Preparation of dense cordierite ceramics from magnesium compounds and kaolinite without additives

Abstract

Thermal reactions of magnesium compounds and kaolinite were investigated to obtain dense cordierite ceramics without additives. Magnesium hydroxide was precipitated from aqueous solution in the form of ultrafine hexagonal tabular particles of about 0.1 μm, and heating this mixture with submicron particles of tabular kaolinite in a molar ratio of MgO·Al 2O 3·2SiO 2 resulted in the formation of an amorphous state at about 900°C after thermal decomposition. μ-Cordierite was then crystallized from the amorphous phase at about 950°C, and gradually transformed into α-cordierite from 950 to 1200°C. Firing the pressed specimens at 1350°C yielded a dense α-cordierite ceramics with a relative density higher than 95% and a negligible open porosity, and it showed a linear thermal expansion coefficient of 2.2×10 −6/K.