Oxidation of tungsten and tungsten carbide in dry and humid atmospheres

Oxidation experiments were performed on pure tungsten and hot-pressed tungsten carbide. The chemical state and thickness of the oxide products were determined by ESCA. The oxidation of W and WC in dry atmosphere was performed in oxygen at temperatures ranging from 20 to 500 degrees C. The oxide formed is WO3. The thickness of the oxide layer increases slowly up to 200 degrees C, after which the oxide growth is rapid. The oxidation behaviour of W and WC in humid atmospheres was studied at room temperature in air at relative humidities of 60 and 95%. It was found that the thickness of the oxide layer increases with increased humidity. No formation of hydroxide was observed. Exposing W to water for one week results in a thick layer of WO2, WO3 and hydroxide. In the case of WC no oxide at all was visible after exposure to water. Furthermore, WC is resistant to further oxidation after exposure. (C) 1996 Elsevier Science Limited