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Section: Interpretation. The products that are expected from any given mechanism are determined during the design of the crossover experiment. This can be quite complicated to establish, but it makes for straightforward interpretation of the results. If the observed products match those predicted by a given mechanism, ... | Wikipedia - Crossover experiment (chemistry) - Interpretation | 151 | 863 | null |
Section: Limitations. Crossover experiments have several limitations. Although useful for distinguishing between proposed reaction mechanisms, they are limited in their ability to provide insight into a mechanism beyond what has already been proposed. The design of a useful crossover experiment relies on having a propo... | Wikipedia - Crossover experiment (chemistry) - Limitations | 159 | 918 | null |
Section: Limitations > Solvent cage effect. One of the major limitations of the crossover experiment is that it cannot rule out the possibility that solvent cage effects are masking a dissociation mechanism. If crossover products are observed, the evidence that the mechanism cannot be purely intramolecular is conclusiv... | Wikipedia - Crossover experiment (chemistry) - Limitations > Solvent cage effect | 325 | 1,656 | null |
When the timescale of the reaction is faster than or on the same order as the timescale of the solvent cage effect this is a more accurate representation of the same crossover experiment as above. Although a dissociative or intermolecular mechanism is occurring, no crossover occurs because the timescale of the reaction... | Wikipedia - Crossover experiment (chemistry) - Limitations > Solvent cage effect | 321 | 1,532 | null |
Section: Endocyclic restriction test. The first endocyclic restriction test was a crossover experiment published by Albert Eschenmoser in 1970. Methylation reactions in which a sulfonyl anion acts as a nucleophile and a methyl (arenesulfonate) serves as an electrophile were known to occur, but it was proposed that they... | Wikipedia - Crossover experiment (chemistry) - Endocyclic restriction test | 268 | 1,221 | null |
Section: Inorganic chemistry. Mechanisms in inorganic and organometallic chemistry are often complicated and difficult to determine experimentally. Catalytic mechanisms are particularly challenging to study in cases where no metal complex at all aside from the pre-catalyst can be isolated. In the 2013 themed issue of D... | Wikipedia - Crossover experiment (chemistry) - Inorganic chemistry | 334 | 1,655 | null |
Section: Inorganic chemistry > Reductive elimination. Reductive elimination is a common step in organometallic reaction mechanisms, and particularly in catalytic cycles. In catalytic cycles that form C-H or C-C bonds reductive elimination is often the final product-forming step. Square planar d8 metal complexes are oft... | Wikipedia - Crossover experiment (chemistry) - Inorganic chemistry > Reductive elimination | 320 | 1,593 | null |
Stille were among the first experiments to demonstrate that reductive elimination is an intramolecular process and that non-adjacent groups do not reductively eliminate. Several square planar d8 palladium species were used in the study, with each one having two bound phosphine ligands and two bound methyl groups. One c... | Wikipedia - Crossover experiment (chemistry) - Inorganic chemistry > Reductive elimination | 333 | 1,319 | null |
The only product was the deuterium-labeled product of cis-elimination. This led to the final conclusion that only ligands adjacent to each other on the metal complex are capable of reductively eliminating. This study also tracked and analyzed reaction rate data, demonstrating the value of employing multiple strategies ... | Wikipedia - Crossover experiment (chemistry) - Inorganic chemistry > Reductive elimination | 157 | 810 | null |
Section: Biochemistry. The mechanisms of enzyme-catalyzed reactions can also be studied using crossover experiments. Examples of the application of this technique in biochemistry include the study of reactions catalyzed by nucleoside diphosphohexose-4,6-dehydratases, the aconitase-catalyzed elimination of water from ci... | Wikipedia - Crossover experiment (chemistry) - Biochemistry | 162 | 740 | null |
Section: Biochemistry > Mechanism of aconitase action. Isotope labeling experiments and crossover experiments were essential to early efforts to understand the mechanism of aconitase action. Isotope scrambling experiments using tritium, deuterium, and 18O were carried out on the aconitase hydratase reaction by I.A. Ros... | Wikipedia - Crossover experiment (chemistry) - Biochemistry > Mechanism of aconitase action | 250 | 1,132 | null |
Article: Crystal chemistry. Crystal chemistry is the study of the principles of chemistry behind crystals and their use in describing structure-property relations in solids, as well as the chemical properties of periodic structures. The principles that govern the assembly of crystal and glass structures are described, ... | Wikipedia - Crystal chemistry - Summary | 346 | 1,897 | null |
Article: Crystallography. Crystallography is the branch of science devoted to the study of molecular and crystalline structure and properties. The word crystallography is derived from the Ancient Greek word κρύσταλλος (krústallos; "clear ice, rock-crystal"), and γράφειν (gráphein; "to write"). In July 2012, the United ... | Wikipedia - Crystallography - Summary | 265 | 1,234 | null |
Section: History and timeline. Before the 20th century, the study of crystals was based on physical measurements of their geometry using a goniometer. This involved measuring the angles of crystal faces relative to each other and to theoretical reference axes (crystallographic axes), and establishing the symmetry of th... | Wikipedia - Crystallography - History and timeline | 339 | 1,722 | null |
Section: Methodology. Crystallographic methods depend mainly on analysis of the diffraction patterns of a sample targeted by a beam of some type. X-rays are most commonly used; other beams used include electrons or neutrons. Crystallographers often explicitly state the type of beam used, as in the terms X-ray diffracti... | Wikipedia - Crystallography - Methodology | 328 | 1,728 | null |
Section: Applications in various areas > Materials science. Crystallography is used by materials scientists to characterize different materials. In single crystals, the effects of the crystalline arrangement of atoms is often easy to see macroscopically because the natural shapes of crystals reflect the atomic structur... | Wikipedia - Crystallography - Applications in various areas > Materials science | 347 | 1,868 | null |
In another example, iron transforms from a body-centered cubic (bcc) structure called ferrite to a face-centered cubic (fcc) structure called austenite when it is heated. The fcc structure is a close-packed structure unlike the bcc structure; thus the volume of the iron decreases when this transformation occurs. Crysta... | Wikipedia - Crystallography - Applications in various areas > Materials science | 182 | 933 | null |
Section: Applications in various areas > Biology. X-ray crystallography is the primary method for determining the molecular conformations of biological macromolecules, particularly protein and nucleic acids such as DNA and RNA. The first crystal structure of a macromolecule was solved in 1958, a three-dimensional model... | Wikipedia - Crystallography - Applications in various areas > Biology | 239 | 1,202 | null |
Section: Notation. Coordinates in square brackets such as [100] denote a direction vector (in real space). Coordinates in angle brackets or chevrons such as <100> denote a family of directions which are related by symmetry operations. In the cubic crystal system for example, <100> would mean [100], [010], [001] or the ... | Wikipedia - Crystallography - Notation | 220 | 941 | null |
Section: Reference literature. The International Tables for Crystallography is an eight-book series that outlines the standard notations for formatting, describing and testing crystals. The series contains books that covers analysis methods and the mathematical procedures for determining organic structure through x-ray... | Wikipedia - Crystallography - Reference literature | 182 | 946 | null |
Section: Dodecamethylcyclohexasiloxane (D6). The dodecamethylcyclohexasiloxane silicone liquid has no odor and consists of six repeating units of silicon (Si) and oxygen (O) atoms in a closed loop giving it a circular structure. Each silicon atom has two methyl groups attached (CH3). CASRN: 540-97-6. D6 is also contain... | Wikipedia - Cyclosiloxane - Dodecamethylcyclohexasiloxane (D6) | 197 | 593 | null |
Article: Dark oxygen. Dark oxygen production refers to the generation of molecular oxygen (O2) through processes that do not involve light-dependent oxygenic photosynthesis. The name therefore uses a different sense of 'dark' than that used in the phrase "biological dark matter" (for example) which indicates obscurity ... | Wikipedia - Dark oxygen - Summary | 153 | 782 | null |
Section: Abiotic production. Abiotic production of dark oxygen can occur through several mechanisms, such as: Water radiolysis: This process typically takes place in dark geological ecosystems, such as aquifers, where the decay of radioactive elements in surrounding rock leads to the breakdown of water molecules, produ... | Wikipedia - Dark oxygen - Abiotic production | 190 | 856 | null |
Section: Experimental evidence. Recent studies have provided evidence for dark oxygen production in various geological and subsurface environments: Groundwater ecosystems: Dissolved oxygen concentrations have been measured in old groundwaters previously assumed to be anoxic. The presence of O2 is attributed to microbia... | Wikipedia - Dark oxygen - Experimental evidence | 168 | 937 | null |
Section: Carbocation generation. In the basic method, a molecule (R,R′,R″)C−T is prepared where the vacant bond of the desired radical or ion is satisfied by an atom of tritium 3H, the radioactive isotope of hydrogen with mass number 3. As the tritium undergoes beta decay (with a half-life of 12.32 years), it is transf... | Wikipedia - Decay technique - Carbocation generation | 318 | 1,338 | null |
These events happen very quickly compared to typical molecular relaxation times, so the carbocation is usually created in the same conformation and electronic configuration as the original neutral molecule. For example, decay of tritiated methane, CH3T (R = R′ = R″ = H) produces the carbenium ion H3C+ in a tetrahedral ... | Wikipedia - Decay technique - Carbocation generation | 277 | 1,279 | null |
Section: Persistent bound structures. Whereas the carbon–helium-ion bond breaks spontaneously and immediately to yield a carbocation, bonds of other elements to helium are more stable. For example, molecular tritium T2 or tritium-hydrogen HT. On decay, these form a stable helium hydride ion [HeH]+ (respectively [3HeT]+... | Wikipedia - Decay technique - Persistent bound structures | 216 | 843 | null |
Section: Practical considerations. A major difficulty in using this method in practice is that the energetic electron released by the decay of one atom of tritium can break apart, modify, ionize, or excite hundreds of other molecules in its path. These fragments and ions can further react with the surrounding molecules... | Wikipedia - Decay technique - Practical considerations | 239 | 1,115 | null |
Article: Direct reduction. In the iron and steel industry, direct reduction is a set of processes for obtaining iron from iron ore, by reducing iron oxides without melting the metal. The resulting product is pre-reduced iron ore. Historically, direct reduction was used to obtain a mix of iron and slag called a bloom in... | Wikipedia - Direct reduction - Summary | 191 | 966 | null |
Section: History > Bloomery. Historically, the reduction of iron ore without smelting is the oldest process for obtaining steel. Low-temperature furnaces, unable to reach the melting temperatures of iron alloys, produce a bloom, a heterogeneous agglomerate of metallic iron more or less impregnated with carbon, gangue, ... | Wikipedia - Direct reduction - History > Bloomery | 236 | 1,115 | null |
Section: History > Modern direct reduction. More advanced direct reduction processes were developed at the beginning of the 20th century, when it became possible to smelt pre-reduced ores using the Martin-Siemens process or the electric arc furnace. Based on this technical and economic model, a number of processes were... | Wikipedia - Direct reduction - History > Modern direct reduction | 327 | 1,595 | null |
Although profitable and innovative, the processes invented did not ultimately prove to be a technological revolution capable of supplanting the traditional blast furnace-based process. However, the quantity of steel produced from pre-reduced materials grew steadily, outstripping world steel production: in 1975, NML pla... | Wikipedia - Direct reduction - History > Modern direct reduction | 315 | 1,534 | null |
Section: Chemical reactions > Reducing gas production > Coal-fired processes. In coal-fired processes, part of the fuel is first burnt to heat the charge. The product of this combustion is CO2. When the temperature reaches 1,000 °C, the CO2 reacts with the unburned carbon to create CO: CO2 + C ⇌ 2 CO when T > 1 000 °C ... | Wikipedia - Direct reduction - Chemical reactions > Reducing gas production > Coal-fired processes | 173 | 730 | null |
Section: Procedures. Plants for the production of pre-reduced iron ore are known as direct reduction plants. The principle involves exposing iron ore to the reducing action of a high-temperature gas (around 1000 °C). This gas is composed of carbon monoxide and dihydrogen, the proportions of which depend on the producti... | Wikipedia - Direct reduction - Procedures | 271 | 1,415 | null |
Section: Procedures > Tank processes > Retorts. These are exclusively coal-fired processes, with the reducing gases generated inside the reduction vessel. The ore is charged with coal into a closed container. This is then heated until the oxygen present in the ore combines with the carbon before being discharged, mainl... | Wikipedia - Direct reduction - Procedures > Tank processes > Retorts | 333 | 1,605 | null |
Section: Procedures > Tank processes > Continuous processes. Based on the principle of counter-current piston flow, these processes are the closest to the blast furnace or, more accurately, the stückofen. Hot reducing gases are obtained from natural gas, in a separate unit from the shaft, and injected at the bottom of ... | Wikipedia - Direct reduction - Procedures > Tank processes > Continuous processes | 326 | 1,612 | null |
compared with the often dashed hopes of competing processes. Its direct competitor, the HYL III process, is the result of a research effort by the Tenova Group (de), heir to the Mexican Hylsa pioneers. Accounting for almost 20% of pre-reduced product production, it differs from the Midrex process in that it features an... | Wikipedia - Direct reduction - Procedures > Tank processes > Continuous processes | 281 | 1,331 | null |
Section: Procedures > Tank processes > Fluidized beds. Given that direct reduction is a chemical exchange between gas and solid, the fluidization of ore by reducing gases is an attractive line of research. However, the changing nature of the constituents, combined with the high temperature and the difficulty of control... | Wikipedia - Direct reduction - Procedures > Tank processes > Fluidized beds | 226 | 1,091 | null |
Section: Procedures > Rotating furnace processes > Rotary hearth. These processes consist of an annular furnace in which iron ore mixed with coal is circulated. Hot reducing gases flow over, and sometimes through, the charge. The ore is deposited on a tray, or carts, rotating slowly in the furnace. After one rotation, ... | Wikipedia - Direct reduction - Procedures > Rotating furnace processes > Rotary hearth | 311 | 1,512 | null |
Section: Procedures > Rotating furnace processes > Rotary drums. These processes involve high-temperature blending of iron ore and coal powder, with a little limestone to reduce the acidity of the ore. Processes such as Carl Wilhelm Siemens', based on the use of a short drum, first appeared at the end of the 19th centu... | Wikipedia - Direct reduction - Procedures > Rotating furnace processes > Rotary drums | 329 | 1,513 | null |
Section: Procedures > Reduction-melting processes. As the smelting stage is necessary to obtain alloys and shape the product, direct reduction processes are frequently combined with downstream smelting facilities. Most pre-reduced iron ore is smelted in electric furnaces: in 2003, 49 of the 50 Mt produced went into ele... | Wikipedia - Direct reduction - Procedures > Reduction-melting processes | 342 | 1,665 | null |
The COREX process, in operation since 1987, consists of a direct-reduction shaft reactor feeding a blast furnace crucible, in which the pre-reduced ore is brought to a liquid smelting state, consuming only coal. This process also produces a hot reducing gas, which can be valorized in a Midrex-type unit. An equivalent t... | Wikipedia - Direct reduction - Procedures > Reduction-melting processes | 334 | 1,551 | null |
Section: Economic importance > Controlling capital and material requirements. In the US, where the Midrex process was first developed, direct reduction was seen in the 1960s as a way of breathing new life into electric steelmaking. The techno-economic model of the mini-mill, based on flexibility and reduced plant size,... | Wikipedia - Direct reduction - Economic importance > Controlling capital and material requirements | 292 | 1,451 | null |
Section: Economic importance > The benefits of direct fuel reduction. Although gas handling and processing are far more economical than converting coal into coke (not to mention the associated constraints, such as bulk handling, high sensitivity of coking plants to production fluctuations, environmental impact, etc.), ... | Wikipedia - Direct reduction - Economic importance > The benefits of direct fuel reduction | 342 | 1,799 | null |
In 2007, the breakdown was as follows: natural gas processes are concentrated in Latin America (where many have already been developed) and the Middle East; coal-fired processes are remarkably successful in India, maintaining the proportion of steel produced by direct reduction despite the strong development of the Chi... | Wikipedia - Direct reduction - Economic importance > The benefits of direct fuel reduction | 261 | 1,334 | null |
Article: Double layer forces. Double layer forces occur between charged objects across liquids, typically water. This force acts over distances that are comparable to the Debye length, which is on the order of one to a few tenths of nanometers. The strength of these forces increases with the magnitude of the surface ch... | Wikipedia - Double layer forces - Summary | 334 | 1,761 | null |
Section: Poisson–Boltzmann model. The most popular model to describe the electrical double layer is the Poisson-Boltzmann (PB) model. This model can be equally used to evaluate double layer forces. Let us discuss this model in the case of planar geometry as shown in the figure on the right. In this case, the electrical... | Wikipedia - Double layer forces - Poisson–Boltzmann model | 310 | 1,137 | null |
These profiles can be related to the electrical potential by considering the fact that the chemical potential of the ions is constant. For both ions, this relation can be written as μ ± = μ + ( 0 ) + k T ln c ± ± q ψ {\displaystyle \mu _{\pm }=\mu _{+}^{(0)}+kT\ln c_{\pm }\pm q\psi } where μ ± ( 0 ) {\displaystyle \m... | Wikipedia - Double layer forces - Poisson–Boltzmann model | 243 | 849 | null |
This relation reflects the Boltzmann distribution of the ions with the energy ±qψ. Inserting these relations into the Poisson equation one obtains the PB equation d 2 ψ d z 2 = q c B ϵ 0 ϵ [ e + β q ψ − e − β q ψ ] {\displaystyle {\frac {d^{2}\psi }{dz^{2}}}={\frac {qc_{\rm {B}}}{\epsilon _{0}\epsilon }}[e^{+\beta q\ps... | Wikipedia - Double layer forces - Poisson–Boltzmann model | 183 | 590 | null |
The starting point is the Gibbs–Duhem relation for a two component system at constant temperature − V d Π + N + d μ + + N − d μ − = 0 {\displaystyle -Vd\Pi +N_{+}d\mu _{+}+N_{-}d\mu _{-}=0} Introducing the concentrations c± and using the expressions of the chemical potentials μ± given above one finds d Π = k T ( d c + ... | Wikipedia - Double layer forces - Poisson–Boltzmann model | 350 | 959 | null |
Section: Debye-Hückel model. When the electric potentials or charge densities are not too high, the PB equation can be simplified to the Debye-Hückel (DH) equation. By expanding the exponential function in the PB equation into a Taylor series, one obtains d 2 ψ d z 2 = κ 2 ψ {\displaystyle {\frac {d^{2}\psi }{dz^{2}}}=... | Wikipedia - Double layer forces - Debye-Hückel model | 249 | 769 | null |
In non-aqueous solutions, Debye length can be substantially larger than the ones given in the table due to smaller dielectric constants. The DH model represents a good approximation, when the surface potentials are sufficiently low with respect to the limiting values β q ψ ≪ 1 o r ψ ≪ k T q ≃ 26 m V {\displaystyle \bet... | Wikipedia - Double layer forces - Debye-Hückel model | 327 | 1,106 | null |
Section: Superposition approximation. When the surfaces are sufficiently far apart, the potential profiles originating from each individual surface will not be much perturbed by the presence of the other surface. This approximation thus suggests that one can simply add (superpose) the potentials profiles originating fr... | Wikipedia - Double layer forces - Superposition approximation | 349 | 1,444 | null |
This result can be simply generalized to highly charged surfaces, but only at larger separations. Even if the potential is large close to the surface, it will be small at larger distances, and can be described by the DH equation. However, in this case one has to replace the actual diffuse layer potential ψD with the ef... | Wikipedia - Double layer forces - Superposition approximation | 305 | 1,046 | null |
Section: Charge regulating surfaces. While the superposition approximation is actually exact at larger distances, it is no longer accurate at smaller separations. Solutions of the DH or PB equations in between the plates provide a more accurate picture at these conditions. Let us only discuss the symmetric situation wi... | Wikipedia - Double layer forces - Charge regulating surfaces | 298 | 1,463 | null |
The realistic case will be typically situated in between. By solving the DH equation one can show that diffuse layer potential varies upon approach as ψ ¯ D = 1 1 − p + p tanh ( κ h / 2 ) ψ D {\displaystyle {\bar {\psi }}_{\rm {D}}={\frac {1}{1-p+p\tanh(\kappa h/2)}}\psi _{\rm {D}}} while the surface charged density ... | Wikipedia - Double layer forces - Charge regulating surfaces | 343 | 908 | null |
By solving the DH equation one can show that diffuse layer potential varies upon approach as ψ ¯ D = 1 1 − p + p tanh ( κ h / 2 ) ψ D {\displaystyle {\bar {\psi }}_{\rm {D}}={\frac {1}{1-p+p\tanh(\kappa h/2)}}\psi _{\rm {D}}} while the surface charged density obey a similar relation σ ¯ = tanh ( κ h / 2 ) 1 − p + p... | Wikipedia - Double layer forces - Charge regulating surfaces | 358 | 975 | null |
The result of the superposition approximation is always recovered at larger distances but also for p = 1/2 at all distances. The latter fact explains why the superposition approximation can be very accurate even at small separations. Surfaces regulate their charge and not infrequently the actual regulation parameter is... | Wikipedia - Double layer forces - Charge regulating surfaces | 201 | 1,080 | null |
Section: Extensions to other geometries. Interactions between various objects were studied within the DH and PB models by many researchers. Some of the relevant results are summarized in the following. Non-planar geometries: Objects of other than planar geometries can be treated within the Derjaguin approximation, prov... | Wikipedia - Double layer forces - Extensions to other geometries | 343 | 1,412 | null |
This equation can be extended to more highly charged particles by reinterpreting the charge Q as an effective charge. To address the interactions in other situation, one must resort to numerical solutions of the DH or PB equation. Non-uniform or patchy charge distribution: Interaction between surfaces with non-uniform ... | Wikipedia - Double layer forces - Extensions to other geometries | 282 | 1,312 | null |
Section: Beyond Poisson-Boltzmann approximation. More accurate description of double layer interactions can be put forward on the primitive model. This model treats the electrostatic and hard-core interactions between all individual ions explicitly. However, it includes the solvent only in a "primitive" way, namely as ... | Wikipedia - Double layer forces - Beyond Poisson-Boltzmann approximation | 259 | 1,380 | null |
Section: Like-charge attraction controversy. Around 1990, theoretical and experimental evidence has emerged that forces between charged particles suspended in dilute solutions of monovalent electrolytes might be attractive at larger distances. This evidence is in contradiction with the PB theory discussed above, which ... | Wikipedia - Double layer forces - Like-charge attraction controversy | 298 | 1,723 | null |
Section: Relevance. Double layer interactions are relevant in a wide number of phenomena. These forces are responsible for swelling of clays. They may also be responsible for the stabilization of colloidal suspension and will prevent particle aggregation of highly charged colloidal particles in aqueous suspensions. At ... | Wikipedia - Double layer forces - Relevance | 160 | 828 | null |
Article: Electroconductive carbon black. Made up of primary carbon, carbon black is spherical in shape and arranged into aggregates and agglomerates. It differs from other carbon forms (diamond, graphite, coke) in its complex configuration, colloid dimensions and quasi-graphitic structure. Carbon black's purity and com... | Wikipedia - Electroconductive carbon black - Summary | 331 | 1,722 | null |
At the same time, it consists of primary carbon particles and boasts a high degree of aggregation. Carbon black's grouping facilitates the formation of a conductive structure in plastics, rubbers and other composites. These characteristics predetermine electroconductive carbon black's primary area of application, i.e. ... | Wikipedia - Electroconductive carbon black - Summary | 163 | 852 | null |
Section: Production. Carbon black begins as a byproduct of what is referred to as partial oxidation, a process during which crude oil residues, such as vacuum residues from crude oil distillation or residues from the thermic cracking process, split due to the effects of the mixture of oxygen and water steam under high ... | Wikipedia - Electroconductive carbon black - Production | 326 | 1,601 | null |
Section: Physical and chemical characteristics of electroconductive carbon black > Structure. Carbon black is essentially formed out of primary carbon, but its structure is much less arranged than that of, for example, graphite. Carbon black exists in the form of discrete particles, however, during the production proce... | Wikipedia - Electroconductive carbon black - Physical and chemical characteristics of electroconductive carbon black > Structure | 162 | 900 | null |
Section: Physical and chemical characteristics of electroconductive carbon black > Surface. The most important characteristic of carbon black is the size of its primary particles and the related surface area. The size of the primary particles describes the size of individual spherical particles that form a primary stru... | Wikipedia - Electroconductive carbon black - Physical and chemical characteristics of electroconductive carbon black > Surface | 154 | 826 | null |
Section: Physical and chemical characteristics of electroconductive carbon black > Texture. Another significant characteristic of carbon black is its structure and the size of its aggregates. The size and complexity of the aggregate structure is determined by the volume of the carbon black spherical primary particles, ... | Wikipedia - Electroconductive carbon black - Physical and chemical characteristics of electroconductive carbon black > Texture | 178 | 1,042 | null |
Section: Creation. The electrolysis occurs in a specially designed reactor which allows the separation of the cathodic and anodic solutions. In this process, hydrogen gas and hydroxide ions can be produced at the cathode, leading to an alkaline solution that consists essentially of sodium hydroxide. At the anode, chlor... | Wikipedia - Electrolysed water - Creation | 333 | 1,389 | null |
Section: Efficient disinfectant. Both sodium hydroxide and hypochlorous acid are efficient disinfecting agents; as mentioned above, the key to effective sanitation is to have a high proportion of hypochlorous acid present, this happens between acidic and neutral pH conditions. EOW will kill spores and many viruses and ... | Wikipedia - Electrolysed water - Efficient disinfectant | 195 | 908 | null |
Article: Energy-rich species. In chemistry and particularly biochemistry, an energy-rich species (usually energy-rich molecule) or high-energy species (usually high-energy molecule) is a chemical species which reacts, potentially with other species found in the environment, to release chemical energy. In particular, th... | Wikipedia - Energy-rich species - Summary | 319 | 1,475 | null |
Article: Environmental chemistry. Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It should not be confused with green chemistry, which seeks to reduce potential pollution at its source. It can be defined as the study of the sources, reactions, tra... | Wikipedia - Environmental chemistry - Summary | 225 | 1,355 | null |
Section: Contaminant. A contaminant is a substance present in nature at a level higher than fixed levels or that would not otherwise be there. This may be due to human activity and bioactivity. The term contaminant is often used interchangeably with pollutant, which is a substance that detrimentally impacts the surroun... | Wikipedia - Environmental chemistry - Contaminant | 175 | 825 | null |
Section: Applications. Environmental chemistry is used by the Environment Agency in England, Natural Resources Wales, the United States Environmental Protection Agency, the Association of Public Analysts, and other environmental agencies and research bodies around the world to detect and identify the nature and source ... | Wikipedia - Environmental chemistry - Applications | 225 | 1,155 | null |
Section: Methods. Quantitative chemical analysis is a key part of environmental chemistry, since it provides the data that frame most environmental studies. Common analytical techniques used for quantitative determinations in environmental chemistry include classical wet chemistry, such as gravimetric, titrimetric and ... | Wikipedia - Environmental chemistry - Methods | 317 | 1,566 | null |
Article: Equivalent weight. In chemistry, equivalent weight (more precisely, equivalent mass) is the mass of one equivalent, that is the mass of a given substance which will combine with or displace a fixed quantity of another substance. The equivalent weight of an element is the mass which combines with or displaces 1... | Wikipedia - Equivalent weight - Summary | 316 | 1,477 | null |
Section: In history. The first equivalent weights were published for acids and bases by Carl Friedrich Wenzel in 1777. A larger set of tables was prepared, possibly independently, by Jeremias Benjamin Richter, starting in 1792. However, neither Wenzel nor Richter had a single reference point for their tables, and so ha... | Wikipedia - Equivalent weight - In history | 349 | 1,692 | null |
Nevertheless, many chemists found equivalent weights to be a useful tool even if they did not subscribe to atomic theory. Equivalent weights were a useful generalisation of Joseph Proust's law of definite proportions (1794) which enabled chemistry to become a quantitative science. French chemist Jean-Baptiste Dumas (18... | Wikipedia - Equivalent weight - In history | 350 | 1,691 | null |
Equivalent weights were not without problems of their own. For a start, the scale based on hydrogen was not particularly practical, as most elements do not react directly with hydrogen to form simple compounds. However, one gram of hydrogen reacts with 8 grams of oxygen to give water or with 35.5 grams of chlorine to g... | Wikipedia - Equivalent weight - In history | 346 | 1,543 | null |
Instead, these chemists had settled on a list of what were universally called "equivalents" (H = 1, O = 8, C = 6, S = 16, Cl = 35.5, Na = 23, Ca = 20, and so on). However, these nineteenth-century "equivalents" were not equivalents in the original or modern sense of the term. Since they represented dimensionless number... | Wikipedia - Equivalent weight - In history | 246 | 1,192 | null |
Section: Use in general chemistry. The use of equivalent weights in general chemistry has largely been superseded by the use of molar masses. Equivalent weights may be calculated from molar masses if the chemistry of the substance is well known: sulfuric acid has a molar mass of 98.078(5) g mol−1, and supplies two mole... | Wikipedia - Equivalent weight - Use in general chemistry | 325 | 1,277 | null |
Section: Use in volumetric analysis. When choosing primary standards in analytical chemistry, compounds with higher equivalent weights are generally more desirable because weighing errors are reduced. An example is the volumetric standardisation of a solution of sodium hydroxide which has been prepared to approximately... | Wikipedia - Equivalent weight - Use in volumetric analysis | 329 | 1,507 | null |
In analytical chemistry, a solution of any substance which contains one equivalent per litre is known as a normal solution (abbreviated N), so the example sodium hydroxide solution would be 0.0893 N. The relative uncertainty (ur) in the measured concentration can be estimated by assuming a Gaussian distribution of the ... | Wikipedia - Equivalent weight - Use in volumetric analysis | 384 | 908 | null |
The relative uncertainty (ur) in the measured concentration can be estimated by assuming a Gaussian distribution of the measurement uncertainties: u r 2 = ( u ( V ) V ) 2 + ( u ( m ) m ) 2 = ( 0.03 22.45 ) 2 + ( 0.1 781.4 ) 2 = ( 0.001336 ) 2 + ( 0.000128 ) 2 u r = 0.00134 u ( c ) = u r c = 0.1 m e q / L {\displaystyle... | Wikipedia - Equivalent weight - Use in volumetric analysis | 524 | 1,213 | null |
Section: Use in gravimetric analysis. The term “equivalent weight” had a distinct meaning in gravimetric analysis: it meant the mass of precipitate produced from one gram of analyte (the species of interest). The different definitions came from the practice of quoting gravimetric results as mass fractions of the analyt... | Wikipedia - Equivalent weight - Use in gravimetric analysis | 347 | 1,154 | null |
For example, 215.3±0.1 mg of [Ni(dmgH)2] precipitate is equivalent to (215.3±0.1 mg) × 0.203151(5) = 43.74±0.2 mg of nickel: if the original sample size was 5.346±0.001 g, the nickel content in the original sample would be 0.8182±0.0004%. Gravimetric analysis is one of the most precise of the common methods of chemical... | Wikipedia - Equivalent weight - Use in gravimetric analysis | 156 | 535 | null |
Section: Use in polymer chemistry. In polymer chemistry, the equivalent weight of a reactive polymer is the mass of polymer which has one equivalent of reactivity (often, the mass of polymer which corresponds to one mole of reactive side-chain groups). It is widely used to indicate the reactivity of polyol, isocyanate,... | Wikipedia - Equivalent weight - Use in polymer chemistry | 200 | 902 | null |
Article: Eutectic system. A eutectic system or eutectic mixture ( yoo-TEK-tik) is a type of a homogeneous mixture that has a melting point lower than those of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the eutectic temperature. On a phase diagram, the... | Wikipedia - Eutectic system - Summary | 323 | 1,485 | null |
Section: Eutectic phase transition. The eutectic solidification is defined as follows: Liquid → cooling eutectic temperature α solid solution + β solid solution {\displaystyle {\text{Liquid}}\quad {\xrightarrow[{\text{cooling}}]{{\text{eutectic}} \atop {\text{temperature}}}}\quad \alpha {\text{ solid solution}}\ +\ \be... | Wikipedia - Eutectic system - Eutectic phase transition | 250 | 1,047 | null |
Section: Non-eutectic compositions. Compositions of eutectic systems that are not at the eutectic point can be classified as hypoeutectic or hypereutectic: Hypoeutectic compositions are those with a greater composition of species α and a smaller percent composition of species β than the eutectic composition (E) Hypereu... | Wikipedia - Eutectic system - Non-eutectic compositions | 170 | 758 | null |
Section: Types > Alloys. Eutectic alloys have two or more materials and have a eutectic composition. When a non-eutectic alloy solidifies, its components solidify at different temperatures, exhibiting a plastic melting range. Conversely, when a well-mixed, eutectic alloy melts, it does so at a single, sharp temperature... | Wikipedia - Eutectic system - Types > Alloys | 316 | 1,355 | null |
Casting alloys, such as aluminium-silicon and cast iron (at the composition of 4.3% carbon in iron producing an austenite-cementite eutectic) Silicon chips are eutectic bonded to gold-plated substrates through a silicon-gold eutectic by the application of ultrasonic energy to the chip. Brazing, where diffusion can remo... | Wikipedia - Eutectic system - Types > Alloys | 170 | 787 | null |
Section: Types > Others. Sodium chloride and water form a eutectic mixture whose eutectic point is −21.2 °C and 23.3% salt by mass. The eutectic nature of salt and water is exploited when salt is spread on roads to aid snow removal, or mixed with ice to produce low temperatures (for example, in traditional ice cream ma... | Wikipedia - Eutectic system - Types > Others | 338 | 1,372 | null |
Section: Strengthening mechanisms > Alloys. The primary strengthening mechanism of the eutectic structure in metals is composite strengthening (See strengthening mechanisms of materials). This deformation mechanism works through load transfer between the two constituent phases where the more compliant phase transfers s... | Wikipedia - Eutectic system - Strengthening mechanisms > Alloys | 314 | 1,659 | null |
The spacing of the eutectic phase can be controlled during processing as it is directly related to the cooling rate during solidification of the eutectic structure. For example, for a simple lamellar eutectic structure, the minimal lamellae spacing is: λ ∗ = 2 γ V m T E Δ H ∗ Δ T 0 {\displaystyle \lambda ^{*}={\frac {2... | Wikipedia - Eutectic system - Strengthening mechanisms > Alloys | 337 | 1,302 | null |
Section: Other critical points > Peritectic. Peritectic transformations are also similar to eutectic reactions. Here, a liquid and solid phase of fixed proportions react at a fixed temperature to yield a single solid phase. Since the solid product forms at the interface between the two reactants, it can form a diffusio... | Wikipedia - Eutectic system - Other critical points > Peritectic | 260 | 1,178 | null |
Section: Other critical points > "Bad solid solution". Not all minimum melting point systems are "eutectic". The alternative of "poor solid solution" can be illustrated by comparing the common precious metal systems Cu-Ag and Cu-Au. Cu-Ag, source for example https://himikatus.ru/art/phase-diagr1/Ag-Cu.php, is a true eu... | Wikipedia - Eutectic system - Other critical points > "Bad solid solution" | 336 | 1,452 | null |
On further heating, the solid solution residue dissolves in the melt and changes its composition until the liquidus line is reached and the whole residue has dissolved away. Cu-Au source for example https://himikatus.ru/art/phase-diagr1/Au-Cu.php does display a melting point minimum at 910 °C and given as 44 atom % Cu,... | Wikipedia - Eutectic system - Other critical points > "Bad solid solution" | 333 | 1,533 | null |
Therefore when a silver-copper alloy is frozen, it actually separates into crystals of 912 fineness silver and 80 fineness silver - both are saturated and always have the same composition at the freezing point of 780 °C. Thus the alloy just below 780 °C consists of two types of crystals of exactly the same composition ... | Wikipedia - Eutectic system - Other critical points > "Bad solid solution" | 236 | 1,154 | null |
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