Thermal analysis and volume properties of the systems (LiF–CaF2)eut.–LnF3 (Ln = Sm, Gd, and Nd) up to 1273 K

Abstract

Systems (LiF–CaF2)eut.–LnF3 (Ln = Sm, Gd, and Nd) were investigated by means of thermal analysis and density measurements. Temperatures of primary crystallisation were measured and solidified samples were analysed by XRD as well as by SEM images and EDX mapping of the solidified samples. Densities of individual melts were measured by hydrostatic weighting (Archimedean method). Consequently, molar volumes were calculated. Unusual behaviour was observed in all three cases, when molar volumes decrease with initial LnF3 additions up to 1 mol % of LnF3. Further LnF3 additions result in molar volumes increase. In the case of GdF3 system, anomalous molar volume behaviour was observed: over 1 mol % of GdF3 molar volume is higher at lower temperatures. Partial molar volumes of LnF3 components were analysed by both simple linear or polynomial regression and multicomponent polynomial regression using least square parameters minimisation procedure. With increasing temperature, partial molar volumes of LnF3 decrease even to negative values.