Controlling the morphology of plate-like α-Al2O3 powders is essential since Al2O3 platelets of different sizes and shapes are needed in numerous applications. In this work, non-aggregated α-Al2O3 single-crystal platelets with diameters ranging from ~1 µm to more than 20 µm and thicknesses from ~0.1 µm to 1.3 µm were produced by molten salt synthesis. The effects of alumina precursor and molten salt compositions on phase formation and morphology development of Al2O3 particles were investigated. Al2(SO4)3 precursor reacts with K2SO4 salt to form K3Al(SO4)3 liquid phase at ~625 °C. The α-Al2O3 seeds generated in-situ from the decomposition of K3Al(SO4)3 can serve as low energy nucleation sites, and thus accelerate complete transformation to α-Al2O3 at much lower temperatures, yielding platelets of ≥20 µm diameter. Conversely, γ-Al2O3 precursor is stable until higher temperatures, resulting in the formation of small hexagonal α-Al2O3 platelets (1–2 µm in diameter) in the K2SO4 molten salt. In addition to alumina precursors, the salt species also strongly affect the morphology of Al2O3 particles. Compared with chloride salts (NaCl and KCl), sulfate salts (K2SO4 and Na2SO4) create favorable conditions for growth of higher- aspect-ratio α-Al2O3 hexagonal platelets.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Process Chemistry and Technology
- Surfaces, Coatings and Films
- Materials Chemistry