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

本研究尝试在较低温度下合成Ce_2S_3粉末，并对合成粉末的烧结致密化行为进行了研究。首先用CS_2气体代替H_2S气体对CeO_2粉末进行硫化反应，制备Ce_2S_3粉末。CS_2气体比H_2S气体容易处理，因为它是一种易挥发的液体，毒性较小。此外，还有望降低硫化反应温度。通过在CS_2气体中对CeO_2粉末进行硫化反应，确定了制备Ce_2S_3各晶型单相的适宜条件。其次，利用合成的Ce_2S_3粉末进行热压制备烧结体，并对其致密化行为进行了探讨。反应初期在923K及以上的温度下生成CeS_2，最终在较短的时间内在较高的温度下生成α α - ce_2s_3代替CeS_2。在973K的条件下，经过28.8ks的硫化反应，可以合成出单相的α - ce_2s_3。由于在CeO_2粉末中加入炭黑加速了α - ce_2s_3的形成，因此随着温度的升高，碳热还原反应成为主导反应。对真空加热法制备的ce_2s_3粉末在热压下的致密化行为进行了研究。由于在rho=0.77 ~ 0.88的相对密度范围内晶粒生长受到抑制，因此利用该区域的数据对烧结过程进行了动力学分析。结果表明，烧结动力学可以用晶界扩散机制来解释，表观活化能为382kJ/mol。

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.