Preparation of gamma -alumina precursors for metal reinforcement

• Published in: Applied composite materials 1995-01, Vol.2 (4), p.245-255
• Main Authors: Kuang, X, Carotenuto, G, Nicolais, L, Mao, M, Liang, H, Hu, S, Yu, K, Yu, D
• Format: Article
• Language: English
• Subjects: Dehydration; Heating; Metallic matrix composites; Morphology; Nitric acid; Phase transitions; Reinforcement; Sodium compounds
• ISSN: 0929-189X
• DOI: 10.1007/BF00567195

In the metal matrix composite field, both fine ( < 0.5 mu m) 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 ( gamma -AlOOH), precursor of the gamma -Al sub 2 O sub 3 , on the product morphology. The material was produced by heating three kinds of hydrothermal precursors at different pH, and for 2 h at 200 deg C, using constant stirring. Under the conditions investigated (i.e. 0.12 mol/dm exp 3 of Al(OH) sub 3 and only diluted NaOH and HNO sub 3 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) sub 3 to gamma -AlOOH is believed to be dissolution/reprecipitation rather than a direct dehydration.