Morphology-controlled synthesis of α-alumina microplatelets through an additive-assisted molten salt reaction

Highly dispersed α-Al₂O₃ microplatelets of various sizes and aspect ratios were prepared by additive-assisted molten salt synthesis. The effects of SiO₂ and SiO₂ + CaO additions on phase formation and morphology development of α-Al₂O₃ particles were investigated. Introducing additives are very effective in controlling α-Al₂O₃ morphology. SiO₂ additive significantly enhances shape anisotropy of α-Al₂O₃ platelets, where a particle aspect ratio ∼23.8 was achieved, about 2.7–6.0 times higher than those of the platelets prepared without additives. When using SiO₂ + CaO mixture, low concentration additive facilitates the growth of large platelets (∼9.8 µm), while increasing its content dramatically reduces the platelet size to ∼3.7 µm. These findings provide a new insight for the design and synthesis of novel advanced anisotropic microcrystals with improved quality.