Low temperature synthesis of polyhedral α-Al2O3 nanoparticles through two different modes of planetary ball milling

Abstract

Herein, nano-sized α-Al2O3 powders were successfully synthesized at low temperatures via unidirectional ball milling of Al(OH)3 and addition of an AlF3 additive. The effects of the rotational direction in planetary ball milling on the α-phase transformation and morphology of α-Al2O3 were studied. Unidirectional rotation was observed to be significantly more helpful than bidirectional rotation with regard to improving the α-phase transformation and microstructure of α-Al2O3. Further, α-Al2O3 was obtained at a lower temperature (800 °C) by employing unidirectional ball milling; this was because gibbsite agglomerates (20–100 μm) could be refined into micro-sized curled flocs with a high specific surface area (124.95 m2 ∙ g−1) by performing unidirectional ball milling for 9 h. The addition of 1 wt% AlF3 accelerated the gas-phase mass transfer, which could effectively promote α-phase transformation and decrease the temperature at which α-Al2O3 was obtained. In comparison with the pyramidal α-Al2O3 polyhedron that exhibited a size range of 0.2–2 μm, homogeneous α-Al2O3 polyhedron with the size of approximately 100 nm was prepared at the temperature range of 910–940 °C via unidirectional ball milling.