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Tungsten bronze is a non-stoichiometric compound containing tungsten. It looks like copper but is chemically inert. Tungsten bronze usually appears as cubic or tetragonal crystals. It is insoluble in water and all acids except hydrofluoric acid, but soluble in alkaline reagents. It can be used as a catalyst for carbon monoxide oxidation reaction and a degasser in fuel cells.
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MyanmarTungsten bronze
Product Description
Tungsten bronze
Tungsten bronze is a non-stoichiometric compound containing tungsten. It looks like copper but is chemically inert. Tungsten bronze usually appears as cubic or tetragonal crystals. It is insoluble in water and all acids except hydrofluoric acid, but soluble in alkaline reagents. It can be used as a catalyst for carbon monoxide oxidation reaction and a degasser in fuel cells.
A non-stoichiometric compound with the empirical formula MxWO3, where M is usually an alkali metal, but can also be an alkaline earth metal, ammonium ion, rare earth metal ion, etc. x is between 0 and 1. Tungsten bronze generally has a metallic luster and a special color. The type of M and the change in the value of x can make it have conductor or semiconductor properties. Crystallization chemistry research has shown that tungsten bronze is essentially a solid solution formed by the insertion of alkali metal atoms into the WO3 lattice. When all vacancies are filled, the resulting compound is MWO3. The formation of tungsten bronze is related to the variable atomic valence of tungsten. If only part of the vacancies are replaced by alkali metal atoms, part of the tungsten atoms will change from hexavalent to pentavalent.
Physical and chemical properties:
The most common tungsten bronze is sodium tungsten bronze, which has a metallic luster and its color varies with the value of x, ranging from golden yellow to light blue-gray. For example, NaWO3 is golden yellow, Na0.67WO3 is crimson, Na0.5WO3 is purple-red, and Na0.2WO3 is blue. When the ratio of Na:WO3 is greater than 0.3, its temperature coefficient of resistance is positive, extremely unstable, and has semi-metallic properties; when it is less than 0.3, it is negative and is a semiconductor. All tungsten bronzes are extremely inert in nature, semi-metallic, metallic, and conductive. Their chemical inertness is manifested in their insolubility in water and resistance to all acids except hydrofluoric acid. However, they can reduce silver nitrate from their ammonia solution to metallic silver, and in the presence of alkali, they can be oxidized by oxygen to tungstate (VI). Their semiconductor properties mean that all tungsten atoms in them are W(VI), and the valence electrons of metallic sodium move freely in the lattice of tungsten bronze, just like in metallic sodium. Lithium can also form tungsten bronze, but it is not conductive.
Composition:
The color of tungsten bronze varies greatly with the composition. For example, in NaxWO3, when x is ~ 0.9, it is golden yellow, when x is ~ 0.6, it is orange red, when x is ~ 0.45, it is red purple, and when x is ~ 0.3, it is dark blue purple. Structurally, for every Na ion removed from NaxWO3, a W atom should change from W(V) to W(VI). Therefore, in this defective NaxWO3, there are (1-x) W(VI) atoms and (1-x) empty Na atom positions. Completely pure NaxWO3 has not yet been produced, and WO3 (i.e., the number of Na atoms is the minimum limit x=0) is a slightly distorted ReO3 structure (i.e., the structure without the large cation in the perovskite structure). So in fact, the composition of tungsten bronze is close to Na0.3WO3-Na0.9WO3.
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