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Thermodynamic Modelling of Multicomponent Silicate Melts With Special Emphasis on Liquid Immiscibility

Title data

Kirschen, Marcus:
Thermodynamic Modelling of Multicomponent Silicate Melts With Special Emphasis on Liquid Immiscibility.
1999
Event: Société Française de Minéralogie et de Cristallographie (SFMC) Meeting Verre '99 , 29.-30. November 1999 , Montpellier.
(Conference item: Conference , Speech )

Abstract in another language

Modelling of crystallization processes and phase separation in silicate glasses and ceramics requires both simulation software and thermodynamic models of the reaction phases. While the software becomes more and more sophisticated, thermodynamic models used for multicomponent silicate melts are largely unrefined: Most solution models are still restricted to some binary and ternary systems. Their extrapolation to more complex systems is difficult. The mathematical formulation of the thermodynamic excess function, Gxs, is crucial for its extrapolation capacity to higher order systems. This important property has been outlined by introducing variable weights to the Kohler extrapolation strategy. The modification leads to a flexible generalized excess function for multicomponent systems (1).
The calculation of miscibility gaps is an excellent test for thermodynamic solution models of silicate melts. Compositions of coexisting liquids depend only on the topology of the free energy surface of mixing of the melt. We constrained the excess free energy expression to measured composition of coexisting liquids in the system MgO-CaO-SiO2-Al2O3-TiO2. Thermodynamic parameters for liquid and some crystalline phases were derived from solvus and liquidus data with large-scale mathematical programming techniques. The observed liquid miscibility gap of the systems CaO-MgO-SiO2-TiO2, SiO2-TiO2-Al2O3 and their subsystems is reproduced in detail with a polynomial expression but minimum of excess parameters: The ternary Gxs is approximated from binary contributions, additional ternary excess terms are not required in the systems CaO-SiO2-TiO2 (2), MgO-SiO2-TiO2 (2) and SiO2-TiO2-Al2O3 (3). The extrapolation to compositions and temperatures outside the calibration range yields an excellent first order approximation of the free energy of mixing surface: calculated phase diagrams agree well with experimental data. However, from superposition of binary interaction terms alone we could not achieve a satisfactory model for the system CaO-SiO2-TiO2-Al2O3. Additional higher order excess terms indicate the presence of considerable ternary and quaternary interactions in these melts.
Recent extensions focuse on hydrous silicate melts in the model system NaAlSi3O8-KAlSi3O8-Si4O8-H2O and on phase separation in borosilicate melts. Results of model calculations will be presented.

Further data

Item Type: Conference item (Speech)
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 07:30
Last Modified: 03 Jul 2019 07:30
URI: https://eref.uni-bayreuth.de/id/eprint/49789