Physical and mechanical properties of hexagonal boron nitride ceramic fabricated by pressureless sintering without additive

Hexagonal boron nitride (h-BN) ceramic was successfully fabricated by pressureless sintering at 2100 degrees C using submicrometre h-BN powders without any sintering additive. The as-prepared h-BN ceramic showed a room temperature flexural strength of 30.7 MPa. Its flexural strength increased with the increment of temperature in N-2 atmosphere, and it retained a strength of 57.2 MPa (nearly two times of the room temperature strength) at 1600 degrees C due to clean grain boundaries with no glassy phase. Additionally, the as-prepared h-BN ceramic showed a high thermal conductivity of 31.76 W m(-1). k(-1) and a good thermal shock resistance, which retained a relatively high residual flexural strength of 22.6 MPa (73.5% of the original flexural strength) at Delta T=800 degrees C. The as-prepared h-BN ceramic presents a good application prospect at high temperature.