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Abstract: A new route for the preparation of magnesium silicon nitride (MgSiN2) powder by combustion synthesis (CS) in nitrogen gas from several different starting mixtures (Mg+Si, Mg2Si, Mg+Si3N4) was investigated. The results showed that the compositions of the combustion products depended on the starting mixtures. Single-phase MgSiN2 powder can be fabricated from Mg2Si or the mixtures of Mg and Si3N4 powders. The oxygen content of the resulting powder was as low as 0.356wt.%. However, the product from Mg and Si mixtures consists mainly of MgSiN2 together with free Si, MgO and not identified phases. [Copyright &y& Elsevier]

α/β-Si3N4 composites with various α/β phase ratios were prepared by hot pressing at 1600°–1650°C with MgSiN2 as sintering additives. An excellent combination of mechanical properties (Vickers indentation hardness of 23.1 GPa, fracture strength of about 1000MPa, and toughness of 6.3 MPa·m1/2) could be obtained. Compared with conventional Si3N4-based ceramics, this new material has obvious advantages. It is as hard as typical in-situ-reinforced α-Sialon, but much stronger than the latter (700 MPa). It has comparable fracture strength and toughness, but is much harder than β-Si3N4 ceramics (16 GPa). The microstructures and mechanical properties can be tailored by choosing the additive and controlling the heating schedule. [ABSTRACT FROM AUTHOR]

A translucent α/β Si3N4 composite, consisting of 85% α-Si3N4 and 15% β-Si3N4, was fabricated by hot-pressing at 1563°C for 1h, using an MgSiN2 additive. The α/β Si3N4 composite achieves a maximum transmittance of 66% for a 0.42mm thick specimen in the medium infrared region, which is attributed to its high density and to a small amount of intergranular phase and β-Si3N4. In addition to optical transmittance, the sample showed a very high hardness of 24.0±0.5GPa. [ABSTRACT FROM AUTHOR]