Formation of α-Alumina Around 500°C in Alkoxy-Derived Alumina Gels Under Ambient Pressure—Effects of Starting Solution Composition and Seeding

The hydrolysis of aluminum-sec-butoxide (ASB) in the ASB-H2O-C2H5OH-HCl solutions at 0°C for 18 h and subsequent aging of the sol for 30 days at 5°C provided an alumina gel which was partially (20–30 wt%) transformed to α-Al2O3 when heat-treated at 500°–600°C under ambient pressure. In addition to the hydrolysis and aging conditions, the amounts of water and HCl in the starting solution were found to be very important factors for the low temperature formation of α-Al2O3 in the resultant gel. Some difference in the chemical environment of involved OH groups was found between the alumina gel forming α-Al2O3 at 500°–600°C and the conventional gel. Corundum seeding was found to be effective; thus, 1 wt% seeding brought about an increase in the fraction of α-Al2O3 formed at 600°C to 40–50 wt%.