Effect of hydrothermal process for inorganic alumina sol on crystal structure of alumina gel

This paper reports the effect of a hydrothermal process for alumina sol on the crystal structure of alumina gel derived from hydrothermally treated alumina sol to help push forward the development of low temperature synthesis of alpha-Al2O3. White precipitate of aluminum hydroxide was prepared with a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution. The obtained aluminum hydroxide precipitate was peptized by using acetic acid at room temperature, which resulted in the production of a transparent alumina sol. The alumina sol was treated with a hydrothermal process and transformed into an alumina gel film by drying at room temperature. Crystallization of the alumina gel to alpha-Al2O3 with 900 degrees C annealing was dominant for a hydrothermal temperature of 100 degrees C and a hydrothermal time of 60 min, as production of diaspore-like species was promoted with the hydro thermal temperature and time. Excess treatments with hydrothermal processes at higher hydrothermal temperature for longer hydrothermal time prevented the alumina gel from being crystallized to ce.-Al2 03 because the excess hydrothermal treatments promoted production of boehmite. (C) 2016 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://cleativecommons.orgi licensesiby-nc-nd/4.0J).