Computer study of structure, thermodynamic, and electrical transport properties of Na3AlF6-Al2O3 and CaF2-Al2O3 melts |
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| Authors: | D. K. Belashchenko O. I. Ostrovski S.Yu. Saposznikova |
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| Affiliation: | (1) the Moscow Steel and Alloys Institute, 117936 Moscow, Russia;(2) the School of Materials Science and Engineering, University of New South Wales, 2052 Sydney, Australia;(3) Present address: Energetics and Conversion Co, 23 Pravdy, 125015 Moscow, Russia |
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| Abstract: | Structure, thermodynamic, and electrical transport properties of Na3AlF6-Al2O3 and CaF2-Al2O3 melts were examined by molecular dynamics. Ionic models were constructed for Na3AlF6-Al2O3 and CaF2-Al2O3 melts at 1283 and 2000 K, respectively. It was found that in the Na3AlF6-Al2O3 melts, stable aluminum-fluorine-oxygen groups are formed. Although bonds between F− and Al3+ ions in the first coordination shell are weaker than between O2− and Al3+ ions, very stable negatively charged AlF 6 3− groups are formed at low oxygen concentrations in the Na3AlF6-Al2O3. This results in migration of aluminum to the anode in an external electric field. In the CaF2-Al2O3 melts, positively charged aluminum-oxygen groups dominate. This results in migration of aluminum to the cathode at almost all Al2O3 concentrations. Therefore, in Na3AlF6-Al2O3 melts, the Al3+ ion as a component of the complex anion has a negative partial conductivity and the O2− ion has positive partial conductivity; in CaF2-Al2O3 melts, Al3+ has a positive transport number while O2− has a negative transport number. |
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