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Effect of Seeding and Water Vapor on the Nucleation and Growth of α‐Al 2 O 3 from γ‐Al 2 O 3
Author(s) -
Bagwell Roger B.,
Messing Gary L.
Publication year - 1999
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1999.tb01842.x
Subject(s) - nucleation , seeding , activation energy , diffusion , water vapor , isothermal process , kinetics , chemistry , analytical chemistry (journal) , materials science , chemical engineering , thermodynamics , chromatography , organic chemistry , quantum mechanics , engineering , physics
Isothermal transformation kinetics and coarsening rates were studied in unseeded and alpha‐Al 2 O 3 ‐seeded γ‐Al 2 O 3 powders heated in dry air and water vapor. Unseeded samples heated in dry air transformed to alpha‐Al 2 O 3 with an activation energy of 567 kJ/mol. Seeding with alpha‐Al 2 O 3 increased the transformation rates and reduced incubation times by providing low‐energy sites for nucleation/growth of the alpha‐Al 2 O 3 transformation. The activation energy for the transformation was reduced to 350 kJ/mol in seeded samples heated in dry air. Seeded samples completely transformed to alpha‐Al 2 O 3 after 1 h at 1050°C when heated in dry air compared to 1 h at 925°C when heated in saturated water vapor. The combined effects of a lower nucleation barrier due to seeding and the increased diffusion due to water vapor reduced the activation energy for the transformation by 390 kJ/mol and the transformation temperature by ∼225°C compared to the unseeded samples heated in dry air. The accelerated kinetics is believed to be due to increased surface diffusion.