High thermal resistance of γ-Al2O3 prepared by the selective leaching of calcined kaolin minerals

Abstract

The thermal resistance of mesoporous γ-Al2O3 prepared by selective leaching of calcined kaolin minerals has been investigated. γ-Al2O3 prepared from four types of kaolin minerals calcined at 950 C for 24 h followed by leaching with KOH at 90 C for 1–3 h had specific surface areas as high as 200–300 m2 g-1 and pores with uniform radii of ca. 3 nm. The specific surface area decreased gradually with higher heating temperatures. However, the specific surface areas of the samples from kaolin minerals with low impurities were maintained at 70–110 m2 g-1 after heating at 1200 C for 1 h. This high thermal resistance was due to the characteristic microtexture of the γ-Al2O3, which consisted of fine γ-Al2O3 grains interspaced with residual amorphous silica in the pseudomorph particles of kaolin minerals. Amorphous silica suppressed the gamma- -> alpha-Al2O3 phase transition by preventing γ-Al2O3 grains from coming into contact and coalescing to give a lower specific surface area.