Mechanism of WC Formation from WO<SUB>3</SUB> Added Co<SUB>3</SUB>O<SUB>4</SUB> and C

The processes for the formation of WC and Co mixtures from a mixed powder of WO3, Co3O4 and carbon by heating in H2 atmospher were investigated by means of differential thermal analysis and identification of the compounds by X-ray analysis.In the usual formation process of WC from the mixture of W and C, W2C was formed at about 980°C and the reaction between W2C and C occurred above about 980°C, but WC formation was incomplete even at 1150°C. However, WC was formed completely at about 900°C when Co took part in the reaction between W and C, as WC was produced from eta carbides of W, Co and C. The reduction of Co3O4 and WO3 by H2 occurred at a lower temperature and Co6W6C was formed above about 740°C. An abrupt exothermic reaction occurred at about 840°C and terminated at about 900°C. In this temperature range there occurred the reactions to form Co3W3C from Co6W6C and further to form WC and Co from Co3W3C. At the same time, W2C was also formed from W and C, which immediately reacted with Co and changed to Co6W6C and WC. The carburization of eta carbides and the reaction between W2C and Co simultaneously occurred from about 840°C and the perfect mixed powder of WC and Co was produced at 900°C.