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Annealing experiments on CO2-bearing jadeite glass: an insight into the true temperature dependence of CO2 speciation in silicate melts

Published online by Cambridge University Press:  05 July 2018

Y. Morizet ,
S. C. Kohn  and
R. A. Brooker
Y. Morizet
Affiliation:
Department of Earth Sciences, Wills Memorial Building, University of Bristol, Queen's Rd., Bristol BS8 1RJ, UK
S. C. Kohn*
Affiliation:
Department of Earth Sciences, Wills Memorial Building, University of Bristol, Queen's Rd., Bristol BS8 1RJ, UK
R. A. Brooker
Affiliation:
Department of Earth Sciences, Wills Memorial Building, University of Bristol, Queen's Rd., Bristol BS8 1RJ, UK
*
*E-mail: simon.kohn@bristol.ac.uk
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Abstract

The thermodynamics and kinetics of CO2 speciation in silicate melts have been studied by measuring the concentration of CO2mol and carbonate in jadeite glass annealed at 575, 450 and 400°C. Assuming that the reaction is

1

where CO2mol..Obr represents a CO2 molecule weakly bonded to a bridging oxygen in the network and CO3 represents a bridging carbonate group with no net negative charge, ΔH for the reaction is –17 (+4/–8) kJ mol−1 and ΔS is –24 (+6/–9) J K−1 mol−1. The rate of equilibration of the species was measured at each temperature and the rate constants were deduced. The temperature dependence of the rate constants was used to determine the activation energy of the forward and reverse reactions which are 68 (+3/–31) kJ mol−1 and 86 (+1/–69) kJ mol−1 respectively. The data suggest that CO2mol may be much more abundant in silicate melts than previously assumed on the basis of studies of CO2-bearing glasses. Models of solubility, diffusion, and isotope fractionation should take this into account.

Keywords

jadeite glasssilicate meltsCO2 speciationannealing experiments
Type
Research Article
Information
Mineralogical Magazine , Volume 65 , Issue 6 , December 2001 , pp. 701 - 707
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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