Effect of cristobalite formation and glaze on bending strength of α-alumina reinforced porcelain

The purpose of this study was to elucidate the effect of body and glaze composition on the mechanical properties of porcelain strengthened by addition of 15 mass% of α-alumina fine powder and by crystallization of cristobalite. With the increase in amount of cristobalite, thermal expansion coefficient of bodies increased. Precise control of cristobalite content in a body proper for glaze to generate compressive stress of 90 MPa improved the bending strength of porcelain from 160 MPa up to 230 MPa. Excess compressive stress in glaze induced by much difference in thermal expansion coefficient had to be avoided, because it led to shivering in glaze and body. Stress and strain in glaze were calculated, and the fracture mechanism was theoretically considered from the viewpoint of a fracture criterion taking into account fracture origins and mechanical properties.