Mechanical and Thermal Properties of Pressureless-Sintered MgO-Mg4Ta2O9 Composites

MgO-based composites containing 10 to 30vol% Mg4Ta2O9 were fabricated by pressureless sintering of MgO and Ta2O5 powders at 1400° to 1600°C. Mechanical properties and the thermal expansion coefficient of the composites were studied. Under all sintering conditions, Ta2O5 reacted with MgO completely to form Mg4Ta2O9 and dense (>95% of theoretical density) composites were obtained. Dispersion of Mg4Ta2O9 particles inhibited the grain growth of MgO and improved mechanical properties. The maximun bending strength and fracture toughness of composites were 260MPa and 3.2MPa⋅m1/2, respectively, in contrast with 150MPa and 1.6MPa⋅m1/2 for a MgO monolith. The composites may be toughened by the crack deflection due to Mg4Ta2O9 particles. The thermal expansion coefficient of the composites decreased slightly with increasing Mg4Ta2O9 content and was 12.9×10-6°C-1 for the composite with 30vol% Mg4Ta2O9.