Abstract:
Nanosized alumina powder was obtained from the calcination of ammonium aluminum carbonate hydroxide (AACH) which was synthesized by precipitation method. Effects of calcination time, milling of AACH, the use of ultrasonic during synthesis of AACH and surface modification of AACH by surfactant were investigated. It was found that AACH which was calcined 1 h at 1200 ํC would become alpha-alumina completely, but it contained small degree of agglomeration. When AACH was suddenly calcined at high temperature without long heating up period, it would be able to reduce hard agglomeration in alumina particle. Furthermore, AACH milling and using of ultrasonic during AACH synthesis would also reduce hard agglomerates in the alumina particle. However, modification of AACH surface before calcination could not reduce the agglomeration. The synthesized alumina powder was fabricated into compacted bodies by biaxial press and cold isostatic press, respectively. The compacted bodies were then sintered at 1350 ํC for 2 h, sintered at 1550 ํC for 2 h in air and hot-isostatic pressed, repeatedly. The relative density of the sintered specimens prepared from various samples was in the range of 62-99% of theoretical density, whereas grain size was in the range of 0.5-1.7 um. The transmittance of the specimens was in the range of 30-60% at wave length 700 nm.
