High‐Temperature Reactions of Clay Mineral Mixtures and Their Ceramic Properties: II, Reactions of Kaolinite‐Mica‐Quartz Mixtures Compared with the K2O— Al2O3—SiO2 Equilibrium Diagram

Abstract

Two series of mixtures containing respectively 15 and 35% quartz, together with kaolinite and muscovite in varying proportions, were fired at 1000°, llOO°, 1200°, and 1300°C. for 2‐hour periods. The resulting crystalline phases were measured quantitatively by X‐ray diffraction and the amount of noncrystalline material was estimated by difference. The results for samples fired to 1300°C. are compared with data calculated from the K2O‐Al2O3‐SiO2 equilibrium diagram, and a general agreement is obtained with the calculated equilibrium relations for this temperature. In particular, the observed and calculated amounts of mullite agree within 5%. The main departure from equilibrium is the persistence of unreacted quartz, and consequently the estimated amount of noncrystalline residue tends to be less than the calculated liquid (viz. glassy) component. At 1100° and 1200°C., the fired materials approach less closely to the equilibrium relations. The decomposition products of muscovite are discussed in an appendix.