Effect of Polymorphism of SiO2 Addition on Mechanical Properties of Feldspathic Porcelains

The present study aimed to investigate the effects of SiO2 polymorphism on the mechanical properties of feldspathic porcelains. Seven kinds of experimental feldspathic porcelains were prepared using chemical reagents; three types of low-fusing feldspathic glasses and four types of two-phase porcelains by adding 10 or 20 mass% of fused silica (T-F) or cristobalite (T-C). Flexural strength and fracture toughness of these porcelains were evaluated. Flexural strengths of two-phase porcelains did not show any significant increase when compared with those of single-phase glasses. On the other hand, fracture toughnesses of porcelains with cristobalite showed a significant increase when compared with those of single-phase glasses. Circumferential cracks were observed in the porcelains with cristobalite. These results suggested that cristobalite could strengthen fracture toughness of feldspathic porcelains, but not flexural strength.