Preparation, microstructure and properties of MgSiN2 ceramics

The synthesis of MgSiN2 powder, starting from the metal nitrides, is described. The powder is resistant against oxidation in air up to 800 C. From the prepared powder full dense MgSiN2 ceramics can be sintered at 1550 C. The samples were sintered in a closed Mo vessel to prevent evaporation of magnesium nitride. Phase composition, chemical properties and the mechanical properties of the as-prepared ceramics are described. The ceramics are oxidation resistant in air at least up to 920 C. The thermal conductivity at room temperature is estimated at 17 W/mK. A reasonable strength of 270 MPa and a rather good fracture toughness of about 4.3 MPa.m1/2 are obtained. A hardness of about 15 GPa and a Young's modulus of 235 GPa have been measured. Considerable improvement in properties is expected when the processing conditions, well within reach, are optimised. 30 refs.