PHASE TRANSITION OF W－Co OXIDE MIXTURE DURING DIRECT REDUCTION／CARBURIZATION BY H2／CH4
(Powder Metallurgy Research Institute; Central South University of Technology; Changsha 410083)
Abstract: The processes of the H2-reduction and the carburization by hydrogen/methane mixtures with various gas phase composition for the tungsten-cobalt oxide mixture(W20O58+Co3O4) were investigated by means of XRD and SEM analyses. The results shows that the oxide mixture was reduced to a-W, Co3W and Co7W6 at the temperatures higher than 850℃ in H2. The pure blue tungsten oxide(W20O58) or W-Co oxide mixture can be carburized with H2/CH4 gas mixture at lower temperatures (900～1 000℃) . Both the carburizing rate and the deposition of free carbon are closely related to the carburizing temperature and the H2/CH4 mixture constitution. The present paper gives an optimal combination of processing parameters for the carburization.
Key words: tungsten oxide; cobalt oxide; H2-reduction; carburization; X-ray diffraction; phase transition