Crystallization behaviors in the plasma-spheroidized alumina/zircon mixtures

Dissociation of zircon in a thermal plasma jet stream is utilized as a sing le-step process to prepare mullite/zirconia ceramic composites by plasma sp raying zircon/alumina mixtures. The crystallization behavior of the zircon and alumina mixtures after plasma spraying was studied in the present paper . The spheroidized powders appear to have the characteristics of a single-p hase mixture as well as that of diphasic mixture. Two exotherms were detect ed in the differential thermal analysis (DTA) curve up to 1600 degreesC. Th e first exothermic peak in the DTA curve at 985 degreesC is found to be due to the formation of primary mullite and spinel, while the second exotherm at 1250 degreesC is due to secondary mullite formation. Cristobalite was fo und at a very narrow temperature range between 1050 degreesC and 1100 degre esC. The mullite that crystallized in the initial stage had a larger lattic e parameter than the stoichiometric mullite. (C) 2001 Elsevier science B.V. All rights reserved.