Electrochemical reduction mechanism of Zn^(2+)in molten NaCl-KCl eutectic

A process comprising selective chlorination and molten salt electrolysis was proposed to develop an efficient and environmental-friendly technology for zinc recovery from metallurgical dusts.The theoretical feasibility of this technology was firstly estimated based on thermodynamic fundamentals.Subsequently,the electrochemical behavior of Zn^(2+)on tungsten electrode was investigated in molten NaCl-KCl eutectic at 973 K by many electrochemical transient methods.The results showed that the reduction of Zn^(2+)on tungsten electrode was found to be a one-step process exchanging two electrons with the initial reduction potential of-0.74 V(vs Ag/AgCl),and the electrode process was considered as quasi-reversible and controlled by diffusion.The diffusion coefficient of Zn^(2+)ions in the melts was determined in the order of 10^(-5)cm^(2)/s.Finally,the electrolytic preparation of zinc was carried out by potentiostatic electrolysis in molten NaCl-KCl-ZnCl_(2)eutectic at-1.6 V(vs Ag/AgCl).Spheroidic granular metal with silver-white luster was attained after electrolysis for 9.5 h,and identified as pure Zn.The present study confirms that it is practically feasible to extract pure zinc metal by direct electrolysis of ZnCl_(2)in molten NaCl-KCl eutectic,and provides a valuable theoretical reference for the efficient recovery of zinc from metallurgical dusts.

Electrochemical behavior of zirconium in molten NaCl-KCl-K_2ZrF_6 system

The electrochemical reduction of Zr^4＋（complex） ions in NaCl-KCl-K2ZrF6 molten salt on Pt electrode was investigated using cyclic voltammetry and square wave voltammetry at 1023 K.Two cathodic reduction peaks related to Zr^4＋/Zr^2＋ and Zr^2＋/Zr steps were observed in the cyclic voltammograms.The result was also confirmed by square wave voltammetry.The diffusion coefficient of Zr^4＋（complex） ions at 1023 K in NaCl-KCl-K2ZrF6 melt,measured by cyclic voltammetry,is about 4.22×10^-6 cm^2/s.The characterization of the deposits obtained by potentiostatic electrolysis at different potentials was investigated by XRD,and the results were well consistent with the electrochemical reduction mechanism of Zr^4＋（complex） ions.

Electrodeposition of Ir on platinum in NaCl-KCl molten salt

The reduction mechanism of Ir in the NaCl-KCl-IrCl3 molten salt was investigated by cyclic voltammetry and chronopotentiometry, and Ir film was deposited effectively on platinum in potentiostatic mode. The morphology and constitution of Ir film were examined by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. It is found that the reduction mechanism of Ir（III） is a three-electron step and electro reaction is a reversible diffusion controlled process; the diffusion coefficients of Ir（III） at 1083, 1113, 1143 and 1183 K are 1.56×10-4, 2.23×10-4, 2.77×10-4 and 4.40×10-4 cm2/s, respectively, while the activation energy of the electrode reaction is 102.95 kJ/mol. The compacted Ir film reveals that the applied potential greatly affects the deposition of Ir, the thickness of Ir film deposited at the potential of reduction peak is the highest, the temperature of the molten salt also exerts an influence on deposition, the film formed at a lower temperature is thinner, but more micropores would occur on film when the temperature went too high.

用于稀土废料电解回收的LiF-NaF-KF和NaCl-KCl熔盐体系物化性质研究

熔盐电解法是回收钕铁硼废料的重要方法,氟化物和氯化物常被用来当作回收稀土废料熔盐体系中的电解介质。熔盐物性对电流效率、电耗、回收率以及回收产物形态等具有重要的影响。首先对Nd、Pr和Fe在LiF-NaF-KF和NaCl-KCl中的热力学行为进行讨论,进一步采用旋转法、阿基米德法和拉筒法研究了不同配比熔盐体系在不同温度下的黏度、密度和表面张力变化。结果表明:在LiF-NaF-KF系中Nd、Pr会与NaF、KF自发反应;Nd和Pr元素平衡溶解度分别为2.34 mg/g以及1.07 mg/g,而Fe元素则基本不溶解。对于NaCl-KCl体系,钕铁硼废料各组分的反应都不会自发进行,在电解之前需将Fe^(3+)沉淀以免在电解时优先沉积。两种熔盐体系的黏度、密度和表面张力均随温度的升高而降低,密度随温度的改变更符合线性关系,线性程度均大于0.95;随着NdF 3和AlCl_(3)-Nd_(2)O_(3)用量的增加,两种体系的黏度、密度和表面张力均有所增加,但电解原料的添加未改变温度对体系密度的影响规律。

Measurement on Physicochemical Properties ofNaCl-KCl-ScCl_3 System for Manufacture of Al-Sc Alloy by Molten Salt Electrolysis

The physicochemical properties of the system, such as density, surface tension, specific conductance and melting point were measured. The results were discussed.

Dynamic simulation analysis of molten salt reactor-coupled air-steam combined cycle power generation system

A nonlinear dynamic simulation model based on coordinated control of speed and flow rate for the molten salt reactor and combined cycle systems is proposed here to ensure the coordination and stability between the molten salt reactor and power system.This model considers the impact of thermal properties of fluid variation on accuracy and has been validated with Simulink.This study reveals the capability of the control system to compensate for anomalous situations and maintain shaft stability in the event of perturbations occurring in high-temperature molten salt tank outlet parameters.Meanwhile,the control system’s impact on the system’s dynamic characteristics under molten salt disturbance is also analyzed.The results reveal that after the disturbance occurs,the controlled system benefits from the action of the control,and the overshoot and disturbance amplitude are positively correlated,while the system power and frequency eventually return to the initial values.This simulation model provides a basis for utilizing molten salt reactors for power generation and maintaining grid stability.

Electrochemistry of Hf(Ⅳ)in NaCl-KCl-Na-K_(2)HfF_(6) molten salts

The cathodic reduction mechanism of Hf(Ⅳ)ions in a fused Na Cl–KCl–Na F–K_(2) HfF_(6) salt system was studied in various Na F concentrations at 1073 K to obtain a purified dendritic Hf metal.The results of cyclic voltammetry and square wave voltammetry indicated that the reduction process comprised two steps of Hf(Ⅳ)→Hf(Ⅱ)and Hf(Ⅱ)→Hf at low Na F concentrations(0<molar ratio of[F-/Hf 4+]≤17.39)and one step of Hf(Ⅳ)→Hf at high Na F concentrations(17.39<molar ratio of[F-/Hf 4+]<23.27).The structure and morphology of the deposits obtained in potentiostatic electrolysis in the one-step reduction process were analyzed and verified by X-ray diffraction,scanning electron microscopy,and energy dispersive X-ray spectrometry.In the one-step reduction process,the disproportionation reaction between the Hf metal and Hf complex ions was inhibited,and a large dendrite Hf metal was achieved in molten salt electrorefining.

高温储热用MgCl_(2)-NaCl-KCl熔盐的研究进展

随着化石能源短缺和环境问题加剧,聚光太阳能(concentrated solar power,CSP)技术与热储能技术(thermal energy storage,TES)的结合成为有效利用太阳能的重要途径。熔盐是常见的中高温储热材料,而MgCl_(2)-NaCl-KCl三元氯化物熔盐凭借其优异的热物理性能、较高的热稳定性和低成本,成为下一代熔盐储能技术(工作温度>700℃)中最有前途的材料之一。熔盐的热物理性能,例如熔点、比热容、密度、热导率等,对储热系统的设计和优化具有重要意义。同时,氯化物熔盐对金属材料的强腐蚀性也威胁着整个系统的安全。因此,针对目前MgCl_(2)-NaCl-KCl熔盐面临着热物理性能参数难获取,对金属的腐蚀性较强等问题,本文对近期的相关研究成果进行了汇总及探讨。首先从实验研究和模拟研究两方面综述了MgCl_(2)-NaCl-KCl熔盐的热物理性能的确定。随后,基于现有与腐蚀相关的研究成果,介绍了此体系熔盐对常用镍基、铁基合金的腐蚀机理,并从降低熔盐的腐蚀性、提高金属材料的耐蚀性能和腐蚀监测系统三方面综述了目前腐蚀缓解的策略。最后,总结了当前研究现状,并展望了未来发展方向。

NaCl-KCl-ZnCl_(2)-LiCl混合熔盐的制备及其热性能

为获得太阳能光热发电用的低熔点高热稳定温度的蓄热熔盐,采用材料掺杂法,往NaCl-KCl-ZnCl_(2)三元体系的两个共晶点E1和E2中掺杂不同质量分数的无水LiCl,得到了12种不同组成比例的混合熔盐,并对其进行了差式扫描量热法(DSC)熔点测试、热重(TG)动态热稳定测试、52 h静态热稳定测试和熔盐密度测定。DSC试验结果表明,制备的四元混合熔盐的最低熔点为174.2℃,比其掺杂前的E1共晶点的熔点210.4℃降低了36.2℃,相应的相变潜热为78 J/g;TG动态热稳定和长时间静态热稳定试验表明,新四元混合盐的热稳定温度为700℃;熔盐液态密度测试表明,新四元混合熔盐在250~700℃的液态密度为2.35~2.58 g/cm^(3)。该四元混合熔盐有可能用作太阳能光热发电的蓄热储能材料。

Growth kinetics of titanium carbide coating by molten salt synthesis process on graphite sheet surface

The synthesis of carbide coatings on graphite substrates using molten salt synthesis(MSS),has garnered significant interest due to its cost-effective nature.This study investigates the reaction process and growth kinetics involved in MSS,shedding light on key aspects of the process.The involvement of Ti powder through liquid-phase mass transfer is revealed,where the diffusion distance and quantity of Ti powder play a crucial role in determining the reaction rate by influencing the C content gradient on both sides of the carbide.Furthermore,the growth kinetics of the carbide coating are predominantly governed by the diffusion behavior of C within the carbide layer,rather than the chemical reaction rate.To analyze the kinetics,the thickness of the carbide layer is measured with respect to heat treatment time and temperature,unveiling a parabolic relationship within the temperature range of 700-1300℃.The estimated activation energy for the reaction is determined to be 179283 J·mol^(-1).These findings offer valuable insights into the synthesis of carbide coatings via MSS,facilitating their optimization and enhancing our understanding of their growth mechanisms and properties for various applications.

304不锈钢在NaCl-KCl-FeCl_(3)熔盐和蒸气中的 腐蚀行为研究

为拓展氯化物熔盐的应用场景,在300℃的氩气中,研究了304不锈钢在NaCl-KCl-FeCl_(3)熔盐和盐蒸气中腐蚀500h的质量和微观形貌变化。结果表明:304不锈钢试样在NaCl-KCl-FeCl_(3)熔盐和盐蒸气中的质量损失分别为2.1mg/cm^(2)和11.2mg/cm^(2),腐蚀深度分别为10.9μm和17.4μm。腐蚀后304不锈钢的表面凹凸不平,有明显的脱落,但其结晶结构未发生明显变化。氯化物熔盐中微量的H2O引起304不锈钢的腐蚀加剧。该研究不仅为结构材料的筛选提供直接依据,而且为304不锈钢在NaCl-KCl-FeCl_(3)中腐蚀提供了重要的数据,具有重要的科学意义和研究价值。

Etching Mechanism of Ti_(3)C_(2)Cl_(2) MXene Phases by CuCl_(2)-Lewis Molten Salt Method

We described a method for obtaining fluorine-free Ti_(3)C_(2)Cl_(2)MXene phases by melting copper in CuCl_(2)instead of aluminum in Ti_(3)AlC_(2).XRD results show that when molten salt CuCl_(2)etches Ti_(3)AlC_(2),it forms an intermediate product Ti_(3)CuC_(2),and then reacts with Ti_(3)CuC_(2)to obtain Ti_(3)C_(2)Cl_(2).The reaction of Ti_(3)AlC_(2)and CuCl_(2)at a temperature of 800℃for 2 h to obtain Ti_(3)C_(2)Cl_(2)with an optimal lamellar structure is shown in SEM results.The pseudopotential plane-wave(PP-PW)method is used to calculate on the electronic structure.The etching mechanism is investigated by the total energies of each substance.The chemical reaction of Ti_(3)AlC_(2)and CuCl_(2)will first become Ti_(3)CuC_(2)and Cu,and then become Ti_(3)C_(2)Cl_(2)during the Lewis acid etching process,which are consistent with the experimental results.

A Novel High Temperature Apparatus for in situ Synchrotron X-ray Diffraction Studies of Molten Salt

This study demonstrates the design and application of a novel high temperature rotatory apparatus for insitu synchrotron X-ray diffraction studies of molten salts,facilitating investigation into the interaction between various structural materials and molten salts.The apparatus enables accurate detection of every phase change during hightemperature experiments,including strong reaction processes like corrosion.Molten salts,such as chlorides or fluo⁃rides,together with the structure materials,are inserted into either quartz or boron nitride capillaries,where X-ray diffraction pattern can be continuously collected,as the samples are heated to high temperature.The replacement re⁃action,when molten ZnCl2 are etching Ti3AlC2,can be clearly observed through changes in diffraction peak intensity as well as expansion in c-axis lattice parameter of the hexagonal matrix,due to the larger atomic number and ionic ra⁃dius of Zn2+.Furthermore,we investigated the high-temperature corrosion process when GH3535 alloy is in FLiNaK molten salt,and can help to optimize its stability for potential applications in molten salt reactor.Additionally,this high temperature apparatus is fully compatible with the combined usage of X-ray diffraction and Raman technique,providing both bulk and surface structural information.This high temperature apparatus has been open to users and is extensively used at BL14B1 beamline of the Shanghai Synchrotron Radiation Facility.

Preliminary safety analysis for heavy water-moderated molten salt reactor

The heavy water-moderated molten salt reactor(HWMSR)is a newly proposed reactor concept,in which heavy water is adopted as the moderator and molten salt dissolved with fissile and fertile elements is used as the fuel.Issues arising from graphite in traditional molten salt reactors,including the positive temperature coefficient and management of highly radio-active spent graphite waste,can be addressed using the HWMSR.Until now,research on the HWMSR has been centered on the core design and nuclear fuel cycle to explore the viability of the HWMSR and its advantages in fuel utilization.However,the core safety of the HWMSR has not been extensively studied.Therefore,we evaluate typical accidents in a small modular HWMSR,including fuel salt inlet temperature overcooling and overheating accidents,fuel salt inlet flow rate decrease,heavy water inlet temperature overcooling accidents,and heavy water inlet mass flow rate decrease accidents,based on a neutronics and thermal-hydraulics coupled code.The results demonstrated that the core maintained safety during the investigated accidents.

Electrochemical behavior of Fe(Ⅲ)in Na_(2)SiO_(3)-SiO_(2)-Fe_(2)O_(3)molten salt

The high-temperature requirement for liquid iron smelting via molten oxide electrolysis presents significant challenges.This study investigates the electrochemical reduction of Fe(Ⅲ)in a novel low-temperature electrolyte,Na_(2)SiO_(3)-SiO_(2)-Fe_(2)O_(3),utilizing cyclic voltammetry and square wave voltammetry techniques.The results show that Fe(Ⅲ)reduction occurs in two steps:Fe(Ⅲ)+e^(−)→Fe(Ⅱ),Fe(Ⅱ)+2e^(−)→Fe,and that the redox process of Fe(Ⅲ)/Fe(Ⅱ)at the tungsten electrode is an irreversible reaction controlled by diffusion.The diffusion coefficients of Fe(Ⅲ)in the molten Na_(2)SiO_(3)-SiO_(2)-Fe_(2)O_(3)in the temperature range of 1248–1278 K are between 1.86×10^(−6)cm^(2)/s and 1.58×10^(−4)cm^(2)/s.The diffusion activation energy of Fe(Ⅲ)in the molten salt is 1825.41 kJ/mol.As confirmed by XRD analysis,potentiostatic electrolysis at−0.857 V(vs.O_(2)/O_(complex)^(2-))for 6 h produces metallic iron on the cathode.

Multidisciplinary treatment of molten aluminum combined burn:An unusual case report

Molten aluminum is among the most common causes of burns in the metal industry.However,only few reports are available on molten aluminum injuries.Herein,we report an unusual case of molten aluminum burn.The patient had burns not only on the body surface but also in the respiratory tract and esophagus,adding to the difficulty of treatment.Multidisciplinary consultation and cooperation led to the development of a treatment plan for the patient,which included tracheotomy,respiratory management,endoscopic therapy,infection control,and psychological support.To our knowledge,this is the first report of molten aluminum-induced burns involving the face,neck,respiratory tract,esophagus,and eyes.We also describe our experience with multidisciplinary treatment for the management of molten aluminum burns.

A general descriptor for guiding the electrolysis of CO_(2)in molten carbonate

Molten carbonate is an excellent electrolyte for the electrochemical reduction of CO_(2)to carbonaceous materials.However,the electrolyte–electrode-reaction relationship has not been well understood.Herein,we propose a general descriptor,the CO_(2)activity,to reveal the electrolyte–electrode-reaction relationship by thermodynamic calculations and experimental studies.Experimental studies agree well with theoretical predictions that both cations(Li^(+),Ca^(2+),Sr^(2+)and Ba^(2+))and anions(BO_(2)^(-),Ti_(5)O_(14)^(8-),SiO_(3)^(2-))can modulate the CO_(2)activity to control both cathode and anode reactions in a typical molten carbonate electrolyzer in terms of tuning reaction products and overpotentials.In this regard,the reduction of CO_(3)^(2-)can be interpreted as the direct reduction of CO_(2)generated from the dissociated CO_(3)^(2-),and the CO_(2)activity can be used as a general descriptor to predict the electrode reaction in molten carbonate.Overall,the CO_(2)activity descriptor unlocks the electrolyte–electrode-reaction relationship,thereby providing fundamental insights into guiding molten carbonate CO_(2)electrolysis.

Molten salt construction of core-shell structured S-scheme CuInS_(2)@CoS_(2) heterojunction to boost charge transfer for efficient photocatalytic CO_(2) reduction

Weak redox ability and severe charge recombination pose significant obstacles to the advancement of CO_(2) photoreduction.To tackle this challenge and enhance the CO_(2) photoconversion efficiency,fabricating well-matched S-scheme heterostructure and establishing a robust built-in electric field emerge as pivotal strategies.In pursuit of this goal,a core-shell structured CuInS_(2)@CoS_(2)S-scheme heterojunction was meticulously engineered through a two-step molten salt method.This approach over the CuInS_(2)-based composites produced an internal electric field owing to the disparity be-tween the Fermi levels of CoS_(2) and CuInS_(2) at their interface.Consequently,the electric field facili-tated the directed migration of charges and the proficient separation of photoinduced carriers.The resulting CuInS_(2)@CoS_(2) heterostructure exhibited remarkable CO_(2) photoreduction performance,which was 21.7 and 26.5 times that of pure CuInS_(2) and CoS_(2),respectively.The S-scheme heterojunc-tion photogenerated charge transfer mechanism was validated through a series of rigorous anal-yses,including in situ irradiation X-ray photoelectron spectroscopy,work function calculations,and differential charge density examinations.Furthermore,in situ infrared spectroscopy and density functional theory calculations corroborated the fact that the CuInS_(2)@CoS_(2) heterojunction substan-tially lowered the formation energy of *COOH and *CO.This study demonstrates the application potential of S-scheme heterojunctions fabricated via the molten salt method in the realm of ad-dressing carbon-related environmental issues.

Plutonium utilization in a small modular molten-salt reactor based on a batch fuel reprocessing scheme

A molten salt reactor(MSR)has outstanding features considering the application of thorium fuel,inherent safety,sustainability,and resistance to proliferation.However,fissile material^(233)U is significantly rare at the current stage,thus it is difficult for MSR to achieve a pure thorium-uranium fuel cycle.Therefore,using plutonium or enriched uranium as the initial fuel for MSR is more practical.In this study,we aim to verify the feasibility of a small modular MSR that utilizes plutonium as the starting fuel(SM-MSR-Pu),and highlight its advantages and disadvantages.First,the structural design and fuel management scheme of the SM-MSR-Pu were presented.Second,the neutronic characteristics,such as the graphite-irradiation lifetime,burn-up performance,and coefficient of temperature reactivity were calculated to analyze the physical characteristics of the SM-MSR-Pu.The results indicate that plutonium is a feasible and advantageous starting fuel for a SM-MSR;however,there are certain shortcomings that need to be solved.In a 250 MWth SM-MSR-Pu,approximately 288.64 kg^(233)U of plutonium with a purity of greater than 90% is produced while 978.00 kg is burned every ten years.The temperature reactivity coefficient decreases from -4.0 to -6.5 pcm K^(-1) over the 50-year operating time,which ensures a long-term safe operation.However,the amount of plutonium and accumulation of minor actinides(MAs)would increase as the burn-up time increases,and the annual production and purity of^(233)U will decrease.To achieve an optimal burn-up performance,setting the entire operation time to 30 years is advisable.Regardless,more than 3600 kg of plutonium eventually accumulate in the core.Further research is required to effectively utilize this accumulated plutonium.

Preparation of low-oxygen titanium powder by magnesiothermic reduction of TiO2 assisted by MgCl_(2)−HoCl_(3) molten salt

To reduce the production cost of titanium,a new method for direct preparation of low-oxygen titanium powder by the magnesiothermic reduction of TiO_(2) with the assistance of a MgCl_(2)−HoCl_(3) molten salt was proposed.Thermodynamic calculations showed that the magnesiothermic reduction of TiO_(2) was feasible.However,hindrance of the reduction reaction by the reduction by-product of MgO resulted in a considerably high O concentration in the titanium powder.The addition of HoCl_(3) to the system significantly reduces the activity of MgO to produce low-oxygen titanium powder.Thermochemical deoxidation and reduction experiments were conducted with MgCl_(2)−HoCl_(3) molten salt in the temperature range of 1023−1273 K.The results showed that titanium powder with oxygen concentration(mass fraction)below 5.00×10^(-4) can be prepared at the Mg−MgCl_(2)−HoOCl−HoCl_(3) equilibrium.