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Fabrication of Nano‐Scaled α‐Al 2 O 3 Crystallites Through Heterogeneous Precipitation of Boehmite in a Well‐Dispersed θ‐Al 2 O 3 ‐Suspension
Author(s) -
Yu PeiChing,
Yang RungJe,
Chang YaTing,
Yen FuSu
Publication year - 2007
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.1551-2916.2007.01746.x
Subject(s) - boehmite , crystallite , materials science , nucleation , agglomerate , calcination , precipitation , chemical engineering , phase (matter) , mineralogy , crystallography , composite material , chemistry , aluminium , metallurgy , organic chemistry , physics , meteorology , engineering , catalysis
The possibility of eliminating finger or vermicular growth of α‐Al 2 O 3 particles obtained by calcination of boehmite was examined. Heterogeneous precipitation of boehmite in a well‐dispersed θ‐Al 2 O 3 suspension was first prepared, in which the mass ratio of boehmite to θ‐crystallite was evaluated to form agglomerates of similar sizes that will form α‐Al 2 O 3 crystallites of <100 nm in diameter. θ‐ to α‐phase transformation of alumina experiences a nucleation and growth mechanism, with the critical size of nucleation being ∼25 nm for θ‐Al 2 O 3 and the size for accomplishment of transformation followed by finger growth being ∼100 nm. Hence, fabricating agglomerates that would form α‐Al 2 O 3 crystallites with sizes <100 nm accompanied with appropriate thermal treatments can be a method for obtaining α‐Al 2 O 3 crystallites free of finger growth. It is found that proper preparation of the agglomerate with appropriate size may initiate a simultaneous and lower temperature θ‐ to α‐Al 2 O 3 phase transformation for such powder systems, substantially limiting the mass transfer among the newly formed α‐Al 2 O 3 particles. Moreover, α‐Al 2 O 3 crystallites free of finger growth can be obtained.