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Excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations

Calculations using the density-functional theory (DFT) in combination with the single defect method were carried out to determine the heat of mixing behaviour of mineral solid solution phases. The accuracy of this method was tested on the halite–sylvite (NaCl–KCl) binary, pyrope–grossular garnets (M...

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Autores principales: Benisek, Artur, Dachs, Edgar
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Springer Berlin Heidelberg 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7024695/
https://www.ncbi.nlm.nih.gov/pubmed/32116405
http://dx.doi.org/10.1007/s00269-020-01085-8
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author Benisek, Artur
Dachs, Edgar
author_facet Benisek, Artur
Dachs, Edgar
author_sort Benisek, Artur
collection PubMed
description Calculations using the density-functional theory (DFT) in combination with the single defect method were carried out to determine the heat of mixing behaviour of mineral solid solution phases. The accuracy of this method was tested on the halite–sylvite (NaCl–KCl) binary, pyrope–grossular garnets (Mg(3)Al(2)Si(3)O(12)–Ca(3)Al(2)Si(3)O(12)), MgO–CaO (halite structure) binary, and on Al/Si ordered alkali feldspars (NaAlSi(3)O(8)–KAlSi(3)O(8)); as members for coupled substitutions, the diopside–jadeite pyroxenes (CaMgSi(2)O(6)–NaAlSi(2)O(6)) and diopside–CaTs pyroxenes (CaMgSi(2)O(6)–CaAlAlSiO(6)) were chosen for testing and, as an application, the heat of mixing of the tremolite–glaucophane amphiboles (Ca(2)Mg(5)Si(8)O(22)(OH)(2)–Na(2)Mg(3)Al(2)Si(8)O(22)(OH)(2)) was computed. Six of these binaries were selected because of their experimentally well-known thermodynamic mixing behaviours. The comparison of the calculated heat of mixing data with calorimetric data showed good agreement for halite–sylvite, pyrope–grossular, and diopside–jadeite binaries and small differences for the Al/Si ordered alkali feldspar solid solution. In the case of the diopside–CaTs binary, the situation is more complex because CaTs is an endmember with disordered cation distributions. Good agreement with the experimental data could be, however, achieved assuming a reasonable disordered state. The calculated data for the Al/Si ordered alkali feldspars were applied to phase equilibrium calculations, i.e. calculating the Al/Si ordered alkali feldspar solvus. This solvus was then compared to the experimentally determined solvus finding good agreement. The solvus of the MgO–CaO binary was also constructed from DFT-based data and compared to the experimentally determined solvus, and the two were also in good agreement. Another application was the determination of the solvus in tremolite–glaucophane amphiboles (Ca(2)Mg(5)Si(8)O(22)(OH)(2)–Na(2)Mg(3)Al(2)Si(8)O(22)(OH)(2)). It was compared to solvi based on coexisting amphiboles found in eclogites and phase equilibrium experiments. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00269-020-01085-8) contains supplementary material, which is available to authorized users.
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spelling pubmed-70246952020-02-28 Excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations Benisek, Artur Dachs, Edgar Phys Chem Miner Original Paper Calculations using the density-functional theory (DFT) in combination with the single defect method were carried out to determine the heat of mixing behaviour of mineral solid solution phases. The accuracy of this method was tested on the halite–sylvite (NaCl–KCl) binary, pyrope–grossular garnets (Mg(3)Al(2)Si(3)O(12)–Ca(3)Al(2)Si(3)O(12)), MgO–CaO (halite structure) binary, and on Al/Si ordered alkali feldspars (NaAlSi(3)O(8)–KAlSi(3)O(8)); as members for coupled substitutions, the diopside–jadeite pyroxenes (CaMgSi(2)O(6)–NaAlSi(2)O(6)) and diopside–CaTs pyroxenes (CaMgSi(2)O(6)–CaAlAlSiO(6)) were chosen for testing and, as an application, the heat of mixing of the tremolite–glaucophane amphiboles (Ca(2)Mg(5)Si(8)O(22)(OH)(2)–Na(2)Mg(3)Al(2)Si(8)O(22)(OH)(2)) was computed. Six of these binaries were selected because of their experimentally well-known thermodynamic mixing behaviours. The comparison of the calculated heat of mixing data with calorimetric data showed good agreement for halite–sylvite, pyrope–grossular, and diopside–jadeite binaries and small differences for the Al/Si ordered alkali feldspar solid solution. In the case of the diopside–CaTs binary, the situation is more complex because CaTs is an endmember with disordered cation distributions. Good agreement with the experimental data could be, however, achieved assuming a reasonable disordered state. The calculated data for the Al/Si ordered alkali feldspars were applied to phase equilibrium calculations, i.e. calculating the Al/Si ordered alkali feldspar solvus. This solvus was then compared to the experimentally determined solvus finding good agreement. The solvus of the MgO–CaO binary was also constructed from DFT-based data and compared to the experimentally determined solvus, and the two were also in good agreement. Another application was the determination of the solvus in tremolite–glaucophane amphiboles (Ca(2)Mg(5)Si(8)O(22)(OH)(2)–Na(2)Mg(3)Al(2)Si(8)O(22)(OH)(2)). It was compared to solvi based on coexisting amphiboles found in eclogites and phase equilibrium experiments. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00269-020-01085-8) contains supplementary material, which is available to authorized users. Springer Berlin Heidelberg 2020-02-17 2020 /pmc/articles/PMC7024695/ /pubmed/32116405 http://dx.doi.org/10.1007/s00269-020-01085-8 Text en © The Author(s) 2020 Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
spellingShingle Original Paper
Benisek, Artur
Dachs, Edgar
Excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations
title Excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations
title_full Excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations
title_fullStr Excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations
title_full_unstemmed Excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations
title_short Excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations
title_sort excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations
topic Original Paper
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7024695/
https://www.ncbi.nlm.nih.gov/pubmed/32116405
http://dx.doi.org/10.1007/s00269-020-01085-8
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