Thermolysis of Nanoparticulate Boehmite Prepared via Aluminum Isopropylate Hydrolysis

Resumo

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.