Effects of Glaze Variables on the Mechanical Strength of Whitewares

Abstract

Glaze thickness and glaze composition were systematically altered to study their effects on the mechanical strength of two commercial porcelain bodies, an alumina body and a silica body. This study determined that glaze composition affects the mechanical strength of porcelain piece in a linear fashion. The mechanical strength of a porcelain piece can then be predicted, accounting for the Young’s Modulus of the body. Maximum strengths values were achieved for the silica body at a thermal expansion mismatch level, between the body and glaze, of 0.93x10-6/K. This corresponded to a mechanical strength of 97 MPa. It was not determined if a maximum had been reached for the alumina body, because when the amount of thermal expansion mismatch was the greatest, a surface layer was present on the body that caused large voids at the glaze/body interface during application of the glaze. Fractography analysis was used to identify, when possible, fracture origins. This analysis attempts to correlate fracture origin sizes with strength, and the variation in fracture origin size to the scatter in the strength data. Fracture origins were, generally, identified as bubbles in the glaze for the lowest-strength samples, grains and pores at the glaze/body interface for the intermediate-strength samples, and grains and inclusion in the body for the highest-strength samples.