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

Research areas:
Year:
2001
Authors:
Journal:
MINERALOGICAL MAGAZINE
Volume:
65
Number:
6
Pages:
701-707
Month:
December
ISSN:
0026-461X
BibTex:
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 degreesC. Assuming that the reaction isCO2mol..O-br reversible arrow CO3 (1)where CO2mol..O-br, 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, DeltaH for the reaction is -17 (+4/-8) kJ mol(-1) and DeltaS 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.