Synthesis of alpha-Alumina Nanoparticles Through Partial Hydrolysis of Aluminum Chloride Vapor

Spherical alumina precursors represented by AlOxCly(OH2) 30 similar to 200 nm in particle diameter, were prepared by partial hydrolysis of AlCl3 vapor in a 500 ml reactor. Investigated on the particle morphology and size were the effects of the reaction time, the stirring speed and the reaction temperature. The particle morphology and size was insensitive to the reaction time in the range 20 to 300 s. The variation of the stirring speed from 0 to 300 and 800 rpm showed that the particle size was the largest at 0 rpm. As the temperature was varied from 180 to 190, 200, 140 degrees C, the particle size showed a maximum at 190 degrees C. By calcination of the as -produced particles at 1,200 degrees C for 6h with a heating rate of 10 degrees C/min, alpha-alumina particles 45 nm in surface area equivalent diameter were obtained. The particle shape after calcination turned wormlike due to sintering between neighboring particles. A rapid calcination at 1400 degrees C for 0.5 h with a higher heating rate of 50 degrees C/min reduced the sintering considerably. An addition of SiCl4 or TMCTS(2,4,6,8-tetrameth-ylcyclosiloxane) to the AlCl3 reduced the sintering effectively in the calcination step; however, peaks of gamma or mullite phase appeared. An addition of AlF3 to the particles obtained from the hydrolysis resulted in a hexagonal disc shaped alumina particles.