A New Production Process of Functional Cerium Sulfide by Sulfurization of Cerium Oxide

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In the present study, an attempt has made to synthesized Ce_2S_3 powder at a lower temperature and to elucidate the densification behavior for the sintering of synthetic powders. At first, sulfurization reaction of CeO_2 powder using CS_2 gas instead of H_2S gas was examined for preparing Ce_2S_3 powder. CS_2 gas can be handled easily than H_2S gas since it is a volatile liquid and less virulent. Moreover, it is expected to lower the reaction temperature of the sulfurization. Appropriate conditions for preparing a single phase of each polymorphic forms of Ce_2S_3 were established by sulfurization reaction of CeO_2 powder using CS_2 gas. Second, hot-pressing was also attemped by using synthetic Ce_2S_3 powder to fabricate the sintered compact, and the densification behavior was discussed.CeS_2 was formed in the initial stage of reaction at temperature of 923K and above, and alphaalpha-Ce_2S_3 was finally formed for a shorter period of time at higher temperatures instead of CeS_2. The single phase of alpha-Ce_2S_3 could be synthesized by sulfurization reaction at 973K for 28.8ks. Since the formation of alpha-Ce_2S_3 was accelerated by the addition of carbon black to the CeO_2 powder, the carbothermic reduction was considered to become a dominant reaction with an increase in temperature. The densification behavior of beta-Ce_2S_3 powder prepared by vacuum heating of alpha-Ce_2S_3 was also examined under hot-pressing. Since grain growth was suppressed at a relative density range from rho=0.77 to rho=0.88, kinetic analysis of sintering was made by using the data in this region.As a results, it was found that sintering kinetics were best explained by a grain-boundary diffusion mechanism with an apparent activation energy of 382kJ/mol.