Tungsten bronzes color

Like chemical reactions, electrochemical reactions are often accompanied by a change in color. For example, colorless WO3 can be reduced either chemically or electrochemically to form intensely colored compounds known as tungsten bronzes ... 

Upon reduction, WO3 forms mixed-valence (WjWj W ) tungsten bronzes, H WOj, which have different colors depending on the degree of reduction, x [see Eq. (33.1)]. Due to parasitic reaction, such as hydrogen evolution, and decreased... 

The name tungsten bronzes originates from their characteristic properties intense color, metallic luster, metallic conductivity or semiconductivity, a range of variable composition, and resistance to attack by non-oxidizing acids. The bronzes Na W03 exhibit colors that change with the occupancy factor x as follows ... 

The most intensely colored inorganic substances contain elements of the same atom in two different valence states. Two examples are Prussian Blue KFenFeni(CN)6 (Chap. 24), and the family of tungsten bronzes which may be considered to contain tungsten in both the +5 and +6 states (Chap. 21). 

The largest series of electronically conducting materials are the phosphate tungsten bronzes. These have similar properties to oxides bronzes such as Na WOs (see Oxides Solid-state Chemistry) and are strongly colored metals or semiconductors. They are formed by inserting planes of... 

It can be only mentioned here that isopoly and heteropoly anions also give rise to highly colored mixed oxidation state species the tungsten bronzes and the heteropoly blues.< ... 

The second study involved the local reduction or oxidation of an elec-trochromic material, tungsten oxide (33). This system is of particular interest since it has been the first system where the local injection of charge could be followed by an instantaneous change of color, making it possible to follow the process with an optical microscope. The stable form of tungsten oxide is W03, which is colorless and poorly conductive. The reduction of W03 [Eq. (5)] results in the formation of deep blue tungsten bronze that is substantially more conducting. 

Tungsten bronzes are metallic conductors, and have a metallic luster and colors that go from gold to black depending on composition. They are very resistant chemically, and serve as industrial catalysts and as pigments in bronze colors. Besides bronzes, A-site-defective perovsldte oxides are known to be formed when B =Ti, Nb, Ta, and so on. One interesting example of a similar phase is Cuo.5Ta03, where copper atoms are ordered at the A sites these compounds will exhibit metallic properties if the B atom occurs in a low oxidation state. 

Simple oxotungstates (M2WO4, M = Li, Na, K) may be reduced with H2 at high temperature to give unreactive and intensely colored substances that look like bronze. Tungsten bronzes (M tW03, 0 < X < 1) have semimetallic properties and good electrical conductivity forx >0.3 and they are semiconductors for x < 0.3. 

KTW bullet The original design had a hard steel or tungsten steel core with a copper gas check and the current version is a solid brass or bronze bullet without a gas check. Both have a gliding metal half jacket and the exposed portion of the bullet is coated with green-colored Teflon. 

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