抄録
Reaction bonded MgSiN2 (RBMSN) was prepared by direct nitridation of Si/Mg2Si/Mg/Si3N4 powder compact in a temperature range 1350-1550 C. It was shown that the starting powders should be in a ratio Mg2Si/Mg > 3 and Si3N4/Si < 0.5 respectively, to obtain single-phase MgSiN2. The oxygen content of MgSiN2 was in the range of 0.4 - 0.5 wt%. The thermal stability examination showed that MgSiN2 is stable up to 1420C at 0.1 MPa N2 pressure. The activation energy of decomposition was determined from the temperature dependence of weight loss. The nitrogen pressure dependence of decomposition showed that MgSiN2 is stable at 1560 C in 0.6 MPa N2 atmosphere. Using these experimental data together with the heat capacity published in a literaturte the thermodynamic properties (entropy, enthalpy and Gibbs free energy of formation) were calculated in a temperature range 300-2500 K.Pure MgSiN2 powder or MgSiN2/Si3N4 mixture with fluorine-based additives were densified by hot pressing. The composite materials had a 4-point bending strength and Vickers hardness (HV1) 427 MPa and 20.8 GPa, respectively. The indentation fracture toughness was 5.3 MPa.m1/2, due to the presence of elongated b-Si3N4 grains. The dielectric constant of dense reaction bonded MgSiN2 was 9.5-10, while that of MgSiN2/Si3N4 composite was higher by orders of magnitude in the measured frequency range.
