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Influence of Diaspore Seeding and Chloride Concentration on the Transformation of “Diasporic” Precursors to Corundum
Author(s) -
Smith Richard L.,
Rohrer Gregory S.,
Perrotta Anthony J.
Publication year - 2001
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.1151-2916.2001.tb00933.x
Subject(s) - corundum , diaspore (botany) , alkoxide , calcination , chemistry , amorphous solid , hydrolysis , inorganic chemistry , mineralogy , nuclear chemistry , catalysis , organic chemistry , biological dispersal , population , demography , seed dispersal , sociology
“Diasporic” precursors derived from sols formed by the controlled hydrolysis of aluminum sec‐butoxide in the presence of HCl yielded mixtures of corundum and amorphous alumina when calcined between 500° and 800°C. The fraction of corundum in the calcined products depended on the HCl/alkoxide ratio used during hydrolysis and was maximized at 64 wt% when the molar ratio was 1. Precursors formed from sols hydrolyzed in the presence of HNO 3 rather than HCl yielded only amorphous products or transition aluminas when treated below 900°C. The corundum yield of the precursors was enhanced when they were seeded with diaspore (α‐AlOOH) crystals. Precursors synthesized with an HCl/alkoxide ratio of 1 and seeded with 7.6 × 10 16 diaspore seeds/(mol of Al 2 O 3 ) were transformed to phase‐pure corundum within 12 h at 700°C. Based on studies of the phase evolution of the precursors during calcining, it was concluded that the diaspore seeds promoted conversion by acting as corundum nuclei once they decomposed at ∼450°C.