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The topaz to mullite transformation on heating

Published online by Cambridge University Press:  03 March 2011

R.A. Day
Affiliation:
Advanced Materials Program, Australian Nuclear Science and Technology Organisation, Private Mail Bag I, Menai, New South Wales 2234, Australia
E.R. Vance
Affiliation:
Advanced Materials Program, Australian Nuclear Science and Technology Organisation, Private Mail Bag I, Menai, New South Wales 2234, Australia
D.J. Cassidy
Affiliation:
Advanced Materials Program, Australian Nuclear Science and Technology Organisation, Private Mail Bag I, Menai, New South Wales 2234, Australia
J.S. Hartman
Affiliation:
Chemistry Department, Brock University, St. Catherines, Ontario, L2S3Al. Canada
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Abstract

The decomposition of topaz to mullite and other siliceous phases on heating above about 1100 °C was found to depend on sample size and the presence of water vapor in the heating atmosphere. The principal experimental technique employed was scanning electron microscopy, but the data were supported by x-ray diffraction, thermal analysis, mass spectroscopy of volatile emissions, and solid-state nuclear magnetic resonance. In relatively large samples, the transformation to mullite evidently takes place by a vapor phase mechanism within the bulk. The surface reaction that took place for samples heated in a wet atmosphere allowed the formation of high-silica glass, as well as mullite. The use of a hydrogenous heating atmosphere resulted in the sublimation and reformation of mullite whiskers, well outside the boundary of the original topaz.

Type
Articles
Copyright
Copyright © Materials Research Society 1995

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References

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