Fusion properties and heat capacities of the eutectic lithium fluoride-sodium fluoride-potassium fluoride melt

Abstract

The fusion properties (melting point, enthalpy and entropy of fusion) of the eutectic LIF-NaF-KF and the heat capacity of this system In the poly crystalline state and In the molten state have been Investigated by the technique of hlgh-temperature differential scanning calorimetry. The fusion properties and heat capacities may be summarized as follows: mp 462 ± 2 °C; = 3.98 kcal mol"1; AS*. -5.42 eu; C.(soHd) -12.8218 -(9.851 X 10"3)f + (1.513 X 10-*)?•* and Cp(meK) = 9.8380 + (10.487 X 10"3) , both In cal mol"1 K \ respectively. The heat capacity temperature ranges are 57-450 °C (solid) and 475-590 °C (me#), and the accuracy limits for both the enthalpy and the heat capacities are ±2.0%. For conversion to SI units, 1 cal = 4.184 J.Hlgh-temperature thermodynamic data have been reported previously for UF, NaF, and KF but not for the ternary eutectic, LIF-NaF-KF (FLINAK). As part of our investigations of energy-related candidate salt systems using the technique of hlghtemperature differential scanning calorimetry (DSC), It was decided to extend the fluoride data to the ternary eutectic. Measurements were undertaken also on a series of eutectics that had been subjected to various me# pretreatments. These results, and a redetermination of the melting point of this eutectic, are reported herewith. Experimental SectionOur high-temperature differential scanning calorimetry facility has been described In detail elsewhere (1). The facility centers around a Perkin-Elmer DSC-Model 2 calorimeter, with ancillary microprocessor components and software for computer-assisted data acquisition, base-one corrections, and data analysis in enthalpy and heat capacity measurements (2). A quantitative and accurate small mass measurement capability completes the assembly. The latter, together with the sample capsules, and seal-press, was housed in a dry N2 atmosphere glovebag so that the final sample transfer and encapsulation could be completed In an Inert environment.Cross-check measurements for energy calibration were made with three metals, indium, tin, and lead, and two salt systems, KNOs and the UCI-KCI eutectic (3-5). The accuracy limits of the measurements thus established were as follows: temperatures, ±0.5 °C; heats of fusion, ±2%; heat capacities, ±2%.

Heat capacity and thermal conductivity of molten ternary lithium, sodium, potassium, and zirconium fluorides mixtures

“…The results of the subsequent experiments with the same sample did not differ. After the third reading the position of the melting peak remained unchanged, and its maximum corresponded to the melting temperature of the eutectic reported in [18]. The melting enthalpy measured equal to 385 ± 12 J/g is in agreement with the results obtained previously.…”

“…As noted in [18], the melting temperature of eutectic LiF-NaF-KF mixture decreased in subsequent repeated measurements. This decrease can be due to a slow homogenization of the salt melt (the highest experimental temperature was 1133 K, whereas the melting points for the mixture components are 1121, 1261, and 1129 K for LiF, NaF, and KF, respectively).…”

“…The monocrystalline sapphire and molten FLINAK [18] were used as standard samples for the measurements of heat capacity.…”

Thermal conductivity of high temperature fluoride molten salt determined by laser flash technique

“…The specific heat capacity of FLiNaK molten salt has been experimentally and theoretically studied [23][24][25][26], as summarized in Fig. 4, suggesting the specific heat capacity obtained in this work is very close to the extensively accepted value of 1.88 J/g K [2,4,5,23,27].…”

“…The available value from the ORNL in 1950s was 4.5 W/(m K) using a self-developed variable gap device, and the experimental error was less than 25% [31], however, this result was verified to be far away from the real values during the calculation for system design in MSRE project. Smirnov et al [32] measured the thermal conductivity of the FLiNaK molten salt by the method of coaxial cylinders and the values located in the range from 0.80 to 0.95 W/(m K) in the temperature range of 800-1100 K with the accuracy less than 4%, and it was reported to be 0.82-0.96 W/(m K) in 800-1100 K recently [25]. Serrano-López et al [27] suggested the thermal conductivity of the FLiNaK molten salt was a constant of 0.85 W/(m K), but the deviation was 0.206 W/(m K).…”