Tungsten trioxide

Tungsten oxide is a light yellow orthorhombic crystalline powder, insoluble in water, soluble in alkali and slightly soluble in acid. The color of Tungsten oxide changes from light to dark when heated. The specific gravity is 7.16g/cm3, the melting point is 1473°C, the boiling point is 1750°C, it sublimates significantly at 850°C, and turns green when melted. Tungsten oxide is stable in air.
​Tungsten trioxide (WO₃), also known as tungsten(VI) oxide, is a yellow crystalline solid with notable physical and chemical properties. It has a density of approximately 7.16 g/cm³ and exhibits polymorphism, undergoing structural transitions at various temperatures: tetragonal above 740°C, orthorhombic between 330°C and 740°C, monoclinic from 17°C to 330°C, triclinic between -50°C and 17°C, and reverting to monoclinic below -50°C. The compound is insoluble in water but slightly soluble in hydrofluoric acid. It can be synthesized through the calcination of ammonium paratungstate (APT) under oxidizing conditions, yielding WO₃ along with the release of ammonia and water vapor. ​
Tungsten trioxide is a chemical compound consisting of oxygen and the transition metal tungsten. It occurs naturally but rarely in the form of hydrates in some kinds of minerals. It has various applications. In industry, it can be used for making x-ray screen phosphors, fireproofing fabrics and gas sensors as well as a pigment in ceramics and paints. It can also be used for the preparation of electrochromic windows or smart windows. In addition, it can be used in semiconductors. It, together with titanium dioxide, has the potential to become an efficient photo-catalyst under visible light irradiation. Recent study has shown that mesoporous tungsten trioxide polyaniline nanocomposite can be used as an anode material for high-performance lithium-ion batteries.
Tungsten trioxide is a bright canary-yellow coloured powder which becomes dark-orange on heating, but regains its bright yellow colour on cooling. A very slight admixture of sodium salt imparts to the oxide a greenish tint which no amount of oxidation can remove (Roscoe). It also becomes greenish on exposure to light. Tungsten trioxide has been obtained in the crystalline state by Debray, by igniting a mixture of tungstate and carbonate of sodium in a current of hydrochloric acid, when the trioxide is obtained in olive-green rectangular prisms which sublime at a white heat. The crystalline trioxide has also been prepared by heating hydrated tungstic acid with borax in a porcelain furnace (Nordenskjold). The specific gravity of tungsten trioxide thus obtained is 6.34.When heated in a current of hydrogen to 250° the trioxide is converted into the blue oxidc, 2WO3+WO2 and if the heat be raised to dull redness the brown oxide, WO2 is formed, whilst at a higher temperature the metal is obtained. Acted upon by reducing agents such as zinc and hydrochloric acid, stannous chloride, or organic matter, tungsten trioxide is trans-formed successively into the blue and brown oxides.
Canary-yellow, heavy powder, darkorange when heated and regains original color on cooling. Insoluble in water, soluble in caustic alkalies, soluble with difficulty in acids. Noncombustible.