Identification of the Complex Ions in Liquid Cryolite

The Raman spectrum of molten cryolite, Na3AlF6, at 1030°C has been investigated using laser excitation. A novel “windowless” Raman cell was used in order to overcome the problem of corrosion. One band that was observed at 633 Δ cm−1 (polarized) is assigned to the symmetric stretching frequency (ν1) of tetrahedral AlF4− by comparison with the spectrum of crystalline cryolite and with the spectra of other halide complexes of known structure. A much weaker band at 575 Δ cm−1 (polarized) is assigned to the symmetric stretching frequency (ν1) of AlF63−. The Raman evidence suggests that AlF63− dissociates into AlF4− and F− ions to a considerable extent (70%–75%) in molten cryolite.