Jarmila Mlynáriková

Critical evaluation of partial molar volumes and excess partial molar volumes of molten fluoride melts

Different procedures of evaluation of partial molar volume and excess partial molar volume have been applied for three binary or quasi-binary molten fluoride systems: KF–K2TaF7, K2ZrF6–K2TaF7 and (LiF–NaF–KF)eut–K2ZrF6. In the first procedure partial molar volume is calculated based on mathematical fitting of molar volume, while in the second procedure partial molar volume is calculated based on mathematical fitting of excess molar volume. It was shown that both procedures are in principle consistent. However, some inconsistencies on values of partial molar volume can occur when local extremes are observed on concentration dependence of molar volume. In such situation, proper selection of mathematical functions is essential which requires relatively high density of experimental data. Moreover, when data on only restricted concentration range are available, only procedure of molar volume fitting is applicable for calculation of partial molar volume.

Analysis of the extremely rapidly cooled molten system (LiF–CaF2)eut–LaF3

A rapid solidification process (melt spinning) was applied to the fluoride molten salt system (LiF–CaF2)eut–xLaF3 (x = 0, 5, 10, 20, and 30 mol%). Two types of undercooled fragment were identified: riffle-like and sphere-like fragments that differ in morphology, but whose phase composition seems to be comparable. The phase composition of these rapidly cooled samples revealed the presence of a metastable fcc type phase based on (Ca0.65La0.35)F2.35, in contrast to when the system was spontaneously cooled, which showed only the presence of the initial components. The cell parameters of the metastable phase vary based on the composition and due to fast cooling. After thermal relaxation the metastable phase decomposes to CaF2 and LaF3 phases.