Abstract
In this study, the phase formation of aluminum oxide nanopowder during thermal heating of chemically precipitated aluminum hydroxide was discussed. Nanopowders of aluminum oxide and hydroxide were characterized by X-ray diffraction and thermogravimetric analysis, electron microscopy, energy dispersive X-ray spectroscopy analysis. XRD analysis detected a complex phase composition consisting of different modifications of aluminum hydroxide. It was shown that the precipitated aluminum hydroxide has a flake morphology with an average particle diameter of 5.5 nm. The differential thermal analysis showed that as-deposited aluminum hydroxide undergoes a multiple stage phase transformation. The deconvolution of the experimental differential curve by the Gaussian function and comparison of the temperature intervals of mass change with the literature data revealed that the precipitated aluminum hydroxide powder consists of bayerite α-Al(OH)3 and aluminum oxyhydroxide AlOH. It was found that bayerite is transformed to boehmite in the temperature range of 100 – 400 °C. After that γ-Аl2O3 is formed during the thermal decomposition of boehmite in the temperature range of 400 – 530 °C. The second hydroxide phase formed during the chemically precipitated method has a single stage phase transformation from AlO(OH) to γ-Аl2O3 in the temperature range of 260 – 500 °C. The nanopowder of γ-Аl2O3 formed at the temperature of higher than 600 °C has an equiaxed particle shape and an average size of 7 nm.
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