Binary Molten Salt Research Articles

Innovative and cost-effective nanodiamond based molten salt nanocomposite as efficient heat transfer fluid and thermal energy storage media

Novel and efficient molten salt nanocomposites as heat transfer nano-fluids and thermal energy storage materials have been developed. Cost-effective detonation nanodiamonds (NDs) of an average particle size of 10 nm were uniformly dispersed in binary nitrate molten salt using the ultrasonication process to achieve well dispersion of NDs. NDs mass loadings were varied and optimized, furthermore, the optimized mass loading of NDs was dispersed using solid state method for comparison. The thermo-physical properties of the developed ND-molten salt nanocomposites were studied in terms of melting point temperature, thermal stability temperature, thermal conductivity, volume heat capacity and thermal diffusivity and were enhanced in terms of their applications as heat transfer nano-fluids and thermal energy storage media. Therefore, melting point was reduced by 16 °C and the thermal stability was improved by 35 °C displayed enhanced temperature range compared to base binary molten salt. On other hand, the thermal conductivity and volume heat capacity were significantly improved achieving enhancement by 93 and 38% respectively, compared to base binary molten salt. Furthermore, the thermal diffusivity of developed ND based molten salt was enhanced by 43% compared to blank molten salt recorded superior values among reported nano-fluids. The surface morphology and dispersion of NDs in binary nitrate molten salt was studied and visualized using SEM and TEM.

Binary molten salts mediated defect engineering on hexagonal boron nitride catalyst with long-term stability for aerobic oxidative desulfurization

Molten salts mediation is a potential strategy for the development of functional materials. Herein, a controllable defect engineering on the hexagonal boron nitride (h-BN) was approached via the binary molten salts (BMS) mediated strategy. The as-synthesized h-BN catalyst had a high crystalline structure with adequate nitrogen-terminated defects, which can work as the reactive sites for the adsorption and activation of molecular oxygen in the aerobic oxidative desulfurization of fuel. These reactive sites on the high crystalline h-BN catalyst showed outstanding stability with only a 1% loss of activity after continuous operation for 120 h. Moreover, the induced number of defects in the high-crystalline h-BN varied with the melting point of BMS, which could be simply modulated by adjusting its binary composition. Thus, via adjusting the melting temperature of BMS close to the eutectic point, a defective high-crystalline h-BN was optimized as the high-performance catalyst, achieving 96% of sulfur conversion in the aerobic oxidation of refractory aromatic sulfur compounds, and remaining active after 15 times of the recycling experiment. This work provides a new approach for the controllable synthesis of high-performance h-BN in the mediation of molten salts.

Experimental research on latent heat characteristics of binary mixed molten salt

At present, thermal storage is considered as one of the key technologies to alleviate the problem of instability and intermittence for renewable energy. Due to relatively high latent heat, latent heat storage by molten salt is considered to a potential technology. Because of the restriction of different thermophysical parameters, the application of latent heat storage by molten salt has many technical obstacles. So, it is an urgent work to find a better mixed molten salt formula with comprehensive thermophysical properties. In this paper, we selected halogen salts (NaCl, NaF) and alkali (NaOH) to prepare binary mixed molten salts. From the results, for the mixed molten salt of NaCl-NaOH, NaCl:NaOH=1:9 has a maximum latent heat value of 301.2J/g. The initial melting temperature is about 200°C. With the increase of the mass ratio of NaCl, the termination melting temperature increases firstly then decreases. For mixed molten salt of NaF-NaOH, NaF:NaOH=1:9 has a maximum latent heat value of 199.5J/g, the initial and termination melting temperatures are about 265°C and 380°C, repectively. The latent heat value of NaCl-NaOH and NaF-NaOH mixed molten salts decreased with the increase of the mass ratio of halogen salts.

A low-charge-overpotential lithium-CO2cell based on a binary molten salt electrolyte

A eutectic molten mixture was introduced to Li-CO2 battery as electrolyte to realize a low charge overpotential and better reversibility. The overall performance could be further promoted by ruthenium catalyst.

Detoxification and Recovery of Spent Carbon Cathodes via NaOH–Na2CO3 Binary Molten Salt Roasting–Water Leaching: Toward a Circular Economy for Hazardous Solid Waste from Aluminum Electrolysis

The conversion of solid waste into secondary resources has become a prerequisite for the sustainable development of the industry. This study focused on the development of the detoxification process for spent carbon cathode (SCC) without environmental pollution risks and the exploration of the recycling direction of recovered carbonaceous materials. First, the mechanism of thermodynamic conversion and decomposition of toxic substances was explored. Parameters of NaOH–Na₂CO₃ binary molten salt roasting were optimized through an orthogonal design and a single-factor experiment, and gas release behavior during detoxification treatment was investigated. Results showed that most of the fluoride and cyanide were dissociated and decomposed, and the leaching concentration of fluoride and cyanide was as low as 7.58 and 0.12 mg/L after detoxification treatment, respectively. Then, a multistage recovery process of fluorine from fluorine-containing leachate was designed, and the comprehensive utilization of exhaust gas and the recycling of the reaction reagent were realized simultaneously. The possibility of recovering graphitized carbon blending to prepare carbon anodes was discussed in detail, and the catalytic mechanism of main impurity elements on the O₂/CO₂ reactivity of carbon anodes was investigated via density-functional-based tight binding (DFTB). The results showed that the Boudouard reaction and carbon–O₂ reaction were affected because of the presence of Ca or Na, and the recovered graphitized carbon with a low blending ratio was more suitable for the preparation of carbon anodes. Finally, an economic benefit analysis was conducted to evaluate the industrial application potential of the proposed detoxification treatment. Compared with landfills, the proposed process reduced the disposal cost while eliminating environmental pollution risks and realized the on-site recovery and reuse of valuable components, showing considerable environmental and economic benefits.

Thermal energy storage characteristics of binary molten salt nanofluids: Specific heat and latent heat

This study aims to examine the thermal energy storage characteristics, in terms of specific heat and latent heat, of nanoparticle-doped binary molten salt nanofluids. Two different binary molten salt mixtures, namely carbonate salts (Li2CO3 and K2CO3) and nitrate salts (NaNO3 and KNO3), were used as base solvents. Graphite nanoparticles were dispersed into the salt mixtures. The chemical compositions (molar fractions) of the two salt components were varied from hypoeutectic to hypereutectic, including eutectic compositions, to investigate their effects on the specific heat and latent heat of both the pure salts and their nanofluids. The specific heat of the carbonate salt nanofluid was enhanced, irrespective of the chemical composition, and the enhancement was proportional to the nanoparticle concentration. However, the specific heat of the nitrate salt nanofluid was decreased by the addition of 0.1 wt% of graphite nanoparticles and increased by the addition of a larger amount of 1 wt%. The latent heat of the nanofluids was enhanced by doping nanoparticles into the salt mixtures and was affected by the chemical composition of the solvent salt mixtures. The distinct behaviors of specific heat and latent heat obtained in this study were discussed based on a compressed liquid (solid-like) layer formed near the nanoparticles. The thermal energy storage capacities of the nanofluids were estimated and compared by using their specific heat and latent heat.

Preparation and Electrochemical Properties of Ambient Temperature Molten Chlorides Based on Quaternary Ammonium Chloride and MgCl2

The research and development of magnesium secondary batteries using magnesium anode have been attracted much attention as one of the prospective post-lithium ion batteries due to the high theoretical capacity (3830 Ah/dm3) and without no resource constraints. However, it has been quite difficult to construct the magnesium batteries because practical electrolytes for the battery has not yet been developed.We previously reported that TFSA-based ILs were not suitable for a Mg anode even in alkali metal binary molten salt such as MgTFSA2-KTFSA, which indicated that the existence of the TFSA anion disturbed a magnesium redox on Mg electrodes. [1] On the other hand, relatively smooth magnesium redox could be observed in 1-butyl-3-methylimidazolium chloride melts containing Mg[TFSA]2. [2] However, the electrochemical window of the imidazolium melt was limited by the reduction decomposition of the imidazolium.In this study, we reported that ambient temperature molten chlorides could be obtained by mixing a quaternary ammonium chloride and MgCl2, which did not contain the TFSA anion and also imidazolium cations. The thermal properties and also physicochemical properties were investigated. The electrochemical response of a magnesium metal in the melt were also shown to indicate the possibility as an electrolyte for a magnesium anode battery.[1] K. Kubota, H. Matsumoto, J. Electrochem. Soc., 167 (2020) 020541.[2] H. Matsumoto, K. Kubota, ECS Transactions, 86(14) (2018) 21.

Low-melting-temperature binary molten nitrate salt mixtures for solar energy storage

Thermal analysis of the binary system (Al(NO3)3)–(Cu(NO3)2) of different ratios was performed by using differential scanning calorimetry and thermogravimetric analysis. The eutectic temperature of the binary salt mixture was determined to be 65 °C. Moreover, the degradation temperature, specific heat, latent heat of fusion and thermal stability were reported, respectively. Further, this work focuses on synthesising low-temperature salt mixtures comprised of aluminium nitrate non-hydrate (Al(NO3)3) and copper nitrate hydrate (Cu(NO3)2) of varying compositions (60:40, 50:50, 55:45 and 57.5:42.5), respectively, which are optimised using Design of Expert v13. The performance of the binary salt mixture was determined from the results obtained from thermal stability measurements after the exposure of salt mixture to 120 h at a higher temperature. The results showed that the novel binary molten salt mixtures exhibit decomposition at 215 °C and the latent heat was found to increase from 17.7 to 20.73 J g−1 with the increase in aluminium nitrate composition with excellent repeatability after three sets of experiments. The average specific heat of binary molten salt mixture was observed from 2.73 to 2.13 J g−1 K−1. The optimal molar ratio of binary molten salts is found to be 60:40 (Al/Cu) from the obtained results. Field emission scanning electron microscopy and energy-dispersive X-ray showed a uniform distribution of both the salts in the mixture. The average specific heat of the optimal molar ratio was 21.8% higher compared to other molar ratios, indicating the most promising material to be used in solar applications.

Experimental Assessment of a Novel Eutectic Binary Molten Salt-based Hexagonal Boron Nitride Nanocomposite as a Promising PCM with Enhanced Specific Heat Capacity

In this study, novel nanocomposites containing the pre-defined mass ratio of binary molten salt (NaNO3-KNO3: 60-40 wt. %) dispersed with hexagonal boron nitride (hBN) nanoparticles with nominal size of 70 nm, were prepared through one-phase preparation method. Four different types of samples including pure binary molten salt and binary molten salt-based hBN nanocomposites with loading concentrations of 0.5, 1 and 1.5 wt. % were prepared. The proposed amount of sodium nitrate and potassium nitrate was added to certain amount of DI water, comprising with 0.5, 1 and 1.5 wt. % concentration of hBN nanoparticles. Scanning electronic microscopy (SEM) was conducted to evaluate the uniformity of the synthesized binary molten salt-based hBN nanocomposites. The SEM images revealed uniform dispersion of hexagonal boron nitride nanoparticles and fractal-like structures were observed clearly. Specific heat capacity (cp) and melting temperature measurements were performed using a differential scanning calorimetry (DSC). The experimental achieved data for melting temperature proved that hexagonal boron nitride nanoparticles do not affect the melting temperature of the synthesized nanocomposites. The experimentally achieved data for the average cp values of the binary molten salt in solid and liquid phases were 1.14 and 1.13 J/g K, respectively. While, the average cp values for the binary molten salt-based hBN nanocomposite with the highest loading concentration of nanoparticles (1.5 wt. %) in solid and liquid phases were 2 and 3.17 J/g K, respectively. The measured average cp value in the liquid phase for binary molten salt-based hBN nanocomposite with the highest loading concentration (1.5 wt. %) of nanoparticles revealed enhancement of ~180% in comparison with pure binary molten salt. Thermal stability measurements expressed enhancement of thermal stability in binary molten salt induced with hBN nanoparticles. Binary molten salt-based hBN nanocomposite with loading concentration of 1.5 wt. % represented ~16% enhancement in thermal stability over the binary molten salt.

Enhanced heat conduction in molten salt containing nanoparticles: Insights from molecular dynamics

The addition of nanoparticles is a promising strategy to manipulate the thermal transport property of molten salt, which is an important thermal energy storage material for concentrating solar power. The molecular dynamics simulations have been conducted to investigate the mechanisms of enhanced heat transfer in binary molten salt based nanocomposite with nonmetallic nanoparticle SiO2. The results show that the thermal conductivity of molten salt is increased by introducing nanoparticles, which is up to 54.5% increase under 10%wt. loading of SiO2 nanoparticle. Moreover, the thermal conductivity increases as the nanoparticle loading rises. To elucidate the underlying mechanisms for the enhancement of thermal conductivity, the mean square displacement and size effect of nanoparticle, the structure and density of the ordered layer were analyzed. It is found that the possible mechanisms, including the Brownian motion of nanoparticle, the micro-convection of base fluid, and the ordered layer at the solid-liquid interface, for enhanced heat transfer proposed in previous literatures cannot explain the change in thermal conductivity of molten salt. The increment in thermal conductivity can be attributed to the improved probability and frequency of ion collision, as evidenced by the change of potential energy. The present findings verify the applicability for the molten salt-nanoparticle composite, moreover, highlight the correlation between the potential energy and the enhancement of thermal conductivity, which may provide guidance on the chosen of materials and design of the molten salt-nanoparticle composite.

The promotional effect of sodium chloride on thermophysical properties of nitrate

Nitrate are the excellent phase change materials (PCMs) for thermal energy storage. Nitrate has no phase separation during phase transition and has good chemical stability. The present study concentrates on improving the latent heat of phase change and of heat absorption rate by adding various proportions NaCl into the nitrate/mixed nitrate. Sodium nitrate and sodium chloride were selected to prepare binary mixture by static melting method. The melting point and latent heat of phase change were measured by differential scanning calorimetry (DSC). Compared with pure sodium nitrate, the melting point and solidification point of binary molten salt containing 5% NaCl are reduced by 9°Cand 16°C, respectively. On the other hand, the latent heat of melting and solidification increased by 12J/g and 10J/g, respectively.

Influence of preparation processes on thermophysical properties of molten salt

Molten salt has been widely studied as a heat storage material, but some properties of molten salt reported in different literature studies are not completely consistent. In order to make data comparison more convenient and improve the effectiveness of scientific research communication, reasons for the data discrepancy were studied. In this work, the relationship between the preparation of NaNO3–KNO3 binary molten salt and thermophysical properties was studied. Six preparation methods including static melting method, dissolution method, stirring evaporation method, boiling evaporation method, tap water dissolution method, and grinding method were adopted. The thermophysical properties studied include melting range, latent heat, and decomposition temperature. The experimental results show that all the above methods can be used to prepare NaNO3–KNO3 molten salt with good thermophysical properties except for the dissolution method, which would lead to uneven distribution of compositions. For the grinding method, it is found that the properties of molten salt are stable when the particle size is less than 96 µm. Samples prepared by these feasible methods have a melting point range of 220–240 °C. Their latent heat is more than 100 J/g and the decomposition temperature up to ∼580 °C. Thermal properties are affected to some extent by the preparing process, such as impurities in the solvent or the drying process.

РОЛЬ КОМБІНОВАНИХ СОЛЬОВИХ РОЗПЛАВІВ У СИНТЕЗІ ПОДВІЙНОГО ОРТОФОСФАТУ НАТРІЮ-ЦЕРІЮ(ІІІ)

The efficient crystallization conditions for high temperature synthesis of sodium-cerium(III) orthophosphate from binary molten salts have been investigated in a light of influence of the inert reaction media addition. Taking into consideration NaF and Na2MoO4 as an addictives to a convention phosphate melt the crystallization regions of CePO4 and Na3Ce(PO4)2 have been identified by means of IR spectroscopy and powder X-Ray diffraction methods. The initial Na/P ratio in the melt has been shown to play the key role in pure Na3Ce(PO4)2 phase formation. The concentration of NaF has been chosen as 20–60 mol. % and MoO3 in a range of 30–60 mol. %, while the cerium(III) content has been maintained equal to 10 mol. %. Additional application of NaF or Na2MoO4 lowers the temperature from 1400 in comparison to Na4P2O7 flux to 1000°C and homogenization time from 12 to 1h., respectively. Thus, the optimal conditions for the high-temperature growth has been found to be Na/P = 1.67 and NaF content equal to 30–45% mol. in case of fluoride-containing systems, and Na/P> 4,00 with MoO3 content of 25–36% mol for a molybdate one. In case of both fluoride and molybdate addition the crystallization region of the target compound has been bordered by a wide area of CePO4 phase. Three crystallization regions has been estimated during crystallization process: CePO4, Na3Ce(PO4)2 and a wide field of their co-crystallization. With Na/P ratio in the binary melt there is a simultaneous change in the solids structure prepared. Thus, when CePO4 possesses highly condensed CeO8 polyhadra in the framework and crystallizes at lower Na/P ratio, Na3Ce(PO4)2 corresponds to isolated CeO8 moieties that are stabilized under higher Na/P values. Within the synthetic conditions investigated, the melts have shown to play a depolymerizing role for the phosphate chains found in the melt, leading to crystallization temperature lowering in initial melt. The approach proposed for the of Na3Ce(PO4)2 synthesis allows to expand the temperature range of its formation and to carry out its uniform doping with fluorescent activators to modify its characteristic spectrum for the needs of modern inorganic LEDs.

Low-Temperature Preparation of α-Si3N4 Powder via Combined High-Energy Ball Milling and Molten Salt Nitridation Method

In this work, α-Si3N4 powder was synthesized by a combined high-energy ball milling and molten salt nitridation method using silicon powder as raw materials, and NaCl-NaF binary molten salt as reaction medium and diluents. The effects of nitridation temperature, soaking time, and NaF content in the molten salt on the formation of α-Si3N4 were investigated. The results show that the nitridation of silicon powder was completed at NaF content of 10wt% in the molten salt after nitridation at 1200°C and held for 4 h. The α-Si3N4 content in the as synthesized powder is 96wt%. The α-Si3N4 whiskers with 40-280 nm in diameter and several microns to tens of microns in length appear in the final products. The crystal growth process of α-Si3N4 whiskers follows vapor-crystal (VC) mechanism.

Preparation of Two-dimensional Ti2CTx by Molten Fluorinated Salt Method

We prepared a two-dimensional transition metal carbide Ti2CTx by treatment of Ti2AlC in molten fluoride salt. Two fluorinated salt systems were used to etch Al from Ti2AlC powder precursor under the argon atmosphere, and then the resulting MXene was delaminated with TBAOH to produce few-layered nanosheets of Ti2CTx. The reaction was undergone at different temperatures to study the effect of temperature. The results show that the optimal reaction temperature is 600 °C in LiF-NaF-KF system, and 850 °C in NaFKF system. The molten salt treated products are delaminated and quasi-2D MXene sheets can be obtained. The thickness of the MXene sheets prepared from the binary molten salt system is smaller than that of the ternary molten salt system.

Experimental investigations on the thermal properties of binary molten salt based AlN nanofluids for high temperature applications

Typical binary nitrate (NaNO3-KNO3 as 60:40 rat io by weight) based AlN nanofluid was prepared by a two-step solutionmethod. The specific heat capacities of nanofluids with AlN amount ranging from 0.5 to 4 wt. % were investigated. The results suggest a good compatibility between AlN and molten binary nit rates. Meanwhile, AlN nanoparticles are proved to be an effective additive in improving the thermal properties of binary nitrates. For binary nitrate-based materials, samples with AlN amount as 1 wt. % shows the best thermal enhancement of specific heat capacity.

Experimental study on the effect of SiO2 nanoparticle dispersion on the thermophysical properties of binary nitrate molten salt

Molten salts, good heat transfer and thermal storage media, show potential for various applications, particularly solar thermal power. Nanofluid technology has been applied to molten salts to improve specific heat. In this study, molten salt nanofluids with a base solution of binary molten salt and SiO2 nanoparticles were prepared through high-temperature melting. The specific heat of the molten salt nanofluids was examined with different diameters and mass fractions of nanoparticles, and their optimal diameter and mass fraction were determined. The thermophysical properties of the optimized molten salt nanofluids were experimentally tested and compared with those of pure molten salt. Results reveal that the specific heat of the molten salt nanofluids is higher than that of the pure molten salt. The optimal mass fraction and size of SiO2 nanoparticles at the improved specific heat of the molten salt nanofluids are 1% and 20 nm, respectively. The optimal specific heat of the molten salt nanofluids is 17.8% more than that of the pure molten salt. The density of the optimized molten salt nanofluids is similar to that of the pure molten salt, and the average thermal conductivity is 20.2% more than that of the pure molten salt.

Effect of Chloride Ions on Electrochemical Behaviors of Magnesium Anode in Ionic Liquids Based on TFSA-

Cyclic voltammetry was conducted in various binary molten salts such as K-Mg-Cl, Cs-Mg-Cl, K-Mg-NO3, K-Mg-TfO (TfO−: trifluoromethansulfonate), K-Mg-TFSA (TFSA−, bis(trifluoro-methanesulfonyl)amide) and [C4mim]-Mg-Cl ([C4mim]+, 1-butyl-3-methyl-imidazolium chloride ). Based on the results, it was found that Cl− was essential for a smooth magnesium redox as an anode. The redox potential of a magnesium electrode in a chloride containing IL ([C4mim]0.6Cl0.4[TFSA] + 0.25 mol dm-3 Mg[TFSA]2) was estimated to be located at the theoretical redox potential for magnesium (= +0.7 V vs Li/Li+) by using the redox of the potential of ferrocene observed in the same ILs.

Thermodynamic and phase diagram modeling of CsF-MF4(M=U, Th) systems

Phase diagrams for the CsF-UF4 and CsF-ThF4 systems were modeled in the present work through computational thermodynamics. The associate solution model with various complex species(CsMF5, Cs2MF6 and Cs3MF7; M=Th, U) was used to thermodynamically describe the binary molten salts. A total of ten intermediate phases were treated as stoichiometric compounds with their Gibbs energies modeled according to the Neumann-Kopp rule. All these model parameters were optimized by the least squares procedure until good coincidence was achieved between the calculated results and most of the experimental data. The derived thermodynamic parameters will be merged into the multicomponent CsF-LiF-BeF2-ThF4-UF4 database for analyzing physicochemical behavior of CsF in the fuel salt of the molten salt breeder reactor.

Novel low melting point binary nitrates for thermal energy storage applications

19 kinds of different ratio of binary mixed molten salt have been formulated, and the formulation of a low melting point binary molten salt has been exploited and its primary thermophysical properties were presented here. The eutectic temperature of the selected binary salt mixture was determined to be 116.9℃. Further the decomposition point, specific heat, density, viscosity, thermal conductivity and corrosion were determined respectively. Sensible thermal storage cost of the novel eutectic mixture was found to be lower than that of conventional solar salt and HITEC salt. The performance of the binary salt mixture taken at different stages during the test of 1200-h exposure to constant high temperature was discussed based on the results obtained from long-term thermal stability studies. The results show that thermodynamic properties of the molten salt show perfect repeatability before and after the experiments, and most variations rate of the thermal physical properties is within±10%, which can be considered as an implication that the candidate has good thermal stability. Therefore, this new kind of binary molten salt thermal storage materials is more competitive and promising to be used in solar power generation systems while providing a comprehensive data for its engineering application and theoretical research.