Growth of α‐AI₂O₃ Platelets in the HF‐γy‐AI₂O₃ System

In the presence of a fluorine mineralizer, highly aggregated, <5 μm α‐Al₂O₃ platelet particles form by vapor transport during the thermal transformation of γ‐alumina. Platelet aggregation was determined to occur by platelet inter‐growth and by edge nucleation on primary α‐Al₂0₃ platelets. The addition of 10¹⁰α‐alumina seed particles/cm³γ–Al₂O₃ resulted in the development of discrete particles during the initial stage of transformation. Impingement of the growing platelets during the latter stage of transformation, however, resulted in intergrowth, a process which was not changed by seeding. Particle size distribution broadening was observed to increase with increasing HF and H₂O concentrations because vapor reactant supersaturation increases the degree of edge nucleation. When initially low HF and H₂O concentrations were used in seeded systems, however, essentially aggregate‐free α‐Al₂O₃ platelets of 10–15 μm were obtained.