Structural entities in NaF---AlF3 melts containing alumina

An ionic structure model is developed for NaFAlF₃ melts containing alumina. The model can be described by the following dissociation equilibria,

Na⁺ is proposed to be the only cation present in the system. The model is derived from activity data for NaF and AlF₃ in melts saturated with alumina at 1285 K and the assumption of an ideal ionic mixture, with randomly distributed anions on the anion positions in the melt. The available data for the system seem to fit the model reasonably well. The entity Al₂F^?₇ will only be present in AlF₃ rich melts. Oxygen atoms in the complexes are most probably involved in bridging bonds of the type AlOAl and

. It appears that aluminium atoms are involved in 4 bonds in AlF₃-rich melts. The number of bonds changes partly towards 5 and/or 6 with increasing NaF content of the melt.