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Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis

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Abstract

Temperatures for primary crystallization of Na3AlF6 in multicomponent electrolyte systems of interest for the aluminum electrolysis process were determined by thermal analysis. The results are presented as binary and quasibinary diagrams and discussed in view of the literature data. An empirical equation describing liquidus temperatures for primary crystallization of Na3AlF6 was derived:

$$\begin{gathered} t/(^\circ C) = 1011 + 0.50[AlF_3 ] - 0.13[AIF_3 ] - \frac{{3.45[CaF_2 ]}}{{1 + 0.0173[CaF_2 ]}} \hfill \\ + 0.124[CaF_2 ] \cdot [AlF_3 ] - 0.00542([CaF_2 ] \cdot [AlF_3 ])^{1.5} \hfill \\ - \frac{{7.93[Al_2 O_3 ]}}{{1 + 0.0936[Al_2 O_3 ] - 0.0017[Al_2 O_3 ]^2 - 0.0023[AlF_3 ] \cdot [Al_2 O_3 ]}} \hfill \\ - \frac{{8.90[LiF]}}{{1 + 0.0047[LiF] + 0.0010[AlF3]^2 }} - 3.95[MgF_2 ] - 3.95 \hfill \\ \end{gathered} $$

wheret is the temperature in degree Celsius and the square brackets denote the weight percent of components in the system Na3AlF6-AlF3-CaF2-Al2O3-LiF-MgF2-KF. The composition limitations are [AlF3] ≈ [CaF2] ≈ [LiF] < 20 wt pct, [MgF2] ≈ [KF] < 5 wt pct, and [A12O3] up to saturation.

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Authors and Affiliations

  1. SINTEF Metallurgy, N-7034, Trondheim, Norway

    Asbjørn Solheim, Sverre Rolseth, Egil Skybakmoen & Lisbet Støen

  2. Department of Electrochemistry, The Norwegian Institute of Technology, N-7034, Trondheim, Norway

    Åsmund Sterten & Trond Støre

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  1. Asbjørn Solheim
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  2. Sverre Rolseth
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  3. Egil Skybakmoen
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  4. Lisbet Støen
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  5. Åsmund Sterten
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Solheim, A., Rolseth, S., Skybakmoen, E. et al. Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis. Metall Mater Trans B 27, 739–744 (1996). https://doi.org/10.1007/BF02915602

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