Preparation and characterisation of MgSiN2 powders

Abstract

The powder preparation of MgSiN₂ was studied using several starting mixtures (Mg₃N₂/Si₃N₄, Mg/Si₃N₄ and Mg/Si) in the temperature range 800–1500°C in N₂ or N₂/H₂ atmospheres. The phase formation was followed with TGA/DTA and powder X-ray diffraction (XRD). At 1250°C Mg/Si mixtures did not yield single phase MgSiN₂ whereas for Mg/Si₃N₄ and Mg₃N₂/Si₃N₄ mixtures nearly single-phase powders were obtained. The Mg/Si₃N₄ mixtures yielded MgSiN₂ at the lowest processing temperature but the Mg₃N₂/Si₃N₄ mixtures yielded the most pure MgSiN₂ powder with respect to secondary phases. The main secondary phase detectable with XRD was MgO when starting from Mg₃N₂/Si₃N₄ or MgO and metallic Si when starting from Mg/Si₃N₄ mixtures. When the processing starting from Mg₃N₂/Si₃N₄ mixtures was optimised MgSiN₂ powders containing only 0.1 wt % O could be prepared. Using XRD the solubility of oxygen in the MgSiN₂ lattice was estimated to be at maximum 0.6 wt %. The MgSiN₂ powder was oxidation resistant in air till 830°C. The morphology and particle size were studied with the scanning electron microscope (SEM) and the sedimentation method. Two different kinds of morphology were observed determined by the morphology of the Si₃N₄ starting material.