Thermal and mechanical properties of sintered LaPO4-Al2O3 composites

Mixtures of (1 − x)LaPO4 and xAl2O3 (x = 0 to 1 mass) were dry-pressed to disks or bars. Relative densities larger than 94% and apparent porosities less the 6% were achieved when the specimens were sintered at 1600°C for 5 hours in air. The sintered ceramics (x = 0 to 0.7) were found to be machinable — they could be drilled easily using conventional metallic WC drills. The thermal and mechanical properties of the sintered (1 − x)LaPO4 - xAl2O3 composites had the following ranges: 10 × 10−6/°C (x = 0) to 9.0 × 10−6/°C(x = 1) (linear thermal expansion coefficient at 200°–1000°C); 5.0 (x = 0) to 43 W/(m·K)(x = 1) (thermal conductivity at 25°C); 140±19 (x=0) to 352±23 MPa (x = 1)(bending strength at room temperature); 5.7 (x = 0) to 16.5 GPa (x = 1) (Vickers hardness); and 155 (x = 0) to 400 GPa (x = 1) (Young’s modulus).