硅粉直接氮化反应合成氮化硅研究

Preparation of Silicon Nitride Powder by Direct Nitridation Process

研究了硅粉直接氮化反应合成氮化硅粉末的工艺因素 (包括硅粉粒度、氮化温度、成型压力、稀释剂含量等 ) ,借助XRD ,SEM等测试手段测定和观察了氮化产物的物相组成和断口形貌。研究结果表明 :硅粉在流动氮气氛下 ,高于 1 2 0 0℃氮化产物中氮含量明显增加 ;在氮化反应同时还伴随着硅粉的熔结过程 ,它阻碍硅粉的进一步氮化 ,其影响程度与氮化温度、氮化速度 ,素坯成型压力及硅粉粒度等工艺因素有关。在硅粉素坯中引入氮化硅作为稀释剂 ,提高了硅粉的氮化率 ,使产物中残留硅量降低 ;同样在实际生产中可以通过控制适当热处理制度 (如分段保温、慢速升温 ) ,达到硅粉的完全氮化。在生产中批量合成了含氮量为 3 2 .5 % ,残留硅量为 0 .0 5 % ,主要为α相 ,含少量 β相的针状。

Silicon nitride powder was prepared via direct nitridation process of silicon powders.The influences of temperature,compact pressure,particle size and diluents on the nitridation progress were studied with XRD,SEM and EMPA.The results show that silicon reacts with N_2 gas remarkably at 1200℃ and sharply at the range of 1300～1350℃.It is found that sintering phenomena occurs in nitridation process of silicon compact,which hinders the further nitridation of silicon.Adding Si_3N_4 as diluents in compact can improve the nitridation degree,and decrease the residual Si content in the final product.Additionally,the appropriate temperature profile is drawn up in order to complete the reaction of silicon with nitrogen gas ,such as slow heating rate,several steps of holding time at temperatures. In practice, the elongated silicon nitride powder was prepared with 32.5%N_2,0.5%Si in large-scale production,whose phase compositions were mainly α-Si_3N_4 and little β-Si_3N_4.