Abstract:Raman spectrum of molten cryolite was recorded. Based on the new understanding of the scattering coefficients, contents of various structural entities in acidic NaF-AlF₃ melts at 942−1 024 °C in previous research were reanalyzed. The new quantitative analysis results show that when cryolite ratio(CR) is less than 2, AlF₄⁻ is the dominant anion in the melts, and its mole fraction is about 0.70 for melts with CR=1.5 and 0.50 for melts with CR=2. When CR is more than 2.5, the mole fraction of AlF₆³⁻ is relatively large, which is around 0.45 for melts with CR=2.5. Ionic structure of Na₃AlF₆-Al₂O₃ melts was investigated by UV-Raman spectroscopy. Octahedral AlF₆³⁻ and tetrahedral AlF₄⁻ are proved to exist with possible partial replacement of F⁻ by O²⁻. Al₂O₂F₄²⁻ with a large scattering coefficient also exists in the melts in which alumina concentration is more than 4% (mass fraction). The increase of temperature causes blue-shift of the bands in the Raman spectra.

Key words: Raman spectroscopy; Na₃AlF₆-Al₂O₃ melts; scattering coefficient; complex ion; aluminum electrolysis; sealed cell