Effect of Coarse Quartz Grains on Mechanical Strength of Porcelain Body

Abstract

Effect of coarse quartz grains on mechanical properties of triaxial porcelain body was examined. Bodies composed of 50 kaolin, 25 potash feldspar and 25wt% fine quartz, which was replaced in turn with 74-149μm coarse ones, were fired at 1400°C for 1h. Their bulk density was about 2.38g/cm3 and hardly changed with the amount of coarse quartz. Bending strength of the fired specimens was markedly decreased from 1350kgf/cm2 for the body free from the coarse quartz grains to about 900kgf/cm2 by addition of only 0.03% of the coarse grains, and further decreased with an increase in the amount of coarse grains. Weibull coefficient of the bending strength increased with increase in the amount of the coarse quartz grains. Scattering in the bending strength values and also mean deviation of starting point of failure from the maximum stressed point decreased with increase in the content of the coarse quartz grains. From these relations, it was inferred that most failures of the specimens were started at the origin associated with the coarse quartz grains. The results clearly shows that not only the control of the quartz grain size within an appropriate range but also the prevention of the contamination by coarse quartz grains are indispensable for the increase in the mechanical strength of a porcelain body.