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，并探讨合成粉末烧结的致密化行为。本文首先研究了用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气体是一种易挥发的液体，毒性较小，比H_2S气体容易处理。此外，预期降低硫化的反应温度。通过CS_2气体对CeO_2粉末的硫化反应，确定了制备Ce_2S_3各晶型物相的适宜条件。其次，采用合成的Ce_2S_3粉末进行热压烧结，并对其致密化行为进行了讨论，结果表明：在923 K及以上的温度下，反应初期生成CeS_2，在较高温度下，反应后期生成α-Ce_2S_3，而不是CeS_2。在973 K，28.8ks的硫化反应条件下，可以得到单相的α-Ce 2S 3。在CeO_2粉末中加入炭黑，加速了α-Ce_2S_3的生成，随着温度的升高，碳热还原反应成为主要反应。研究了α-Ce_2S_3经真空加热制备的β-Ce_2S_3粉末在热压条件下的致密化行为。在相对密度为rho=0.77 ~ rho=0.88的范围内，晶粒生长受到抑制，利用这一范围内的数据进行烧结动力学分析，发现烧结动力学可用晶界扩散机制解释，表观活化能为382 kJ/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.