The role of MgSiN2 during the sintering process of silicon nitride ceramic

The reaction process between MgSiN2 SiO2 and Si3N4 was investigated by analyzing the composition change of the powder mixture of 61 wt% MgSiN2, 34 wt% SiO2 and 5 wt% α-Si3N4 after heat treatment at different temperatures. The phase and chemical compositions of the grain boundary phase in the silicon nitride ceramic was analyzed by x-ray diffraction, transmission electron microscope, and energy-dispersive x-ray spectroscopy. The results demonstrated that MgSiN2 reacted with the surface silica and Si3N4 to form Mg–Si–O–N liquid phase, which promoted the consolidation densification of silicon nitride powders through liquid-phase sintering mechanism. The amount of Mg–Si–O–N glass boundary phase using MgSiN2 as additives is much less than that using the same amount of MgO additive, owing to the lower oxygen concentration and higher nitrogen content.