本文以高岭土和纳米碳黑颗粒为原料,采用碳热还原原位合成工艺制备SiC_w/Al_2O_3复相陶瓷粉体.通过研究合成温度、保温时间、原料配比以及氩气流量对合成产物的影响,借助XRD、SEM等技术手段进行测试表征,得到了合成工艺的最优参数,并探讨了碳热还原反应的机理.实验结果表明:高岭土与碳黑的摩尔比为1∶ 8,氩气流量为80 mL/min,在1500 ℃下保温2 h,可获得纯净的SiC_w和Al_2O_3复相陶瓷粉体,SiC晶须的平均直径为300 nm左右,长度大于6 μm,长径比大于20,SiC晶须表面光洁,与氧化铝颗粒呈均匀分布.碳热还原高岭土合成SiC_w/Al_2O_3,包括碳热还原SiO_2 与碳热还原莫来石两个阶段,碳化硅晶须的生成遵循气-固(V-S)生长机理.
SiC_w/Al_2O_3 ceramic composites were successfully prepared by in-situ carbothermal synthesis using gaolinite nano carbon black as raw material. Effects of synthesis temperature, holding time, material ratio and the flow rate of argon atmosphere on products were studied, and the reaction mechanism was also discussed. The synthesized products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that pure and uniformly distribute SiC whiskers and Al_2O_3 particles ceramic composite powder can be obtained at 1500 ℃ for holding 2 h when the molar ratio of kaolinite/carbon was 1/8 and the argon flow was 80 mL/min. The SiC whiskers displayed an ideal aspect ratio of more than 20 with a length over 6 μm and a diameter 300 nm. The carbothermal reaction of kaolinite was included two stages: the carbothermal of SiO_2 and the carbothermal of mullite, the growth mechanism of SiC whiskers is V-S mechanism.
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