Low Temperature Molten Salt Synthesis of Perovskite-type ACeO3(A=Sr,Ba) in Eutectic NaCl-KCl

A molten salt method was developed for the synthesis of ACeO₃(A=Sr, Ba) with perovskite structure at 750 ℃(SrCeO₃) and 850 ℃(BaCeO₃) in the eutectic NaCl-KCl. The synthetic temperature was much lower than that of the conventional method(generally>1000 ℃). The structure and morphology of the product were characterized by means of X^-ray diffraction(XRD), field emission scanning electron microscopy(FESEM) and transmission electron microscopy(TEM). The results show that the synthesized octahedral SrCeO₃ crystallizes in the orthorhombic system with the unit cell parameters of a=0.85855 nm, b=0.61523 nm, c=0.60059 nm, and the synthesized cuboid BaCeO₃ crystallizes in the cubic system with the unit cell parameter of a=0.43962 nm. The result of X^-ray photoelectron spectroscopy(XPS) analysis indicates that both Ce⁴⁺ and Ce³⁺ exist in the two structures, and the Ce⁴⁺/Ce³⁺ peak area ratios for SrCeO₃ and BaCeO₃ are 1.93 and 2.12, respectively. Meanwhile, the adsorbed/lattice oxygen ratios(1.87 for SrCeO₃ and 3.04 for BaCeO₃) indicate the existence of a lot of oxygen vacancies in the structures of SrCeO₃ and BaCeO₃, which indicates a far-reaching significance to study the corresponding physicochemistry performance.     

Markedly enhancing the visible-light photocatalytic activity of LaFeO3 by post-treatment in molten salt

The visible-light photoactivity of LaFeO₃ prepared by conventional co-precipitation method can be markedly enhanced by a simple and efficient post-treatment method. The catalyst treated with molten KNO₃ exhibited the highest rate constant of 0.061 min⁻¹ and after 60 min visible-light irradiation, 98% Acid Red 18 was decolorized, which was much higher than P25 TiO₂.     

Preparation and Magnetic Property of La_(0.7)Sr_(0.3)MnO_3 Nanorod by Combination Sol-Gel with Molten Salt

La0.7Sr0.3MnO3(LSMO) nanorods were synthesized by a method combining sol-gel with molten salts at 950 °C for 10 h, which employed KCl+NaCl(mass ratio 4:1) as eutectic molten salts. The morphologies and magnetic properties of the resulting LSMO nanorods were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), and vibrating sample magnetometer(VSM) measurements. It was found that the obtained perovskite manganite LSMO was a uniform nanorod with a d...     

Preparation and Magnetic Property of La0.7Sr0.3MnO3 Nanorod by Combination Sol-Gel with Molten Salt

La0.7Sr0.3MnO3（LSMO） nanorods were synthesized by a method combining sol-gel with molten salts at 950 ℃ for 10 h, which employed KCl＋NaCl（mass ratio 4：1） as eutectic molten salts. The morphologies and magnetic properties of the resulting LSMO nanorods were investigated by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, and vibrating sample magnetometer（VSM） measurements. It was found that the obtained perovskite manganite LSMO was a uniform nanorod with a diameter of about 50 nm and a length of longer than 500 rim. The Curie temperature（To） of the LSMO nanorod used here was 262 K, much lower than that of bulky single crystal LSMO（360 K）. The low Curie temperature might be a result of the great disorder near the grain boundary, which could be observed clearly from the TEM picture.     

熔盐中熟化处理提高BiFeO3的可见光催化活性

研究发现, 通过熔盐中熟化处理可以显著地提高BiFeO3的可见光催化活性.     

Materials corrosion in molten LiF-NaF-KF salt

Corrosion tests of high temperature alloys, Hastelloy-N, Hastelloy-X, Haynes-230, Inconel-617, and Incoloy-800H were performed in molten fluoride salt, FLiNaK (LiF-NaF-KF:46.5-11.5-42 mol%) with the goal of understanding the corrosion mechanisms and ranking these alloys for their suitability for molten fluoride salt heat exchanger and thermal storage applications. The tests were performed at 850 °C for 500 h in sealed graphite crucibles under an argon cover gas. Corrosion was noted to occur predominantly by dealloying of Cr from the alloys, an effect that was particularly pronounced at the grain boundaries of these alloys. Weight-loss due to corrosion generally correlated with the initial Cr-content of the alloys, and was consistent with the Cr-content measured in the salts after corrosion tests. Two Cr-free alloys, Ni-201 and Nb-1Zr, were also tested. Ni-201, a nearly pure Ni alloy with minor alloying additions, exhibited good resistance to corrosion, whereas Nb-1Zr alloy exhibited extensive corrosion attack. The graphite crucible may have accelerated the corrosion process by promoting the formation of carbide phases on the walls of the test crucibles, but did not alter the basic corrosion mechanism.     

Electrodeposition of Zr on graphite in molten fluorides

The electrochemical behavior of Zr⁴⁺ using graphite working electrode has been studied in fused LiF–NaF–ZrF₄ eutectic mixture (temperature range 923–1123 K). In addition to the electrochemical profile related to the deposition/dissolution of Zr metal, the cyclic voltammograms exhibit well-defined peaks attributed to the formation of zirconium carbide. A third contribution relative to the formation of Li–graphite intercalation compound and/or lithium carbide was also proposed for a better interpretation of the voltammogram. Depending on the experimental deposition conditions, the analysis of the deposits by SEM/EDX has revealed the presence of a Zr metal thin film with various porosities and compositions. Moreover, the electrochemical reduction of Zr(IV) in molten fluorides using a graphite electrode allows the extraction of pure Zr metal.     

Electrochemical synthesis of coatings in the system Ti-Si-B from molten salts

Powder and coatings of metal-like refractory compounds (MLRC) can be produced by electrochemical synthesis from molten salts. The stoichiometry of the deposited MLRC was found to correlate with the molar ratio of MLRC component ions in the melts. The system Ti-Si-B is of particular interest in terms of electrochemical synthesis since the titanium, silicon and boron potentials in the melt are close together. The electrochemical synthesis has been investigated in the system NaCl-KCl-NaF-K₂TiF₆-K₂SiF₆-KBF₄ at 700°C. The opportunity of deposition of new ternary compound in the system Ti-Si-B is shown by the electrochemical synthesis from molten salts.     

Electrochemical investigation of lithium intercalation into graphite from molten lithium chloride

Lithium reduction at a graphite electrode in molten lithium chloride was studied at temperatures from 650 to 900 °C using cyclic voltammetry and chronoamperometry. It was found that, during cathodic polarization, lithium intercalation into graphite occurred before deposition of metallic lithium started. This process was confirmed to be rate-controlled by the diffusion of lithium in the graphite. When the cathodic polarization potential was more negative than that for metallic lithium deposition, exfoliation of graphite particles from the electrode surface was observed. This was caused by fast and excessive accumulation of lithium intercalated into the graphite, which produced mechanical stress too high for the graphite matrix to accommodate. The erosion process was abated once the graphite surface was covered by a continuous layer of liquid lithium. These results are of relevance to the mechanism of carbon nanotube and nanoparticle formation by electrochemical synthesis in molten lithium chloride.     

Advancements and potentials of molten salt CO2 capture and electrochemical transformation (MSCC-ET) process

Electroreduction of CO₂ in molten salts, also called molten salt carbon capture and electrochemical transformation (MSCC-ET), can convert CO₂ into value-added carbonaceous materials or CO in a comparably high rate with high energy efficiency. It shows a promising potential to contribute to the earth's atmospheric carbon balance, the intermittent renewable energy storage, carbon materials production, and air quality control of the local environment. This short review briefly introduces the principle of the MSCC-ET process, the state-of-the-art of the process, its potential of commercialization in terms of process efficiency, product marketing and economy, and finally, the opportunities and challenges in future research and development.     

Preparation of Mg-Li alloys by electrolysis in molten salt at low temperature

A new technology for preparation of low cost Mg-Li alloys was studied. The alloys were prepared by electrolysis in molten LiCl-KCl (weight ratio is 1:1) electrolyte with Mg rod severing as the consumed cathode. Main factors that affect current efficiency were investigated, and optimal electrolysis parameters were obtained. Mg-Li alloys with low lithium content (about 25%) were prepared by the unique method of a higher post-thermal treatment temperature after electrolysis at low temperature. The results showed that the electrolysis can be carried out at low temperature, which resulted in reducing preparation cost due to energy saving.The new technology for the preparation of Mg-Li alloy by electrolysis in molten salt was proved to be feasible.     

Amorphous silicon from low-temperature reduction of silica in the molten salts and its lithium-storage performance

Amorphous silicon(a-Si) is one of the most promising anode-materials for the lithium-ion battery owing to its large capacity and superior fracture resistance.However,a-Si is usually fabricated with the sophisticated chemical vapor deposition or pulse laser deposition in a limited scale.In this work,we have succes s fully pre pared a-Si spheres(～200 nm) by reducing the TiO_2-coated silica spheres with Al powders in the molten salts at 300℃.The coated TiO_2 layer acts as a protective layer for structural maintenance during the reduction and a precursor for doping.The doped Ti element may suppress the crystal growth of Si to facilitate the formation of a-Si.The observation with in-situ transmission electron microscopy(TEM) further reveals that lithiation kinetics of the synthesized a-Si is controlled by the interfacial reaction.The Li+diffusivity in a-Si determined from the observation is in the order of 10 ~(14) cm~2/s.The anode of a-Si spheres together with crystalline Si nanoparticles exhibits excellent electrochemical performance,delivering a reversible capacity of 1604 mAh/g at 4 A/g and a capacity retention of 78,3%after 500 cycles.The low temperature reduction process reported in this study provides a low-cost method to fabricate a-Si nanostructures as high-capacity durable anode materials     

Heat-transport properties of molten fluorides: Determination from first-principles

The construction of an interaction potential for mixtures of LiF, NaF, KF and ZrF₄ on a purely first-principles basis is described. Many-body interactions are included via a polarization term. The predictions of the heat-transfer properties of two mixtures, LiF-NaF-KF (FLiNaK) and NaF-ZrF₄, are then compared with experimental values. Values for the densities, thermal expansions, heat capacities and viscosities are compiled into figures of merits in order to compare the suitability of those molten salts to serve as primary or secondary coolants in a nuclear reactor.     

Sr掺杂钙钛矿体系中高活性氧析出反应机制（英文）

析氧反应(oxygen evolutionreaction OER)是电催化分解水、二氧化碳还原、金属-空气电池以及燃料电池等能源转化及存储技术的关键过程,因此被广泛关注和研究.OER过程涉及四个电子转移,是动力学迟滞过程,具有较大的过电位,此外OER催化反应的同时也可能改变电极表面状态,故其机理的研究十分困难.设计和开发高效OER催化剂材料是提高电解水效率的关键.最近的研究发现反应后催化剂表面会发生重构,进而形成无定形层,该无定形层被认为会改善催化活性.我们的前期研究也发现了表面不饱和配位无定形层的存在,但对于重构机制尚没有明确的解释.本文在上述研究基础上,利用熔盐法合成了一系列具有多孔结构的不同Sr含量的LaCo0.8Fe0.2O3-δ钙钛矿材料,通过电化学装置测试其催化活性,并采用X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨透射电镜(HRTEM)、比表面积测试(BET)和软硬X射线吸收谱技术等表征手段对其进行了深入探索.XRD测试结果表明,Sr掺杂LaCo0.8Fe0.2O3-δ钙钛矿材料的主峰随着Sr含量增加向低角度偏移,这是由于Sr的离子半径较La的大.SEM和BET测试结果表明,不同Sr含量样品均表现出多孔的钙钛矿结构,并具有相似的比表面积,说明Sr含量变化不影响催化剂的形貌和比表面积.利用硬X射线吸收谱对体相Co和Fe元素的价态进行了研究,发现随着Sr含量的增加,Co和Fe离子的价态没有明显变化.类似地,利用软X射线吸收谱对表面层Co和Fe价态进行的研究发现,Co和Fe均表现出+3价,但在氧元素的K边吸收谱上观察到明显的氧空穴存在.电化学测试结果表明,催化剂的活性随Sr含量增加而增大.总之,随着Sr的掺杂,催化剂形貌及活性元素价态均无明显变化,但样品的电化学性能却发生了明显改善,这意味着尚有其它因素影响催化剂活性.利用HRTEM对OER反应前后的样品进行了形貌分析,发现在OER反应后Sr掺杂的催化剂表面出现了明显的无定形层,而无Sr掺杂的样品反应前后几乎未观察到表面形貌的变化.由此我们推断,Sr掺杂可诱导催化剂表面出现无定形层,进而提高OER反应活性.因此,在LaCo0.8Fe0.2O3-δ钙钛矿材料体系中,Sr掺杂是影响OER催化剂表面重构和制约催化活性的关键.     

Transport in molten LiF-NaF-ZrF4 mixtures: A combined computational and experimental approach

The transport properties of several LiF-NaF-ZrF₄ mixtures have been determined. Our work primarily consisted in the determination of the electrical conductivity from experimental measurements and from computer simulations. A good agreement was observed between both approaches. The simulations are based on the molecular dynamics technique and they employ a polarizable interaction potential, which was parameterized from first-principles calculations only. The diffusion coefficients were also determined from the simulations, which allowed us to understand the mechanisms responsible for the variations of electrical conductivity with temperature and composition of the melt.     

Reactor physic and reprocessing scheme for innovative molten salt reactor system

The molten salt reactor is one of the six concepts retained by the Generation IV forum in 2001. Based on the MSRE and MSBR concepts developed by ORNL in the 60s which involve a liquid fuel constituted of fluorine molten salt at a temperature close to 600 °C, new developments with innovative approach and technology have been realized which contribute to strongly improve the concept. The thorium breeder potentiality is closely related to the use of a liquid fuel which is able to be periodically treated. A reprocessing scheme has been established to treat used fuel by extraction of fission products. According to the Gen IV philosophy for closed cycle nuclear reactor, the actinides are sent back in the reactor core. In this way, the wastes radiotoxicity is strongly decreased and the use of natural resource is optimized. This paper describes an innovative reactor concept, the TMSR-NM (non-moderated thorium molten salt reactor), from the nuclear physic point of view and the different steps involving in the reprocessing scheme from the chemical point of view.     

KMnF3的熔盐法合成及掺铕体系的发光性质

采用简单的熔盐法合成了KMnF₃单相样品及稀土离子铕掺杂的KMnF₃（KMnF₃：Eu）荧光样品. X射线粉末衍射（XRD）表征结果显示,KMnF₃属立方晶系,为AMF₃型钙钛矿结构氟化物. 对样品KMnF₃：Eu的发光性质进行了研究,荧光光谱分析结果表明,Mn²⁺,Eu²⁺与Eu³⁺这3个发光中心共存于KMnF₃：Eu体系中. 讨论了改变掺入Eu离子的摩尔分数对Mn²⁺,Eu²⁺以及Eu³⁺发光强度的影响.     

XAFS analyses of molten metal fluorides

X-ray absorption fine structure studies of molten metal fluorides containing the materials related to nuclear engineering are intensively summarized. By using XAFS spectra data of divalent and trivalent cation metal fluorides in molten state which have been collected by authors’ group for a few years, local structure have been extracted and discussed systematically in conjunction with other spectroscopic studies and numerical calculations. In molten divalent fluorides, tetrahedral coordination of fluorides around a cation is predominant. In the case of pure molten trivalent fluorides, structure with more than 6-coordination has been suggested in some cases, but octahedral coordination structure is much stabilized at heavier rare earth metal fluorides. By mixing with alkali metal fluorides, it is a general trend that inter-ionic distances keep constant, but coordination number of fluorides decreases. In experimental chapter, all the details of sample preparation, furnace installation, X-ray optics setups and data analyses procedures are explained. Finally, future expectations of XAFS technique are also suggested.     

Efficient one-pot synthesis of polyhydroquinoline derivatives using Cs2.5H0.5PW12O40 as a heterogeneous and reusable catalyst in molten salt media

Polyhydroquinoline derivatives have been prepared efficiently in a one-pot synthesis via Hantzsch condensation using Cs_2.5H_0.5PW₁₂O₄₀ as a heterogeneous and reusable catalyst. The present method uses molten salt media instead of hazardous organic solvents. The present methodology offers several advantages such as simple procedure, excellent yields, and a short reaction time.     

Recent progress in nitrates and nitrites sensor with graphene-based nanocomposites as electrocatalysts

Nutrients based on nitrogen elements such as nitrite and nitrate have long been served as food preservatives in the food industry, as fertilizer in agriculture, and as color formers and rust inhibitors in the chemical industry. Due to the extensive nitrite and nitrate usage, the leakage or pollution discharge resulted in a large amount wasted in water sources and soil. As they are highly toxic inorganic pollutant, excess consumption and nitrite exposure can trigger several diseases and damage human health. As a consequence, an urgent need to develop a particular device for detecting and monitoring the presence of nitrite, specifically to measure drinking water quality and control remediation procedures. Owing to the merits of graphene, including broad theoretical surface area, high conductivity at room temperature, and a wider electrochemical window, graphene now serves as an excellent host material for anchoring nanomaterials to enhance the performance of electrochemical applications. There has been rapid progress in developing nitrite and nitrate sensors based on an electrochemical approach with the assistance of graphene-based nanocomposite material as the electrocatalysts. The electrically conductive graphene has high surface areas that allow the deposition of high-density analyte molecules, facilitating better selectivity and high sensitivity compared to other materials. The present review provides an overview on the recent development of electrochemical sensors for detecting nitrates and nitrites using graphene-based nanocomposites as electrocatalysts based on selective reports.