New approach to prepare the highly pure ceramic precursor for the sapphire synthesis

Abstract In the present work, a new method for the synthesis of a highly pure ceramic precursor for the synthesis of sapphire has been developed. The method consists in hydrothermal treatment of a mixture of gibbsite and nanosized powder γ-Al2O3 in a solution of 1.5 wt % HCl at 200 °C followed by heat treatment of the resulting compact at 1700 °C. The conversion of a mixture of gibbsite and nanopowder γ-Al2O3 into compact boehmite has been studied using atomic emission analysis, X-ray powder diffraction, infrared spectroscopy, scanning electron microscopy, differential thermal analysis, and the Brunauer–Emmett–Teller method. It has been found that the formation of boehmite compact is affected by the addition of nanosized powder γ-Al2O3 and the duration of the autoclave treatment of the reaction mixture in a solution of 1.5 wt % HСl at 200 °C. The optimal results in the synthesis of a highly pure ceramic precursor were obtained when the mixture of gibbsite and 1 wt % of nanosized powder γ-Al2O3 was treated for 7 h. The effect of the heat treatment conditions of the synthesized compact boehmite on the sintering density of a ceramic precursor has been studied.