Modification of non-hydrolytic sol-gel derived alumina by solvent treatments

The effect of wetting non-hydrolytic derived alumina xerogels with water and organic solvents in the 20-70 degreesC range on the alumina's properties was investigated. Wetting with organic solvents does not affect the alumina. However, contact with water was found to change the sharp crystallization at similar to 800 degreesC to a continuous crystallization starting at similar to 450 degreesC. Water treatment for a day at room temperature (RT) followed by second calcination decreased the surface area by 10%. This decrease in surface area is less pronounced with increasing wetting periods. On the other hand water treatment at 50-70 degreesC followed by a second calcination resulted in a surface area increase of up to 15%. Upon water treatment the total pore volume has decreased from 0.65 (cm(3)/gr) to 0.48 (cm(3)/gr) and the average pore size decreased from 6.8 nm to 4.1 nm. The Cl content was found to be uneffected by the water treatment, remaining at similar to2.5% wt. Wetting with water at elevated temperature (70 degreesC) accelerated the morphological changes, eliminating the crystallization peak at 800 degreesC in one hour. A dissolution-reprecipitation mechanism is suggested to explain the results. In addition, Mass-Spectroscopy of the effluent gas during heat treatment revealed the emission of CO2 and water upon phase transition into alpha -Al2O3, at 1150-1300 degreesC.