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Fusibility and structure of the NaF-rich melts in the NaF-NaAlSi3O8 and NaF-KAlSi3O8 systems

K. Grjotheim, V. Daněk, K. Matiašovský, and J. Stubergh

Department of Chemistry, University of Oslo, N-0315 Oslo 3, Norway


Abstract: The liquidus curves of NaF in the NaF—NaAlSi3O8  and NaF— KAlSi3O8 systems were determined using the thermal analysis and the visual thermal analysis methods. Different courses of the liquidus curves were found de­pending on the nature of the system under investigation. Various ther­modynamic approaches were applied for the NaF activity calculation. The best fit of the experimental and calculated values of the temperature of primary crystallization of NaF was obtained if neither a chemical reaction between the fluoride anions and the feldspar polyanions nor a full disin­tegration of the feldspar anions were considered. In the NaF— NaAlSi3O8 system, the interaction energy of 21 kJmol-1 is probably necessary for the exchange reaction of the accompanying calcium oxide (as impurity) with sodium fluoride. In the NaF—KAlSi3O8  reciprocal system, the standard Gibbs energy of the exchange reaction was included in the calculation.

Full paper in Portable Document Format: 445a685.pdf


Chemical Papers 44 (5) 685–691 (1990)

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