Reduction of tungsten oxides with carbon monoxide

The reduction of WO₃ with CO was studied using thermogravimetry, evolved gas analysis, X-ray powder diffraction, and scanning electron microscopy. The intermediate phases W₂₀O₅₈, W₁₈O₄₉, and WO₂ were observed in the reduction. The final product of the reduction with CO was WC, compared with the tungsten formed when hydrogen and/or carbon was used. The reactant-to-product gas ratio has a considerable influence on the reactions taking place. The morphology of the sample was characterised at different stages of the reduction. The kinetics and mechanism of the reduction of WO₃ with CO were studied in isothermal experiments, from 650 to 900°C. Reduction occurred at a phase boundary with an activation energy of 40 kJ mol^-1. The reduction of WO₂ was studied under similar conditions. The reaction also occurred at a phase boundary and had an activation energy of 62 kJ mol^-1.