Effect of Precipitation Acidity on the Structure and Morphology of α-Al2O3 Powder Particles

Abstract

The effect of the solution acidity on the phase composition and morphology of alumina powers precipitated from solution using Al(NO₃)₃·9H₂O and NH₄HCO₃ was studied. In the рН range of 5–7, an amorphous precursor powder was typically formed; at рН 8–9, NH₄AlCO₃(OH)₂ crystals were formed. When annealed, the powders precipitated from acidic solutions were 100% α-Al₂O₃, which was represented by agglomerated equiaxed particles sized ca. 100–200 nm. The powders prepared in neutral or alkaline solutions, when annealed, formed additional minor θ-Al₂O₃ and γ-Al₂O₃ phases in equiaxed particles sized ca. 20–25 nm.