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Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Temperatures of Primary Crystallization and Density of the KF + AlF3 + LiF + Al2O3 Molten System Blanka Kubíkova,́ *,† Jarmila Mlynaŕ ikova,́ † Miroslav Bocǎ ,† Zhongning Shi,‡ Bingliang Gao,‡ and Niketan Patel† †

Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, 845 36 Bratislava, Slovakia School of Metallurgy, Northeastern University, Shenyang 110819, China

‡

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S Supporting Information *

ABSTRACT: This work deals with the investigation of the temperatures of primary crystallization and density of the KF + AlF3 + LiF + Al2O3 molten system for three cryolite ratios (CR = 1.3, 1.5 and 1.7). Thermal analysis and the Archimedean method of hydrostatic weighing were used for the determination of studied properties. The dependence of liquidus temperature on composition shows different trends for different CRs, whereas the density increased with increasing content of LiF for all CRs.

1. INTRODUCTION Aluminum is the second most widely used metal after iron. Its remarkable properties include low density, malleability, being easy to work, corrosion resistance, and ability to conduct electricity and heat, as a result of which aluminum and its alloys are used in electronics, the transport industry, construction, packaging, engineering, etc. These days aluminum is produced by the Hall-Héroult process, which involves electrolysis of a molten salt bath containing dissolved aluminum oxide in cryolite. The process operates in a temperature range of T = (1223 to 1253) K. However, this process has two big disadvantages (huge energy consumption and emission of gases, mostly CO2); to mitigate these, research is ongoing into low-melting cryolite mixtures based on potassium fluoride. In the last 20 years many authors have carried out investigations of the physicochemical properties of various molten systems containing mixed Na/K cryolite or pure K cryolite. Investigation has mostly focused on liquidus temperatures,1−11 alumina solubility,5,8,9,12−17 and conductivity.5,8,10,11,18−20 Information on the density of potassium-based cryolite systems is very scarce.8,21,22 Owing to the different cryolite ratios (CRs; n(KF)/n(AlF3)) of the mixtures investigated, it is very difficult to compare published data. The most frequently investigated system is the KF−AlF3 binary system. Philips et al.23 measured lower temperatures of primary crystallization than other studies,1,11,24 with the difference between reported values reaching 100 K for CR = 1.7. The values obtained by the other authors were close to each other, ranging from 1153 to 1168 K. Similar results were obtained for cryolite ratios CR = 1.5 and 1.3, for which the © XXXX American Chemical Society

lowest temperatures of primary crystallization (T = 995 K at CR = 1.5 and T = 882 K at CR = 1.3) were measured by Philips et al.23 Values very close to these were obtained by Apisarov et al.1 (T = 1000 K at CR = 1.5 and T = 893 K at CR = 1.3); in contrast, Danielik et al.11 and Fedotieff et al.24 found the liquidus temperature to have values of T = 1076 and 1105 K, respectively, at CR = 1.5, and T = 946 K and 936 T at CR = 1.3). This paper focuses on the determination of the liquidus temperatures and density of KF + AlF3 + LiF + Al2O3 molten systems at three different cryolite ratios (CR = 1.3, 1.5 and 1.7), observing the influence of LiF and Al2O3 content on the investigated properties. Changes in the composition influence the physicochemical properties, which makes knowledge of temperatures of primary crystallization and densities vitally important when considering suitable electrolytes for aluminum production at low temperatures.

2. MATERIALS AND EXPERIMENTAL METHODS 2.1. Chemicals. For preparation of the samples, the following chemicals were used: KF, AlF3, LiF, and Al2O3. LiCl, NaCl, and Na2SO4 were additionally used for calibration of thermocouples for thermal analysis measurements. Prior to the experiments the chemicals were purified by heating to certain temperatures. These are given in Table 1. All handling of salts was done in a glovebox (Jacomex, O2 content < 2 ppm, water content < 5 ppm) under a high-purity argon atmosphere (fraction purity: 0.99999; SIAD Slovakia). Received: April 18, 2018 Accepted: July 10, 2018

A

DOI: 10.1021/acs.jced.8b00157 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Table 1. Table of Sample Descriptions with Purification Temperature (Tp/Ka) chemical name potassium fluoride aluminum fluorideb aluminum fluoridec lithium fluoride aluminum oxided sodium chloride lithium chlorided sodium sulfatee

source

initial mole fraction purity

Aldrich

0.99

Aldrich

purification method

Tp/K 473

0.999

drying under vacuum none

0.99

sublimation

1423

Aldrich Slavus

0.99

drying

773

CentralChem Merck Merch

0.999

drying drying drying

773 573 423

a

Standard uncertainty u is u(Tp) = 0.5 K. bChemical used for thermal analysis investigation. cChemical used for density experiments. d Supplier has indicated purity only as p.a. (per analysis). eSupplier has indicated purity only as suprapur.

Table 2. Temperatures of Primary Crystallization, T/K, of the KF(1) + AlF3(2) + LiF(3) + Al2O3(4) Molten System for Three Cryolite Ratios (CR, CR = n(KF)/n(Al2O3)) Obtained at p = 0.1 MPaa. Contents of LiF (3) and Al2O3 (4) Are Expressed in Mass Fractions, wi w3 0.00 0.05 0.10 0.00 0.05 0.10 0.00 0.05 0.10 0.00 0.05 0.10 0.00 0.05 0.10 0.00 0.05 0.10

w4 CR = 1.3 0.00 0.00 0.00 0.05 0.05 0.05 CR = 1.5 0.00 0.00 0.00 0.05 0.05 0.05 CR = 1.7 0.00 0.00 0.00 0.05 0.05 0.05

Figure 1. Temperatures of primary crystallization of KF (1) + AlF3 (2) + LiF (3) + Al2O3 (4) for three investigated CRs; circle, CR = 1.3; triangle, CR = 1.5; square, CR = 1,7; filled symbol, w4 = 0.00; empty symbol, w4 = 0.05.

T/K 930 1024 1022 896 993 1005 1070 1034 1051 1005 1026 1031 1148 1095 1070 1095 1062 1044

Figure 2. Comparison of temperatures of primary crystallization of the KF (1) + AlF3 (2) molten system: (×) ref 23; (▲) ref 24; (○) ref 11; () ref 11; (●) this work.

a

Standard uncertainties u are u(w3) = 0.001, u(w4) = 0.001, u(T) = 3 K, u(CR) = 0.01 and u(p) = 10 kPa.

calibration, the uncertainty in the temperature measurement was determined to be u(T) = 3 K. Data processing was performed using a computerized measuring device (a multicomponent online instrument for thermal analysis data collections using components from the National Instruments, running LabVIEW software), Further information about the experimental device and measuring procedure may be found in one of our previous publications.25 2.3. Density. The density of the studied system was determined by the Archimedean method of weighing a measuring body (made of platinum) immersed into the liquid mixture. The measuring body is attached to the bottom of an electronic balance unit and together they form the essential parts of the experimental device. The temperature dependence of the volume of the measuring body was calibrated using molten

2.2. Thermal Analysis. The temperatures of primary crystallization of the investigated mixtures were determined by a thermal analysis method based on recording the heating and cooling curves of 10 g of homogenized salts in a resistant furnace under an inert Ar atmosphere (fraction purity, 0.9998; SIAD Slovakia). The default heating rate of 5 K·min−1 and cooling rate of 1.5 K·min−1 were adjusted when recording the experimental curves. A Pt−Pt10Rh thermocouple was used for determination of temperatures and the precision of the thermocouple was determined by measuring the melting temperatures of certain pure salts and a mixture (NaCl, LiCl, KF, LiF, and (NaCl + Na2SO4)eut) for which reference values exist. On the basis of this B



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Table 3. Regression Coefficients a/g·cm−3, b/g·cm−3·K−1, Corresponding Standard Deviations sda/g·cm−3, sdb/g·cm−3·K−1, and Temperature Range T/K of Investigated Melts in the System (KF(1) + AlF3 (2) + LiF (3) + Al2O3 (4) for Three Cryolite Ratios (CR; CR = n(KF)/n(Al2O3)) Obtained at Pressure p = 0.1 MPaa. Density, in ρ/g·cm−3, Calculated at 1093 K. Contents of LiF (3) and Al2O3 (4) Are Expressed in Mass Fractions, wi T

a

sda×103

b × 104

sdb × 106

ρ1093K

g·cm−3

g·cm−3·K−1

g·cm−3·K−1

g·cm−3

1.0 2.0 1.1 3.0 1.1 0.9 2.0 1.6 1.3 1.2 1.0 1.0

9.389 9.214 10.810 11.755 10.108 10.351 7.294 7.546 9.117 9.000 9.614 9.350

0.9 2.1 1.0 3.0 1.0 0.8 2.3 1.6 1.1 1.1 1.0 0.9

1.748 1.747 1.863 1.867 1.960 1.964 1.745 1.738 1.863 1.860 1.940 1.943

9.0 0.9 5.6 2.9 1.2 1.7 1.5 1.9 0.5

7.546 10.400 10.471 10.136 10.143 8.675 10.048 9.194 9.117

0.8 0.9 0.5 2.7 1.1 1.4 1.4 1.8 0.5

1.771 1.920 1.920 1.998 1.998 1.766 1.895 1.969 1.966

2.7 7.3 2.1 1.2 0.8 0.8 3.1 2.3 1.3 0.8 1.2 0.9

8.907 9.274 8.615 9.334 9.692 9.739 8.443 9.294 8.121 8.796 8.935 8.772

2.2 6.1 1.8 1.0 0.7 0.7 2.6 1.9 1.1 0.7 1.1 0.8

1.927 1.930 1.974 1.983 2.019 2.019 1.897 1.900 1.940 1.933 1.979 1.976

w3

w4

K

g·cm−3

0.00 0.00 0.05 0.05 0.10 0.10 0.00 0.00 0.05 0.05 0.10 0.10

0.00 0.00 0.00 0.00 0.00 0.00 0.05 0.05 0.05 0.05 0.05 0.05

1102−992 1053−953 1153−993 1134−1000 1173−1018 1163−1020 1053−953 1064−953 1173−1003 1163−995 1133−1023 1173−1023

2.774 2.754 3.044 3.152 3.065 3.096 2.542 2.563 2.859 2.844 2.991 2.965

b

0.00 0.05 0.05 0.10 0.10 b 0.00 0.05 0.10 0.10

0.00 0.00 0.00 0.00 0.00 0.05 0.05 0.05 0.05

1136−1060 1143−1023 1163−1023 1144−1044 1173−1043 1273−1223 1153−1038 1122−1028 1153−1028

2.596 3.057 3.065 3.106 3.107 2.714 2.993 2.974 2.963

0.00 0.00 0.05 0.05 0.10 0.10 0.00 0.00 0.05 0.05 0.10 0.10

0.00 0.00 0.00 0.00 0.00 0.00 0.050 0.05 0.05 0.05 0.05 0.05

1215−1163 1223−1163 1196−1102 1213−1111 1213−1069 1213−1074 1243−1124 1248−1139 1173−1060 1163−1063 1153−1053 1159−1053

2.901 2.944 2.916 3.004 3.078 3.084 2.820 2.916 2.828 2.895 2.955 2.935

CR = 1.3

CR = 1.5

CR = 1.7

a Standard uncertainties u are u(w3) = 0.001, u(w4) = 0.001, u(T) = 3 K, u(CR) = 0.01, u(p) = 10 kPa, and combined expanded uncertainty Uc is Uc(ρ) = 0.009 g·cm−3 (0.95 level of confidence). bReference 21.

fractions (wi) and were w3 = 0.00, 0.05, and 0.10, and w4= 0.00 or 0.05. 3.1. Thermal Analysis. The temperatures of primary crystallization of all investigated mixtures are listed in Table 2. Figure 1 depicts the dependence on LiF content of temperature of primary crystallization for each of the investigated cryolite ratios. Completely different behavior was observed for each cryolite ratio. After the addition of LiF (w3 = 0.05) to the KF + AlF3 mixture at CR = 1.3, the temperature of primary crystallization increased by about 100 K. Further addition of lithium fluoride to KF + AlF3 did not significantly change the value of the liquidus temperature. This result is in good agreement with the results of Tkacheva et al.8 Those authors made measurements at four LiF concentrations ((x3 = 0.00, 0.05, 0.07 and 0.09); w3 = 0.05 corresponds to x3 = 0.12). However, their reported temperatures of primary crystallization were about 140 K lower than those found in this work: for w3 = 0.05, we measured T = 1024 K,

NaCl and KF. 50 g of the relevant homogenized mixture in a platinum crucible was placed into a preheated resistant furnace. The measurements were carried out at temperature intervals of approximately T = (100 to 160) K, starting at 20 K above the temperature of primary crystallization. An online PC XT computer (a multicomponent online instrument for density data collections, again from National Instruments and running under LabVIEW software) was used to control the measuring device and evaluate the experimental data. Detailed information about the measuring device and procedure has been given in a previous publication.26

3. RESULTS AND DISCUSSION For both investigated properties, six different mixtures at n(KF) three cryolite ratios (CR = n(AlF ) ) were analyzed (18 points). 3

The LiF (3) and Al2O3 (4) contents are expressed in mass C



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whereas they found T = 883 K for x3 = 0.09, and trends that indicated even lower T values for higher x3 (liquidus temperatures decreased from 933 to 883 K on going from x3 = 0.05 to x3 = 0.09). A similar trend was observed in the KF + AlF3 system with w4 = 0.05, although in that case the increase in temperature of primary crystallization was visible over the whole concentration range. The results obtained for the KF + AlF3 system at CR = 1.7 showed the opposite tendency to those at CR = 1.3. In both cases (w4 = 0.00 and 0.05) the addition of LiF (w3 = 0.05 and 0.10) decreased the temperatures of primary crystallization. These results are very close to the results reported by Thoma et al.27 Those authors investigated the KF + AlF3 system without any Al2O3 content. The difference in liquidus temperatures for w3 = 0.05 is less than 5 K (their reported liquidus temperature is approximately 1098 K) and for w3 = 0.10 is approximately 10 K (their reported liquidus temperature is approximately 1078 K). The values of liquidus temperatures have been read from the Phase Equilibria Diagrams Search Database, version 4.2.0, ACerSNIST. For the KF + AlF3 system at CR = 1.5, inclusion of LiF (w3 = 0.05) led to a decrease in liquidus temperatures of about 35 K. For a LiF content of w3 = 0.10, the liquidus temperature increased to a value of 1050 K. For systems containing Al2O3 (w4 = 0.05), the temperature of primary crystallization increased with increasing LiF content. It is worth noting that the system with CR = 1.5 and without alumina behaves like the system with CR = 1.7, that is, with the addition of LiF the temperature of primary crystallization decreases (at least up to w3 = 0.10). Conversely, the system with CR = 1.5 and with Al2O3 (w4 = 0.05) behaves like the alumina-free system with CR = 1.3, that is, upon LiF addition the temperature of the primary crystallization increases (at least up to w3 = 0.10, the highest LiF content measured). Liquidus temperatures for the systems with Al2O3 are lower than for the same systems without Al2O3 content at all investigated cryolite ratios. To demonstrate the accuracy of the present results, a comparison of liquidus temperatures of the KF + AlF3 binary system for all three cryolite ratios (free of LiF and Al2O3) is shown in Figure 2 and is in very good agreement with previously reported data. 3.2. Density. The temperature dependence of the density for each composition at all investigated cryolite ratios can be expressed as a linear equation ρ = a − bT

Figure 3. Experimental dependencies of density of KF (1) + AlF3 (2) + LiF (3) + Al2O3 (4) for all compositions at cryolite ratio CR = 1.7, black symbols−first measurement, red symbols−repeated measurement: □, w3 = 0.00 and w4 = 0.00; ○, w3 = 0.00 and w4 = 0.05; ◇, w3 = 0.05 and w4 = 0.05; △, w3 = 0.10 and w4 = 0.05; ⎔, w3 = 0.05 and w4 = 0.00; ▽, w3 = 0.10 and w4 = 0.00.

On the basis of the data from Figure 4 one can say that • for systems with CR = 1.3 and 1.5 the values of the density do not significantly depend on the presence or absence of Al2O3; however, for CR = 1.7, the density is affected by the presence of Al2O3.

(1)

where ρ/g·cm−3 is density, T/K is temperature, and the coefficients a/g·cm−3 and b/g·cm−3·K−1 are constants. Table 3 lists the regression coefficients a/g·cm−3 and b/g·cm−3·K−1, along with the standard deviations obtained by linear regression analysis of the experimentally obtained data for the density of the mixtures. All of the investigated mixtures were measured twice, with the exception of those measured in our previous publication,21 which are marked with an asterisk (∗) in Table 3. Since the values of density are recorded every 5 s, experimental data are provided as Supporting Information. Figure 3 shows recorded temperature dependencies of density for all compositions measured at CR = 1.7. Similar dependencies were obtained for other two investigated cryolite ratios (CR = 1.5 and 1.3). For direct comparison, the density was calculated at a temperature of 1093 K for all systems. This temperature was chosen as all systems are liquid at that temperature, and it is within or near the investigated temperature range of all systems (making extrapolation to that temperature justifiable).

Figure 4. Calculated density of KF (1) + AlF3 (2) + LiF (3) + Al2O3 (4) for all investigated mixtures at T = 1093 K: circle, CR = 1.3; triangle, CR = 1.5; square, CR = 1,7; filled symbol, w4 = 0.00; empty symbol, w4 = 0.05.

• for all values of CR (1.3, 1.5, and 1.7), the density increases upon addition of LiF. For CR = 1.3 or 1.5, this increase is by about 11%, but for the system with CR = 1.7 the increase is only by ca. 2.5%. D



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• the density increases with increasing CR (e.g., for systems without LiF and Al2O3 it changes from 1.748 g·cm−3 for CR = 1.3 to 1.772 g·cm−3 for CR = 1.5, and 1.928 g·cm−3 for CR = 1.7). As mentioned in the introduction, data on the density of potassium cryolite molten systems is very sparse. Tkacheva et al.8 have investigated the KF + NaF + AlF3 system at CR = 1.3 and the density was calculated for T = (1033 and 1073) K. The density of the KF + AlF3 system without NaF addition was approximately 1.78 g·cm−3 and 1.74 g·cm−3 at 1033 and 1073 K, respectively. These values are slightly lower than the values of (1.748 and 1.747) g·cm−3 obtained in this work at 1093 K.

(2) Apisarov, A.; Dedyukhin, A.; Redkin, A.; Tkacheva, O.; Nikolaeva, E.; Zaikov, Y.; Tinghaev, P. Physical-chemical properties of the KFNaF-AlF3 molten system with low cryolite ratio. Light Met. (Warrendale, PA, U. S.) 2009, 401−403. (3) Danielik, V. Phase equilibria in the system KF-AlF3-Al2O3. Chem. Pap. 2005, 59, 81−84. (4) Danielik, V.; Gabcova, J. Phase Diagram of the System NaF-KFAlF3. J. Therm. Anal. Calorim. 2004, 76, 763−773. (5) Cassayre, L.; Palau, P.; Chamelot, P.; Massot, L. Properties of lowtemperature melting electrolytes for the aluminum electrolysis process: A review. J. Chem. Eng. Data 2010, 55, 4549−4560. (6) Chen, R.; Wu, G.; Zhang, Q. Phase Diagram of the System KF− AlF3. J. Am. Ceram. Soc. 2000, 83, 3196−3198. (7) Schamm, S.; Rabaidel, L.; Grannec, J.; Naslain, R.; Bernard, C.; Relave, O. Partial phase diagram of the ternary reciprocal system potassium fluoride-aluminum fluoride-alumina-potassium oxide. CALPHAD: Comput. Coupling Phase Diagrams Thermochem. 1990, 14, 385− 402. (8) Tkacheva, O.; Redkin, A.; Kataev, A.; Zaikov, Y. In Pottasium cryolite as a basic electrolyte component for the low-temperature aluminum production, The Eights International Conference on Material Technologies and Modeling, Ariel, Israel, 2014; Ariel, Israel, 2014; pp 152−159. (9) Yuan, M.; Kan, S.; Meng, Q.; Zhang, X.; Lu, S. Effect of LiF and Al2O3 on the physical and chemical characters in containing elpasolite aluminium electrolyte system. Rare Met. 2011, 30, 595−598. (10) Dedyukhin, A. E.; Apisarov, A. P.; Redkin, A. A.; Tkacheva, O. Y.; Zaikov, Y. P. Influence of CaF2 on the properties of the low-temperature electrolyte based on the KF-AlF3 (CR = 1.3) system. Light Met. (Warrendale, PA, U. S.) 2008, 509−511. (11) Danielik, V.; Hives, J. Low-Melting Electrolyte for Aluminum Smelting. J. Chem. Eng. Data 2004, 49, 1414−1417. (12) Apisarov, A. P.; Dedyukhin, A. E.; Red’kin, A. A.; Tkacheva, O. Y.; Zaikov, Y. P. Physicochemical properties of KF-NaF-AlF3 molten electrolytes. Russ. J. Electrochem. 2010, 46, 633−639. (13) Robert, E.; Olsen, J. E.; Danek, V.; Tixhon, E.; Oestvold, T.; Gilbert, B. Structure and thermodynamics of alkali fluoride-aluminum fluoride-alumina melts. Vapor Pressure, Solubility, and Raman Spectroscopic Studies. J. Phys. Chem. B 1997, 101, 9447−9457. (14) Yang, J.; Graczyk, D. G.; Wunsch, C.; Hryn, J. N. Alumina solubility in KF-AlF3-based low-temperature electrolyte system. Light Met. (Warrendale, PA, U. S.) 2007, 537−541. (15) Tkacheva, O.; Zaikov, Y.; Apisarov, A.; Dedyukhin, A.; Redkin, A. In The aluminum oxide solubility in the KF-NaF-AlF3 melts, The seventh “Bi-National workshop Russia−Israel”, Jerusalem, Israel, 2009; Jerusalem, Israel, 2009; pp 175−182. (16) Yan, H.; Yang, J.; Li, W.; Chen, S. Alumina solubility in KF-NaFAlF3-based low-temperature electrolyte. Metall. Mater. Trans. B 2011, 42, 1065−1070. (17) Frazer, E. J.; Thonstad, J. Alumina solubility and diffusion coefficient of the dissolved alumina species in low-temperature fluoride electrolytes. Metall. Mater. Trans. B 2010, 41, 543−548. (18) Apisarov, A. P.; Kryukovskii, V. A.; Zaikov, Y. P.; Red’kin, A. A.; Tkacheva, O. Y.; Khokhlov, V. A. Conductivity of low-temperature KFAlF3 electrolytes containing lithium fluoride and alumina. Russ. J. Electrochem. 2007, 43, 870−874. (19) Dedyukhin, A.; Apisarov, A.; Tkacheva, O.; Redkin, A.; Zaikov, Y.; Frolov, A.; Gusev, A. Electrical conductivity of the (KF-AlF3)-NaFLiF molten system with Al2O3 additions at low cryolite ratio. ECS Trans. 2008, 16, 317−324. (20) Híveš, J.; Thonstad, J. Electrical conductivity of low-melting electrolytes for aluminium smelting. Electrochim. Acta 2004, 49, 5111− 5114. (21) Vasková, Z.; Kontrík, M.; Mlynáriková, J.; Boča, M. Density of Low-Temperature KF-AlF3 Aluminum Baths with Al2O3 and AlPO4 Additives. Metall. Mater. Trans. B 2015, 46, 485−493. (22) Chrenkova, M.; Silny, A.; Simko, F.; Thonstad, J. Density of the NaAlF4 + KAlF4 Electrolyte, Saturated with Alumina. J. Chem. Eng. Data 2010, 55, 3438−3440.

4. CONCLUSION This work has presented an investigation into the temperatures of primary crystallization and density of a potassium cryolite molten system. On the basis of the obtained results it seems that it cannot be predicted how systems at different cryolite ratios will behave. For molten systems containing alumina, liquidus temperatures sometimes increase and sometimes decrease with CR; there is no consistent trend. For the alumina-free molten systems, there is actually a local minimum in the liquidus temperature at CR = 1.5. The composition had little effect on the density of the KF + AlF3 + LiF + Al2O3 molten system, however, except at CR = 1.7 where the density changed by 0.0418 g·cm−3 at T = 1093 K.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00157.

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Temperatures of primary crystallization and density of KF + AlF3 + LiF + Al2O3 molten system (XLSX)

AUTHOR INFORMATION

Corresponding Author

*Tel.: +421 2 59410 421. E-mail: [email protected]. ORCID

Blanka Kubíková: 0000-0002-0144-1962 Funding

This work was financially supported by the Scientific Grant Agency of the Ministry of Education of the Slovak Republic and the Slovak Academy of Sciences under Grant No. 2/0114/16. It was also supported by the Slovak Research and Development Agency under Contract No. APVV-15-0479 and SK-CN-20150014. This publication is the result of implementation of the project “Applied research of technology of thermal plasma processes”, ITMS code 26240220070, supported by the Research & Development Operational Programme funded by the ERDF. This work was supported by programme SASPRO (Mobility Programme of the Slovak Academy of Sciences), Marie Curie Actions of the European Union’s Seventh Framework Programme under the Grant Agreement No. 1119/02/02. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Apisarov, A.; Dedyukhin, A.; Nikolaeva, E.; Tinghaev, P.; Tkacheva, O.; Redkin, A.; Zaikov, Y. Liquidus temperatures of cryolite melts with low cryolite ratio. Metall. Mater. Trans. B 2011, 42, 236−242. E



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(23) Phillips, B.; Warshaw, C. M.; Mockrin, I. Equilibria in potassiumaluminum-fluorine-containing systems. J. Am. Ceram. Soc. 1966, 49, 631−634. (24) Fedotieff, P. P.; Timofeeff, K. The melting diagram of the systems: KF-AlF3 and LiF-AlF3. Z. Anorg. Allg. Chem. 1932, 206, 263− 266. (25) Kubíková, B.; Boča, M.; Mlynáriková, J.; Gurišová, V.; Š imurda, M.; Netriová, Z.; Korenko, M. Physicochemical properties of the (LiF + CaF2)eut+ LaF3 system: phase equilibria, volume properties, electrical conductivity, and surface tension. J. Chem. Eng. Data 2016, 61, 1395− 1402. (26) Mlynáriková, J.; Boča, M.; Gurišová, V.; Macková, I.; Netriová, Z. Thermal analysis and volume properties of the systems (LiF− CaF2)eut.−LnF3 (Ln = Sm, Gd, and Nd) up to 1273 K. J. Therm. Anal. Calorim. 2016, 124, 973−987. (27) Thoma, R. E.; Sturm, B. J.; Guinn, E. H.. Molten-salt solvents for fluoride volatility processing of aluminum-matrix nuclear fuel elements; Report No. 3594, Oak Ridge National Laboratory: OakRidge, TN, August 1964.

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