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Determination of non-ideal solution parameters of hydrous melts from phase equilibria in the system Ab-Or-Qtz-H2O

Title data

Kirschen, Marcus ; De Capitani, Christian ; Pichavant, Michel:
Determination of non-ideal solution parameters of hydrous melts from phase equilibria in the system Ab-Or-Qtz-H2O.
1999
Event: European Union of Geosciences (EUG10) Meeting , 28. März - 1. April 1999 , Strasbourg.
(Conference item: Conference , Paper )

Abstract in another language

The computation of equilibrium phase diagrams of hydrous silicate systems requires a model of the Gibbs free energy of the melt defining the activity of the solution end-members at given composition, pressure, temperature. There is limited experimental indication showing that Henry's law is obeyed for volatile components like H2O and CO2. Extension to more complex systems was made assuming ideal mixing of the melt species normalized to 8 oxygens (Burnham & Nekvasil 1986). Recent developments include water speciation (e.g. Stolper 1989), higher order excess polynomials (e.g. Blencoe 1992) and non-ideal solution parameters between melt species including water (Ghiorso 1995). Systematic data have been obtained on the effect of water on solid-liquid equilibria and the effect of composition, pressure and temperature on water solubility in the system Ab-Or-Qtz-H2O (e.g. Holtz et al. 1995). Therefore it seems appropriate to use this system (1) to test existing solution models and (2) to develop thermodynamic modelling of hydrous melts.
Non-ideal solution parameters for the silicate liquid were derived simultaneously from liquidus and solubility data using mathematical programming techniques (e.g. Murtagh & Saunders 1987). For this purpose a Fortran program was written that converts experimental liquidus (and solvus) data to linear constraints of the optimization problem using bracketing relations drG <> 0. The use of a highly symbolic input code of experimental results improves significantly the transparency of the optimization problem. The linear problem is changed to a linearly constrained optimization when constraints from solubility and/or activity measurements are available. Margules-type polynomials were used to fit the excess free energy of the hydrous melt as a first approach. Predictions of existing solution models will be compared with results from this study.

Further data

Item Type: Conference item (Paper)
Refereed: Yes
Institutions of the University: Faculties > Faculty of Engineering Science
Research Institutions > Affiliated Institutes > Fraunhofer Center for High Temperature Materials and Design (HTL)
Result of work at the UBT: No
DDC Subjects: 500 Science > 530 Physics
500 Science > 540 Chemistry
500 Science > 550 Earth sciences, geology
Date Deposited: 03 Jul 2019 07:36
Last Modified: 03 Jul 2019 07:36
URI: https://eref.uni-bayreuth.de/id/eprint/49792