Alumina-Precursor Nanoparticles Prepared by Partial Hydrolysis of AlCl₃Vapor in Tubular Flow Reactor: Effect of Hydrolysis Conditions on Particle Size Distribution

Abstract

Aluminum chloride (AlCl 3 ) was evaporated and partially hydrolyzed in water vapor at 300–700 °C in a tubular reactor, 2.4 cm in diameter and 50 cm in length, to form alumina-precursor particles that were more spherical and less agglomerated compared with the fumed alumina produced by flame hydrolysis and oxidation. This study was focused on the effects of the H 2 O to AlCl 3 molar ratio, the reactor temperature, the AlCl 3 concentration, and the contact point of AlCl 3 with H 2 O vapors on the morphology, size, and chemical composition of the obtained particles. The primary particle size ranged from 50 to 200 nm depending upon the operating conditions. The particle size increased with increasing AlCl 3 concentration but decreased with increasing reactor temperature or with increasing molar ratio of H 2 O to AlCl 3 . The particle size became smaller and the particle size distribution narrower as the contact point of AlCl 3 with H 2 O vapors was moved from the inlet of the reactor to a point 10 cm inward toward the center of the reactor. The primary particle sizes were simulated with a discrete-sectional model under different operating conditions. The as-produced particles contained chlorine because of the incomplete hydrolysis; the atomic ratio of Cl to Al in the resulting particles was measured to be 0.21–0.47 or 10–15% of the chlorine in the AlCl 3 charged for the hydrolysis. The particles prepared at the reactor temperature of 500 °C were calcined at 1200 °C for 1 h. The calcined particles were chlorine free, α in crystalline phase, 98 nm in surface-area equivalent diameter, and 0.81 g/cm 3 in bulk density.