Search

The effects of size (0.88-11μm) and shape of alumina particles on the densification, flexural strength and microstructure were investigated in the quartz-feldspar-kaolinite system. Relative density and flexural strength were demonstrated to have linear relationships and the slope of these lines (κ-value) was dependent upon the size and shape of alumina particles. The flexural strength reached its maximum value when particles of 2μm diameter were used. This phenomenon is explainable for coarse alumina due to the enlargement of the Griffith flaw for a small number of particles, but can not be explained in the case of fine alumina. The shape of alumina particles did not affect the flexural strength or the fracture toughness in any of our experiments.

Densification process, phase component and mechanical strength of the feldspathic porcelain bodies were investigated. Packing ratio and flexural strength showed a linear correlation and its gradient (k-value) indicated a degree of the effect for the reinforcement during densification. The k-value was greatly influenced by mullite/glass ratio, and needlelike crystals of mullite was considered to accelerate the reinforcement of bodies. Fracture toughness increased with the residual amount of quartz. It is considered that, although the mechanisms are different, mullite and quartz strengthen the body.

Influence of Y2O3 content on the thermal shock resistance of ZrO2-Y2O3 ceramics including 12vol% of ZrO2-Y2O3 fiber was investigated by varying the content of Y2O3 from 1.5 to 8.0mol%. After specimens were sintered at 1300, 1400 and 1500°C for 2h, bending strength, fracture toughness, thermal conductivity, and thermal expansion coefficient were measured. Thermal shock resistance was characterized by strength degradation before/after thermal shock experiment (quenching temperature difference; ΔT=600K), and it was increased as the Y2O3 content was decreased. It is considered that this is due to the decrease in thermal expansion coefficient caused by the increase in monoclinic phase in the matrix, and the increasing of fracture toughness.