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

Thermal reactions of magnesium compounds and kaolinite were investigated to obtain dense cordierite ceramics without additives. Magnesium hydroxide wa s precipitated from aqueous solution in the form of ultrafine hexagonal tab ular particles of about 0.1 mu m, and heating this mixture with submicron p articles of tabular kaolinite in a molar ratio of MgO.Al2O3.2SiO(2) resulte d in the formation of an amorphous state at about 900 degrees C after therm al decomposition. mu-Ciordierite was then crystallized from the amorphous p hase at about 950 degrees C, and gradually transformed into alpha-cordierit e from 950 to 1200 degrees C. Firing the pressed specimens at 1350 degrees C yielded a dense alpha-cordierite ceramics with a relative density higher than 95% and a negligible open porosity, and it showed a linear thermal exp ansion coefficient of 2.2 x 10(-6)/K. (C) 2000 Elsevier Science Ltd and Tec hna S.r.l. All rights reserved.