Title: Comparison between thermochemical and phase stability data for the quartz-coesite-stishovite transformationsl
Abstract: Phase stability and elasticity data have been used to calculate the Gibbs free energy, enthalpy, and entropy changes at 298 K and I bar associated with the quartz-coesite and coesite-stishovite transformations in the system SiOr. For the quartz-coesite transformation, these changes disagree by a factor of two or three with those obtained by calorimetric techniques. The phase boundary for this transformation appears to be well determined by experiment; the discrepancy, therefore, suggests that the calorimetric data for coesite are in error. Although the calorimetric and phase stability data for the coesite-stishovite transformation yield the same transition pressure at298K, the phase-boundary slopes disagree by a factor of two. At present, it is not possible to determine which of the data are in error. Thus serious inconsistencies exist in the thermodynamic data for the polymorphic transformations of silica.
Publication Year: 1979
Publication Date: 1979-01-01
Language: en
Type: article
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