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|Title:||Mechanical-Activation-Triggered Gibbsite-to-Boehmite Transition and Activation-Derived Alumina Powders|
|Citation:||Yong, C.C.,Wang, J. (2001-06). Mechanical-Activation-Triggered Gibbsite-to-Boehmite Transition and Activation-Derived Alumina Powders. Journal of the American Ceramic Society 84 (6) : 1225-1230. ScholarBank@NUS Repository.|
|Abstract:||Mechanical activation of monoclinic gibbsite (Al(OH)3) in nitrogen led to the formation of nanocrystalline orthorhombic boehmite (AlOOH) at room temperature. The boehmite phase formed after merely 3 h of mechanical activation and developed steadily as the mechanical-activation time increased. Forty hours of mechanical activation resulted in essentially single-phase boehmite, together with α-alumina (α-Al2O3) nanocrystallites 2-3 nm in size. The sequence of phase transitions in the activation-derived boehmite was as follows: boehmite to γ-Al2O3 and then to α-Al2O3 when flash-calcined at a heating rate of 10°C/min in air. γ-Al2O3 formed at 520°C, and flash calcination to 1100°C led to the formation of an α-Al2O3 phase, which exhibited a refined particle size in the range of 100-200 nm. In contrast, the gibbsite-to-boehmite transition in the unactivated gibbsite occurred over the temperature range of 220°-330°C. A flash-calcination temperature of 1400°C was required to complete the conversion to α-Al2O3 phase, with both δ-Al2O3 and θ-Al2O3 as the transitional phases. The resulting alumina powder consisted of irregularly shaped particles 0.4-0.8 μm in size, together with an extensive degree of particle agglomeration.|
|Source Title:||Journal of the American Ceramic Society|
|Appears in Collections:||Staff Publications|
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