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Sulfiding
Sulfidation (British spelling also sulphidation) is a process of installing sulfide ions in a material or molecule. The process is widely used to convert oxides to sulfides but is also related to corrosion and surface modification. Inorganic, materials, and organic chemistry Sulfidation is relevant to the formation of sulfide minerals. A large scale application of sulfidation is the conversion of molybdenum oxides to the corresponding sulfides. This conversion is a step in the preparation of catalysts for hydrodesulfurization wherein alumina impregnated with molybdate salts are converted to molybdenum disulfide by the action of hydrogen sulfide. In organosulfur chemistry, sulfiding is often called thiation. The preparation of thioamides from amides involves thiation. A typical reagent is phosphorus pentasulfide (P4S10). The idealized equation for this conversion is: :RC(O)NH2 + 1/4 P4S10 → RC(S)NH2 + 1/4 P4S6O4 This conversion where an oxygen atom in the ami ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (H2S) and bisulfide (SH−) are the conjugate acids of sulfide. Chemical properties The sulfide ion, S2−, does not exist in aqueous alkaline solutions of Na2S. Instead sulfide converts to hydrosulfide: :S2− + H2O → SH− + OH− Upon treatment with an acid, sulfide salts convert to hydrogen sulfide: :S2− + H+ → SH− :SH− + H+ → H2S Oxidation of sulfide is a complicated process. Depending on the conditions, the oxidation can produce elemental sulfur, polysulfides, polythionates, sulfite, or sulfate. Metal sulfides react with halogens, forming sulfur and metal salts. :8 MgS + 8 I2 → S8 + 8 M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolated as a metal in 1783. Its important ores include scheelite and wolframite, the latter lending the element its alternate name. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all known elements barring carbon (which sublimes at normal pressure), melting at . It also has the highest boiling point, at . Its density is , comparable with that of uranium and gold, and much higher (about 1.7 times) than that of lead. Polycrystalline tungsten is an intrinsically brittle and hard material (under standard conditions, when uncombined), making it difficult to work. However, pure single-crystalline tungsten is more ductile and can be cut with a hard-steel hacksaw. Tungsten occurs in many ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen, hydrogen or hydroxide. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal and results in a distinctive orange colouration. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term "degradation" is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases. Many structural ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friction Coefficient
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into ''static friction'' ("stiction") between non-moving surfaces, and ''kinetic friction'' between moving surfaces. With the exception of atomic or molecular friction, dry friction generally arises from the interaction of surface features, known as asperities (see Figure 1). *Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. *Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces. *Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. *Internal friction is the force resisting motion between the elements making up a sol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diamond-like Carbon
Diamond-like carbon (DLC) is a class of amorphous carbon material that displays some of the typical properties of diamond. DLC is usually applied as coatings to other materials that could benefit from such properties. DLC exists in seven different forms. All seven contain significant amounts of sp3 hybridized carbon atoms. The reason that there are different types is that even diamond can be found in two crystalline polytypes. The more common one uses a cubic lattice, while the less common one, lonsdaleite, has a hexagonal lattice. By mixing these polytypes at the nanoscale, DLC coatings can be made that at the same time are amorphous, flexible, and yet purely sp3 bonded "diamond". The hardest, strongest, and slickest is tetrahedral amorphous carbon (ta-C). Ta-C can be considered to be the "pure" form of DLC, since it consists almost entirely of sp3 bonded carbon atoms. Fillers such as hydrogen, graphitic sp2 carbon, and metals are used in the other 6 forms to reduce productio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromium
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardness. A major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating (electroplating with chromium) together comprise 85% of the commercial use. Chromium is also greatly valued as a metal that is able to be highly polished while resisting tarnishing. Polished chromium reflects almost 70% of the visible spectrum, and almost 90% of infrared light. The name of the element is derived from the Greek word χρῶμα, ''chrōma'', meaning color, because many chromium compounds are intensely colored. Industrial production of chromium proceeds from chromite ore (mostly FeCr2O4) to produce ferro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromium Oxide
Chromium oxide may refer to: * Chromium(II) oxide, CrO * Chromium(III) oxide, Cr2O3 * Chromium dioxide (chromium(IV) oxide), CrO2, which includes the hypothetical compound chromium(II) chromate * Chromium trioxide (chromium(VI) oxide), CrO3 * Chromium(VI) oxide peroxide, CrO5 * Mixed valence species, such as Cr8 O21 See also * Chromate and dichromate Chromate salts contain the chromate anion, . Dichromate salts contain the dichromate anion, . They are oxyanions of chromium in the +6 oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate i ... * CRO (other) {{Chemistry index Chromium compounds Transition metal oxides ja:酸化クロム ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Tungsten Bronze
Sodium tungsten bronze is a form of insertion compound with the formula Na''x''WO3, where ''x'' is equal to or less than 1. So named because of its metallic lustre, its electrical properties range from semiconducting to metallic depending on the concentration of sodium ions present; it can also exhibit superconductivity. History Prepared in 1823 by the chemist Friedrich Wöhler, sodium tungsten bronze was the first alkali metal bronze to be discovered. Tungsten bronzes owe some of their properties to the relative stability of the tungsten(V) cation that is formed. A similar family of molybdenum bronzes may have been discovered in 1885 by Alfred Stavenhagen and E. Engels, but they are formed in a very narrow range of temperatures and were not reported again until the 1960s. Properties Sodium tungsten bronze, like other tungsten bronzes, is resistant to chemical reaction under both acidic and basic conditions. Colour is dependent upon the proportion of sodium in the compound, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state. There are two classes of redox reactions: * ''Electron-transfer'' – Only one (usually) electron flows from the reducing agent to the oxidant. This type of redox reaction is often discussed in terms of redox couples and electrode potentials. * ''Atom transfer'' – An atom transfers from one substrate to another. For example, in the rusting of iron, the oxidation state of iron atoms increases as the iron converts to an oxide, and simultaneously the oxidation state of oxygen decreases as it accepts electrons released by the iron. Although oxidation reactions are commonly associated with the formation of oxides, other chemical species can serve the same function. In hydrogenation, C=C (and other) bonds ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphorus Pentasulfide
Phosphorus pentasulfide is the inorganic compound with the formula (monomer) or (dimer). This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities. It is soluble in carbon disulfide but reacts with many other solvents such as alcohols, DMSO, and DMF. Structure and synthesis Its tetrahedral molecular structure is similar to that of adamantane and almost identical to the structure of phosphorus pentoxide. Phosphorus pentasulfide is obtained by the reaction of liquid white phosphorus () with sulfur above 300 °C. The first synthesis of by Berzelius in 1843 was by this method. Alternatively, can be formed by reacting elemental sulfur or pyrite, , with ferrophosphorus, a crude form of (a byproduct of white phosphorus () production from phosphate rock): : : Applications Approximately 150,000 tons of are produced annually. The compound is mainly converted to other derivatives for use as lubrication ad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfide Mineral
The sulfide minerals are a class of minerals containing sulfide (S2−) or disulfide (S22−) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts.http://www.minerals.net/mineral/sort-met.hod/group/sulfgrp.htm Minerals.net Dana Classification, SulfidesKlein, Cornelis and Cornelius S. Hurlbut, Jr., 1986, ''Manual of Mineralogy'', Wiley, 20th ed., pp 269-293 Sulfide minerals are inorganic compounds. Minerals Common or important examples include: * Acanthite *Chalcocite *Bornite * Galena * Sphalerite *Chalcopyrite *Pyrrhotite *Millerite *Pentlandite *Covellite *Cinnabar *Realgar *Orpiment *Stibnite *Pyrite *Marcasite *Molybdenite Sulfarsenides: *Cobaltite *Arsenopyrite *Gersdorffite Sulfosalts: *Pyrargyrite *Proustite *Tetrahedrite *Tennantite *Enargite *Bournonite * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is part of the main chain of a protein, and an isopeptide bond when it occurs in a side chain, such as in the amino acids asparagine and glutamine. It can be viewed as a derivative of a carboxylic acid () with the hydroxyl group () replaced by an amine group (); or, equivalently, an acyl (alkanoyl) group () joined to an amine group. Common examples of amides are acetamide (), benzamide (), and dimethylformamide (). Amides are qualified as primary, secondary, and tertiary according to whether the amine subgroup has the form , , or , where R and R' are groups other than hydrogen. The core of amides is called the amide group (specifically, carboxamide group). Amides are pervasive in nature and technology. Proteins and important plastics l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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