Abstract
China clay (Kaolin) and quartz in the ratio of 1:2 was progressively replaced by pyrophyllite in a conventional porcelain mix. Addition of 15% pyrophyllite as a replacement of a combination of china clay and quartz decreased the linear shrinkage by 5.03% while fired strength was improved by about 31.5% compared to that of the conventional body fired at 1300 °C. Incorporation of pyrophyllite beyond 15% resulted in early vitrification of porcelain composition, although in lower proportion the effect is not so significant. Percentage of mullite was found to increase in the fired specimens even when kaolinite was progressively replaced by pyrophyllite. However, beyond 22.5% pyrophyllite addition, there occurred large volume of glass formation. Presence of large volume of glassy phase as well as formation of large pores of various shapes resulted in deterioration in ceramic properties. The size and shape of mullite crystals is to a large extent controlled by the fluidity of the liquid matrix from which they grow and this is again a function of temperature and composition.
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