化学激励燃烧合成Si3N4/SiC复合粉体的研究

研究了利用聚四氟乙烯作活化剂时Si／C混合粉末在氮气中燃烧合成Si3N4／SiC复合粉体。结果表明：当聚四氟乙烯的加入量为10％(质量分数)时可有效激励Si-C弱放热反应，使之以燃烧合成方式生成Si3N4／SiC复相粉。在埋粉条件下Si／C／SiC混合粉末也可以实现燃烧合成Si3N4／SiC复相粉。氮气参与反应时可进一步提高燃烧反应温度，并且首先以气相-晶体生长机制生成Si3N4，然后在高温贫氮的反应前沿Si3N4分解，再与C反应生成SiC。在Si3N4／SiC复合粉中Si3N,形貌以晶须为主。综合X射线衍射分析、扫描电镜观察及原子力显微镜观察对实验结果进行了讨论，解释了Si3N4晶须的形成原理。

INVESTIGATION ON THE COMBUSTION SYNTHESIS OF Si3N4/SiC COMPOSITE POWDERS BY CHEMICAL STIMULATION

Combustion synthesis of Si_3N_4/SiC composite powders from Si/C powder mixture with the addition of polytetrafluoroe thylene(-C_2F_4-)_n as activator in pressurized nitrogen atmosphere was investigated. It is demonstrated that 10% (in mass) addition of (-C_2F_4-)_n can stimulate effectively the weak exothermic reaction between Si and C by self_sustaining combustion synthesis, and Si_3N_4/SiC composite powder can be formed even from Si/C/SiC compact sample . The combustion temperature can be enhanced further if the reaction is carried out in pressurized nitrogen atmosphere, where a sequential reaction takes place with the formation of Si_3N_4 via vapor_crystal mechanism as the first step followed by the decomposition of the nascent Si_3N_4 at the combustion wave zone and the reaction between Si and C, thus SiC is finally obtained. The Si_3N_4 morphology in the composite powder formed in N_2 is predominately in the form of whiskers in the as_synthesized Si_3N_4/SiC composites. The experimental results are discussed based on XRD analysis, SEM and AFM observation, and the formation mechanism of Si_3N_4 whiskers are explained then.