抄録
A modified homogeneous precipitation technique involving the enzymatic decomposition of urea was proposed and was applied to the synthesis of alumina precursors. Spherical aluminum hydroxide aggregates were prepared at 298K from aqueous solutions containing aluminum sulfate, urea and urease. In contrast to the conventional technique involving the thermally-induced decomposition of urea, the resultant aggregates were amorphous with no trace of pseudoboehmite. The apparent rate of nucleation of the aggregates was found to correlate with the concentration of urease. As the result, the mean size of the aggregates could be controlled in a range between 0.3 to 1.9μm by adjusting the urease concentration. The precursors remained amorphous after calcination at 1073K for 2 hours, then transformed to γ-alumina after being calcined at 1273K, and the transformation to α-alumina was completed after calcination at 1473K.
