Decarburization in molten salts

Conclusion The decarburizing influence and corrosive effect of molten halides depend on the concentration of impurities in them. With use of slags as heat-transfer agents there is no decarburization. However, the iron oxide concentration in the bath should not exceed 5%.E. O. Paton Institute of Electric Welding. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 10–12, December, 1971.     

熔盐加热炉控制系统

本文介绍了中国长城铝业公司引进管道化溶出装置中熔盐加热炉的作用和控制系统构成 ,着重阐述了熔盐温度控制系统、重油与助燃风比值控制系统和盘管预热控制系统。     

熔盐电解制备四元Mg-Zn-Li-Ca合金(英文)

在LiCl-KCl-MgCl2-ZnCl2-CaCl2熔盐体系中,以钼为惰性电极,在温度为943K时,直接电解制备Mg-Zn-Li-Ca四元合金。循环伏安研究表明,在LiCl-KCl熔盐体系中,添加MgCl2、ZnCl2和CaCl2后,Li的析出电位明显正移。计时电位研究表明,当阴极电流密度等于或者更负于-1.55A/cm2时,Mg、Li/Zn和Ca能够实现四元沉积。X射线衍射研究表明,恒电流电解可以制备出由不同相组成的Mg-Zn-Li-Ca合金。采用金相显微镜和电子扫描显微镜对合金样品进行表征。能谱分析结果表明,Mg元素和Ca元素在合金中分布均匀,而Zn元素主要分布在基体的边缘。     

Structure and properties of steel after nitriding in molten salts

Conclusions The phase composition and thickness of the diffusion coating on steel obtained by electrolytic deposition of aluminum from molten salts vary with the annealing temperature and time. At low annealing temperatures (600–700°) phase Fe₂Al₅ extends from the surface into the depth of the sample, and at 800–900° FeAl is also observed (in addition to Fe₂Al₅) near the base metal.The strength of steel 08kp with an aluminum coating as much as 50 thick does not decrease in sulfur dioxide at temperatures of 20–400°.Scientific-Research Institute of Sanitary Engineering and Equipment, Buildings, and Structures, T. G. Shevchenko Kiev State University. Institute of General and Inorganic Chemistry, Academy of Sciences of the Ukrainian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, 49–51, February, 1979.     

Formation of metal chloride-graphite intercalation compounds in molten salts

Three molten salt systems, FeCl₃KCl, CuCl₂KCl and CuCl₂NaCl, were used to synthesize metal chloride-graphite intercalation compounds. Binary compounds, FeCl₃GICs and CuCl₂CICs, were obtained in the corresponding molten salts. The stage structure of GICs obtained was found to be governed by the composition of the molten salt and the reaction temperature. The behaviour of the formation of GICs in a molten salt has a close relation to its phase diagram: the formation of a complex chloride, e.g., KFeCl₄, reduces the amount of reagent chloride and its reactivity, and consequently has a strong influence on the final stage of the compound and the intercalating rate.     

Corrosion behaviour of Ni-based superalloys in molten FLiNaK salts

High-temperature corrosion tests of alloys, Nimonic 80A, Inconel 718 and Inconel C-276, were investigated at 680°C in molten alkali fluoride salt (LiF–NaF–KF: 46.5–11.5–42%) environment. In this work, techniques included were weight loss measurements and potentiodynamic polarisation curves measurements. Inconel C-276 and Inconel 718 showed better corrosion resistance, while Nimonic 80A exhibited comparatively lower corrosion resistance. The high-temperature corrosion behaviour was observed using measurements of the oxide morphology and thickness. The corrosion rates were determined by recording the weight changes of the sample alloys at different time intervals. Microstructural examination showed the depletion of Cr near the surface of the alloys and hence the significant weight loss in the early stages of corrosion tests. The corrosion mechanism of the alloys is discussed in detail.     

Electrochemical production of Sn-filled carbon nanotubes in molten salts

Sn-filled carbon nanotubes(CNTs) were prepared in situ by electrolysis of graphite in molten LiCl/SnCl2 mixtures. Transmission electron microscopy(TEM) investigation shows that the as-made products contain abun-dance of carbon nanotubes and most of them are filled with metal nanoparticles or nanorods. Some nanotubes are e-ven inserted with long continuous nanowires more than several micrometers in length. Selected area electron diffrac-tion(SAED) patterns and energy dispersive X-ray spectroscopy(EDS) of the filled nanotubes confirm the presence of Sn inside the nanotubes. The encapsulated Sn was further identified as β-Sn with tetragonal structure. Based on the experimental results, a possible growth mechanism of the Sn-filled nanotubes was also discussed.     

Electrochemical co-deposition of magnesium based alloy from molten salts

Magnesium based alloys with aluminum and zinc were obtained through electrochemical co-deposition from LiCl-NaCl-MgCl2 melt. The possibility of electrochemical co-deposition was discussed in detail by electro-analytical methods including cyclic voltametry, square wave voltametry, and chronopotentiometry. The co-deposition happens when the concentration of aluminum and zinc ions is kept at low value and the current density is high enough. The components of alloy elements can be controlled by fixing the components of the feeding salts. A laboratory experiment of the preparation by step-current co-deposition was also performed and certain compositions of the Mg-Al, and Mg-Zn were obtained. The alloys obtained from the co-deposition show a typical as-cast microstructure. The best conditions of electrolysis such as temperature, amount of addition and mode of feeding were discussed in detail.     

高温熔盐电导率测试方法

熔盐电解质的导电性对熔盐电解的能耗有极大的影响,直接关系到熔盐电解生产的能耗和成本。介绍了四电极法、连续改变电导池、交流电桥法和交流阻抗法测量高温熔盐电导率的基本原理、优点和存在的问题,为高温熔盐电导率测量方法的选择提供了参考。     

Employing a new bath- and liquidus temperature sensor for molten salts

In this article, a newly developed sensor that measures bath and liquidus temperatures is described. The accuracy and reproducibility of the sensor are discussed, and the sensor’s output is compared with results obtained using other techniques. A series of measurements in point-feed and center-worked cells are given. Finally, the evolution of bath and liquidus temperature is shown with respect to feed strategies. P. Verstreken earned his Met.Eng. in metallurgy at the University of Louvain, Belgium, in 1978. He is currently senior manager in the aluminum business area at Heraeus Electro-Nite. Mr. Verstreken is also a member of TMS.     

熔盐电解精炼提纯金属硅(英文)

对熔盐电解质中硅的沉积过程进行电化学研究。在 973~223K,在硅氯化物熔盐中采用电解精炼提纯金属硅。结果表明,液态硅铜合金阳极有利于 CaCl2-NaCl-CaO-Si 熔盐体系的电解精炼。ICP-AES 分析结果显示,通过电解精炼可有效去除原料中大量的钛、铝、铁等金属杂质,硅中的硼和磷含量分别由 36×106和 25×106降低至 4.6×10 6和 2.8×10 6,电解能耗约为 9.3 kW·h/kg。     

Preparation and characterization of tungsten nanopowders from WC scrap in molten salts

Tungsten carbide (WC) scrap was used as a consumable anode to prepare tungsten powder in NaCl–KCl melt at 1023 K for the first time. The electrolysis process was investigated. Results showed that the tungsten component in WC anode was dissolved as W^2 + into the NaCl–KCl melt. The cathode reaction was controlled by the diffusion of tungsten ions. The effect of electrolysis parameters, including the anode–cathode distance, cathode current density and different electrolysis ways (galvanostatic and potentiostatic electrolysis), on the purity and grain size of the cathode deposits was studied. It showed that a large anode–cathode distance was beneficial to the formation of pure tungsten powder at the cathode. With increasing the cathode current density, the tungsten grain size first decreased and then increased. When the cathode current density was 0.125 A cm^− 2, tungsten powder with a diameter of smaller than 100 nm was obtained. Deposits prepared through galvanostatic and potentiostatic electrolysis was compared in the end.     

Synthesis of Ni3Al intermetallic powder in eutectic molten salts

The powders of Ni₃Al intermetallic compounds were simply and economically synthesized by the chemical reaction in the various molten salts systems. In the relatively low temperature ranges, we studied to synthesize Ni₃Al intermetallic powders from Al and NiCl₂ in five kinds of eutectic molten salts by varying the reaction time and mole ratio of reactants. Ni₃Al intermetallic powders could be synthesized in AlCl₃–NaCl (63:37 in mol%), AlCl₃–NaCl–KCl (66:20:14 mol%), NaCl–KCl (50:50 mol%) and MgCl₂–NaCl–KCl (50:30:20 mol%) systems. However, it was impossible to separate the Ni₃Al powders from MgCl₂–NaCl–KCl (50:30:20 mol%) system. The Ni₃Al powders could not be synthesized in AlCl₃–NaCl (50:50 mol%) molten salt. The obtained powders were uniformly sub-micrometer sized. The reaction temperature at 500 °C, the reaction time for 3 h and the mole ratio of NiCl₂/Al=1.3 were the optimum conditions for synthesis of Ni₃Al intermetallic powders in AlCl₃–NaCl (63:37 mol%) molten salt.     

A critical discussion of chronopotentiometric measurement of diffusion coefficients in molten salts

This paper discusses the basic equations used in chronopotentiometry. It shows that the Sand equation can be derived from a more general equation. Particular emphasis is placed on the assumption of a diffusion coefficient independent of concentration in the diffusion layer. It then compares diffusion coefficients obtained by anodic and cathodic chronopotentiometry in two different ranges of concentration. The agreement of these two sets of results (from different laboratories) gives reason for confidence in the assumption.     

Corrosion of stainless steels and carbon steel by molten mixtures of commercial nitrate salts

The isothermal corrosion behavior of two stainless steels and a carbon (C) steel in mixtures of NaNO₃ and KNO₃ was evaluated to determine if the impurities found in commodity grades of alkali nitrates aggravate corrosivity as applicable to an advanced solar thermal energy system. Corrosion tests were conducted for approximately 7000 hours with Types 304 and 316 stainless steels at 570 °C and A36 C steel at 316 °C in seven mixtures of NaNO₃ and KNO₃ containing variations in impurity concentrations. Corrosion tests were also conducted in a ternary mixture of NaNO₃, KNO₃, and Ca(NO₃)₂. Corrosion rates were determined by descaled weight losses while oxidation products were examined by scanning electron microscopy (SEM), electron microprobe analysis (EPMA), and x-ray diffraction (XRD). The nitrate mixtures were periodically analyzed for changes in impurity concentrations and for soluble corrosion products. Results of these tests indicated that the short-term corrosion rates of the stainless steel specimens in many of the mixtures could be described in terms of parabolic kinetics. However, no single rate law could be assigned to the corrosion kinetics resulting from exposure in all of the mixtures. For engineering applications, corrosion rates over the entire exposure period are best described as linear with respect to time. In the binary nitrate mixtures, the annualized rates of metal loss were found to be between 6 and 15 μm/year for the stainless steel specimens at 570 °C depending on the particular mixture. Metal loss for the C steel specimens immersed in these same mixtures at 316 °C extrapolated to approximately 1–4 μm/year. SEM and XRD revealed that the complex, multiphase surface oxides formed on the stainless steel coupons were composed primarily of iron-chromium spinel, iron oxides, and sodium ferrite. Magnetite was the principal corrosion product formed on the carbon steel specimens. Overall, for the typical range of impurities in commercially available nitrate salts, corrosion rates for solar thermal energy applications remained acceptable for all of the materials examined.     

Rare metals preparation by electro-reduction of solid compounds in high-temperature molten salts

Direct electro-reduction of solid compounds in molten salts is a simple and straightforward electrolytic metallurgical method, which outperforms traditional pyrometallurgical methods such as carbothermic and metallothermic reductions in terms of economic viability,energy efficiency and carbon footprint. To better highlight the features of the direct electro-reduction of solid compounds in molten salts in extraction of rare metals, the scope of this paper is focused on the know-how of the cathodic process of the direct electro-reduction of solid compounds in molten salts in extraction of rare refractory metals including Ti, Zr, Hf, V, Nb, Ta, Mo and W, and rare disperse metals including Ga and Ge. In line with an introduction of the basic concept of the method, the characteristics of reaction paths in different systems are summarized and the corresponding strategy on tailoring energy efficiency and microstructure of electrolytic products are rationalized. The economic competence of the method might be enhanced by extending the method to controllable production of rare metals with high added values, welldefined microstructure and intriguing functionality.     

Chromosiliciding in molten salts to improve the cavitation resistance of cast iron

Conclusions Chromosiliciding in molten salts is recommended for protecting cast iron and steel parts against cavitation erosion.Dagestan Polytechnic Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 17–18, March, 1980.