Cost effective preparation of Si3N4 ceramics with improved thermal conductivity and mechanical properties

High-purity silicon powder is used as the starting material for cost-effective preparation of silicon nitride ceramics with both high thermal conductivity and excellent mechanical properties using RE2O3 (RE= Y, La or Er) and MgO as sintering additives. Nitridation is a key procedure that would affect the properties of green bodies and the sintered samples. The beta: (alpha+beta) ratio can be increased as the samples nitrided at 1450 degrees C and a large amount of long rod-like beta-Si3N4 grains were developed in the samples. It was found that the addition of Er2O3-MgO could help to improve the mechanical properties of the sintered Si3N4 ceramics, the thermal conductivity, flexural strength and fracture toughness of the sample were 90 W/(m.K), 953 +/- 28.3 MPa and 10.64 +/- 0.61 MPa.m(1/2), respectively. The RE3+ species with larger ionic radius tended to increase the oxygen of nitrided samples and decrease N/O ratio (triangle grain boundary) of sintered samples.