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Glaze surface Defects causes and Prevention Controls
E. Youssef, E. Youssef, N. Mostafa, J.E. Khoury, T. Merhej, R. Lteif
Abstract
Glaze defects adversely affect the quality of sanitaryware pieces and occur in form of pinholes, crawling or crazing. Pinholes are caused by the migration of gas from the body, which is either trapped by the glaze or released at a later stage during the firing process leaving the glaze insufficient time to heal. Several factors increase the development of glaze pinholes like high glaze viscosity during firing, high surface tension, and improper grain size distribution of raw materials. The choice of suitable materials and adjustment of the glaze formula combined with the optimum firing conditions contribute to minimizing pinholes. Crawling happens when the molten glaze withdraws from the ceramic body during firing leaving bare patches on the ceramic body. It is caused by high surface tension in the melting glaze. To prevent crawling, it is necessary to control all the measures that reduce surface tension. In the case of both crazing and peeling, the eradication of problems relies on matching the thermal expansion characteristics of the body and glaze. Crazing can occur when the body absorbs water and expands so the thermal expansion coefficient should be controlled. This work summarizes the reasons for glaze surface defects based on the recently published research and the suggested practical remedies.
Keywords
Ceramic, glaze defects, glaze pinholes, crawling, crazing
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