Phase Equilibria in the System CaF2-AlF3-Na3AlF6 and Part of the System CaF2-AlF3-Na3AlF6-Al2O3 |
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| Authors: | DOUGLAS F. CRAIG&# ,JESSE J. BROWN,JR.,&# |
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| Affiliation: | Department of Materials Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 |
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| Abstract: | The complete phase-equilibrium diagram of the system CaF2-AlF3-Na3AlF6 and the subsolidus portion of the system CaF2-AlF3-Na3AlF6-Al2O3 were established from microscopic, powder X-ray diffraction, quench, and DTA data obtained from samples encapsulated in sealed tubes and either reacted in the solid state or melted and recrystallized. The system Na3AlF6-CaF2 contains a simple eutectic with no compound formation or solid solution. The system CaF2-AlF3-Na3AlF6 contains two ternary compounds, NaCaAlF6 and NaCaAl2F9, which melt incongruently at 735° and 712°C, respectively; NaCaAlF6 exists in three polymorphic forms with transitions at 610° and 722°C and NaCaAl2F9 is body-centered cubic with a0= 10.765 Å. The three binary and two ternary compounds divide the system into eight compatibility triangles. Along the NaCaAlF6-Na3AlF6 join, 7 mol% NaCaAlF6 is soluble in α-cryolite at 525° and 42% in β-cryolite at 731°C. The quaternary system Na3AlF6-AlF3-CaF2-Al2O3 contains eight compatibility tetrahedra. |
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