Characterisation of fine polycrystals of metastable η-alumina obtained through a wet chemical precursor synthesis

An inexpensive and easy wet chemical synthesis is described which involves a mild base hydrolysis of an aqueous solution of aluminium sulfate with aqueous hydrazine hydrate solution as the hydrolysing precipitant, leading to the preparation of the basic aluminium sulfate (BAS) precursor. Heat treatment of the BAS precursor produces η-alumina (η-Al2O3) when calcined at 900°C for 2 h; high temperature calcination at 1200°C of the precursor or of the above-mentioned calcined material leads to the formation of the thermodynamically stable α-alumina (α-Al2O3). The alumina phases have been characterised by FTIR, X-ray diffraction, particle size measurements, electron micrography, weight-loss measurements and TGA-DTA analysis.