Density, Viscosity, Surface Tension, and Interfacial Tension in the Systems NaF(KF) + AlF₃

Abstract

The temperature dependence of density, viscosity, and surface tension was determined in the system 55 mol % NaF + 45 mol % AlF3. The interfacial tension between aluminum and the above melt plus the melt 55 mol % KF + 45 mol % AlF3 was measured at 750 °C. These molten salts are potential low-temperature electrolytes for aluminum electrolysis. It was found that the temperature dependence of density and surface tension could be described by linear equations within the measured temperature ranges. The temperature dependence of viscosity can be described by a quadratic equation.

A Density Model Based on the Modified Quasichemical Model and Applied to the NaF-AlF3-CaF2-Al2O3 Electrolyte

“…The calculated density of NaF-AlF 3 melts for various mole fractions of AlF 3 is shown in Figure 8, along with the available measurements. [14][15][16][17]56] As explained previously, a decrease of 0.08 g/cm 3 was applied in Figure 8 to the original density values of Abramov and Kozunov, [14] for the melt with X AlF 3 ¼ 0.374 only. As shown in Figure 8, the model gives less satisfactory results for very acidic melts: for the melt with X AlF 3 ¼ 0.45 (i.e., CR = 1.22), the calculated temperature dependence does not compare very well to the experimental data of Paucirova et al [17] and Silny et al [56] Note, however, that the measurements of Silny et al extrapolated at high temperatures are significantly lower than the measurements of Paucirova et al The data of Silny et al for the melt with X AlF 3 ¼ 0.45 are expected to be more reliable: measurements were performed both upon heating and upon cooling and, after the completion of the entire temperature cycle, the initial and final density values did not differ by more than 0.5 pct.…”

“…[14][15][16][17]56] As explained previously, a decrease of 0.08 g/cm 3 was applied in Figure 8 to the original density values of Abramov and Kozunov, [14] for the melt with X AlF 3 ¼ 0.374 only. As shown in Figure 8, the model gives less satisfactory results for very acidic melts: for the melt with X AlF 3 ¼ 0.45 (i.e., CR = 1.22), the calculated temperature dependence does not compare very well to the experimental data of Paucirova et al [17] and Silny et al [56] Note, however, that the measurements of Silny et al extrapolated at high temperatures are significantly lower than the measurements of Paucirova et al The data of Silny et al for the melt with X AlF 3 ¼ 0.45 are expected to be more reliable: measurements were performed both upon heating and upon cooling and, after the completion of the entire temperature cycle, the initial and final density values did not differ by more than 0.5 pct. [56] The optimized pressure-dependent terms of the Gibbs energies of Reaction [2] for the [Na-(F)-Al V ], [Na-(F)-Al IV ], and [Na-(F)-Al 2 ] pairs are, respectively, Dg P NaAl V =F ¼ À0:2092 Á ðP À 1Þ J/mol ½14 Dg P NaAl IV =F ¼ ð1:0209 À 1:4644v NaAl IV =F Þ Á ðP À 1Þ J/mol ½15 Dg P NaAl 2 =F ¼ 5:8576 Á ðP À 1Þ J/mol ½16…”

Alumina Solubility and Diffusion Coefficient of the Dissolved Alumina Species in Low-Temperature Fluoride Electrolytes

“…The diffusion coefficient can be calculated from the slope of these plots, but to do this, it is necessary to obtain values for the melt density and the kinematic viscosity. Using the recently published work of Silny et al, [24] the density and dynamic viscosity of the NaF-AlF 3 eutectic at 1023 K (750°C) were estimated to be 1.908 g cm À3 and 1.246 mPa.s, respectively; this gives a kinematic viscosity of~0.653 cm 2 s À1 . These values would be expected to change slightly during the run as the alumina dissolves and approaches saturation.…”

A viscosity model for the (NaF + AlF3+ CaF2+ Al2O3) electrolyte

“…The main relevant articles are dealing with the following systems: (NaF + AlF 3 ) [24][25][26], (NaF + AlF 3 + CaF 2 ) [27,28], (NaF + AlF 3 + Al 2 O 3 ) [27,29], and (NaF + AlF 3 + CaF 2 + Al 2 O 3 ) [28,30]. All measurements have been performed using the oscillating body method, with either a cylinder geometry [24][25][26]28,29] or a sphere geometry [27,30].…”

“…The main relevant articles are dealing with the following systems: (NaF + AlF 3 ) [24][25][26], (NaF + AlF 3 + CaF 2 ) [27,28], (NaF + AlF 3 + Al 2 O 3 ) [27,29], and (NaF + AlF 3 + CaF 2 + Al 2 O 3 ) [28,30]. All measurements have been performed using the oscillating body method, with either a cylinder geometry [24][25][26]28,29] or a sphere geometry [27,30]. In particular, Dumas et al [31] carefully designed their own experimental set-up, and the measurements of Brockner et al [24], Torklep and Øye [29] and Hertzberg et al [28], originating from the same group as Dumas et al, were favoured in this work.…”