Thermolysis of Nanoparticulate Boehmite Prepared via Aluminum Isopropylate Hydrolysis
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Boehmite gel was prepared via hydrolysis of aluminum isopropylate in a water–alcohol solution. Electron-microscopic examination showed that the boehmite particles were highly uniform in diameter, at ~70 nm. X-ray fluorescence analysis demonstrated high purity of the material. The boehmite was heat-treated in air at 50, 165, 250, 400, 600, 800, 1000, and 1200°C and characterized by X-ray diffraction after each step. The crystallite size of the thermolysis products was found to increase from 1.1 to 3.6 nm in the range 50 to 1000°C. The gel sample dried at 50°C was characterized by simultaneous thermal analysis in combination with mass spectrometry of released gases. According to the thermal analysis results, the total weight loss in the sample was 45%. The mass spectrometry data allowed us to determine the overall formula of the synthesized gel. In the range 100–200°C, the gel lost the residual adsorbed isopropanol and isopropoxide groups, whereas water release continued up to 1000°C. We conclude that the degree of structural order, water content, and purity of the material influence the thermal stability of the metastable phases of aluminum oxide.
Keywords:alumina aluminum oxyhydroxide phase transformations crystal structure
This work was supported by the Russian Federation Government (Decree no. 211, March 16, 2013; agreement no. 02.A03.21.0011) and the Russian Federation Ministry of Education and Science (state research target no. 4.5749.2017/7.8).
We are grateful to Prof. A.V. Tochev for supplying the gibbsite.
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