A freeze casting technique was processed to fabricate porous mullite/alumina-layered composite with a gradient in porosity and pore size. In this work, a camphene/coal fly ash slurry system with an appropriate addition of Al2O3 was used. The pore channels with circular-shaped cross-sections were aligned along the solidification direction of molten camphene and connected with each other. The pore morphology was influenced by the starting solids loading and sintering temperature. The compressive strength of monolithic specimen greatly decreased when the porosity increased. However, the layered composites with a graded porosity exhibited improved compressive strength with minor decrease in porosity, probably due to the formation of residual compressive stress and relatively dense glass phase in the outer layer.

The effect of thermo-cycling treatment on the bond strength and flexural strength of porcelain veneered zirconia was evaluated. After thermo-cycling treatment between 5 degrees C to 55 degrees C, porcelain-zirconia bond strength and zirconia flexural strength was not significantly affected. In the phase analyses using XRD after thermo-cycling treatment, both the experimental group and the control group showed only tetragonal phases. That is, the porcelain-zirconia bond strength and zirconia flexural strength were not affected by low temperature degradation. So low temperature aging treatment did not reduce the flexural strength and the effect of temperature applied to the aging treatment could beignorable.