PTFE添加剂对燃烧合成氮化硅的影响

Effects of PTFE Additive on the Combustion Synthesis of Silicon Nitride

发现了一种PTFE(聚四氟乙烯)催化剂,在其作用下,实现了在2 MPa的氮气压力下Si+NH_4Cl混合粉末燃烧合成Si_3N_4。结果表明:PTFE有效的促进了反应,产物表层的Si粉也实现了完全氮化,且合成产物中α-Si_3N_4的含量随着反应剂中PTFE含量的增加表现出规律性的变化。当PTFE的添加量为4%(质量分数,下同)时,可以制备出α相含量为77.7%的粒度均匀的等轴状Si_3N_4粉末;产物中心部位含有少量残余Si,但经过后续热处理,可以实现完全氮化。分析了产物中不同部位相组成和形貌产生差异的原因,并对PTFE作用下燃烧合成Si_3N_4的机制作了初步探讨。

The feasibility of Mechanical-Activation （MA） assisted combustion synthesis of silicon nitride with the PTFE as additive was demonstrated using silicon/ammonia chloride as reactants at nitrogen pressure below 2 MPa. The addition of PTFE enhances the reactivity significantly, which promote the nitridation of silicon in the outer layer of the reactant compact. The increase of PTFE content in the green mixture stimulates the increase of a-silicon nitride content in the surface of the reactant compact. The equiaxed silicon nitride grain with α-phase content up to 77.7% was obtained when PTFE addition was 4%. The residual silicon left in the center of the combustion synthesis product was completely nitridated by further heat treatment at 1300 ℃ for 1 hour in nitrogen atmosphere. The temperature difference between the centre and the edge of the sample was responsible for the difference in both phase composition and morphology of the product.