Phase Diagram of a Portion of the System Na ₃ AlF ₆ ‐AlF ₃ ‐Al ₂ O ₃ .

Abstract

The system Na 3 AlF 6 ‐AlF 3 ‐Al 2 O 3 was investigated by a combination of quenching, optical microscopy, and X‐ray powder diffraction techniques in order to define liquidus temperatures, univariant lines, and invariant points. Phase fields for the primary crystallization of cryolite, chiolite, aluminum fluoride, α‐alumina, and η‐alumina were located. A ternary peritectic point contained 28.3% AlF 3 ‐4.4% Al 2 O 3 ‐67.3% Na 3 AlF 6 at 723°C. A eutectic point of composition 37.3% AlF 3 ‐3.2% Al 2 O 3 ‐59.5% Na 3 AlF 6 occurs at 684°C.