碳热还原法合成TiB2-SiC复合粉末及其机理分析

以硅溶胶、炭黑、TiO2和B4C为原料,采用碳热还原法合成TiB2-SiC复合粉末.研究了反应温度、TiO2添加量对合成TiB2-SiC复合粉末的物相组成和显微形貌的影响;对反应过程进行了热力学分析和计算,并探讨了TiB2-SiC复合粉末的生长机理.结果表明:TiB2-SiC复合粉末适宜的合成条件为在1 600℃保温1h.在反应过程中,TiB2先于SiC生成,TiB2的生成改变了SiC的生长方式.当复合粉末中TiB2的质量分数为10%左右时,SiC的合成过程由气-固(V-S)反应转变为气-固(V-S)和气-气(V-V)共同反应,复合粉末主要由少量球状颗粒、短棒状颗粒以及大量的晶须组成.当体系中生成的TiB2质量分数(≥20%左右)较大时,生成的晶须数量减少,同时球状、片状和短棒状等结构颗粒明显增多,出现多样化结构并存的现象,SiC的生长仍然由V-S反应和V-V反应共同控制.

Synthesis and Mechanism of TiB2-SiC Composite Powders by Carbothermal Reduction Method

TiB2-SiC composite powders were synthesized by carbothermal reduction using silica sol,carbon black,TiO2 and B4C as the raw materials.The effects of reaction temperature and titanium oxide content on the phase composition and morphology of TiB2-SiC composite powders were investigated.Thermodynamic analysis and calculation were performed systematically during the reaction,and the growth mechanism of TiB2-SiC composite powders was discussed.The results have shown that the suitable condition for synthesizing TiB2-SiC composite powders is at 1 600 ℃ for 1h.In the reaction process,TiB2 is formed before SiC,and the formation of TiB2 alters the growth mode of SiC.When TiB2 content is about 10%,the formation of SiC is controlled by the vapor-solid reaction to the combination of vapor-solid and vapor-vapor reaction.The composite powders are mainly composed of a small amount of round-like particles,short rod-like particles and a lot of whiskers.With the increase of TiB2 content in the composite powders,the growth of SiC whiskers is inhibited.When TiB2 content is more than 20%,the number of whiskers in the composite powders reduces,and the number of round-like,plate-shaped and short rod-like particles increases noticeably,which results in a variety of the morphology.The growth of SiC is still controlled by the combination of vapor-solid and vapor-vapor reaction.