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Preparation of hexagonal micro-sized α-Al₂O₃ platelets from a milled Al(OH)₃ precursor with NH₄F and NH₄Cl additives

Liu, Luoqiang, Zhang, Xing, Zhu, Lingling, Wei, Yazhu, Guo, Chao, Li, Hongxia
Zeitschrift für Naturforschung 2019 v.74 no.7-8 pp. 579-583
additives, aluminum hydroxide, aluminum oxide, ammonium chloride, blood platelets, gases, mass transfer, microstructure, milling, particle size distribution
Hexagonal α-Al₂O₃ platelets with about 1-μm diameter and 0.2-μm thickness are prepared by the calcination of a milled Al(OH)₃ precursor with NH₄F and NH₄Cl additives. The influences of the ball milling treatment and the composite additive on the microstructure of α-Al₂O₃ micro-powders are studied. The results indicate that the particle size distribution of α-Al₂O₃ is highly dependent on the aggregate size of the Al(OH)₃ precursor and that the morphology of α-Al₂O₃ can be significantly favored by the addition of 5 wt.% NH₄F and 5 wt.% NH₄Cl as additives. The growth velocity of the (0001) plane is significantly reduced because of the accelerated growth rate of other crystal faces caused by the increase of gas phase mass transfer. The combined effect of composite additives and precursor ball milling treatment leads to the generation of well-developed α-Al₂O₃ platelets with uniform size distribution.