自蔓燃高温合成法合成氮化硅粉体的研究

采用自蔓燃高温合成方法合成β-氮化硅粉体,分析了合成氮化硅过程中氮气、温度、稀释剂与孔隙率等方面的影响。采用XRD研究相的组成,用SEM观察粉末的显微结构。研究结果表明:自蔓燃合成方法制备的氮化硅陶瓷粉体,β相含量由块状产物中心向表层减少,得到的β-氮化硅晶体结构完整,表面光滑无缺陷,考虑到燃烧温度(Tcom),在氮化硅粉体的合成过程中,涉及到3个反应机制:低温机制、中温机制、高温机制。NH4Cl在反应中分解,为反应提供了NH3,并与硅粉反应;氮气压力下硅粉的自蔓燃合成反应,必须要引入Si3N4稀释剂来控制反应温度和反应速度,获得不同相含量的粉体;压坯气孔率控制在30%～70%,否则反应不能进行。

Research on Silicon Nitride Powder Prepared by Self-propagating High-temperature Synthesis

β-Si3N4 powder was prepared by the self-propagating high-temperature synthesis (SHS) and examined by X-ray diffraction and SEM. It was studied how the following parameters influenced the final product: nitrogen purity and pressure, combustion temperature, diluents content, the porosity, and so on. The experimental results showed that the different type of β -Si3N4 powder with integrated crystalloid structure and smooth surface could be prepared by SHS as long as the parameters be controlled during the reaction,β phase content decreased from the center of the cake to the surface. Because of the existence of the NH4Cl, the reaction involved not only the silicon nitriding mechanism,but also other mechanisms. Considering the combustion temperature,the SHS Si3N4 process involves three mechanisms: low-temperature mechanism, moderate-temperature mechanism, high-temperature mechanism. During the process Si3N4 powder could be introduced as starting raw materia1 in order to control reaction temperature and obtain the desired α content of Si3N4 powder, the porosity of body should be controlled at 30%～70% ,otherwise, SHS reaction would not carry on. The Si3N4 powder with high α content could be prepared when fine silicon metal powder used.