Crystallization behaviors in the plasma-spheroidized alumina/zircon mixtures

Dissociation of zircon in a thermal plasma jet stream is utilized as a single-step process to prepare mullite/zirconia ceramic composites by plasma spraying 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-phase mixture as well as that of diphasic mixture. Two exotherms were detected in the differential thermal analysis (DTA) curve up to 1600 degreesC. The 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 found at a very narrow temperature range between 1050 degreesC and 1100 degreesC. The mullite that crystallized in the initial stage had a larger lattice parameter than the stoichiometric mullite. (C) 2001 Elsevier science B.V. All rights reserved.