A novel α-Al2O3 powders with regular shape prepared by sol-gel: effect of aluminum sources and pH value

In this paper, regular shape α-Al₂O₃ powders were fabricated via an inorganic sol-gel method, using aluminum sulfate (Al₂(SO₄)₃ ∙ 18H₂O), aluminum nitrate (Al(NO₃)₃ ∙ 9H₂O) and ammonia water (NH₃ ∙ H₂O) as raw materials. Then, the effect of the mass ratio of aluminum sources and the pH value of the solution on the phase composition, morphology and dispersity of alumina powders were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the thermogravimetric-differential scanning calorimetry (TG-DSC) and Fourier transform infrared spectroscopy (FTIR). The results revealed that the main impact of sulfate ions could be favorable for the formation of regular shape α-Al₂O₃ powders. Although the particles were nonuniformity and the particle size distribution was bimodal, the particle dispersity and morphology can be changed by adjusting to the proportion of aluminum nitrate and aluminum sulfate. As the pH value increased, the precursor’s phase was transformed from amorphous aluminum hydroxide through boehmite to bayerite. Additionally, the serious agglomeration caused the morphology of α-Al₂O₃ powders gradually change from regular shape to irregular block, and the particle size distribution became wider, from unimodal distribution to bimodal distribution. When the mass of aluminum nitrate and aluminum sulfate were 75 wt.% and 25 wt.% and the pH value of the solution was 7, respectively, precursors were evolved into well-dispersed α-Al₂O₃ powders with regular morphology heated at 1200 °C for 2 h.

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