Eutectic Molten Salt Research Articles

Experimental and numerical study of heat transfer performance of nitrate/expanded graphite composite PCM for solar energy storage

Eutectic molten salt can be used as the latent thermal energy storage medium in solar energy applications. Nitrates and their binary mixtures are suitable phase change material (PCM) for solar energy applications in middle-temperature-range of 200–300°C. In the present study, binary nitrate (50wt.% NaNO3, 50wt.% KNO3) with a melting temperature of about 220°C was employed as the PCM, and expanded graphite (EG) with the mass fraction of 5%, 10% or 20% was used to enhance the thermal conductivity. The thermal conductivities of pure nitrates and nitrate/EG shape-stabilized composites were measured with a steady-state test rig firstly. Results showed that the addition of EG significantly enhanced the thermal conductivities, e.g., the thermal conductivities of sodium nitrate/20wt.% EG composite PCM were measured to be 6.66–7.70W/(mK) in the temperature range of 20–120°C, indicating about seven times larger than those of pure sodium nitrate. Furthermore, pure binary nitrate and nitrate/EG composite PCM were encapsulated in a cylindrical storage unit with a diameter of 70.0mm and a length of 280.0mm. Heat storage and retrieval tests were conducted extensively at different heating temperatures of 250°C, 260°C and 270°C, and different cooling temperatures of 30°C, 70°C and 110°C. Time-durations from temperature evolutions showed that both the melting and solidification processes were accelerated by EG, and the heat transfer characteristics were interpreted by the numerical analysis based on enthalpy–porosity and volume-of-fluid models. The evolution of nitrate/air interface caused by volume expansion ascended gradually during melting, while that caused by volume shrinkage descended during freezing.

Corrosion Behavior of Eutectic Molten Salt solution on Stainless Steel 316L

The effect of eutectic molten salt on the corrosion behavior of a stainless steel 316L was investigated. To be used as thermal energy storage fluid, low melting point is one of the utmost important thermal properties amongst other. Eutectic salt was defined as a combination of two or more salt at different composition producing lower melting point than of it purest form. Four types of salts, sodium chloride (NaCl), potassium nitrate (KNO3), lithium nitrate (LiNO3), and sodium nitrate (NaNO3) were used to form fifteen mixtures of different composition to be tested on SS316L. The composition based on weight ratio was generated using response surface methodology (RSM). Eutectic composition of molten salt used as thermal energy storage fluid can possibly affect the corrosion occurrences due to the existence of Cl− ion and thereby influence the lifespan of the 316L stainless steel. This study indicates that the compositional different of eutectic mixture significantly affected the lifespan of the 316L stainless steel against corrosion. Two types of approaches are used in describing the corrosion behavior, which are resistance potential, Rp and corrosion rate. After test of 24hours in total immersion condition, 316L stainless samples have developed a scale of corrosion products made up of multiple oxides. Highest proportion of NaCl salt inhibits higher corrosion rate in eutectic molten salt as observed in resistance potential value and corrosion rate. Morphology of the stainless steel SS316L was further investigated under scanning electron microscope (SEM).

Thermal Property of Eutectic Molten Salts by Using Thermogravimetric Analyzer (TGA)

The thermal property of new composition of eutectic molten salt was investigated to obtain low melting point and better stability at temperature of 500°C as heat transfer fluid in solar thermal energy system. The NaCl used was purified from seawater. The eutectic molten salts were prepared in ten different weight ratios and experiments were carried out using nitrogen as inert gas with heating of 10°C/min to the temperature from 25°C to 500°C. Experimental results indicated that all mixtures exhibited low melting point (<163°C) and high stability. The thermal degradation of LiNO3, NaNO3, KNO3 and NaCl exhibit in the DTG profiles respectively. From the present study it can be concluded that major weight loss of the system is due to the dissociation of lithium nitrate to lithium oxides.

Clean and efficient extraction of copper ions and deposition as metal

Abstract A simple, clean and efficient one-pot process is offered as an alternative to the conventional complex processing presently used to extract copper ions from copper containing materials, like copper concentrate or slag, and to form copper metal. The alternative process uses a eutectic molten salt of potassium chloride, sodium chloride and zinc chloride as the reaction fluid which is recyclable, low in cost, environmentally benign, low melting (melting point 204°), high boiling (vapor pressure is only a few psi at 800°) and chemically, thermally and physically stable. The metal completely dissolves out of copper concentrate or slag in the aerobic eutectic molten chloride salt in a graphite or glassy carbon pot, which serves as a cathode, with a graphite anode, to reduce the metal ions to metal which sinks to the bottom of the graphite pot. The total efficiency for extraction and deposition is virtually 100% as determined by elemental and gravimetric analyses.

Mechanical and thermal properties of chemical vapor infiltration engineered 2D-woven and 3D-braided carbon silicate composites

SiCf/SiC composites reinforced with either two-dimensional woven or three-dimensional braided preforms were fabricated by the chemical vapor infiltration (CVI) process. The microstructure, mechanical and thermal properties of the composites were studied. In comparison, the 3D-braided out-performed 2D-woven composites based on the mechanical and thermal properties. The geometry and microstructure determinants of the properties of the composites were investigated. Additionally, we tested how resilient the SiCf/SiC composites were in contact with eutectic molten salt of LiF, NaF and KF to determine whether such materials could function in a molten salt reactor. The molten salt had minimal influence on mechanical properties of SiCf/SiC composites due to the SiC coating blocking the infiltration of molten salt. Our data demonstrated the feasibility of CVI produced SiCf/SiC composites with potential applications in molten salt reactor.

Following the electroreduction of uranium dioxide to uranium in LiCl–KCl eutectic in situ using synchrotron radiation

The electrochemical reduction of uranium dioxide to metallic uranium has been investigated in lithium chloride–potassium chloride eutectic molten salt. Laboratory based electrochemical studies have been coupled with in situ energy dispersive X-ray diffraction, for the first time, to deduce the reduction pathway. No intermediate phases were identified using the X-ray diffraction before, during or after electroreduction to form α-uranium. This suggests that the electrochemical reduction occurs via a single, 4-electron-step, process. The rate of formation of α-uranium is seen to decrease during electrolysis and could be a result of a build-up of oxygen anions in the molten salt. Slow transport of O2− ions away from the UO2 working electrode could impede the electrochemical reduction.

A new strategy for synthesis of lithium zinc titanate as an anode material for lithium ion batteries

Lithium zinc titanate (Li2ZnTi3O8) anode materials have been firstly synthesized via a molten-salt method using 0.38LiOH·H2O–0.62LiNO3 as eutectic molten salts. The effects of sintering temperature and sintering time on the structures and physicochemical properties of the Li2ZnTi3O8 materials are also studied in detail. It is found that Li2ZnTi3O8 obtained by sintering at 700°C for 3h exhibits a typical cubic spinel structure with P4332 space group. Nano-sized particles are presented and the particles are homogeneous for the Li2ZnTi3O8 prepared by sintering at 700°C for 3h. Electrochemical tests demonstrate that the sample possesses large capacities. The largest capacities of 167.8 and 142.4 mAh g−1 are delivered at 2 and 3Ag−1, respectively. 137.8 and 113.3mAhg−1 are kept for the sample at the 100th cycle at the two current densities, respectively. The large discharge specific capacities may be attributed to the good crystallinity, small particle size and low charge-transfer resistance of Li2ZnTi3O8.

Heat transfer characteristics of a molten-salt thermal energy storage unit with and without heat transfer enhancement

Eutectic molten salt can be used as the latent thermal energy storage (LTES) medium in solar energy applications. In the present study, eutectic salt (50wt% NaNO3, 50wt% KNO3) with a melting temperature of about 220°C was employed as the PCM for the middle-temperature solar energy application, which can be powered by the parabolic-trough solar collector using oil as the heat transfer fluid. There are many LTES units in which the molten salt is encapsulated in the thermal energy storage tank, where the heat transfer characteristic of the LTES unit is very important for the overall performance of the entire thermal energy storage tank. We experimentally and numerically investigated the heat transfer characteristics of the molten-salt in a LTES unit with and without heat transfer enhancement. Various heating temperatures of 240°C, 250°C, and 260°C and cooling temperatures of 30°C, 70°C, and 110°C were employed in the study, so as to extensively reveal the heat transfer characteristics during heat storage and retrieval. It was found that natural convection was very dominant during heat storage in the case of pure molten-salt, especially when the heating temperature was higher, and it was weakened in the case of molten-salt with metal foam; while the heat retrieval process was enhanced by the presence of the metal foam. The numerical results were compared with the experimental results, showing reasonable agreement, which indicated that such numerical model could be used for the further study of the performance of the LTES system.

Influence of zirconia particle size on the synthesis of CaZrO3 nano-powders from Na2CO3–NaCl molten eutectic salt

Nano-particles of CaZrO3 were successfully synthesized at 850°C using the molten-salt method, and the influence of using nano-size ZrO2 on formation of CaZrO3 was investigated. CaCO3, Na2CO3, NaCl, nano-ZrO2 and micro-ZrO2 were used as starting materials. On heating, Na2CO3–NaCl molten eutectic salt provided a liquid medium for reaction of CaCO3 and ZrO2 to form CaZrO3. The results demonstrated that in both nano and micro-ZrO2 inclusive samples, CaZrO3 started to form at about 750°C and that, after the temperature was increased to 1050°C, the amounts of CaZrO3 in the resultant powders increased with a concomitant decrease in CaCO3 and ZrO2 contents. After washing with hot-distilled water, the samples containing nano and micro-ZrO2 heated for 4h at 850°C and 1050°C, were single-phase CaZrO3 with 90–95nm and 400–500nm particle size, respectively. Furthermore, the synthesized CaZrO3 particles retained the size and morphology of the ZrO2 powders, which indicated that a template formation mechanism dominated the formation of CaZrO3 by molten-salt synthesis.

The effects of processing parameters on molten salt synthesis of CaZrO3 nano-powders using oxide precursors

Nano-powders of CaZrO3 were successfully synthesized at 650°C using the molten-salt method, and the effects of processing parameters, such as temperature, holding time and amount of salt on the crystallization of CaZrO3 were investigated. CaCl2, LiCl, CaCO3 and nano-ZrO2 were used as starting materials. On heating, CaCl2–LiCl molten eutectic salt provided a liquid medium for reaction of CaCO3 and ZrO2 to form CaZrO3. The results demonstrated that CaZrO3 started to form at about 550°C and that, after the temperature was increased to 1000°C, the amounts of CaZrO3 in the resultant powders increased with a concomitant decrease in CaCO3 and ZrO2 contents. After washing with hot-distilled water, the samples heated for 3h at 650°C were single-phase CaZrO3 with 90–95nm particle size. Furthermore, the synthesized CaZrO3 particles retained the size and morphology of the ZrO2 powders, which indicated that a template formation mechanism dominated the formation of CaZrO3 by molten-salt method.

Corrosion resistance of Hastelloys in molten metal-chloride heat-transfer fluids for concentrating solar power applications

Corrosion rates have been estimated for commercial Hastelloys C-276, C-22 and N types in eutectic molten salts containing NaCl, KCl and ZnCl2 using steady-state potentiodynamic method (0.2mVs−1 within ∼±30mV from the open circuit voltage). Hastelloy C-276 exhibited the lowest corrosion rates of ∼10 and 40μm per year in 13.4NaCl–33.7KCl–52.9ZnCl2 (mol%) salt at 250 and 500°C, respectively. The potentiodynamic method was validated by conducting traditional immersion test for corrosion rate estimation on C-276 Hastelloy in 13.4NaCl–33.7KCl–52.9ZnCl2 (mol%) at 500°C (corrosion rate ∼50μm per year). Among the samples evaluated, Hastelloy N showed highest corrosion rate of >150μm per year at 500°C.

Molten salt synthesis and electrochemical properties of LiNi1/3Co1/3Mn1/3O2 cathode materials

LiNi1/3Co1/3Mn1/3O2 cathode materials were synthesized by molten salt method. The preparation was performed by sintering the mixture of Ni1/3Co1/3Mn1/3(OH) 2 and the eutectic molten salts 0.76LiOH·H2O-0.24Li2CO3 at 750–900°C for 2–11h. The prepared particles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge test. XRD analysis shows the molten salt method can enhance the ordering degree of the layered structure and reduce the cation mixing of LiNi1/3Co1/3Mn1/3O2 compounds. The sample prepared at 850°C for 5h exhibits an excellent electrochemical performance. It can deliver an initial discharge capacity of 175.6mAhg−1 at a current density of 16mAg−1 between 2.8 and 4.4V, and a capacity of 156.7mAhg−1 is retained after 2, 10, 20 and 20 cycles at the corresponding current density of 16mAg−1, 32mAg−1, 80mAg−1 and 160mAg−1, respectively. At a current density of 320mAg−1 followingly, it still exhibits a capacity of 150.5mAhg−1 after 20 cycles. The electrochemical impedance shows the charge–discharge process of electrode is controlled by the lithium ion diffusion. It is concluded that the molten salt synthesis can substantially reduce the calcination temperature and shorten the soaking time.

The effects of processing parameters on molten salt synthesis of CaZrO3 nanopowders using oxide precursors

Nanoparticles of CaZrO3 were successfully synthesized at 850°C using the molten-salt method, and the effects of processing parameters such as temperature, holding time and amount of salt on the crystallization of CaZrO3 were investigated. CaCO3, Na2CO3, NaCl and nano-ZrO2 were used as starting materials. On heating, Na2CO3–NaCl molten eutectic salt provided a liquid medium for reaction of CaCO3 and ZrO2 to form CaZrO3. The results demonstrated that CaZrO3 started to form at about 750°C and that, after the temperature was increased to 1000°C, the amounts of CaZrO3 in the resultant powders increased with a concomitant decrease in CaCO3 and ZrO2 contents. After washing with hot distilled water, the samples heated for 4h at 850°C were single-phase CaZrO3 with 90–95nm particle size. Furthermore, the synthesized CaZrO3 particles retained the size and morphology of the ZrO2 powders, which indicated that a template formation mechanism dominated the formation of CaZrO3 by the molten-salt method.

Influence of different raw materials on molten salt synthesis of nano-CaZrO3 using oxide precursors

Nanoparticles of CaZrO3 were successfully synthesized at 850°C using the molten-salt method, and the influence of different raw materials on the formation of CaZrO3 was investigated. CaCO3, Na2CO3, NaCl, nano-ZrO2 and micro-ZrO2 were used as starting materials. On heating, Na2CO3–NaCl molten eutectic salt provided a liquid medium for the reaction of CaCO3 and ZrO2 to form CaZrO3. The results demonstrated that in both nano- and micro-ZrO2 inclusive samples, CaZrO3 started to form at about 750°C and that, after the temperature was increased to 1050°C, the amount of CaZrO3 in the resultant powders increased with a concomitant decrease in CaCO3 and ZrO2 contents. After washing with hot-distilled water, the samples containing nano- and micro-ZrO2 heated for 4h at 850°C and 1050°C were single-phase CaZrO3 with 90–95nm and 400–500nm particle size, respectively. Furthermore, the synthesized CaZrO3 particles retained the size and morphology of the ZrO2 powders, which indicated that a template formation mechanism dominated the formation of CaZrO3 by molten-salt synthesis.

Low temperature synthesis of CaZrO3 nanopowders from CaCl2–NaCl molten eutectic salt

Nano-particles of CaZrO3 were successfully synthesized at 700°C using the molten-salt method, and the effects of processing parameters, such as temperature, holding time and amount of salt on the crystallization of CaZrO3 were investigated. CaCl2, Na2CO3, and nano-ZrO2 were used as starting materials. On heating, CaCl2–NaCl molten eutectic salt provided a liquid medium for reaction of CaCO3 and ZrO2 to form CaZrO3. The results demonstrated that CaZrO3 started to form at about 600°C and that, after the temperature was increased to 1000°C, the amounts of CaZrO3 in the resultant powders increased with a concomitant decrease in CaCO3 and ZrO2 contents. After washing with hot-distilled water, the samples heated for 3h at 700°C were single-phase CaZrO3 with 90–95nm particle size. Furthermore, the synthesized CaZrO3 particles retained the size and morphology of the ZrO2 powders, which indicated that a template formation mechanism dominated the formation of CaZrO3 by the molten-salt method.

Purification of used eutectic (LiCl–KCl) salt electrolyte from pyroprocessing

The separation characteristics of surrogate rare-earth fission products in a eutectic (LiCl–KCl) molten salt were investigated. This system is based on the eutectic salt used for the pyroprocessing treatment of used nuclear fuel (UNF). The investigation was performed using an integrated rare-earth separation apparatus comprising a precipitation reactor, a solid detachment device, and a layer separation device. To separate rare-earth fission products, a phosphate precipitation method using both Li3PO4 and K3PO4 as a precipitant was performed. The use of an equivalent phosphate precipitant composed of 0.408 molar ratio-K3PO4 and 0.592 molar ratio-Li3PO4 can preserve the original eutectic ratio, LiCl-0.592 molar ratio (or 45.2wt%), as well as provide a high separation efficiency of over 99.5% under conditions of 550°C and Ar sparging when using La, Nd, Ce, and Pr chlorides. The mixture of La, Nd, Ce, and Pr phosphate had a typical monoclinic (or monazite) structure, which has been proposed as a reliable host matrix for the permanent disposal of a high-level waste form. To maximize the reusability of purified eutectic waste salt after rare-earth separation, the successive rare-earth separation process, which uses both phosphate precipitation and an oxygen sparging method, were introduced and tested with eight rare-earth (Y, La, Ce, Pr, Nd, Sm, Eu and Gd) chlorides. In the successive rare-earth separation process, the phosphate reaction was terminated within 1h at 550°C, and a 4–8h oxygen sparging time were required to obtain over a 99% separation efficiency at 700–750°C. The mixture of rare-earth precipitates separated by the successive rare-earth separation process was found to be phosphate, oxychloride, and oxide. Through the successive rare-earth separation process, the eutectic ratio of purified salt maintained its original value, and impurity content including the residual precipitant of purified salt can be minimized.

The effects of processing parameters on molten salt synthesis of CaZrO3 nano powders using oxide precursors

Nano-particles of CaZrO3 were successfully synthesized at 850°C using the molten-salt method, and the effects of processing parameters, such as temperature, holding time and amount of salt on the crystallization of CaZrO3 were investigated. CaCO3, Na2CO3, NaCl and nano-ZrO2 were used as starting materials. On heating, Na2CO3-NaCl molten eutectic salt provided a liquid medium for reaction of CaCO3 and ZrO2 to form CaZrO3. The results demonstrated that CaZrO3 started to form at about 750°C and that, after the temperature was increased to 1000°C, the amounts of CaZrO3 in the resultant powders increased with a concomitant decrease in CaCO3 and ZrO2 contents. After washing with hot- distilled water, the samples heated for 4h at 850°C were single- phase CaZrO3 with 90–95nm particle size. Furthermore, the synthesized CaZrO3 particles retained the size and morphology of the ZrO2 powders, which indicated that a template formation mechanism dominated the formation of CaZrO3 by molten-salt method.

Cyclic Voltammetric Experiment - Simulation Comparisons of the Complex Mechanism Associated with Electrochemical Reduction of Zr4+ in LiCl-KCl Eutectic Molten Salt

Nuclear energy increasingly represents an important option for generating largely clean CO2-free electricity and zirconium is a fission product that is expected to be present in irradiated fuels. The present investigation addresses the electrochemical reduction of Zr4+ to Zro in LiCl - KCl eutectic molten salt in the temperature range 425–550°C using cyclic voltammetry (CV), square-wave voltammetry (SWV) and bulk electrolysis. Simulations of the CV data indicate that the initial reduction proceeds through surface confined steps: Zr4+* + 2e− ↔ Zr2+* and Zr2+* + 2e− ↔ Zr* processes (* adsorbed species) followed by a peak-shaped complex diffusion controlled step that consists of a combination of closely spaced processes associated with the reactions Zr4+ + 4e− → Zro and Zr4+ + 3e− → Zr+*. Zr+*, probably in the form of ZrCl* is then further reduced to Zro* at even more negative potentials. The simulations provide the first quantitative analysis of the thermodynamics and kinetics of the Zr4+ reduction in the LiCl-KCl eutectic.

Catalytic oxidation of methane on KCl-MClx (M = Li, Mg, Co, Cu, Zn) eutectic molten salts

The partial oxidation of methane (POM) was studied over eutectic potassium chloride molten salts of the type KCl-MClx (M=Li, Mg, Co, Cu, Zn). The catalytic performance is clearly different and depends on the metal M. The reaction products were CO, CO2, C2 (C2H4, C2H6), C3 (C3H6, C3H8) and C4 (C4H10). The formation of hydrogen was never detected. The best results for the formation of hydrocarbons were those obtained over the potassium–copper molten salt (KCl-CuCl2, Sel. ≥80%) whereas, on the contrary, over KCl-ZnCl2 the formation of CO2 is always dominant. The addition of CeCl3 to KCl-CuCl2 leads to higher conversion of methane and higher selectivity to hydrocarbons. To explain such results, the molten salts liquid phase specificities, namely ion mobility, melting point and redox properties were taken into account. To the best of our knowledge, it is the first time that high selectivities to hydrocarbons are reported over molten salt catalysts.

The effects of raw materials particle size and salt type on formation of nano-CaZrO3 from molten salts

Nano-CaZrO3 was successfully synthesized at 800°C using the molten-salt method, and the effects of salt type and raw materials particle size on the formation of CaZrO3 were investigated. Na2CO3, CaCl2, nano-ZrO2 and micro-ZrO2 were used as starting materials. On heating, Na2CO3 reacted with CaCl2 to form NaCl and in situ CaCO3. Na2CO3–NaCl molten eutectic salt provided a liquid medium for reaction of CaCO3 and ZrO2 to form CaZrO3. The results demonstrated that in both nano- and micro-ZrO2 inclusive samples, CaZrO3 started to form at about 700°C and that, after the temperature was increased to 1000°C, the amounts of CaZrO3 in the resultant powders increased with a concomitant decrease in CaCO3 and ZrO2 contents. After washing with hot-distilled water, the samples containing nano- and micro-ZrO2 heated for 3h at 800°C and 1000°C, were single-phase CaZrO3 with 70–90nm and 400–450nm particle size, respectively. Also, the synthesis process was completed in lower temperatures using eutectic salts. Furthermore, the synthesized CaZrO3 particles retained the size and morphology of the ZrO2 powders, which indicated that a template formation mechanism dominated the formation of CaZrO3 by molten-salt synthesis.