Tungsten trioxide

In 1841, a chemist named Robert Oxland gave the first procedures for preparing tungsten trioxide and sodium tungstate. He was granted patents for his work soon after, and is considered to be the founder of systematic tungsten chemistry. ==Structure and properties==

The crystal structure of tungsten trioxide is temperature dependent. It is tetragonal at temperatures above 740 °C, orthorhombic from 330 to 740 °C, monoclinic from 17 to 330 °C, triclinic from −50 to 17 °C, and monoclinic again at temperatures below −50 °C. Monoclinic WO3 • Space group: P1/c1 (No. 7) • Lattice parameters (Å): a = 5.27710(1), b = 5.15541(1), c = 7.66297(1) • Angles (°): α = γ = 90°, β = 91.7590(2) • Cell volume: 208.38 Å3 • Z: 4 • Temperature: 5 K • Pressure: Atmospheric • R-value: 0.09 • Reference: Salje, E.K.H. et al. (1997). Journal of Physics: Condensed Matter, 9, 6563–6577. Triclinic WO3 • Space group: P−1 (No. 2) • Lattice parameters (Å): a = 7.309(2), b = 7.522(2), c = 7.678(2) • Angles (°): α = 88.81(2), β = 90.92(2), γ = 90.93(2) • Cell volume: 421.92 Å3 • Z: 8 • Temperature: Room temperature • Pressure: Atmospheric • R-value: 0.05 • Reference: Diehl, R. et al. (1978). Acta Crystallographica Section B, 34, 1105–1111. Hexagonal WO3 A less common hexagonal polymorph of has been reported and characterized using powder X-ray diffraction. It exhibits higher symmetry and potentially distinct electronic properties. • Space group: P6/mmm (No. 191) • Lattice parameters (Å): a = 7.298(2), c = 3.899(2) • Angles (°): α = β = 90°, γ = 120° • Cell volume: 179.84 Å3 • Z: 3 • Temperature: Room temperature • Pressure: Atmospheric • R-value: 0.055 • Reference: Gérand, B. et al. (1979). Journal of Solid State Chemistry, 29, 429–434. ==Preparation==

Industrial Tungsten trioxide is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores can be treated with alkalis to produce soluble tungstates. Alternatively, , or scheelite, is allowed to react with HCl to produce tungstic acid, which decomposes to and water at high temperatures. : : Laboratory Another common way to synthesize WO3 is by calcination of ammonium paratungstate (APT) under oxidizing conditions: : ==Reactions==

Tungsten trioxide can be reduced with carbon or hydrogen gas yielding the pure metal. : (high temperature) : (550–850 °C) ==Uses==

Tungsten trioxide is a starting material for the synthesis of tungstates. Barium tungstate is used as an X-ray screen phosphors. Alkali metal tungstates, such as lithium tungstate and cesium tungstate , give dense solutions that can be used to separate minerals. Other applications, actual or potential, include: • Fireproofing fabrics • Gas and humidity sensors. • Ceramic glazes where it gives a rich yellow color. • Electrochromic glass, such as in smart windows, whose transparency can be changed by an applied voltage. • Photocatalytic water splitting. • Substrate for surface-enhanced Raman spectroscopy replacing noble metals. ==References==