Abstract
The effects of pH value on the composition, structure, morphology, and phase transformation of aluminum hydroxides prepared by chemical precipitation were studied. Aluminum hydroxide precipitated at the pH values of 5 and 6 is amorphous and transforms to α-Al 2O 3 at 950 °C via the amorphous aluminum hydroxide → amorphous Al 2O 3 → α-Al 2O 3 transformation path. Aluminum hydroxide precipitated at pH = 7 is boehmite and transforms to α-Al 2O 3 at 950 °C via the γ-AlOOH → γ-Al 2O 3 → α-Al 2O 3 path. Aluminum hydroxide precipitated at pH values in the 8 to 11 range is bayerite and transforms to α-Al 2O 3 at 1000 °C via the α-Al(OH) 3 → γ-Al 2O 3 → ε-Al 2O 3 + θ-Al 2O 3 → α-Al 2O 3 path. Moreover, the pH value affects not only the morphology of aluminum hydroxide particles which changes from ultrafine floccules through 50 nm blowballs then to 150 nm irregular agglomerates with increasing pH value but also the microstructures of final decomposition products of aluminum hydroxides.
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