Combustion synthesis of MgSiN2 powders and Si3N4-MgSiN2 composite powders: Effects of processing parameters

In the present work, high-quality MgSiN 2 powders were prepared by a combustion synthesis method, based on Mg-Si 3 N 4 -N 2 system. The effects of additive content (NH 4 Cl or NH 4 F) and N 2 pressure on phase composition and crystal morphology of products were investigated. The results suggested that both NH 4 Cl and NH 4 F additives alleviated agglomeration and decreased the grain size of MgSiN 2 . In addition, NH 4 Cl did not result in the formation of an extra impurity, while MgF 2 residue was found when NH 4 F was introduced. Therefore, NH 4 Cl additive was considered as a better choice for the preparation of MgSiN 2 powders in comparison with NH 4 F additive. According to the observation of some MgSiN 2 whiskers and notably increased Si content under low N 2 pressure, the pressure of N 2 over 0.5 MPa was essential to have a complete reaction in the present work. Finally, MgSiN 2 -Si 3 N 4 composite powders with quasi-spherical morphology were prepared by adding excessive Si 3 N 4 and NH 4 Cl additive in reactant. The formation and growth mechanism of MgSiN 2 grains was reasonably speculated based on the experimental results. Because of the remarkable merits, the as-prepared Si 3 N 4 -MgSiN 2 composite powders showed great potential for alternative sintering aid in the sintering of Si 3 N 4 -based ceramics.