High‐Temperature Reactions of Clay Mineral Mixtures and Their Ceramic Properties: I, Kaolinite‐Mica‐Quartz Mixtures with 25 Weight % Quartz

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Abstract
The mineralogy and ceramic properties (linear shrinkage and porosity) of fired compacts of quartz, kaolinite, and mica containing 25% of quartz and variable proportions of kaolinite and mica were studied systematically in relation to composition and firing temperature. A procedure for the quantitative determination of components by X‐ray diffraction measurements is outlined and applied to the determination of quartz and mullite in the fired samples. For a mixture containing 25%, quartz, 75% kaolinite, the amount of mullite developed at 1300°C. is 41% and this contains 85% of the total Alsoa available. In micarich mixtures, mullite develops at lower temperatures and in smaller proportions. The shrinkage and porosity vary systematically with the percentage of mica in the samples and with firing temperature. The formation of cristobalite depends on the kaolinite content and is not related to the quartz content. Mullite and cristobalite develop at about 1100°C. from the transitory Si‐Al spinel‐type phase derived from kaolinite.