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Growth of α‐AI 2 O 3 Platelets in the HF‐γy‐AI 2 O 3 System

1994; Wiley; Volume: 77; Issue: 11 Linguagem: Inglês

10.1111/j.1151-2916.1994.tb04534.x

1551-2916

Charles A. Shaklee, Gary L. Messing,

Metal and Thin Film Mechanics

In the presence of a fluorine mineralizer, highly aggregated, <5 μm α‐Al 2 O 3 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‐Al 2 0 3 platelets. The addition of 10 10 α‐alumina seed particles/cm 3 γ–Al 2 O 3 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 H 2 O concentrations because vapor reactant supersaturation increases the degree of edge nucleation. When initially low HF and H 2 O concentrations were used in seeded systems, however, essentially aggregate‐free α‐Al 2 O 3 platelets of 10–15 μm were obtained.