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

The effect of wetting non-hydrolytic derived alumina xerogels with water an d 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 sim ilar to 450 degreesC. Water treatment for a day at room temperature (RT) fo llowed by second calcination decreased the surface area by 10%. This decrea se in surface area is less pronounced with increasing wetting periods. On t he other hand water treatment at 50-70 degreesC followed by a second calcin ation resulted in a surface area increase of up to 15%. Upon water treatmen t the total pore volume has decreased from 0.65 (cm(3)/gr) to 0.48 (cm(3)/g r) and the average pore size decreased from 6.8 nm to 4.1 nm. The Cl conten t was found to be uneffected by the water treatment, remaining at similar t o2.5% wt. Wetting with water at elevated temperature (70 degreesC) accelera ted 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 tra nsition into alpha -Al2O3, at 1150-1300 degreesC.