Synthesis of alumina nanoparticles by coprecipitation method and studying the effect of temperature on the phases and the specific surface of the synthesized alumina

In this study, coprecipitation has been used to prepare alumina nanoparticles. In order to do that first, the effect of aluminium salt and precipitating agent on the specific surface of alumina was studied. Then under an optimized condition, the effect of reaction temperature on phase changes and its specific surface were studied. Generally in order to prepare different phases of alumina nanoparticles, crystalline boehmite was prepared by heating the gelatinous white precipitate which first formed when precipitating agent was added to acid solutions of aluminium salt and finally, by dehydration of crystalline boehmite, nanoparticles of alumina were obtained with different phases. Different physical and chemical tests such as X-ray diffraction (XRD), X-ray fluorescence (XRF), specific surface area measurement (BET), scanning electron microscope (SEM), transmission electron microscope (TEM) and thermogravimetric analysis (TGA) were performed on prepared alumina nanoparticles. The results show that using aluminium nitrate salt and ammonia as precipitating agent yields alumina with the best specific surface area (211 m2/g). Also alumina which is manufactured by using ammonia and aluminium chloride with 58 m2/g has lowest amount of specific surface area. In addition, it was found that after calcinations at 550 °C, gamma-alumina phases appear. While with increasing reaction temperature to 1400 °C, the alpha-alumina phase was produced.