微孔碳陶瓷化反应机理的研究

研究了微孔碳制备SiC陶瓷的反应过程及反应机理.SiC陶瓷的最终组织受C/Si质量比及渗硅时间的影响.较低C/Si质量比时试样中心未被硅化，较高C/Si质量比时制得由SiC、Si及极少量未反应C组成的复相陶瓷.随渗硅时间延长，复相陶瓷中SiC颗粒的形状由长条状向无规则状转变，颗粒分布则由局部有序向无序转变.反应过程为：液硅因毛细作用自发的渗入微孔碳孔道，同时与溶解的碳壁发生反应生成SiC.因孔道及碳壁尺寸的不同造成液硅渗入深度和碳壁被溶解厚度的差异，结果出现被SiC包裹的小颗粒碳.随后被包裹的碳通过SiC层扩散到液硅中，沉积在先形成的SiC上促使大量先形成SiC的合并以及部分硅被SiC包裹，进而改变SiC陶瓷的显微组织.

Microstructure Evolution and Reaction Mechanism of Microporous Carbon Derived SiC Ceramic

The process of reaction of silicon carbide ceramics derived from microporous carbon was investigated. The reaction mechanism was also analyzed. The ultimate microstructure of SiC ceramics are affected by the mass ratio of C to Si and infiltration time. Composite materials, which consist of SiC, Si and a small fraction of unreacted C, are obtained when the mass ratio of C to Si is higher whereas partial infiltration occurs when the mass ratio of C to Si is lower. Composite materials demonstrates many uniformly distributed strip shaped SiC grains in certain region at transitional stage of reaction, and shows irregular SiC grains and an obvious bimodal distribution of grain size at terminal stage of reaction. The process of silicon carbon reaction can be described as follows, melted Si ascends via capillary of micropore carbon and reacts with contacted carbon forming SiC. Size difference of pore and carbon wall induces difference of the infiltration deep of melted Si within micropore carbon and thicknesses of the dissolved carbon layer, respectively. As a result, some carbon particles are embedded in SiC grain and pore channel system is restructured. New pore channel with bigger pore size are formed, which accelerates infiltration rate of melted Si. Then the unreacted carbons embedded in SiC grain are firstly diffuse through the SiC layer and dissolved in the Si melt, and then deposits on the first SiC formed. Finally, liquid epitaxial growth of SiC causes coalescence of SiC grains and envelopment of some Si in SiC grains, resulting in change of microstructure of SiC ceramics.