Physicochemical properties of the system (LiF + NaF + KF(eut.) + Na7Zr6F31): Phase equilibria, density and volume properties, viscosity and surface tension

•The investigated properties were studied in the entire concentration range.•Based on the thermal analysis and XRD the estimation of phase equilibria was deduced.•Density and viscosity increase with increasing content of Na7Zr6F31 in the system.•Surface tension decreases with increasing content of Na7Zr6F31 in the system.•Significant changes in concentration range (0 to 20) mol% of Na7Zr6F31 are discussed.

The aims of the study were to investigate the physicochemical properties, such as the phase equilibria (by the means of thermal analysis), density (by Archimedean method of hydrostatic weighing), viscosity (by torsion pendulum method) and surface tension (by maximum bubble pressure method), of the (LiF + NaF + KF(eut.) + Na7Zr6F31) fluoride system. The obtained data show significant deviation from the ideal/additive behaviour, particularly in the concentration range from (0 to 20) mol% of Na7Zr6F31 while the data sets correspond each other very well. In this range a sharp increase in temperature of primary crystallisation together with volume expansion, positive deviation from “additive” behaviour of viscosity and negative deviation from “additive” behaviour of surface tension were observed. These significant changes are discussed and indicate complicated interactions of the components in the melt.

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