Preparation of cordierite from fibrous sepiolite

Abstract

Mineral sepiolite (Mg₄Si₆O₁₅(OH)₂·6H₂O) with fibrous morphology is one of candidates for substituting asbestos. When sepiolite was used as a matrix of an inorganic insulator, it was expected that formation of cordierite (Mg₂Al₄Si₅O₁₈) at elevated temperatures should improve its thermal shock resistance. We investigated formation of α-cordierite by reacting two kinds of sepiolite (as-received and acid-treated sepiolite) with amorphous aluminosilicate fiber (Al₂O₃·1.88SiO₂), γ-alumina (Al₂O₃) and amorphous silica (SiO₂) at 1100-1300°C. A α-cordierite phase was observed above 1200°C for any starting compound, however, anorthite (CaAl₂Si₂O₈) was produced at 1300°C when as-received sepiolite which contained calcite (CaCO₃) as an impurity was used. A single phase of α-cordierite was prepared by heating the mixture of acid-treated sepiolite, amorphous aluminosilicate fiber and γ-alumina or acid-treated sepiolite, γ-alumina and amorphous silica at 1300°C.