Preparation of Y-Alumina Precursor for Metal Reinforcement

In the metal matrix composite field, both fine (<0.5 µm) and coarse, crystalline, calcined aluminas with narrow or broad particle size distributions, are being used as reinforcement phase. The effect was studied of the preparation method of fine boehmite (?-AlOOH), precursor of the ?-Al2O3, on the product morphology. The material was produced by heating three kinds of hydrothermal precursors at different pH, and for 2 h at 200°C, using constant stirring. Under the conditions investigated (i.e., 0.12 mol/dm3 of Al(OH)3 and only diluted NaOH and HNO3 solutions used to adjust the pH of slurry), the pH of hydrothermal slurry influenced the product morphology; in contrast, the three different hydrothermal precursors, namely dry aluminum hydroxide gel, fresh aluminum hydroxide precipitate and gibbsite reagent powders, had only a little effect on the product morphology. The dehydration/transformation mechanism from Al(OH)3 to ?-AlOOH is believed to be dissolution/reprecipitation rather than a direct dehydration.