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The farringtonite/Mg (sub 3) (PO (sub 4) ) (sub 2) -II transformation; a new curve for pressure calibration in piston-cylinder apparatus

Fabrice Brunet and Daniel Vielzeuf
The farringtonite/Mg (sub 3) (PO (sub 4) ) (sub 2) -II transformation; a new curve for pressure calibration in piston-cylinder apparatus
European Journal of Mineralogy (April 1996) 8 (2): 349-354

Abstract

The polymorphic transition farringtonite-Mg (sub 3) (PO (sub 4) ) (sub 2) -II has been bracketed in a gas-P apparatus between 6100 and 8300 bar in the T range 565-825 degrees C; the equilibrium is expressed as P (bar) = -772 + 8.13 T (K) + or - 200 bar. The small value of the Clapeyron slope is comparable to that of the quartz-coesite transformation and makes the farringtonite-Mg (sub 3) (PO (sub 4) ) (sub 2) -II transformation a good candidate for the calibration of piston-cylinder assemblies at low P (<<<$I> 10 kbar). Thermochemical values for the Mg (sub 3) (PO (sub 4) ) (sub 2) -II polymorph have been retrieved from the reversals: S (super 0) (sub 298 ) = 180.7 J/mole/K and Delta (sub f) H (super 0 ) (sub 298 ) = -3745.8 kJ/mole. In an independent determination of the transition in NaCl-based piston-cylinder assemblies, P was over-estimated by up to 400 bar, possibly reflecting friction inherent in the design of the pressure cell and/or too low a rate of friction-decay compared to the fast kinetics of the polymorphic transformation.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 8
Serial Issue: 2
Title: The farringtonite/Mg (sub 3) (PO (sub 4) ) (sub 2) -II transformation; a new curve for pressure calibration in piston-cylinder apparatus
Affiliation: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, Federal Republic of Germany
Pages: 349-354
Published: 199604
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 24
Accession Number: 1996-044107
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 1 table
Secondary Affiliation: Universite Blaise Pascal, FRA, France
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199615
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