Formation and characterization of stoichiometric mullite (3Al2O3.2SiO2) prepared by the hydrazine method

Mullite (3Al2O3-2SiO2) has been recognized as an important material for high-temperature structural applications because of its good mechanical strength, excellent thermal shock resistance, high creep resistance, low thermal conductivity, and high temperature stability. Several processes for preparing the high-purity and reactive mullite powders have recently been reported. Homogeneous molecular scale mixing of aluminum and silicon-bearing compounds using controlled chemical processing (i.e. monophasic precursors) gives mullite from an amorphous material after heating at 1000 C, while colloidal-scale mixtures of Al2O3 and SiO2 (i.e. diphasic precursors) yield mullite at higher temperatures (1200-1300 C) either via spinel phase or delta- or theta-Al2O3, depending on the starting materials and processing conditions. A new powder preparation method using hydrazine monohydrate has recently been developed in some systems. This method was applied to the preparation of mullite powder. (Author)