常圧焼結MgO-Mg_4Ta_2O_9複合体の機械的,熱的性質  [in Japanese] Mechanical and Thermal Properties of Pressureless-Sintered MgO-Mg_4Ta_2O_9 Composites  [in Japanese]

MgO-based composites containing 10 to 30 vol% Mg_4Ta_2O_9 were fabricated by pressureless sintering of MgO and Ta_2O_5 powders at 1400° to 1600℃. Mechanical properties and the thermal expansion coefficient of the composites were studied. Under all sintering conditions, Ta_2O_5 reacted with MgO completely to form Mg_4Ta_2O_9 and dense (>95% of theoretical density) composites were obtained. Dispersion of Mg_4Ta_2O_9 particles inhibited the grain growth of MgO and improved mechanical properties. The maximum bending strength and fracture toughness of composites were 260 MPa and 3.2 MPa・m^<1/2>, respectively, in contrast with 150 MPa and 1.6 MPa・m^<1/2> for a MgO monolith. The composites may be toughened by the crack deflection due to Mg_4Ta_2O_9 particles. The thermal expansion coefficient of the composites decreased slightly with increasing Mg_4Ta_2O_9 content and was 12.9×10^<-6>℃^<-1> for the composite with 30 vol% Mg_4Ta_2O_9.