Size Control of α‐Alumina Particles Synthesized in 1,4‐Butanediol Solution by α‐Alumina and α‐Hematite Seeding

The effects of seed particles and shear rate on the size and shape of α‐Al 2 O 3 particles synthesized in glycothermal conditions are described. It is proposed that seed particles provide a low‐energy, epitaxial surface in solution to lower the overall surface energy contribution to the nucleation barrier, thus increasing nucleation frequency and subsequently reducing the particle size of hexagonal α‐Al 2 O 3 platelets or polyhedra, depending on synthesis conditions, in 1,4‐butanediol solution. Seeds have a significant effect on the size of hexagonal α‐Al 2 O 3 platelets in samples with high seed concentration. The particle size of α‐Al 2 O 3 platelets decreases from 3 to 4 µm to 100 to 200 nm by increasing the number concentration of seeds. In the case of α‐Fe 2 O 3 seeding, the effect of seeding on the size of α‐Al 2 O 3 particles closely resembles the effects obtained with α‐Al 2 O 3 seeding. Regardless of seed concentration, high stirring rate promotes the formation of hexagonal platelets with high aspect ratio, whereas medium and low stirring rates promote the formation of elongated platelets and polyhedra with 14 faces, respectively.