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Kirschen, Marcus ; Pichavant, Michel:
Thermodynamic modelling of crystal-liquid equilibria in the system Ab-Or-Qtz-H2O.
1999
Veranstaltung: 6th Silicate Melt Workshop
, 13.-17. April 1999
, Arc-et-Senans.
(Veranstaltungsbeitrag: Workshop
,
Vortrag
)
Abstract
Computation of crystal-liquid phase equilibria requires a model of the free energy of the melt that defines the solution endmember activity at given temperature, pressure and composition. Liquidus and solubility data constrain non-ideal solution properties of the melt through identical chemical potentials µ = µ0 + RTln(a) of solution components in coexisting phases. Reported melting data in the system NaAlSi3O8 (ab) - KAlSi3O8 (or) - Si4O8 (qtz) - H2O and all binary and ternary subsystems were used to derive an internally consistent set of solution parameters for hydrous and dry melts by linear programming techniques. Thermodynamic data from Berman & Aranovich (1996) were used for the solid endmembers and the Elkins & Grove (1990) model for feldspar solid solution. SiO2 and H2O solubility in the feldspars was neglected. We assumed pure silica polymorphs. Reported enthalpies of fusion and partial molar heat capacities from Richet & Bottinga (1986) were used to further constrain the free energy of the liquid endmembers. Liquid volumes were approximated to 15 kbar by a Taylor series in p and T as a first approach. Margules-type excess polynomials were used to model non-ideality of the melt. We adopted the symmetric excess term from Hervig & Navrotsky (1984) for liquid ab-or mixing. While or-qtz mixing is close to ideal, a slightly positive excess function is required to model reported ab-qtz liquidus phase relations. Qtz-H2O, ab-H2O and or-H2O mixing behaviour is more complex. To constrain the free energy of the hypothetic H2O melt component we used solubility data from Paillat et al. (1992) and Holtz et al. (subm.) as additional constraints assuming the vapour phase to be pure H2O (Haar, 1984) below 1100C and 3kbar. Using Cp(T) from Richet (1987) and pressure independent V0 = 1.2 J/bar (Richet & Polian, 1998) we obtained H0 and S0 close to -293 kJ/mol and 58 J/Kmol as first estimates for H2O melt. Further refinements of the H2O standard state and improvements of ab, or, qtz liquid volume terms are on the way. Calculated phase relations of this study are compared to predictions of existing solution models.
Weitere Angaben
| Publikationsform: | Veranstaltungsbeitrag (Vortrag) |
|---|---|
| Begutachteter Beitrag: | Ja |
| Institutionen der Universität: | Fakultäten > Fakultät für Ingenieurwissenschaften Forschungseinrichtungen > Institute in Verbindung mit der Universität > Fraunhofer-Zentrum für Hochtemperatur-Leichtbau (HTL) Fakultäten Forschungseinrichtungen Forschungseinrichtungen > Institute in Verbindung mit der Universität |
| Titel an der UBT entstanden: | Nein |
| Themengebiete aus DDC: | 500 Naturwissenschaften und Mathematik > 530 Physik 500 Naturwissenschaften und Mathematik > 540 Chemie 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie |
| Eingestellt am: | 03 Jul 2019 07:32 |
| Letzte Änderung: | 03 Jul 2019 07:32 |
| URI: | https://eref.uni-bayreuth.de/id/eprint/49791 |