pteris vittata) hyperaccumulates arsenic from the soil into its leaves and has a proposed use in phytoremediation. === Biomethylation === Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolized through a process of methylation. For example, the mold Scopulariopsis brevicaulis produces trimethylarsine if inorganic arsenic is present. The organic compound arsenobetaine is found in some marine foods such as fish and algae, and also in mushrooms in larger concentrations. The average person's intake is about 10–50 μg/day. Values about 1000 μg are not unusual following consumption of fish or mushrooms, but there is little danger in eating fish because this arsenic compound is nearly non-toxic. == Environmental issues == === Exposure === Naturally occurring sources of human exposure include volcanic ash, weathering of minerals and ores, and mineralized groundwater. Arsenic is also found in food, water, soil, and air. Arsenic is absorbed by all plants, but is more concentrated in leafy vegetables, rice, apple and grape juice, and seafood. An additional route of exposure is inhalation of atmospheric gases and dusts. During the Victorian era, arsenic was widely used in home decor, especially wallpapers. In Europe, an analysis based on 20,000 soil samples across all 28 countries show that 98% of sampled soils have concentrations less than 20 mg/kg. In addition, the arsenic hotspots are related to both frequent fertilization and close distance to mining activities. Chronic exposure to arsenic, particularly through contaminated drinking water and food, has also been linked to long-term impacts on cognitive function, including reduced verbal IQ and memory. === Occurrence in drinking water === Extensive arsenic contamination of groundwater has led to widespread arsenic poisoning in Bangladesh and neighboring countries. It is estimated that approximately 57 million people in the Bengal basin are drinking groundwater
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
with arsenic concentrations elevated above the World Health Organization's standard of 10 parts per billion (ppb). However, a study of cancer rates in Taiwan suggested that significant increases in cancer mortality appear only at levels above 150 ppb. The arsenic in the groundwater is of natural origin, and is released from the sediment into the groundwater, caused by the anoxic conditions of the subsurface. This groundwater was used after local and western NGOs and the Bangladeshi government undertook a massive shallow tube well drinking-water program in the late twentieth century. This program was designed to prevent drinking of bacteria-contaminated surface waters, but failed to test for arsenic in the groundwater. Many other countries and districts in Southeast Asia, such as Vietnam and Cambodia, have geological environments that produce groundwater with a high arsenic content. Arsenicosis was reported in Nakhon Si Thammarat, Thailand, in 1987, and the Chao Phraya River probably contains high levels of naturally occurring dissolved arsenic without being a public health problem because much of the public uses bottled water. In Pakistan, more than 60 million people are exposed to arsenic polluted drinking water indicated by a 2017 report in Science. Podgorski's team investigated more than 1200 samples and more than 66% exceeded the WHO contamination limits of 10 micrograms per liter. Since the 1980s, residents of the Ba Men region of Inner Mongolia, China have been chronically exposed to arsenic through drinking water from contaminated wells. A 2009 research study observed an elevated presence of skin lesions among residents with well water arsenic concentrations between 5 and 10 μg/L, suggesting that arsenic-induced toxicity may occur at relatively low concentrations with chronic exposure. Overall, 20 of China's 34 provinces have high arsenic concentrations in the groundwater supply, potentially exposing 19 million people to hazardous drinking water. A study
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
by IIT Kharagpur found high levels of Arsenic in groundwater of 20% of India's land, exposing more than 250 million people. States such as Punjab, Bihar, West Bengal, Assam, Haryana, Uttar Pradesh, and Gujarat have highest land area exposed to arsenic. In the United States, arsenic is most commonly found in the ground waters of the southwest. Parts of New England, Michigan, Wisconsin, Minnesota and the Dakotas are also known to have significant concentrations of arsenic in ground water. Increased levels of skin cancer have been associated with arsenic exposure in Wisconsin, even at levels below the 10 ppb drinking water standard. According to a recent film funded by the US Superfund, millions of private wells have unknown arsenic levels, and in some areas of the US, more than 20% of the wells may contain levels that exceed established limits. Low-level exposure to arsenic at concentrations of 100 ppb (i.e., above the 10 ppb drinking water standard) compromises the initial immune response to H1N1 or swine flu infection according to NIEHS-supported scientists. The study, conducted in laboratory mice, suggests that people exposed to arsenic in their drinking water may be at increased risk for more serious illness or death from the virus. Some Canadians are drinking water that contains inorganic arsenic. Private-dug–well waters are most at risk for containing inorganic arsenic. Preliminary well water analysis typically does not test for arsenic. Researchers at the Geological Survey of Canada have modeled relative variation in natural arsenic hazard potential for the province of New Brunswick. This study has important implications for potable water and health concerns relating to inorganic arsenic. Epidemiological evidence from Chile shows a dose-dependent connection between chronic arsenic exposure and various forms of cancer, in particular when other risk factors, such as cigarette smoking, are present. These effects have
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
been demonstrated at contaminations less than 50 ppb. Arsenic is itself a constituent of tobacco smoke. Analyzing multiple epidemiological studies on inorganic arsenic exposure suggests a small but measurable increase in risk for bladder cancer at 10 ppb. According to Peter Ravenscroft of the Department of Geography at the University of Cambridge, roughly 80 million people worldwide consume between 10 and 50 ppb arsenic in their drinking water. If they all consumed exactly 10 ppb arsenic in their drinking water, the previously cited multiple epidemiological study analysis would predict an additional 2,000 cases of bladder cancer alone. This represents a clear underestimate of the overall impact, since it does not include lung or skin cancer, and explicitly underestimates the exposure. Those exposed to levels of arsenic above the current WHO standard should weigh the costs and benefits of arsenic remediation. Early (1973) evaluations of the processes for removing dissolved arsenic from drinking water demonstrated the efficacy of co-precipitation with either iron or aluminium oxides. In particular, iron as a coagulant was found to remove arsenic with an efficacy exceeding 90%. Several adsorptive media systems have been approved for use at point-of-service in a study funded by the United States Environmental Protection Agency (US EPA) and the National Science Foundation (NSF). A team of European and Indian scientists and engineers have set up six arsenic treatment plants in West Bengal based on in-situ remediation method (SAR Technology). This technology does not use any chemicals and arsenic is left in an insoluble form (+5 state) in the subterranean zone by recharging aerated water into the aquifer and developing an oxidation zone that supports arsenic oxidizing micro-organisms. This process does not produce any waste stream or sludge and is relatively cheap. Another effective and inexpensive method to avoid arsenic contamination is to sink
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
wells 500 feet or deeper to reach purer waters. A recent 2011 study funded by the US National Institute of Environmental Health Sciences' Superfund Research Program shows that deep sediments can remove arsenic and take it out of circulation. In this process, called adsorption, arsenic sticks to the surfaces of deep sediment particles and is naturally removed from the ground water. Magnetic separations of arsenic at very low magnetic field gradients with high-surface-area and monodisperse magnetite (Fe3O4) nanocrystals have been demonstrated in point-of-use water purification. Using the high specific surface area of Fe3O4 nanocrystals, the mass of waste associated with arsenic removal from water has been dramatically reduced. Epidemiological studies have suggested a correlation between chronic consumption of drinking water contaminated with arsenic and the incidence of all leading causes of mortality. The literature indicates that arsenic exposure is causative in the pathogenesis of diabetes. Chaff-based filters have recently been shown to reduce the arsenic content of water to 3 μg/L. This may find applications in areas where the potable water is extracted from underground aquifers. ==== San Pedro de Atacama ==== For several centuries, the people of San Pedro de Atacama in Chile have been drinking water that is contaminated with arsenic, and some evidence suggests they have developed some immunity. Genetic studies indicate that certain populations in this region have undergone natural selection for gene variants that enhance arsenic metabolism and detoxification. This adaptation is considered one of the few documented cases of human evolution in response to chronic environmental arsenic exposure. ==== Hazard maps for contaminated groundwater ==== Around one-third of the world's population drinks water from groundwater resources. Of this, about 10 percent, approximately 300 million people, obtains water from groundwater resources that are contaminated with unhealthy levels of arsenic or fluoride. These trace elements derive
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
mainly from minerals and ions in the ground. === Redox transformation of arsenic in natural waters === Arsenic is unique among the trace metalloids and oxyanion-forming trace metals (e.g. As, Se, Sb, Mo, V, Cr, U, Re). It is sensitive to mobilization at pH values typical of natural waters (pH 6.5–8.5) under both oxidizing and reducing conditions. Arsenic can occur in the environment in several oxidation states (−3, 0, +3 and +5), but in natural waters it is mostly found in inorganic forms as oxyanions of trivalent arsenite [As(III)] or pentavalent arsenate [As(V)]. Organic forms of arsenic are produced by biological activity, mostly in surface waters, but are rarely quantitatively important. Organic arsenic compounds may, however, occur where waters are significantly impacted by industrial pollution. Arsenic may be solubilized by various processes. When pH is high, arsenic may be released from surface binding sites that lose their positive charge. When water level drops and sulfide minerals are exposed to air, arsenic trapped in sulfide minerals can be released into water. When organic carbon is present in water, bacteria are fed by directly reducing As(V) to As(III) or by reducing the element at the binding site, releasing inorganic arsenic. The aquatic transformations of arsenic are affected by pH, reduction-oxidation potential, organic matter concentration and the concentrations and forms of other elements, especially iron and manganese. The main factors are pH and the redox potential. Generally, the main forms of arsenic under oxic conditions are H3AsO4, H2AsO−4, HAsO2−4, and AsO3−4 at pH 2, 2–7, 7–11 and 11, respectively. Under reducing conditions, H3AsO4 is predominant at pH 2–9. Oxidation and reduction affects the migration of arsenic in subsurface environments. Arsenite is the most stable soluble form of arsenic in reducing environments and arsenate, which is less mobile than arsenite, is dominant in oxidizing
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
environments at neutral pH. Therefore, arsenic may be more mobile under reducing conditions. The reducing environment is also rich in organic matter which may enhance the solubility of arsenic compounds. As a result, the adsorption of arsenic is reduced and dissolved arsenic accumulates in groundwater. That is why the arsenic content is higher in reducing environments than in oxidizing environments. The presence of sulfur is another factor that affects the transformation of arsenic in natural water. Arsenic can precipitate when metal sulfides form. In this way, arsenic is removed from the water and its mobility decreases. When oxygen is present, bacteria oxidize reduced sulfur to generate energy, potentially releasing bound arsenic. Redox reactions involving Fe also appear to be essential factors in the fate of arsenic in aquatic systems. The reduction of iron oxyhydroxides plays a key role in the release of arsenic to water. So arsenic can be enriched in water with elevated Fe concentrations. Under oxidizing conditions, arsenic can be mobilized from pyrite or iron oxides especially at elevated pH. Under reducing conditions, arsenic can be mobilized by reductive desorption or dissolution when associated with iron oxides. The reductive desorption occurs under two circumstances. One is when arsenate is reduced to arsenite which adsorbs to iron oxides less strongly. The other results from a change in the charge on the mineral surface which leads to the desorption of bound arsenic. Some species of bacteria catalyze redox transformations of arsenic. Dissimilatory arsenate-respiring prokaryotes (DARP) speed up the reduction of As(V) to As(III). DARP use As(V) as the electron acceptor of anaerobic respiration and obtain energy to survive. Other organic and inorganic substances can be oxidized in this process. Chemoautotrophic arsenite oxidizers (CAO) and heterotrophic arsenite oxidizers (HAO) convert As(III) into As(V). CAO combine the oxidation of As(III) with the
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
reduction of oxygen or nitrate. They use obtained energy to fix produce organic carbon from CO2. HAO cannot obtain energy from As(III) oxidation. This process may be an arsenic detoxification mechanism for the bacteria. Equilibrium thermodynamic calculations predict that As(V) concentrations should be greater than As(III) concentrations in all but strongly reducing conditions, i.e. where sulfate reduction is occurring. However, abiotic redox reactions of arsenic are slow. Oxidation of As(III) by dissolved O2 is a particularly slow reaction. For example, Johnson and Pilson (1975) gave half-lives for the oxygenation of As(III) in seawater ranging from several months to a year. In other studies, As(V)/As(III) ratios were stable over periods of days or weeks during water sampling when no particular care was taken to prevent oxidation, again suggesting relatively slow oxidation rates. Cherry found from experimental studies that the As(V)/As(III) ratios were stable in anoxic solutions for up to 3 weeks but that gradual changes occurred over longer timescales. Sterile water samples have been observed to be less susceptible to speciation changes than non-sterile samples. Oremland found that the reduction of As(V) to As(III) in Mono Lake was rapidly catalyzed by bacteria with rate constants ranging from 0.02 to 0.3-day−1. === Wood preservation in the US === As of 2002, US-based industries consumed 19,600 metric tons of arsenic. Ninety percent of this was used for treatment of wood with chromated copper arsenate (CCA). In 2007, 50% of the 5,280 metric tons of consumption was still used for this purpose. In the United States, the voluntary phasing-out of arsenic in production of consumer products and residential and general consumer construction products began on 31 December 2003, and alternative chemicals are now used, such as Alkaline Copper Quaternary, borates, copper azole, cyproconazole, and propiconazole. Although discontinued, this application is also one of the
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
most concerning to the general public. The vast majority of older pressure-treated wood was treated with CCA. CCA lumber is still in widespread use in many countries, and was heavily used during the latter half of the 20th century as a structural and outdoor building material. Although the use of CCA lumber was banned in many areas after studies showed that arsenic could leach out of the wood into the surrounding soil (from playground equipment, for instance), a risk is also presented by the burning of older CCA timber. The direct or indirect ingestion of wood ash from burnt CCA lumber has caused fatalities in animals and serious poisonings in humans; the lethal human dose is approximately 20 grams of ash. Scrap CCA lumber from construction and demolition sites may be inadvertently used in commercial and domestic fires. Protocols for safe disposal of CCA lumber are not consistent throughout the world. Widespread landfill disposal of such timber raises some concern, but other studies have shown no arsenic contamination in the groundwater. === Mapping of industrial releases in the US === One tool that maps the location (and other information) of arsenic releases in the United States is TOXMAP. TOXMAP is a Geographic Information System (GIS) from the Division of Specialized Information Services of the United States National Library of Medicine (NLM) funded by the US Federal Government. With marked-up maps of the United States, TOXMAP enables users to visually explore data from the United States Environmental Protection Agency's (EPA) Toxics Release Inventory and Superfund Basic Research Programs. TOXMAP's chemical and environmental health information is taken from NLM's Toxicology Data Network (TOXNET), PubMed, and from other authoritative sources. === Bioremediation === Physical, chemical, and biological methods have been used to remediate arsenic contaminated water. Bioremediation is said to be cost-effective and
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
environmentally friendly. Bioremediation of ground water contaminated with arsenic aims to convert arsenite, the toxic form of arsenic to humans, to arsenate. Arsenate (+5 oxidation state) is the dominant form of arsenic in surface water, while arsenite (+3 oxidation state) is the dominant form in hypoxic to anoxic environments. Arsenite is more soluble and mobile than arsenate. Many species of bacteria can transform arsenite to arsenate in anoxic conditions by using arsenite as an electron donor. This is a useful method in ground water remediation. Another bioremediation strategy is to use plants that accumulate arsenic in their tissues via phytoremediation but the disposal of contaminated plant material needs to be considered. Bioremediation requires careful evaluation and design in accordance with existing conditions. Some sites may require the addition of an electron acceptor while others require microbe supplementation (bioaugmentation). Regardless of the method used, only constant monitoring can prevent future contamination. === Arsenic removal === Coagulation and flocculation are closely related processes common in arsenate removal from water. Due to the net negative charge carried by arsenate ions, they settle slowly or not at all due to charge repulsion. In coagulation, a positively charged coagulent such as iron and aluminum (commonly used salts: FeCl3, Fe2(SO4)3, Al2(SO4)3) neutralize the negatively charged arsenate, enable it to settle. Flocculation follows where a flocculant bridges smaller particles and allows the aggregate to precipitate out from water. However, such methods may not be efficient on arsenite as As(III) exists in uncharged arsenious acid, H3AsO3, at near-neutral pH. The major drawbacks of coagulation and flocculation are the costly disposal of arsenate-concentrated sludge, and possible secondary contamination of environment. Moreover, coagulents such as iron may produce ion contamination that exceeds safety levels. == Toxicity and precautions == Arsenic and many of its compounds are especially potent poisons (e.g.
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
arsine). Small amount of arsenic can be detected by pharmacopoial methods which includes reduction of arsenic to arsenious with help of zinc and can be confirmed with mercuric chloride paper. === Classification === Elemental arsenic and arsenic sulfate and trioxide compounds are classified as "toxic" and "dangerous for the environment" in the European Union under directive 67/548/EEC. The International Agency for Research on Cancer (IARC) recognizes arsenic and inorganic arsenic compounds as group 1 carcinogens, and the EU lists arsenic trioxide, arsenic pentoxide, and arsenate salts as category 1 carcinogens. Arsenic is known to cause arsenicosis when present in drinking water, "the most common species being arsenate [HAsO2−4; As(V)] and arsenite [H3AsO3; As(III)]". === Legal limits, food, and drink === In the United States since 2006, the maximum concentration in drinking water allowed by the Environmental Protection Agency (EPA) is 10 ppb and the FDA set the same standard in 2005 for bottled water. The Department of Environmental Protection for New Jersey set a drinking water limit of 5 ppb in 2006. The IDLH (immediately dangerous to life and health) value for arsenic metal and inorganic arsenic compounds is 5 mg/m3 (5 ppb). The Occupational Safety and Health Administration has set the permissible exposure limit (PEL) to a time-weighted average (TWA) of 0.01 mg/m3 (0.01 ppb), and the National Institute for Occupational Safety and Health (NIOSH) has set the recommended exposure limit (REL) to a 15-minute constant exposure of 0.002 mg/m3 (0.002 ppb). The PEL for organic arsenic compounds is a TWA of 0.5 mg/m3. (0.5 ppb). In 2008, based on its ongoing testing of a wide variety of American foods for toxic chemicals, the U.S. Food and Drug Administration set the "level of concern" for inorganic arsenic in apple and pear juices at 23 ppb, based on non-carcinogenic effects,
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
and began blocking importation of products in excess of this level; it also required recalls for non-conforming domestic products. In 2011, the national Dr. Oz television show broadcast a program highlighting tests performed by an independent lab hired by the producers. Though the methodology was disputed (it did not distinguish between organic and inorganic arsenic) the tests showed levels of arsenic up to 36 ppb. In response, the FDA tested the worst brand from the Dr. Oz show and found much lower levels. Ongoing testing found 95% of the apple juice samples were below the level of concern. Later testing by Consumer Reports showed inorganic arsenic at levels slightly above 10 ppb, and the organization urged parents to reduce consumption. In July 2013, on consideration of consumption by children, chronic exposure, and carcinogenic effect, the FDA established an "action level" of 10 ppb for apple juice, the same as the drinking water standard. Concern about arsenic in rice in Bangladesh was raised in 2002, but at the time only Australia had a legal limit for food (one milligram per kilogram, or 1000 ppb). Concern was raised about people who were eating U.S. rice exceeding WHO standards for personal arsenic intake in 2005. In 2011, the People's Republic of China set a food standard of 150 ppb for arsenic. In the United States in 2012, testing by separate groups of researchers at the Children's Environmental Health and Disease Prevention Research Center at Dartmouth College (early in the year, focusing on urinary levels in children) and Consumer Reports (in November) found levels of arsenic in rice that resulted in calls for the FDA to set limits. The FDA released some testing results in September 2012, and as of July 2013, is still collecting data in support of a new potential regulation. It
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
has not recommended any changes in consumer behavior. Consumer Reports recommended: That the EPA and FDA eliminate arsenic-containing fertilizer, drugs, and pesticides in food production; That the FDA establish a legal limit for food; That industry change production practices to lower arsenic levels, especially in food for children; and That consumers test home water supplies, eat a varied diet, and cook rice with excess water, then draining it off (reducing inorganic arsenic by about one third along with a slight reduction in vitamin content). Evidence-based public health advocates also recommend that, given the lack of regulation or labeling for arsenic in the U.S., children should eat no more than 1.5 servings per week of rice and should not drink rice milk as part of their daily diet before age 5. They also offer recommendations for adults and infants on how to limit arsenic exposure from rice, drinking water, and fruit juice. A 2014 World Health Organization advisory conference was scheduled to consider limits of 200–300 ppb for rice. ==== Reducing arsenic content in rice ==== In 2020, scientists assessed multiple preparation procedures of rice for their capacity to reduce arsenic content and preserve nutrients, recommending a procedure involving parboiling and water-absorption. === Occupational exposure limits === === Ecotoxicity === Arsenic is bioaccumulative in many organisms, marine species in particular, but it does not appear to biomagnify significantly in food webs. In polluted areas, plant growth may be affected by root uptake of arsenate, which is a phosphate analog and therefore readily transported in plant tissues and cells. In polluted areas, uptake of the more toxic arsenite ion (found more particularly in reducing conditions) is likely in poorly-drained soils. === Toxicity in animals === === Biological mechanism === Arsenic's toxicity comes from the affinity of arsenic(III) oxides for thiols. Thiols, in
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
the form of cysteine residues and cofactors such as lipoic acid and coenzyme A, are situated at the active sites of many important enzymes. Arsenic disrupts ATP production through several mechanisms. At the level of the citric acid cycle, arsenic inhibits lipoic acid, which is a cofactor for pyruvate dehydrogenase. By competing with phosphate, arsenate uncouples oxidative phosphorylation, thus inhibiting energy-linked reduction of NAD+, mitochondrial respiration and ATP synthesis. Hydrogen peroxide production is also increased, which, it is speculated, has potential to form reactive oxygen species and oxidative stress. These metabolic interferences lead to death from multi-system organ failure. The organ failure is presumed to be from necrotic cell death, not apoptosis, since energy reserves have been too depleted for apoptosis to occur. === Exposure risks and remediation === Occupational exposure and arsenic poisoning may occur in people working in industries involving the use of inorganic arsenic and its compounds, such as wood preservation, glass production, nonferrous metal alloys, and electronic semiconductor manufacturing. Inorganic arsenic is also found in coke oven emissions associated with the smelter industry. The conversion between As(III) and As(V) is a large factor in arsenic environmental contamination. According to Croal, Gralnick, Malasarn and Newman, "[the] understanding [of] what stimulates As(III) oxidation and/or limits As(V) reduction is relevant for bioremediation of contaminated sites (Croal). The study of chemolithoautotrophic As(III) oxidizers and the heterotrophic As(V) reducers can help the understanding of the oxidation and/or reduction of arsenic. === Treatment === Treatment of chronic arsenic poisoning is possible. British anti-lewisite (dimercaprol) is prescribed in doses of 5 mg/kg up to 300 mg every 4 hours for the first day, then every 6 hours for the second day, and finally every 8 hours for 8 additional days. However the USA's Agency for Toxic Substances and Disease Registry (ATSDR) states that
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
the long-term effects of arsenic exposure cannot be predicted. Blood, urine, hair, and nails may be tested for arsenic; however, these tests cannot foresee possible health outcomes from the exposure. Long-term exposure and consequent excretion through urine has been linked to bladder and kidney cancer in addition to cancer of the liver, prostate, skin, lungs, and nasal cavity. == Footnotes == == See also == Aqua Tofana Arsenic and Old Lace Grainger challenge Hypothetical types of biochemistry == References == == Bibliography == Emsley J (2011). "Arsenic". Nature's Building Blocks: An A–Z Guide to the Elements. Oxford, UK: Oxford University Press. pp. 47–55. ISBN 978-0-19-960563-7. Greenwood NN, Earnshaw A (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. Rieuwerts, John (2015). The Elements of Environmental Pollution. Abingdon and New York: Routledge. ISBN 978-0-415-85920-2.{{cite book}}: CS1 maint: publisher location (link) == Further reading == Whorton JG (2011). The Arsenic Century. Oxford University Press. ISBN 978-0-19-960599-6. == External links == WHO fact sheet on arsenic Arsenic Cancer Causing Substances, U.S. National Cancer Institute. CTD's Arsenic page and CTD's Arsenicals page from the Comparative Toxicogenomics Database Contaminant Focus: Arsenic Archived 1 September 2009 at the Wayback Machine by the EPA. Environmental Health Criteria for Arsenic and Arsenic Compounds, 2001 by the WHO. National Institute for Occupational Safety and Health – Arsenic Page
|
{
"page_id": 897,
"source": null,
"title": "Arsenic"
}
|
Antimony is a chemical element; it has symbol Sb (from Latin stibium) and atomic number 51. A lustrous grey metal or metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient times and were powdered for use as medicine and cosmetics, often known by the Arabic name kohl. The earliest known description of this metalloid in the West was written in 1540 by Vannoccio Biringuccio. China is the largest producer of antimony and its compounds, with most production coming from the Xikuangshan Mine in Hunan. The industrial methods for refining antimony from stibnite are roasting followed by reduction with carbon, or direct reduction of stibnite with iron. The most common applications for metallic antimony are in alloys with lead and tin, which have improved properties for solders, bullets, and plain bearings. It improves the rigidity of lead-alloy plates in lead–acid batteries. Antimony trioxide is a prominent additive for halogen-containing flame retardants. Antimony is used as a dopant in semiconductor devices. == Characteristics == === Properties === Antimony is a member of group 15 of the periodic table, one of the elements called pnictogens, and has an electronegativity of 2.05. In accordance with periodic trends, it is more electronegative than tin or bismuth, and less electronegative than tellurium or arsenic. Antimony is stable in air at room temperature but, if heated, it reacts with oxygen to produce antimony trioxide,Sb2O3. Antimony is a silvery, lustrous gray metalloid with a Mohs scale hardness of 3, which is too soft to mark hard objects. Coins of antimony were issued in China's Guizhou in 1931; durability was poor, and minting was soon discontinued because of its softness and toxicity. Antimony is resistant to attack by acids. The only stable allotrope of antimony under standard conditions
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
is metallic, brittle, silver-white, and shiny. It crystallises in a trigonal cell, isomorphic with bismuth and the gray allotrope of arsenic, and is formed when molten antimony is cooled slowly. Amorphous black antimony is formed upon rapid cooling of antimony vapor, and is only stable as a thin film (thickness in nanometres); thicker samples spontaneously transform into the metallic form. It oxidizes in air and may ignite spontaneously. At 100 °C, it gradually transforms into the stable form. The supposed yellow allotrope of antimony, generated only by oxidation of stibine (SbH3) at −90 °C, is also impure and not a true allotrope; above this temperature and in ambient light, it transforms into the more stable black allotrope. A rare explosive form of antimony can be formed from the electrolysis of antimony trichloride, but it always contains appreciable chlorine and is not really an antimony allotrope. When scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony forms; when rubbed with a pestle in a mortar, a strong detonation occurs. Elemental antimony adopts a layered structure (space group R3m No. 166) whose layers consist of fused, ruffled, six-membered rings. The nearest and next-nearest neighbors form an irregular octahedral complex, with the three atoms in each double layer slightly closer than the three atoms in the next. This relatively close packing leads to a high density of 6.697 g/cm3, but the weak bonding between the layers leads to the low hardness and brittleness of antimony. === Isotopes === Antimony has two stable isotopes: 121Sb with a natural abundance of 57.36% and 123Sb with a natural abundance of 42.64%. It also has 35 radioisotopes, of which the longest-lived is 125Sb with a half-life of 2.75 years. In addition, 29 metastable states have been characterized. The
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
most stable of these is 120m1Sb with a half-life of 5.76 days. Isotopes that are lighter than the stable 123Sb tend to decay by β+ decay, and those that are heavier tend to decay by β− decay, with some exceptions. Antimony is the lightest element to have an isotope with an alpha decay branch, excluding 8Be and other light nuclides with beta-delayed alpha emission. === Occurrence === The abundance of antimony in the Earth's crust is estimated at 0.2 parts per million, comparable to thallium at 0.5 ppm and silver at 0.07 ppm. It is the 63rd most abundant element in the crust. Even though this element is not abundant, it is found in more than 100 mineral species. Antimony is sometimes found natively (e.g. on Antimony Peak), but more frequently it is found in the sulfide stibnite (Sb2S3) which is the predominant ore mineral. == Compounds == Antimony compounds are often classified according to their oxidation state: Sb(III) and Sb(V). The +5 oxidation state is more common. === Oxides and hydroxides === Antimony trioxide is formed when antimony is burnt in air. In the gas phase, the molecule of the compound is Sb4O6, but it polymerizes upon condensing. Antimony pentoxide (Sb4O10) can be formed only by oxidation with concentrated nitric acid. Antimony also forms a mixed-valence oxide, antimony tetroxide (Sb2O4), which features both Sb(III) and Sb(V). Unlike oxides of phosphorus and arsenic, these oxides are amphoteric, do not form well-defined oxoacids, and react with acids to form antimony salts. Antimonous acid Sb(OH)3 is unknown, but the conjugate base sodium antimonite ([Na3SbO3]4) forms upon fusing sodium oxide and Sb4O6. Transition metal antimonites are also known.: 122 Antimonic acid exists only as the hydrate HSb(OH)6, forming salts as the antimonate anion Sb(OH)−6. When a solution containing this anion is dehydrated, the
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
precipitate contains mixed oxides.: 143 The most important antimony ore is stibnite (Sb2S3). Other sulfide minerals include pyrargyrite (Ag3SbS3), zinkenite, jamesonite, and boulangerite. Antimony pentasulfide is non-stoichiometric, which features antimony in the +3 oxidation state and S–S bonds. Several thioantimonides are known, such as [Sb6S10]2− and [Sb8S13]2−. === Halides === Antimony forms two series of halides: SbX3 and SbX5. The trihalides SbF3, SbCl3, SbBr3, and SbI3 are all molecular compounds having trigonal pyramidal molecular geometry. The trifluoride is prepared by the reaction of antimony trioxide with hydrofluoric acid: Sb2O3 + 6 HF → 2 SbF3 + 3 H2O It is Lewis acidic and readily accepts fluoride ions to form the complex anions SbF−4 and SbF2−5. Molten antimony trifluoride is a weak electrical conductor. The trichloride is prepared by dissolving stibnite in hydrochloric acid: Sb2S3 + 6 HCl → 2 SbCl3 + 3 H2S Arsenic sulfides are not readily attacked by the hydrochloric acid, so this method offers a route to As-free Sb. The pentahalides SbF5 and SbCl5 have trigonal bipyramidal molecular geometry in the gas phase, but in the liquid phase, SbF5 is polymeric, whereas SbCl5 is monomeric. Antimony pentafluoride is a powerful Lewis acid used to make the superacid fluoroantimonic acid (H2F+·SbF−6). Oxyhalides are more common for antimony than for arsenic and phosphorus. Antimony trioxide dissolves in concentrated acid to form oxoantimonyl compounds such as SbOCl and (SbO)2SO4. === Antimonides, hydrides, and organoantimony compounds === Compounds in this class generally are described as derivatives of Sb3−. Antimony forms antimonides with metals, such as indium antimonide (InSb) and silver antimonide (Ag3Sb). The alkali metal and zinc antimonides, such as Na3Sb and Zn3Sb2, are more reactive. Treating these antimonides with acid produces the highly unstable gas stibine, SbH3: Sb3− + 3 H+ → SbH3 Stibine can also be produced by treating
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
Sb3+ salts with hydride reagents such as sodium borohydride. Stibine decomposes spontaneously at room temperature. Because stibine has a positive heat of formation, it is thermodynamically unstable and thus antimony does not react with hydrogen directly. Organoantimony compounds are typically prepared by alkylation of antimony halides with Grignard reagents. A large variety of compounds are known with both Sb(III) and Sb(V) centers, including mixed chloro-organic derivatives, anions, and cations. Examples include triphenylstibine (Sb(C6H5)3) and pentaphenylantimony (Sb(C6H5)5). == History == Antimony(III) sulfide, Sb2S3, was recognized in predynastic Egypt as an eye cosmetic (kohl) as early as about 3100 BC, when the cosmetic palette was invented. An artifact, said to be part of a vase, made of antimony dating to about 3000 BC was found at Telloh, Chaldea (part of present-day Iraq), and a copper object plated with antimony dating between 2500 BC and 2200 BC has been found in Egypt. Austen, at a lecture by Herbert Gladstone in 1892, commented that "we only know of antimony at the present day as a highly brittle and crystalline metal, which could hardly be fashioned into a useful vase, and therefore this remarkable 'find' (artifact mentioned above) must represent the lost art of rendering antimony malleable." The British archaeologist Roger Moorey was unconvinced the artifact was indeed a vase, mentioning that Selimkhanov, after his analysis of the Tello object (published in 1975), "attempted to relate the metal to Transcaucasian natural antimony" (i.e. native metal) and that "the antimony objects from Transcaucasia are all small personal ornaments." This weakens the evidence for a lost art "of rendering antimony malleable". The Roman scholar Pliny the Elder described several ways of preparing antimony sulfide for medical purposes in his treatise Natural History, around 77 AD. Pliny the Elder also made a distinction between "male" and "female" forms
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
of antimony; the male form is probably the sulfide, while the female form, which is superior, heavier, and less friable, has been suspected to be native metallic antimony. The Greek naturalist Pedanius Dioscorides mentioned that antimony sulfide could be roasted by heating by a current of air. It is thought that this produced metallic antimony. Antimony was frequently described in alchemical manuscripts, including the Summa Perfectionis of Pseudo-Geber, written around the 14th century. A description of a procedure for isolating antimony is later given in the 1540 book De la pirotechnia by Vannoccio Biringuccio, predating the more famous 1556 book by Agricola, De re metallica. In this context Agricola has been often incorrectly credited with the discovery of metallic antimony. The book Currus Triumphalis Antimonii (The Triumphal Chariot of Antimony), describing the preparation of metallic antimony, was published in Germany in 1604. It was purported to be written by a Benedictine monk, writing under the name Basilius Valentinus in the 15th century; if it were authentic, which it is not, it would predate Biringuccio. The metal antimony was known to German chemist Andreas Libavius in 1615 who obtained it by adding iron to a molten mixture of antimony sulfide, salt and potassium tartrate. This procedure produced antimony with a crystalline or starred surface. With the advent of challenges to phlogiston theory, it was recognized that antimony is an element forming sulfides, oxides, and other compounds, as do other metals. The first discovery of naturally occurring pure antimony in the Earth's crust was described by the Swedish scientist and local mine district engineer Anton von Swab in 1783; the type-sample was collected from the Sala Silver Mine in the Bergslagen mining district of Sala, Västmanland, Sweden. === Etymology === The medieval Latin form, from which the modern languages and late Byzantine
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
Greek take their names for antimony, is antimonium. The origin of that is uncertain, and all suggestions have some difficulty either of form or interpretation. The popular etymology, from ἀντίμοναχός anti-monachos or French antimoine, would mean "monk-killer", which is explained by the fact that many early alchemists were monks, and some antimony compounds were poisonous. Another popular etymology is the hypothetical Greek word ἀντίμόνος antimonos, "against aloneness", explained as "not found as metal", or "not found unalloyed". However, ancient Greek would more naturally express the pure negative as α- ("not"). Edmund Oscar von Lippmann conjectured a hypothetical Greek word ανθήμόνιον anthemonion, which would mean "floret", and cites several examples of related Greek words (but not that one) which describe chemical or biological efflorescence. The early uses of antimonium include the translations, in 1050–1100, by Constantine the African of Arabic medical treatises. Several authorities believe antimonium is a scribal corruption of some Arabic form; Meyerhof derives it from ithmid; other possibilities include athimar, the Arabic name of the metalloid, and a hypothetical as-stimmi, derived from or parallel to the Greek.: 28 The standard chemical symbol for antimony (Sb) is credited to Jöns Jakob Berzelius, who derived the abbreviation from stibium. The ancient words for antimony mostly have, as their chief meaning, kohl, the sulfide of antimony. The Egyptians called antimony mśdmt: 230 : 541 or stm. The Arabic word for the substance, as opposed to the cosmetic, can appear as إثمد ithmid, athmoud, othmod, or uthmod. Littré suggests the first form, which is the earliest, derives from stimmida, an accusative for stimmi. The Greek word στίμμι (stimmi) is used by Attic tragic poets of the 5th century BC, and is possibly a loan word from Arabic or from Egyptian stm. == Production == === Process === The extraction of antimony from
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
ores depends on the quality and composition of the ore. Most antimony is mined as the sulfide; lower-grade ores are concentrated by froth flotation, while higher-grade ores are heated to 500–600 °C, the temperature at which stibnite melts and separates from the gangue minerals. Antimony can be isolated from the crude antimony sulfide by reduction with scrap iron: Sb2S3 + 3 Fe → 2 Sb + 3 FeS The sulfide is converted to an oxide by roasting. The product is further purified by vaporizing the volatile antimony(III) oxide, which is recovered. This sublimate is often used directly for the main applications, impurities being arsenic and sulfide. Antimony is isolated from the oxide by a carbothermal reduction: 2 Sb2O3 + 3 C → 4 Sb + 3 CO2 The lower-grade ores are reduced in blast furnaces while the higher-grade ores are reduced in reverberatory furnaces. === Top producers and production volumes === In 2022, according to the US Geological Survey, China accounted for 54.5% of total antimony production, followed in second place by Russia with 18.2% and Tajikistan with 15.5%. Chinese production of antimony is expected to decline in the future as mines and smelters are closed down by the government as part of pollution control. Especially due to an environmental protection law having gone into effect in January 2015 and revised "Emission Standards of Pollutants for Stanum, Antimony, and Mercury" having gone into effect, hurdles for economic production are higher. Reported production of antimony in China has fallen and is unlikely to increase in the coming years, according to the Roskill report. No significant antimony deposits in China have been developed for about ten years, and the remaining economic reserves are being rapidly depleted. === Reserves === === Supply risk === For antimony-importing regions, such as Europe and the U.S.,
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
antimony is considered to be a critical mineral for industrial manufacturing that is at risk of supply chain disruption. With global production coming mainly from China (74%), Tajikistan (8%), and Russia (4%), these sources are critical to supply. European Union: Antimony is considered a critical raw material for defense, automotive, construction and textiles. The E.U. sources are 100% imported, coming mainly from Turkey (62%), Bolivia (20%) and Guatemala (7%). United Kingdom: The British Geological Survey's 2015 risk list ranks antimony second highest (after rare earth elements) on the relative supply risk index. United States: Antimony is a mineral commodity considered critical to the economic and national security. In 2022, no antimony was mined in the U.S. == Applications == Approximately 48% of antimony is consumed in flame retardants, 33% in lead–acid batteries, and 8% in plastics. === Flame retardants === Antimony is mainly used as the trioxide for flame-proofing compounds, always in combination with halogenated flame retardants except in halogen-containing polymers. The flame retarding effect of antimony trioxide is produced by the formation of halogenated antimony compounds, which react with hydrogen atoms, and probably also with oxygen atoms and OH radicals, thus inhibiting fire. Markets for these flame-retardants include children's clothing, toys, aircraft, and automobile seat covers. They are also added to polyester resins in fiberglass composites for such items as light aircraft engine covers. The resin will burn in the presence of an externally generated flame, but will extinguish when the external flame is removed. === Alloys === Antimony forms a highly useful alloy with lead, increasing its hardness and mechanical strength. When casting it increases fluidity of the melt and reduces shrinkage during cooling. For most applications involving lead, varying amounts of antimony are used as alloying metal. In lead–acid batteries, this addition improves plate strength and charging
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
characteristics. For sailboats, lead keels are used to provide righting moment, ranging from 600 lbs to over 200 tons for the largest sailing superyachts; to improve hardness and tensile strength of the lead keel, antimony is mixed with lead between 2% and 5% by volume. Antimony is used in antifriction alloys (such as Babbitt metal), in bullets and lead shot, electrical cable sheathing, type metal (for example, for linotype printing machines), solder (some "lead-free" solders contain 5% Sb), in pewter, and in hardening alloys with low tin content in the manufacturing of organ pipes. === Other applications === Three other applications consume nearly all the rest of the world's supply. One application is as a stabilizer and catalyst for the production of polyethylene terephthalate. Another is as a fining agent to remove microscopic bubbles in glass, mostly for TV screens – antimony ions interact with oxygen, suppressing the tendency of the latter to form bubbles. The third application is pigments. In the 1990s antimony was increasingly being used in semiconductors as a dopant in n-type silicon wafers for diodes, infrared detectors, and Hall-effect devices. In the 1950s, the emitters and collectors of n-p-n alloy junction transistors were doped with tiny beads of a lead-antimony alloy. Indium antimonide (InSb) is used as a material for mid-infrared detectors. The material Ge2Sb2Te5 is used as for phase-change memory, a type of computer memory. Biology and medicine have few uses for antimony. Treatments containing antimony, known as antimonials, are used as emetics. Antimony compounds are used as antiprotozoan drugs. Potassium antimonyl tartrate, or tartar emetic, was once used as an anti-schistosomal drug from 1919 on. It was subsequently replaced by praziquantel. Antimony and its compounds are used in several veterinary preparations, such as anthiomaline and lithium antimony thiomalate, as a skin conditioner in ruminants.
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
Antimony has a nourishing or conditioning effect on keratinized tissues in animals. Antimony-based drugs, such as meglumine antimoniate, are also considered the drugs of choice for treatment of leishmaniasis. Early treatments used antimony(III) species (trivalent antimonials), but in 1922 Upendranath Brahmachari invented a much safer antimony(V) drug, and since then so-called pentavalent antimonials have been the standard first-line treatment. However, Leishmania strains in Bihar and neighboring regions have developed resistance to antimony. Elemental antimony as an antimony pill was once used as a medicine. It could be reused by others after ingestion and elimination. Antimony(III) sulfide is used in the heads of some safety matches. Antimony sulfides help to stabilize the friction coefficient in automotive brake pad materials. Antimony is used in bullets, bullet tracers, paint, glass art, and as an opacifier in enamel. Antimony-124 is used together with beryllium in neutron sources; the gamma rays emitted by antimony-124 initiate the photodisintegration of beryllium. The emitted neutrons have an average energy of 24 keV. Natural antimony is used in startup neutron sources. The powder derived from crushed antimony sulfide (kohl) has been used for millennia as an eye cosmetic. Historically it was applied to the eyes with a metal rod and with one's spittle, and was thought by the ancients to aid in curing eye infections. The practice is still seen in Yemen and in other Muslim countries. == Precautions == Antimony and many of its compounds are toxic, and the effects of antimony poisoning are similar to arsenic poisoning. The toxicity of antimony is far lower than that of arsenic; this might be caused by the significant differences of uptake, metabolism and excretion between arsenic and antimony. The uptake of antimony(III) or antimony(V) in the gastrointestinal tract is at most 20%. Antimony(V) is not quantitatively reduced to antimony(III) in
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
the cell (in fact antimony(III) is oxidised to antimony(V) instead). Since methylation of antimony does not occur, the excretion of antimony(V) in urine is the main way of elimination. Like arsenic, the most serious effect of acute antimony poisoning is cardiotoxicity and the resulting myocarditis; however, it can also manifest as Adams–Stokes syndrome, which arsenic does not. Reported cases of intoxication by antimony equivalent to 90 mg antimony potassium tartrate dissolved from enamel has been reported to show only short term effects. An intoxication with 6 g of antimony potassium tartrate was reported to result in death after three days. Inhalation of antimony dust is harmful and in certain cases may be fatal; in small doses, antimony causes headaches, dizziness, and depression. Larger doses such as prolonged skin contact may cause dermatitis, or damage the kidneys and the liver, causing violent and frequent vomiting, leading to death in a few days. Antimony is incompatible with strong oxidizing agents, strong acids, halogen acids, chlorine, or fluorine. It should be kept away from heat. Antimony leaches from polyethylene terephthalate (PET) bottles into liquids. While levels observed for bottled water are below drinking water guidelines, fruit juice concentrates (for which no guidelines are established) produced in the UK were found to contain up to 44.7 μg/L of antimony, well above the EU limits for tap water of 5 μg/L. The guidelines are: World Health Organization: 20 μg/L Japan: 15 μg/L United States Environmental Protection Agency, Health Canada and the Ontario Ministry of Environment: 6 μg/L EU and German Federal Ministry of Environment: 5 μg/L The tolerable daily intake (TDI) proposed by WHO is 6 μg antimony per kilogram of body weight. The immediately dangerous to life or health (IDLH) value for antimony is 50 mg/m3. === Toxicity === Certain compounds of antimony appear
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
to be toxic, particularly antimony trioxide and antimony potassium tartrate. Effects may be similar to arsenic poisoning. Occupational exposure may cause respiratory irritation, pneumoconiosis, antimony spots on the skin, gastrointestinal symptoms, and cardiac arrhythmias. In addition, antimony trioxide is potentially carcinogenic to humans. Adverse health effects have been observed in humans and animals following inhalation, oral, or dermal exposure to antimony and antimony compounds. Antimony toxicity typically occurs either due to occupational exposure, during therapy or from accidental ingestion. It is unclear if antimony can enter the body through the skin. The presence of low levels of antimony in saliva may also be associated with dental decay. == Notes == == References == == Cited sources == Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0-7506-3365-4. Wiberg, Egon; Wiberg, Nils & Holleman, Arnold Frederick (2001). Inorganic chemistry. Academic Press. ISBN 978-0-12-352651-9. == External links == Public Health Statement for Antimony International Antimony Association vzw (i2a) Chemistry in its element podcast (MP3) from the Royal Society of Chemistry's Chemistry World: Antimony Antimony at The Periodic Table of Videos (University of Nottingham) CDC – NIOSH Pocket Guide to Chemical Hazards – Antimony Antimony Mineral data and specimen images
|
{
"page_id": 898,
"source": null,
"title": "Antimony"
}
|
A nonthermal plasma, cold plasma or non-equilibrium plasma is a plasma which is not in thermodynamic equilibrium, because the electron temperature is much hotter than the temperature of heavy species (ions and neutrals). As only electrons are thermalized, their Maxwell-Boltzmann velocity distribution is very different from the ion velocity distribution. When one of the velocities of a species does not follow a Maxwell-Boltzmann distribution, the plasma is said to be non-Maxwellian. A kind of common nonthermal plasma is the mercury-vapor gas within a fluorescent lamp, where the "electron gas" reaches a temperature of 20,000 K (19,700 °C; 35,500 °F) while the rest of the gas, ions and neutral atoms, stays barely above room temperature, so the bulb can even be touched with hands while operating. == Applications == === Food industry === In the context of food processing, a nonthermal plasma (NTP) or cold plasma is specifically an antimicrobial treatment being investigated for application to fruits, vegetables and meat products with fragile surfaces. These foods are either not adequately sanitized or are otherwise unsuitable for treatment with chemicals, heat or other conventional food processing tools. While the applications of nonthermal plasma were initially focused on microbiological disinfection, newer applications such as enzyme inactivation, biomolecule oxidation, protein modification, prodrug activation, and pesticide dissipation are being actively researched. Nonthermal plasma also sees increasing use in the sterilization of teeth and hands, in hand dryers as well as in self-decontaminating filters. The term cold plasma has been recently used as a convenient descriptor to distinguish the one-atmosphere, near room temperature plasma discharges from other plasmas, operating at hundreds or thousands of degrees above ambient (see Plasma (physics) § Temperature. Within the context of food processing the term "cold" can potentially engender misleading images of refrigeration requirements as a part of the plasma treatment.
|
{
"page_id": 6161283,
"source": null,
"title": "Nonthermal plasma"
}
|
However, in practice this confusion has not been an issue. "Cold plasmas" may also loosely refer to weakly ionized gases (degree of ionization < 0.01%). ==== Nomenclature ==== The nomenclature for nonthermal plasma found in the scientific literature is varied. In some cases, the plasma is referred to by the specific technology used to generate it ("gliding arc", "plasma pencil", "plasma needle", "plasma jet", "dielectric barrier discharge", "piezoelectric direct discharge plasma", etc.), while other names are more generally descriptive, based on the characteristics of the plasma generated ("one atmosphere uniform glow discharge plasma", "atmospheric plasma", "ambient pressure nonthermal discharges", "non-equilibrium atmospheric pressure plasmas", etc.). The two features which distinguish NTP from other mature, industrially applied plasma technologies, is that they are 1) nonthermal and 2) operate at or near atmospheric pressure. ==== Technologies ==== === Medicine === An emerging field adds the capabilities of nonthermal plasma to dentistry and medicine. Cold plasma is used to treat chronic wounds. === Power generation === Magnetohydrodynamic power generation, a direct energy conversion method from a hot gas in motion within a magnetic field was developed in the 1960s and 1970s with pulsed MHD generators known as shock tubes, using non-equilibrium plasmas seeded with alkali metal vapors (like caesium, to increase the limited electrical conductivity of gases) heated at a limited temperature of 2000 to 4000 kelvins (to protect walls from thermal erosion) but where electrons were heated at more than 10,000 kelvins. A particular and unusual case of "inverse" nonthermal plasma is the very high temperature plasma produced by the Z machine, where ions are much hotter than electrons. === Aerospace === Aerodynamic active flow control solutions involving technological nonthermal weakly ionized plasmas for subsonic, supersonic and hypersonic flight are being studied, as plasma actuators in the field of electrohydrodynamics, and as magnetohydrodynamic
|
{
"page_id": 6161283,
"source": null,
"title": "Nonthermal plasma"
}
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.