Multi-component Molten Salts Research Articles

The role of the local structure on the thermal transport within dissociated and complexed Molten salt mixtures

Contrary to the solid state, the understanding of thermal transport within molten salts remains limited. This study aims at establishing a robust theoretical framework for describing and predicting thermal transport in complex and dissociated multicomponent molten salt mixtures, considering both the composition and temperature variables. The proposed approach, based on kinetic theory, considers the local perturbation of kinetic energy through mass fluctuation, weighted by a function dependent on the thermal conductivity of the uncorrelated system and the local structure. The local structure is described in terms of the concentration of free and complex ions, determined either experimentally (using NMR) or through equilibrium atomistic simulations. The thermal transport within several molten salt systems, including KCl, Al2O3, LiF-KF, LiF-NaF-KF (FLiNaK), KCl-MgCl2, NaCl-KCl-MgCl2, and the NaF-AlF3 system, are presented as case studies using the proposed approach. Furthermore, a molecular-level perspective of thermal conduction within molten salts is discussed.

A predictive approach for the compositional and temperature representation of thermal conductivity in multicomponent molten salt systems for advanced energy applications

This study presents a theoretical model, based on kinetic theory, for accurately predicting thermal conductivity in molten salt mixtures, a vital factor in designing advanced energy systems such as concentrating solar power, thermal energy storage, and advanced nuclear reactors. Applicable to non-complex, non-reciprocal systems, the model represents thermal conductivity with respect to composition and temperature. We evaluated the model using molecular dynamics simulations on binary systems from fluoride, chloride, bromide, iodide salt families. The model predictions were also compared against existing experimental datasets for those families as well as binary nitrates and carbonates. The model demonstrated an improvement in predictive accuracy over the ideal linear estimation and showed reasonable agreement with the reliable experimental data. Deviations from ideal conductivity, analyzed using the Redlich-Kister method, pointed to the molecular weight and thermal conductivity of individual compounds as primary influencing factors. When applied to predict the thermal conductivity of higher order eutectic salt mixtures relevant to energy applications, the model showed predictive accuracy comparable to empirical methods. The model was further applied to generate compositional mapping to quantify deviations from ideality over the compositional space. This advance enhances new molten salt mixtures evaluation efficiency and extends the model to complex mixtures.

Transferable Deep Learning Potential Reveals Intermediate-Range Ordering Effects in LiF-NaF-ZrF4 Molten Salt.

LiF-NaF-ZrF4 multicomponent molten salts are promising candidate coolants for advanced clean energy systems owing to their desirable thermophysical and transport properties. However, the complex structures enabling these properties, and their dependence on composition, is scarcely quantified due to limitations in simulating and interpreting experimental spectra of highly disordered, intermediate-ranged structures. Specifically, size-limited ab initio simulations and accuracy-limited classical models used in the past are unable to capture a wide range of fluctuating motifs found in the extended heterogeneous structures of liquid salt. This greatly inhibits our ability to design tailored compositions and materials. Here, accurate, efficient, and transferable machine learning potentials are used to predict structures far beyond the first coordination shell in LiF-NaF-ZrF4. Neural networks trained at only eutectic compositions with 29% and 37% ZrF4 are shown to accurately simulate a wide range of compositions (11-40% ZrF4) with dramatically different coordination chemistries, while showing a remarkable agreement with theoretical and experimental Raman spectra. The theoretical Raman calculations further uncovered the previously unseen shift and flattening of bending band at ∼250 cm-1 which validated the simulated extended-range structures as observed in compositions with higher than 29% ZrF4 content. In such cases, machine learning-based simulations capable of accessing larger time and length scales (beyond 17 Å) were critical for accurately predicting both structure and ionic diffusivities.

Structure and Thermophysical Properties of Molten Calcium-Containing Multi-Component Chlorides by Using Specific BMH Potential Parameters

Chloride molten salts have become a potential heat storage material for the design of a new generation of concentrating solar power (CSP) (>700 °C) due to its abundant reserves and low cost. The difficulty of measuring the high-temperature thermal properties of chlorides can be effectively solved by using molecular dynamics simulation. However, it is challenging to get the thermophysical properties of multi-component molten salts containing CaCl2 due to the lack of Born–Mayer–Huggins (BMH) potential parameters of CaCl2. Through comparative analysis of the structure and thermal properties of CaCl2, including density and thermal conductivity, a set of Born–Mayer–Huggins (BMH) potential parameters of CaCl2 named SP2 is determined in this study. The density, specific heat capacity, and thermal conductivity of nine eutectic molten salts are simulated, including NaCl-CaCl2, KCl-CaCl2, NaCl-CaCl2-MgCl2, and NaCl-CaCl2-KCl, and the simulation results are found to be in good agreement with the experimental results. It is also found that the SP2 parameters are able to predict the thermal properties and structure of molten multicomponent chlorides including calcium.

Thermodynamic re-optimization of the AClx-MgCl2 (A=Na, K, Rb, Cs and Ca, x=1 or 2) systems

Thermodynamic evaluation of the AClx-MgCl2 (A = Na, K, Rb, Cs and Ca, x = 1 or 2) systems were carried out by the CALculation of PHAse Diagrams (CALPHAD) technique. Substitutional solution model (SSM) and associate solution model (ASM) were employed to describe the liquid phase. The eleven intermediate phases, i.e., Na2MgCl4, NaMgCl3, K2MgCl4, K3Mg2Cl7, KMgCl3, Rb2MgCl4, RbMgCl3, Cs3MgCl5, Cs2MgCl4, CsMgCl3 and CsMg3Cl7, were treated as stoichiometric compounds. The thermodynamic parameters for describing the AClx-MgCl2 (A = Na, K, Rb, Cs and Ca, x = 1 or 2) systems were optimized based on the available phase equilibria and thermochemistry data. A set of self-consistent thermodynamic parameters of these binary systems was obtained. The calculated phase equilibria, liquid mixing enthalpy and liquid activity are in good agreement with the experimental data. It indicates that the SSM and ASM are considered as effective models to describe the liquid phase with short-range ordering structure in the molten salt. This work not only enriches the thermodynamic database of the multicomponent molten salts, but also provides one more model choice for optimizing and designing the molten salt systems except modified quasi-chemical model.

Composition-transferable machine learning potential for LiCl-KCl molten salts validated by high-energy x-ray diffraction

Unraveling the liquid structure of multicomponent molten salts is challenging due to the difficulty in conducting and interpreting high-temperature diffraction experiments. Motivated by this challenge, we developed composition-transferable Gaussian approximation potential (GAP) for molten LiCl-KCl. A DFT-SCAN accurate GAP is active-learned from only $\ensuremath{\sim}$1100 training configurations drawn from 10 unique mixture compositions enriched with metadynamics. The GAP-computed structures show strong agreement across high-energy x-ray diffraction experiments, including for a eutectic not explicitly included in model training, thereby opening the possibility of composition discovery.

Short- to Intermediate-Range Structure, Transport, and Thermophysical Properties of LiF–NaF–ZrF4 Molten Salts

LiF–NaF–ZrF4 multicomponent molten salts are identified as promising candidates for coolant salts in molten salt reactors and advanced high-temperature reactors. This study focused on low-melting point salt compositions of interest: 38LiF–51NaF–11ZrF4, 42LiF–29NaF–29ZrF4, and 26LiF–37NaF–37ZrF4. Ab-initio molecular dynamics (AIMD) calculations were performed and compared with available experimental data to assess the ability of rigid ion models (RIM) to reproduce short- to intermediate-range structure, transport, and thermophysical properties of the LiF–NaF–ZrF4 salt mixtures. It is found that as ZrF4 mol% increases, the average cation–anion coordination number (CN) of monovalent cations (Li+, Na+) obtained from RIM calculations decreases, while multivalent Zr4+ CN varied from 15% to 19% in comparison to corresponding AIMD values. In addition, RIM is found to predict the existence of 7, 8, and 9 coordinated fluorozirconate complexes, while AIMD and the available experimental data showed an occurrence of 6, 7, and 8 coordinated complexes in the melt. The intermediate-range structure analysis revealed that while the RIM parameters are able to reproduce a local structure for lower ZrF4 mol% salts such as in 38LiF–51NaF–11ZrF4, an extensive fluorozirconate network formation is observed in RIM simulations for higher ZrF4 mol% compositions. The network generated by RIM parameters is found to be mainly connected by “corner-sharing” fluorozirconate complexes as opposed to both “edge-sharing” and “corner-sharing” connectively portrayed by AIMD. It is found that a close agreement between AIMD and the RIM salt structure for the 11-mol% ZrF4 salt resulted in good agreement in the calculated Zr diffusivities and the viscosity values. However, due to the inaccurate short- to intermediate-range structure prediction by RIM for higher ZrF4 mol% compositions, thermophysical properties such as densities and heat capacity differ by up to 26% and 27%, respectively, upon comparison with AIMD and experimental values. Also, the network-dominated properties such as diffusion coefficients and viscosities differed by up to two and three orders of magnitude, respectively. This study signifies the importance of accurate salt structure generation for an accurate prediction of transport and thermophysical properties of multicomponent molten salts.

A theoretical framework for reliable predictions of thermal conductivity of multicomponent molten salt mixtures: KCl-NaCl-MgCl2 as a case study

The next generations of Concentrated Solar Thermal Power (CSTP) systems use anhydrous salts as the heat transfer fluid and thermal storage medium. Unfortunately, a severe lack of experimental data is observed for the thermal transport properties of molten salt mixtures, generating constraints in exploring new potential materials for CSTP systems. The present paper presents a reliable theoretical framework for the prediction of both the thermal conductivity and thermal diffusivity of multicomponent molten salts. As a case study, the thermal conductivity of the NaCl-KCl-MgCl 2 system is predicted as a function of temperature and composition. This system is considered as a one of the most promising thermal storage medium of the next generation of CSTP systems. The temperature dependent thermal conductivity of pure MgCl 2 is formulated based on atomistic simulations via classical and Ab initio equilibrium molecular dynamics. Thereafter, to assess the predictive capability of the proposed methodology, the thermal conductivity and thermal diffusivity of KCl-MgCl 2 and NaCl-KCl-MgCl 2 molten mixtures are predicted as a function of both temperature and composition and compared to the available experimental data and the present first principles simulations. A good agreement is achieved with both experimental and first principle data, indicating the robustness of the proposed methodology. • A Theoretical framework to predict the thermal conductivity of PCM from 298 K up to above the melting established. • The temperature dependent thermal conductivity of molten MgCl 2 is re-assessed based on AIMD. • The thermal conductivity of NaCl-KCl-MgCl 2 is predicted via Kinetic Theory and Equilibrium Molecular Dynamics. • The predicted capability of the proposed approach is demonstrated through comparison with most recent experimental data.

Empirical estimation of densities in NaCl-KCl-UCl3 and NaCl-KCl-YCl3 molten salts using Redlich-Kister expansion

Densities of molten KCl-NaCl-UCl3 and KCl-NaCl-YCl3 ternary systems have been estimated using a multidimensional Redlich-Kister model. Temperature and composition dependent Redlich-Kister functions have been used to generate binary interaction parameters in the outlined ternary salt systems. These binary interactions have been used in the extrapolation to ternary system densities. The results of the density extrapolations by Muggianu interpolation scheme provide agreement within 2–3% for the NaCl-KCl-YCl3 liquids and 11% in NaCl-KCl-UCl3 liquids compared to the available experimental data. Modeling NaCl-KCl-UCl3 molten phase density with a ternary interaction parameter improved the agreement within 4%. Thermophysical modeling used in this study has shown promising results for use in other material properties, such as viscosity, thermal conductivity, and heat capacity of the molten salts. Furthermore, the outlined modeling method applied in these specific molten salt ternaries can be used for quaternary or higher multicomponent molten salt systems.

Carbon deposition mechanism of molten salt cleaning and optimization of multicomponent molten salt formula for remanufacturing.

In remanufacturing engineering, cleaning is the key factor for subsequent blank inspection and parts repair. Molten salt has the characteristics of low viscosity, good fluidity, and strong chemical stability. Salt bath cleaning can be comprehensively applied to remove various organic pollutants. Molten salt has the function of self-cleaning. The dirt in the cleaning pool can be decomposed and reused. Moreover, the waste molten salt is massive, and the waste residue is easy to treat. The formation and adsorption mechanism of carbon deposition was explored, and the formation mechanism of carbon deposition was verified by experiments. Then, the existing formula was improved by mixing experiment and compared with the current cleaning method; the cleaning effect was excellent. A new molten salt formula is proposed on the basis of the research on solar thermal storage medium. The composition percentage and the optimal process parameters of the new molten salt formula were determined on the basis of the experimental design of mixture. The cleaning effect of the new formula is good.

Complex Structure of Molten NaCl-CrClx Salts: Octahedra Network and Intermediate-Range Order

In the last decade, there has been a sustained resurgence of the Molten-Salt Nuclear Reactor (MSR) concept. As the MSRs operate, chemical compositions and physical properties of salts change because of the creation of fission products, and the effects of corrosion and radiolysis. Therefore, computer simulations of the microscopic structure of multi-component molten salts are necessary to predict changing thermophysical properties. However, first-principles simulations inevitably involve simplifying approximations and therefore require careful experimental validation. Here we present detailed experimental and simulation studies of the structure of molten NaCl-CrCl3 and NaCl-CrCl2 near-eutectic mixtures. These compositions have been chosen to elucidate the behavior of Cr ions in the melts since Cr is the most important corrosion product. Although the corrosion will result in relatively small quantities of Cr in the melt, we used much larger Cr concentration to measure the structure around Cr ions with high resolution. The results of X-ray and neutron diffraction with isotopic substitution, X-ray absorption spectroscopy, and ab initio molecular-dynamic simulations are in agreement. In NaCl-CrCl3 we found CrCl6 3+ octahedra and their networks, as well as intermediate-range order, which manifests itself in the prepeak at ~ 1 Å-1 with non-monotonic temperature behavior.Figure 1 shows one of the main results of this work, namely the comparison of measured and calculated total and partial PDFs of the molten NaCl-CrCl3 near-eutectic mixture. The consistency between the measured and calculated PDFs is remarkable. Neutron diffraction with isotopic substitution allows for a high-fidelity determination of the distances between Cr ions and other species in the melt. By utilizing a combination of neutron diffraction with isotopic substitution of 53Cr, X-ray diffraction, and ab-initio molecular dynamic simulations, we discovered the formation of chains of CrCl6 3- corner-, edge-, and face-sharing octahedra, with Cr-Cl distances of 2.4 Å, and Cl-Cl distance of 3.3 Å. We also found evidence for intermediate-range order that is likely related to inter-chain correlations. In this regard, these ternary salt shows a structure that is reminiscent of that of KCl-MgCl2, LiF-BeF2, and NaCl-UCln.Neutron and X-ray diffraction augment each other to determine partial PDFs Neutrons are particularly useful for studies involving, for example, Cr and Ni, where isotopes with a large difference in neutron cross-section are available. But when isotopic substitution is not achievable, the combination of X-rays and neutrons can extract the information about partial PDFs not otherwise available. The combination of neutrons and X-rays is also useful to overcome experimental constraints, such as compatibility between the salts and crucibles, potential radiation damage to crucibles, and sometimes large background from the sample environment. For example, quartz crucibles are suitable for both neutrons and X-rays and can be used with chloride salts but not with fluoride salts. The latter can be contained in vanadium crucibles for neutrons experiments. Our measurements demonstrate the relative strengths and weaknesses of both techniques for understanding the structure of multi-component salts. In conclusion, the understanding of the structure around Cr ions will be used to calculate properties of molten salt components (e.g., diffusivity) in the presence of Cr impurities. These properties will affect macroscopic thermo-physical properties such as thermal conductivity and viscosity of melts containing that, in turn, are necessary for designing safe and efficient MSRs. The extension of these methods to study melts containing up to 10 components will be discussed.We acknowledge useful discussions with Richard Mayes, Stephen Raiman, Jake Mcmurray (ORNL), and Raluca Scarlat (UC Berkeley). This material is based upon work supported by the Department of Energy under Award Number DE-NE0008751. This research used resources at the Spallation Neutron Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated by the Oak Ridge National Laboratory, and the beamline 28-ID-1 (PDF) of the National Synchrotron Light Source II, a DOE Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. Figure 1

Experimental investigation and thermodynamic assessment of the RbCl[sbnd]CsCl[sbnd]ZnCl2 system and its subsystems

The RbClZnCl2 and CsClZnCl2 binary systems with different proportions are firstly prepared to determine the phase equilibrium relation using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) methods. The phase diagrams of RbClZnCl2, CsClZnCl2 and RbClCsCl are thus critically optimized by thermodynamic modeling based on the available experimental values. The associate solution model (ASM) is used to describe the liquid phases of RbClZnCl2 and CsClZnCl2 binary system, and the substitutional solution model (SSM) is applied for the RbClCsCl binary system. All Gibbs energies of intermediate compounds are treated with the Neumann-Kopp rule. In light of this, a set of self-consistent thermodynamic database is obtained and applied to predict the thermodynamic properties of the RbClCsClZnCl2 ternary system by merging the Gibbs energies in its subsystems via the Kohler-Toop interpolation method. These results could provide effective data supporting for the selection and optimization of multi-component molten salts for the concentrating solar power (CSP) plants.

Influence of α-Al2O3 and AlF3 on pyrohydrolysis of Li3AlF6

In this study, Li3AlF6 was employed to simulate the molten salt LiF–BeF2 to explore its pyrohydrolysis behavior and that of its components, i.e., LiF and AlF3, respectively. The influence of the accelerators α-Al2O3 and AlF3 on the pyrohydrolysis of LiF and Li3AlF6 was investigated. Finally, the solid pyrohydrolytic products were characterized by means of X-ray diffraction, and the corresponding reaction mechanisms were proposed. These experimental results indicated that AlF3 was completely hydrolyzed to the corresponding oxide α-Al2O3 at 650 °C in 1 h, whereas the complete hydrolysis of LiF and Li3AlF6 required the assistance of either α-Al2O3 or AlF3 under the same conditions. The influence of the accelerator α-Al2O3 and AlF3 on the pyrohydrolytic behavior of Li3AlF6 provides references for future research studies on the pyrohydrolysis of LiF–BeF2 and multi-component molten salts.

Experimental investigation and thermodynamic modeling of the LiNO3-RbNO3-AgNO3 system and its subsystems

Computational thermodynamics approach based on experimental values is applied to evaluation and optimization of the LiNO3-RbNO3-AgNO3 system and its subsystems in this work. The substitutional solution model (SSM) was used to describe all liquid phase. All the intermediate compounds were treated as stoichiometric of which Gibbs energies comply with the Neumann-Kopp rule. A set of self-consistent database with thermodynamic model parameters obtained for the LiNO3-RbNO3-AgNO3 subsystems and this database were used to predict thermodynamic properties of the LiNO3-RbNO3-AgNO3 ternary system. The calculated results were verified experimentally using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques, and the agreement between the experimental values and predicted values is satisfactory. The phase diagram of the LiNO3-RbNO3-AgNO3 ternary system contain two eutectic types: one eutectic (Liquid ↔ α-AgNO3 + LiRb(NO3)2 + AgRb(NO3)2) at 385.3 ± 1.5 K and another eutectic (Liquid ↔ LiRb(NO3)2 + AgRb(NO3)2 + AgRb2(NO3)3) at 398.8 ± 1.5 K. Through computational thermodynamics approach, a multi-component system was successfully predicted and this approach will be applied to design and develop multi-component molten salt mixtures as thermal energy storage (TES) materials.

Electrochemical Separation of Barium into Liquid Bismuth by Controlling Deposition Potentials

Electrochemical separation of barium from multi-component molten salt electrolyte (BaCl2-LiCl-CaCl2-NaCl) at 500–700°C is demonstrated using a liquid bismuth electrode which possesses strong chemical interactions with barium. While the standard emf analysis suggests Na to be the first species to deposit in this electrolyte followed by Ca, Li, and finally Ba, barium was found to be the first species to be reduced into the bismuth electrode followed by Ca. The exceptional deposition behavior of barium was ascribed to the activity of the constituent alkali/alkaline-earth metals in the bismuth metal. The activity of barium in bismuth was extremely low (as low as 10−15), shifting the redox potential of barium to the most positive potentials and enabling the separation of barium into liquid bismuth. By exploiting the differential interactions of constituent ions with the liquid bismuth, it was possible to separate conventionally non-separable barium species from the electrolyte solution. In addition, high coulombic efficiencies of the liquid bismuth electrode (>99%) suggest that electrode processes are chemically reversible for co-deposition of barium and calcium. The analyses of electrode potentials at various current densities and electrochemical impedance spectra indicate charge transfer as the most significant overpotential mechanism during electrolysis.

Laminar Natural Convection Heat Transfer Characteristics of Molten Salt Around Horizontal Cylinder

Abstract In order to obtain the laminar natural convection heat transfer mechanism of molten salt, the natural convection heat transfer of multi-component molten salts around a cylinder with different diameters was studied by simulation. The result showed that the natural convective heat transfer of molten salt in the Rayleigh number range of 1.57×10-2 -2.03×106 cound be predicted by Fand's correlation that took the viscous dissipation into consideration, in addition to Prandtl and Rayleigh numbers. With the increasing in Rayleigh number, the effect of viscous dissipation decreased, so the other correlations that neglected the effect of viscous dissipation cound also predict the natural convection of molten salt well. Those results cound be a foundation for predicting the natural convection heat transfer of molten salt.

Preparation and Heat Transfer/Thermal Storage Properties of High-Temperature Molten Nitrate Salts

The thermal stability of molten salts, operating temperature range and latent heat of melting for the molten salts at high temperature have been studied in the present investigation. The multi-component molten salts composed of purified potassium nitrate, purified sodium nitrate were prepared by statical mixing method [1]. The stability experiments were carried out at 500 to 600°C, and the experimental result showed that the purified nitrate molten salts performed better high-temperature thermal stability and its optimum operating temperature was increased from 500°C to 550°C. DSC analysis indicated that the purified nitrate molten had a lower melting point and a higher phase change latent heat. The melting point of purified binary nitrate molten salts was sharp decreased to 225.2°C and latent heat of melting for molten salts was also reduced from 78.41J/g to 81.15J/g compared with unpurified nitrate salts. Besides, the change in the concentration of impurities by analyzing in the binary molten salts, and combination of XRD test results can be found that the degree of degradation reduce and improve the thermal efficiency of the storage of binary molten salts by purified sodium nitrate and potassium nitrate.

Preparation and Thermal Properties of High-Purified Molten Nitrate Salt Materials with Heat Transfer and Storage

Abstract This paper focuses on thermal stability of molten salts, operating temperature range and latent heat of molten salts at a high temperature. In this experiment, multi-component molten salts (purified Solar Salt) composed of purified NaNO3 and purified KNO3 were prepared by statical mixing method. Compared with unpurified Solar Salt, purified Solar Salt had a higher thermal stability. The optimal temperature would be increased from 500°C to 550°C, and the upper limitation temperature increases from 577.5°C to 593.7°C. Meanwhile, thermal stability and thermal cycling analysis showed the purified Solar Salt had a lower melting point and the deterioration time of molten salts was reduced. The melting point of purified Solar Salt decreases sharply to 223.8°C and the latent heat increases from 74.39 J/g to 80.79 J/g. Besides, the XRD and chemical analysis test indicated that the degree of degradation reduced and the thermal storage efficiency of purified Solar Salt was improved.

Relating composition, structural order, entropy and transport in multi-component molten salts

Molecular dynamics simulations of the LiF-BeF(2) molten salt mixture are used to establish relationships between composition, structural order, entropy, and transport properties of multi-component ionic liquids. A sharp rise in tetrahedral order associated with formation of the fluoroberyllate network occurs for compositions with BeF(2) concentrations greater than that of the Li(2)BeF(4)-BeF(2) eutectic. The excess entropy of the liquid in this regime, within the pair correlation approximation, is strongly correlated with the local tetrahedral order. The different degree of participation of beryllium, fluorine, and lithium ions in the cooperative dynamics of the fluoroberyllate network can be related to the degree of deviation from Rosenfeld-type excess entropy scaling, with the lithium ions remaining essentially unaffected by the liquid state network. We demonstrate that the deviations from Nernst-Einstein and Stokes-Einstein behaviour emerge only in temperature-composition regimes where tetrahedral order strongly correlates with the pair entropy. Implications for understanding structure-property relationships in other ionic liquids, such as molten salts, oxide melts, and RTILs are considered.

Multicomponent Molten Salt Mixtures Based on Nitrate/Nitrite Anions

Molten salts are a promising medium for thermal energy transfer and storage. They have a very low vapor pressure and most are unreactive in air. Over the past 3 decades, Sandia National Laboratories has investigated a variety of molten salt mixtures of alkali nitrates and, most recently, quaternary mixtures of sodium, calcium, lithium, and potassium nitrate salts. This effort led to the discovery of mixtures with liquidus temperatures below 100°C. We have now extended this work to the mixed nitrate/nitrite anion system and found compositions with liquidus temperatures below 80°C. In this paper, we present experimental results exploring the lithium, sodium, and potassium compositional space with a 1:1 molar mixture of nitrate/nitrite. From our work, we have identified a five-component system with a liquidus temperature near 70°C. Physical properties of these salts, such as viscosity and density, are reported as well as thermal stability in air. Such a molten salt mixture, with a low liquidus temperature, has the potential to make parabolic trough collectors economically competitive with traditional power generation schemes.