Hydrothermal phase transformation of tungsten trioxide and the associated thermodynamic data

Hydrothermal phase stability studies of tungsten trioxide under water vapour pressure showed a monoclinic to tetragonal phase transformation with a nearly pressure independent invariant equilibrium boundary line. The standard thermodynamic data for the tetragonal form of WO 3 obtained from the experimental PT points on the equilibrium transformation boundary are: ΔG f 0 = − 759.743 kJ/mol., ΔH f 0 = − 836.598 kJ/mol., S f 0 = 82.59 J/mol.deg.