THE TOPAZ TO MULLITE TRANSFORMATION ON HEATING

Citation
Ra. Day et al., THE TOPAZ TO MULLITE TRANSFORMATION ON HEATING, Journal of materials research, 10(11), 1995, pp. 2963-2969
Citations number
12
Categorie Soggetti
Material Science
ISSN journal
08842914
Volume
10
Issue
11
Year of publication
1995
Pages
2963 - 2969
Database
ISI
SICI code
0884-2914(1995)10:11<2963:TTTMTO>2.0.ZU;2-Y
Abstract
The decomposition of topaz to mullite and other siliceous phases on he ating above about 1100 degrees C was found to depend on sample size an d 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 r esonance. In relatively large samples, the transformation to mullite e vidently takes place by a vapor phase mechanism within the bulk. The s urface reaction that took place for samples heated in a wet atmosphere allowed the formation of high-silica glass, as well as mullite. The u se of a hydrogenous heating atmosphere resulted in the sublimation and reformation of mullite whiskers, well outside the boundary of the ori ginal topaz.