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Controlling Crystallization and Sintering of α‐Al 2 O 3 –YAG Fibers by Atmospheric Conditions
Author(s) -
Krüger Reinhard,
Löbmann Peer
Publication year - 2011
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.1551-2916.2010.04253.x
Subject(s) - crystallization , materials science , sintering , corundum , amorphous solid , chemical engineering , nucleation , mesoporous material , porosity , sorption , mineralogy , composite material , adsorption , chemistry , crystallography , catalysis , biochemistry , organic chemistry , engineering
Amorphous sol–gel‐derived fibers of 82 mol% Al 2 O 3 –18 mol% Y 2 O 3 were synthesized for structural and sintering investigations. Three sets of samples were fabricated by treatment up to 500°C in nitrogen (“N 2 500”), water vapor (“H 2 O500”), or an atmosphere that changed from evaporated nitric acid (up to 300°C) to water vapor (“HNO 3 300·H 2 O500”). All other synthesis parameters were unchanged. Residues of carbon or nitrogen in the oxide composition were analyzed. Nitrogen sorption and 27 Al magic angle spinning nuclear magnetic resonance experiments were performed to investigate porosity and Al ion coordination of the xerogel fibers. Crystallization and densification of these pretreated samples were characterized using differential thermal analysis/TG and SEM at 1300°–1700°C. A high nucleation temperature and a vermicular morphology of large corundum grains were observed for the samples N 2 500 and HNO 3 300·H 2 O500. These samples could not be densified completely. Corundum crystallization at a lower temperature, and the formation of small compact grains was found for fibers H 2 O500, which could be sintered to full density. The individual crystallization and sintering behaviors are ascribed to the respective structures in the amorphous intermediate products. The amount of mesopores, internal surface area, and the Al coordination are regarded as the main controlling factors. A low content of residual carbon alone is not sufficient for good sintering results.