Binary Molten Salt Research Articles

Effect of Na2CO3 content on thermophysical properties, corrosion behaviors of KNO3-NaNO2 molten salt

Molten salt is popularly used as high temperature heat transfer and thermal energy storage medium. In order to decrease the melting point and increase decomposition temperature of molten salt, phase diagrams for KNO3-NaNO2 binary nitrates were calculated. And the binary salt with the lowest eutectic point was prepared. Furthermore, the effect of Na2CO3 addition on optimal selected KNO3-NaNO2 binary molten salt thermophysical properties and corrosion behavior are experimentally investigated. The results show that the addition of 7 wt% Na2CO3 to KNO3-NaNO2 binary molten salt can lower the melting point by 5.8 %. The addition of 9 wt% Na2CO3 to KNO3-NaNO2 binary molten salt can increase the decomposition temperature by 20.6 %, enhance the specific heat capacity by 4.8 % and increase the thermal conductivity by 7.5 %, but at the same time viscosity increased about 70 % at 300 °C. Meanwhile, the density increases with the increase of Na2CO3 content addition. The average corrosion rate of 316 stainless steel increases with the increasing of Na2CO3 content, which is consistent with the cross-section SEM results.

Heat Supply to Industrial Processes via Molten Salt Solar Concentrators

About one-third of world energy production is destined to the industrial sector, with process heat accounting for about 70% of this demand; almost half of this quota is required by endothermic processes operating at temperatures above 400 °C. Concentrated solar thermal technology, thanks to cost-effective high-temperature thermal energy storage solutions, can respond to the renewable thermal energy needs of the industrial sector, thus supporting the decarbonization of hard-to-abate processes. Particularly, parabolic trough technology using binary molten salts as heat transfer fluid and storage medium, operating up to 550 °C, could potentially supply a large part of the high-temperature process heat required by the industry. In this work, four industrial processes, representative of the Italian industrial context, that are well suited for integration with molten salt concentrators are presented and discussed, conceiving for each considered process a specific coupling solution with the solar plant, sizing the solar field and the thermal storage unit, and computing the cost of the process heat and its variation with the storage capacity. Considering cost data from the literature associated with the pre-COVID-19 era, an LCOH comprising the range 5–10 c€/kWhth was obtained for all the cases studied, while taking into account more updated cost data, the calculated LCOH varies from 7 to 13 c€/kWhth.

Calculation of liquidus in eutectic alkali halide mixtures using thermodynamic perturbation theory

A statistical-thermodynamic model that makes it possible to describe with good accuracy phase equilibria between melt and crystal in binary alkali halide mixtures with common cations and anions is proposed. This model is based on the thermodynamic perturbation theory, which takes into account the charge-dipole contribution to the interionic interaction of binary molten salts using a multicomponent mixture of charged hard spheres as a reference system. Specific expressions for chemical potentials, taking into account the charge-induced dipole interaction in the molten phase, are presented within the developed approach. Considering binary eutectic mixtures NaF–NaCl, CsF–CsCl, NaF–CsF, and NaCl–CsCl as an example, the liquidus curves obtained in two series of calculations are shown: with the equation of state and without it. The discrepancies between the calculated and experimental data on the position of eutectic equilibrium for most of the considered mixtures do not exceed about 10 percent on the temperature scale and 5 percent on the composition when using only the tabulated values of ionic radii and polarizabilities without any adjustment.

Molecular insights into thermal conductivity enhancement and interfacial heat transfer of molten salt/porous ceramic skeleton composite phase change materials

Molten salt has been considered as one of the most promising candidate materials for thermal energy storage (TES) systems owing to its remarkable energy density and consistent thermal performance. These properties render it particularly advantageous for the applications in concentrated solar power (CSP) and industrial process heat utilization. Nonetheless, their practical applications still face nonnegligible challenges such as the low thermal conductivity and risk of leakage. Packing molten salts into porous skeletons could be an effective way for addressing these issues. In the present work, the heat transfer characteristics of a composite phase change material (CPCM) consisting of binary chloride salt and a porous ceramic skeleton, are investigated at the microscale level using molecular dynamics (MD) simulations. Simulation results indicate that the integration of a porous SiC skeleton can substantially enhance the thermal conductivity of binary molten salt NaCl/KCl. At the temperature of 1000 K, a notable enhancement of 625.74 % in thermal conductivity has been observed. Moreover, the underlying mechanism of heat conduction enhancement has been revealed from the microscopic perspective. The results demonstrate that auxiliary thermal conductivity paths and interfacial heat transfer play primary roles in determining the thermal conductivity of CPCMs. The method of surface charge modification can effectively improve the interfacial heat transfer and the reason can be attributed to the additional thermal conductivity paths and the large number of particles involved in the interfacial heat transfer. The results gained in this work may provide insights into the heat transfer mechanism of composite molten salt/porous skeleton as well as practical guidance for designing CPCM for thermal storage applications.

In situ desulfurization mechanism of molten salt thermal treatment for waste tires

Pyrolysis is regarded as a practical way for waste tires to achieve waste-to-resource objectives. However, the environmental risk of pollution emissions in product utilization caused by the migration of sulfur is an important issue in the waste tire disposal industry. This study introduced a solution to using the binary molten salt system (NaOH-Na2CO3) as a heat transfer and desulfurization medium for the thermal utilization of waste tires. The results demonstrated that molten salts had in-situ desulfurization capability at 425 °C −575 °C and inhibited the migration of sulfur to gas–liquid-solid products with the total sulfur ratio reduced by 50 % − 67 %. The sulfur-containing radical intermediates could be extensively consumed by molten salt, leading to a low concentration level of H2S and COS in gaseous products. Simultaneously, molten salt blocked the traditional pathway of the sulfhydryl radical with inorganic additives, weakening the sulfur enrichment to char. Additionally, molten salt enhanced heat transfer during pyrolysis, facilitating the decomposition of thiazole and the polymerization of sulfur-containing benzene ring (2,3-dimethyl-thiophene to benzothiophene). The online monitoring further corroborated that COS release was preceded by H2S at high temperatures (>500 °C) along with the full degradation of the waste tires. Higher desulfurization efficiency of molten salt was achieved with feedstocks of small particle size, as it allows for adequate exposure of the reaction contact sites. This approach provides a new opportunity for in-situ desulfurization of waste tire pyrolysis via molten salt thermal treatment.

Studies on the Surface Adsorption of Binary Molten Salts.

The surface adsorption of eight binary molten salts, AgNO3-M1NO3(M1 = Li, Na, K, Rb), NaNO3-M2NO3 (M2 = K, Rb), Ca(NO3)2-CsNO3, and Cd(NO3)2-NaNO3, has been investigated. It is found that the surface tension and temperature of molten salts at constant pressure and mole fraction satisfy the same equation as that for pure liquid compounds reported in our previous works. The heats of phase transition from the bulk to the surface phase for eight molten salts are determined. The heats per unit area are all at the order of -10-2 J/m2. The phase transition is exothermic because the entropy in the surface phase is smaller than the entropy in the bulk phase. The ratio of the solute surface concentration to the solute bulk concentration is approximated as the first-order polynomials of the solute bulk concentration. Then, curves of the surface tension vs the solute bulk concentration are well fitted. The ratio (ΔcBs/ΔcBα) is used to interpret the changing trend of the surface tension with bulk concentrations of solute. It is also found that the surface tension of molten salts decreases linearly with the solute surface concentration.

Study on Hot Corrosion of Low-Nickel Cladding Metals Containing Nitrogen in K2SO4-MgSO4 Binary Molten Salt

Molten salt is usually used as the energy storage medium for solar energy heat storage pipes, and 40wt% K2SO4 + 60wt% MgSO4 is very suitable for use as a heat storage material for solar thermal power generation in tower and butterfly parabolic systems. The demand for high-temperature thermal energy storage systems has prompted research on low-cost alloys for use in high-temperature and corrosion-resistant environments. The 44% Ni-24% Cr-0.18N nitrogen-containing low-nickel flux-cored welding wire designed in this article has a corrosion resistance of up to 900 °C after welding repair, which is better than the repair ability of Inconel 625 flux-cored welding wire. Using the high-temperature static immersion corrosion method, the corrosion behavior of two deposited metals immersed in molten salt for 60 h at 900 °C was assessed. The corrosion product phase composition, corrosion morphology, and elemental distribution of the two deposited metals were systematically studied using X-ray diffraction (XRD) and a Gemini SEM 300 (Zeiss thermal field scanning electron microscope). The results showed that the corrosion weight loss of the deposited metals showed the same trend at 900 °C, with corrosion occurring slowly from 0 h to 10 h and increasing after 10 h to 60 h. It was found that 10 h was the boundary point for corrosion behavior, and the corrosion resistance of the low-nickel nitrogen-containing deposited metal is better than that of the Inconel 625 deposited metal. This was because the addition of N energy elements allowed the formation of a stable composite nitride layer to suppress corrosion.

Excellent cycling performance of high-nickel single-crystal cathode material by a well-tailored binary molten-salt method

Nickel-rich LiNixCoyMnzO2 (x + y + z = 1) cathode materials have been extensively studied due to their improved energy density and reduced cost in comparison to conventional layered oxides (LiCoO2) and perovskite-type compounds (LiFePO4). However, the further commercialization of polycrystalline nickel-rich layered cathodes are severely hampered by entrenched particle microcracking that evolves mainly from the randomly oriented grain boundaries in the primary particles. Herein, an environmental-friendly LiOH⋅H2O/Li2CO3 binary molten-salt method is introduced to synthesize single-crystal LiNi0.88Co0.09Mn0.03O2 with good crystallinity and dispersion, and the possible growth mechanism of the particles is inferred. The sample prepared at a lithium ratio of 1.7 (SC1.7) shows a lower degree of cation mixing and larger lithium layer spacing compared to control polycrystalline sample (PC), and the residual alkali is effectively removed from the surface of single crystal particles. These features enable SC1.7 to maintain robust structural stability during cycling, with the cycle retention at 1C rate and a voltage of 4.5 V to be 86.73% after 100 cycles. The desirable performance is rationally derived from the significant inhibition of microcracks in particles, and reduction of parasitic reactions. The unique binary molten-salt strategy provides a new avenue for the design of high-performance high-nickel cathode materials in lithium-ion batteries.

Molecular dynamics analysis of thermophysical properties of Na2CO3-K2CO3 binary molten salts in temperature range of 1125–1475 K

Molten carbonates are highly promising solar thermal storage materials. In this paper, the molecular dynamics (MD) method was used to study the thermal properties of binary molten salt mixtures of Na2CO3-K2CO3 as a function of temperature and composition. Their thermal storage mechanisms were analyzed from the perspectives of microstructure and atomic diffusion. It was confirmed that temperature and various components have significant effects on the density, thermal conductivity and shear viscosity of binary molten salts. Based upon the MD data, the correlation for the temperature-thermal properties-component with the correlation coefficient of higher than 0.98 was obtained. In addition, the radial distribution function (RDF) showed that the change in thermal properties was the result of variation in distance between the ionic clusters. Finally, based on the guidance of material composition design strategy, a coefficient that could reflect the synergistic effect between the binary molten salts was proposed for the first time. The results showed that the synergy coefficient reached its highest point for the molten salt molar ratio of 58:42, and at this point, the positive synergy was most obvious. This study can provide theoretical guidance for the design and enhancement in the performance of molten carbonates as thermal storage materials.

Biocarbon with large specific surface area and tunable pore structure from binary molten salt templating for supercapacitor applications

Tailoring the pore structure while maintaining a large specific surface area (SSA) of biocarbon remains a challenge, especially forsingle activating/templating system. Herein, a new binary ZnCl2-CaCl2 (Zn-Ca) molten salt system is explored for one-step carbonization of chitin to manufacture biocarbon with hierarchically tunable micro/mesoporous structure. By adjusting the salt to chitin ratio, biocarbon with large SSA (>1000 m2/g), controllable mesopore fractions (19.3%–67.9%) and high yield (up to 35%) has been fabricated. The optimal SSA, total pore and mesopore volume are obtained at 1671 m2/g, 1.32 cm3/g and 0.64 cm3/g, respectively, showing the synergistic effect of Zn-Ca on achieving well-balanced pore characteristics. Besides, the total nitrogen contents could also be enhanced. Such balanced physicochemical properties lead to excellent supercapacitor performance, achieving 301.2 F/g specific capacitance at a current density of 0.5 A/g as measured from a three-electrode system. The assembled supercapacitor cell also shows a notable rate capability of 70.2% at an ultrahigh current density of 50 A/g with a low internal resistance, which can reach a remarkable power density of 27 kW/kg. The outstanding capacitive performance is attributed to the modulated micro-mesoporous structure for efficient ion diffusion and adsorption, as well as appropriate heteroatoms for pseudo-capacitance contribution.

Highly efficient leaching of aluminum and chromium from aluminum chromium slag using NaOH-NaNO3 binary molten salt

In this study, the NaOH-NaNO3 binary molten salt was proposed as a highly efficient technique to leach aluminum and chromium from aluminum chromium slag (ACS). Various factors, such as roasting temperature, roasting time, mass ratio of NaOH (or NaNO3)/ACS, water leaching temperature and time, were adjusted to investigate their influence on the activation and extraction of aluminum-chromium resources from ACS. Moreover, the roasting activation conditions were optimized by response surface methodology, and the optimal extraction rates of alumina and chromium (88.72% and 95.64%, respectively) were obtained with the roasting temperature of 451 °C, roasting time of 3.9 h, NaOH/ACS mass ratio of 5.39:1, and NaNO3/ACS mass ratio of 0.79:1. Kinetic studies showed that the roasting process was controlled by the diffusion of the product interface. Finally, based on the comprehensive analysis of leaching data and physicochemical properties change of ACS with roasting, the mechanism of NaOH-NaNO3-ACS activation was revealed: NaOH-NaNO3 melted and encapsulated the ACS during the roasting reaction, NaOH provided a strongly alkaline environmental medium, which facilitated the decomposition of NaNO3 into NaNO2 and reactive oxygen species, thus prompting the oxidative decomposition of aluminum-chromium solid solution to form NaAlO2 and Na2CrO4, further improving the leaching rate of aluminum and chromium.

A thermodynamically stable O2-type cathode with reversible O2-P2 phase transition for advanced sodium-ion batteries

Low-cost sodium-ion batteries (SIBs) have shown very promise in the applications of renewable energy and low-speed electric vehicles. The development of a new O2-type cathode in SIBs is very challenging in that this compound is only stable as an intermediate product of P2-type oxides during redox reactions. Here, we report a thermodynamically stable O2-type cathode obtained by Na/Li ion exchange from P2-type oxide in a binary molten salt system. It is demonstrated that the as-prepared O2-type cathode exhibits a highly reversible O2–P2 phase transition during Na+ de-intercalation. The unusual O2–P2 transition has a low volume change of ∼11%, much lower than that of 23.2% for P2–O2 transformation in the P2-type cathode. The lowered lattice volume change of this O2-type cathode gives rise to superior structural stability upon cycling. Therefore, the O2-type cathode possesses a reversible capacity of about 100 mAh/g with a good capacity retention of 87.3% even after 300 cycles at 1C, indicating outstanding long-term cycling stability. These achievements will promote the development new class of cathode materials with high capacity and structural stability for advanced SIBs.

Binary molten salt in situ synthesis of sandwich‐structure hybrids of hollow β‐Mo2C nanotubes and N‐doped carbon nanosheets for hydrogen evolution reaction

AbstractFocused exploration of earth‐abundant and cost‐efficient non‐noble metal electrocatalysts with superior hydrogen evolution reaction (HER) performance is very important for large‐scale and efficient electrolysis of water. Herein, a sandwich composite structure (designed as MS‐Mo2C@NCNS) of β‐Mo2C hollow nanotubes (HNT) and N‐doped carbon nanosheets (NCNS) is designed and prepared using a binary NaCl–KCl molten salt (MS) strategy for HER. The temperature‐dominant Kirkendall formation mechanism is tentatively proposed for such a three‐dimensional hierarchical framework. Due to its attractive structure and componential synergism, MS‐Mo2C@NCNS exposes more effective active sites, confers robust structural stability, and shows significant electrocatalytic activity/stability in HER, with a current density of 10 mA cm−2 and an overpotential of only 98 mV in 1 M KOH. Density functional theory calculations point to the synergistic effect of Mo2C HNT and NCNS, leading to enhanced electronic transport and suitable adsorption free energies of H* (ΔGH*) on the surface of electroactive Mo2C. More significantly, the MS‐assisted synthetic methodology here provides an enormous perspective for the commercial development of highly active non‐noble metal electrocatalysts toward efficient hydrogen evolution.

Construction of Fe/N/C nano-clusters anchored on porous diatomite for efficient removal of norfloxacin via the adsorption-PMS activation

In this study, natural porous diatomite was utilized as a conciliatory carrier for the fabrication of Fe/N/C nano-clusters with assistance of binary molten salt of NaCl-ZnCl2 under different annealing temperature and used to removal of norfloxacin (NFA). The sample Fe/Dm900 (prepared at 900 °C) exhibited a high surface area and great catalytic performance for antibiotics in the presence of PMS. Over 97% NFA can be decomposed within 5 min and the final degradation rate reached 98%. Meaningfully, high-efficiency Fe/Dm900-PMS system was nearly impervious to pH values and inorganic cations in aqueous solution and could be a likely candidate for degradation of multiple contaminants in pharmaceutical outlet water. Furthermore, the other impacting variables such as catalyst dosage, PMS dosage, NFA concentration and initial pH were moreover explored towards debasement, and conceivable degradation pathways of NFA were presented through LC-MS. This work builds up a compelling procedure to synthesize super-dispersed Fe clusters, which may be amplified to other transition metal-based catalyst via molten salt.

Research on the effect of adding NaCl on the performance of KNO3–NaNO3 binary molten salt

Research on the effect of adding NaCl on the performance of KNO3–NaNO3 binary molten salt

Molecular dynamics simulation of thermophysical properties of NaCl-KCl phase change materials applied to concentrating solar power

Given the current research prospects for the next generation of Concentrated Solar Power (CSP) plants based on the Supercritical carbon dioxide Brayton cycle, NaCl-KCl binary molten salt is a kind of material with application value. In this paper, NaCl-KCl with a Na+ molar concentration of 30–60 was studied based on Molecular Dynamics (MD) method. The thermophysical properties such as latent heat, specific heat and thermal conductivity were simulated and analyzed in molten state. The unit price of energy storage was calculated and discussed. The results showed that when the Na+ content was 36%, the latent heat was the highest with the value of 363.60 J/g. The specific heat capacity and thermal conductivity increased as Na+ molar concentration increased. The unit price of energy storage was the lowest when Na+ content was 60% with the value of 0.043 ¥/kJ. It can be a reference to choose materials for thermal energy storage (TES) system in CSP.

Title Corrosion Behavior of Nitrogenous Low Nickel Weld Cladding in Kcl-Mgcl2 Binary Molten Salt

Title Corrosion Behavior of Nitrogenous Low Nickel Weld Cladding in Kcl-Mgcl2 Binary Molten Salt

Title Corrosion Behavior of Nitrogenous Low Nickel Weld Cladding in Kcl-Mgcl2 Binary Molten Salt

Title Corrosion Behavior of Nitrogenous Low Nickel Weld Cladding in Kcl-Mgcl2 Binary Molten Salt

Improving the Performance of Solar Heat Collector Using Molten Salts

An individual solar collector and two partly freight cylinders filled with molten salts embedded storage tank were connected to each other and forced circulated water by electric pump to improve the thermal performance of residential solar hot water tank. Multi flow rates of 25, 50 and 70 l/h. used to achieve an appropriate flow rate of circulating water. The calcium nitrate tetra hydrate Ca(NO3)2-4H2O and magnesium nitrate hex hydrate Mg(NO3)2-6H2O were mixed to form cheap binary molten salts base on different weight ratios. These molten salts combined could be used as both sensible heat materials and latent heat storage materials, besides they can directly use as heat transfer fluid due to freezing temperature. Six samples of different mixing ratio of molten salts had tested to assess the thermal analysis of each sample. The result indicated that the mixture 60%Ca(NO3)2+40%Mg(NO3)2 had the best performance for thermal storage tank with melting point of 38°C and the thermal value is 8.7 mW, and thermal stability of molten salts were noticed by DSC 60 SHIMADZSU devise.

Study on the preparation and thermal properties of binary mixed chloride salts

Nitrate phase change materials (PCMs) are the most widely used PCMs in solar thermal power generation technology. The maximum service temperature of Nitrate phase change materials is only 600°C. Therefore, to find a phase change material with large heat capacity, wide temperature range, low heat loss and low price is the focus of current research. According to different mass ratios, nine binary molten salt mixtures were prepared by mixing lithium chloride and sodium chloride. The phase change temperature and latent heat of phase transition of them were studied by differential scanning calorimeter (DSC). The experiment results showed that since the melting point of sodium chloride was high, when the content of sodium chloride in the binary mixture of lithium chloride and sodium chloride was large, a small amount of lithium chloride could not reduce the melting point of the mixture below 600°C, the mixture could not be melted. Meanwhile, when sodium chloride and lithium chloride were melted, the phase transition temperature of lithium chloride and sodium chloride remained at about 540°C and floated at ±15°C. The melting temperature and crystallization temperature of the binary mixture of 90% lithium chloride and 10% sodium chloride were quite different, and the latent heat of phase transformation was relatively high. Therefore, the binary mixed molten salt can be used in the heat transfer and storage technology of solar power generation.