Influence of Diaspore Seeding and Chloride Concentration on the Transformation of 'Diasporic' Precursors to Corundum

Autor: Anthony J. Perrotta, Richard L. Smith, Gregory S. Rohrer
Rok vydání: 2004
Předmět:
Zdroj: Journal of the American Ceramic Society. 84:1896-1902
ISSN: 1551-2916
0002-7820
DOI: 10.1111/j.1151-2916.2001.tb00933.x
Popis: “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 HNO3 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 × 1016 diaspore seeds/(mol of Al2O3) 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.
Databáze: OpenAIRE