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Dissociation of the anions AlF63- in the system Na3AlF6 —Na2SO4

I. Koštenská and M. Malinovský

Department of Inorganic Technology, Slovak Technical University, 880 37 Bratislava


Abstract:  The course of the liquidus of Na2SO4 in the system Na3AIF6 —Na2SO4 was determined. The eutectic point was found to be at 9.0 mole % Na3AlF6 and 91.0 mole % Na2SO4, tE = 794.5°C. The solubility of Na3AIF6 in solid Na2SO4 is negligible. The course of the liquidus curve of Na2SO4 in the composition interval of 91.0—96.0 mole % Na2SO4 is consistent with the assumption that the anions AlF63- undergo thermal dissociation according to the scheme AlF63- ⇌ AIF4- + 2F-. At a very low content of Na3AIF6 in Na2SO4 a total destruction of the anions AlF4 takes place under the formation of 7 new elementary particles from each molecule of Na3AIF6 in molten Na2SO4 . In the eutectic point of the system Na3AIF6—Na2SO4 the degree of thermal dissociation of AlF63- anions according to the given scheme equals 0.67. The calculated dissociation degree of pure cryolite is 0.21. The conclusions of some other papers concerning the given problems are discussed.

Full paper in Portable Document Format: 326a821.pdf


Chemical Papers 32 (6) 821–829 (1978)

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