Oxidation and dissolution of tungsten carbide powder in water

The oxidation and dissolution of tungsten carbide powder dispersed in water was investigated using X-ray photoelectron spectroscopy (XPS) and leaching studies. We found that the WO3 surface layer on the oxidised tungsten carbide powder dissolves readily at pH > 3 with the tungsten concentration increasing linearly with time. Adding cobalt powder to the tungsten carbide suspension resulted in a significant reduction of the dissolution rate at pH < 10. Electrokinetic studies indicate that the reduced dissolution rate may be related to the formation of surface complexes; experiments showed that Co species in solution adsorb on the oxidised tungsten carbide powder. The experimental data were discussed in relation to theoretical modelling of the WO3 solution chemistry and the Co2+ adsorption at oxide/water interfaces. (C) 2000 Elsevier Science Ltd. All rights reserved.