Firing of Porcelain

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New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
It is common to think of fast firing of porcelain tiles as unrelated to the conventional firing cycles typically used in the whitewares industry. In other words, it appears that the densification and mineralogy in fast firing appear to be inconsistent with conventional firing. It is also common to evaluate the progress in firing behavior from the perspective of mullite formation, quartz dissolution, and the densification kinetics. This study proposes that mullite formation, quartz dissolution, and densification across all firing conditions are completely consistent from fast firing to conventional firing. The data indicates that mullite formation is completed early and is limited by the solubility of alumina in the glass phase. The amount of mullite appears to be independent of temperature, dwell time, and heating rate above 1200°C but mullite crystallite size increases as a function of temperature, dwell time, with a small dependence on heating rate. The undissolved quartz level—a direct result of quartz dissolution—decreases linearly on a log-time scale. Similar to mullite formation, quartz dissolution is independent of heating rate. It was also confirmed that quartz dissolution is independent of the quartz particle size. Moreover, this work proposes that mullite formation and quartz dissolution are “diffusion limited processes.” In contrast, densification is dependent on temperature, time, and heating rate dependent, presumably due to the mechanics of viscous phase sintering. The results indicate that the minimum amount of glass necessary to achieve full bulk density is about 53.3 weight percent (±0.9%). True density, however, appears to be dependent on temperature and dwell time, but is independent of heating rate, consistent with the measured quartz dissolution behavior.
Advisory committee members: Matthew Hall, Dawei Liu. Dissertation completed in partial fulfillment of the requirements for the degree of Masters of Science in Ceramic Engineering at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University