Fluoroaluminate molten salts are used in the Hall-Heroult industrial process for the production of aluminum by electrolysis. To better understand the mechanism of the dissolution of alumina (Al 2 O 3 ) in cryolitic melts, we have studied the structure of these liquids up to 1025 °C by in-situ NMR of 27 Al, 23 Na, 19 F, and 17 O, using a laser-heated experimental setup. From these experiments we can propose a quantification of the different aluminum-bearing species AlF 4 -, AlF 5 2-, and AlF 6 3in the liquid and give a direct experimental evidence of the existence of at least two different oxy-fluoride species, Al 2 OF 6 2and Al 2 O 2 F 4 2-, when dissolving alumina in the fluoride liquid. The obtained results are compared with other spectroscopic data obtained by in-situ Raman spectroscopy.

The molten NaF−AlF3 system has been studied by 27Al NMR over the composition range 0.2 < X°(AlF3) < 0.5, using a high-temperature laser heating system. The experimental chemical shifts have been compared to the shifts calculated on the basis of a model obtained by the combination of Raman spectroscopy and thermodynamics results. This model involves three fluoroaluminate complexes (AlF4 -, AlF5 2-, AlF6 3-). The agreement between experimental and calculated shifts strengthens the reliability of the suggested model.