闪速燃烧合成的Fe-Si_3N_4中Fe_xSi粒子的形成机理

Formation mechanism of Fe_xSi particles in ferro-silicon nitride prepared via flashing combustion

采用SEM、EDS等手段研究了闪速燃烧合成的氮化硅铁及其原料FeSi75的组成、结构,并结合闪速燃烧合成工艺和热力学分析,揭示氮化硅铁中FexSi粒子的形成机理.结果表明:在以74μm的FeSi75氮化制备氮化硅铁过程中,金属硅和ξ(FeSi2.3)相中部分硅氮化为氮化硅,而氮化硅铁中FexSi粒子则来源于ξ相的氮化;当ξ相被氮化到其中的[Si]摩尔分数降低近25%时,[Si]的活度aSi趋于0,氮化趋于平衡,ξ相中不能被继续氮化的部分即为FexSi粒子,其Fe∶Si原子比例大约为3∶1;FexSi粒子的大小、均匀分布状况与ξ相颗粒粒径大小及分布状况有关.

The composition and structure of ferro-silicon nitride prepared via flashing combustion and the starting material FeSi75 were analyzed by SEM and EDS. The formation mechanism of FexSi particles in ferro-silicon nitride was studied in combination with thermodynamic analysis and flashing combustion. The results show that nitridation of metallic silicon and the silicon part of ξ phase （FeSi2.3） form silicon nitride during the synthesis of ferro-silicon nitride with FeSi75 of 74 μm. FexSi particles in ferro-silicon nitride come from nitridation of ξ phase. When the molar fraction of [ Si] in ξ phase decreases to 25 %, the activity of [ Si] is approaching to zero and the nitridation reaction tends to balance. FexSi particles form from the residual part of ξ phase which can not be nitrided anymore. The atom proportion of Fe to Si is 3 to 1. The size of FexSi particles and homogeneity distribution relate to the particle size of phase.