Electrochemical formation of Sm-Co alloy films by Li codeposition method in a molten LiCl-KCl-SmCl3 system

Electrochemical formation of Sm-Co alloy films at a Co cathode was studied in a molten LiCl-KCl-SmCl₃ (0.5 mol.%) at 723 K. Very thin film (∼100 nm) of SmCo₂ alloy was obtained by potentiostatic electrolysis at 0.20 V (vs. Li⁺/Li) for 24 h. Much thicker alloy film (∼5 μm) was formed by Li codeposition method (cathodic galvanostatic electrolysis at 50 mA cm⁻²) for 1 h. The formed alloy phase was suggested as Li_xSm₄Co₆ (x∼3). The formed alloy film was changed to various Sm-Co alloy phases by anodic potentiostatic electrolysis depending on the applied potentials. The formation potentials of Sm₂Co₁₇, SmCo₃, SmCo₂ and Li_xSm₄Co₆ were found to be 1.40, 0.80, 0.30 and 0.05 V, respectively.     

Electrochemical formation of Sm-Co alloys by codeposition of Sm and Co in a molten LiCl-KCl-SmCl3-CoCl2 system

Electrocodeposition of Sm and Co on a Cu substrate was investigated in a molten LiCl-KCl-SmCl₃ (0.5 mol.%)-CoCl₂ (0.1 mol.%) system at 723 K. Phase of the deposited Sm-Co alloys could be controlled by electrolysis potential. SmCo₃ was formed on a Cu substrate by potentiostatic electrolysis in the potential range of 0.20-0.90 V (vs. Li⁺/Li). Sm₂Co₁₇ was obtained in the potential range of 0.90-1.50 V.     

Formation of Dy-Fe alloy films by molten salt electrochemical process

The electrochemical formation of Dy-Fe alloy films was investigated in a molten LiCl-KCl-DyCl₃ (0.50 mol%) system at 773 K. The deposition potential of Dy metal was 0.47 V (vs. Li⁺/Li) at a Mo electrode. Repetition of the potential sweep treatment at a fresh Fe electrode was effective in increasing the rate of formation of Dy-Fe alloys. Using an Fe electrode activated by repetition of the potential sweep treatment, a DyFe₂ film was formed by potentiostatic electrolysis at 0.55 V. However, the alloy film was thin and not adhesive. An adhesive DyFe₂ film was formed at the activated Fe electrode by potentiostatic anodic electrolysis at 0.55 V after cathodically electrodepositing Dy meal at 0.40 V. By using a similar procedure, Dy₆Fe₂₃ was formed at 0.68 V. The equilibrium potential for (2/11)Dy₆Fe₂₃+Dy(III)+3e⁻?(23/11)DyFe₂ was estimated as 0.62 V.     

Electrochemical formation of Mg-Li alloys at solid magnesium electrode from LiCl-KCl melts

This work presents a study on electrochemical formation of Mg-Li alloys on solid magnesium electrode in a molten LiCl-KCl (50:50, wt.%) system at 753 K. Cyclic voltammetry and open circuit chronopotentiometry were employed to investigate the electrode reaction. For an Mg electrode, the electroreduction of Li(I) takes place at more positive potential values than at the inert W electrode indicating the formation of Mg-Li alloys. X-ray diffraction and scanning electron microscopy (SEM) analysis of the deposits indicated that α, α + β and β phases Mg-Li alloys with the thickness of 182, 365 and 2140 μm were obtained by potentiostatic electrolysis at −2.26, −2.30 and −2.39 V (vs. Ag/AgCl), respectively. The results showed that formation of α, α + β and β phases Mg-Li alloys could be controlled by applied potential. Lithium contents of Mg-Li alloys can be decreased via electrolysis at low temperature followed by thermal treatment at higher temperature. Mg-Li alloys with excellent mechanical properties can be produced by this novel method.     

Electrochemical formation of AlN in molten LiCl-KCl-Li3N systems

Electrochemical formation of aluminum nitride was investigated in molten LiCl-KCl-Li₃N systems at 723 K. When Al was anodically polarized at 1.0 V (versus Li⁺/Li), oxidation of nitride ions proceeded to form adsorbed nitrogen atoms, which reacted with the surface to form AlN film. The obtained nitrided film had a thickness of sub-micron order. The obtained nitrided layer consisted of two regions; the outer layer involving AlN and aluminum oxynitride and the inner layer involving metallic Al and AlN. When Al electrode was anodically polarized at 2.0 V, anodic dissolution of Al electrode occurred to give aluminum ions, which reacted with nitride ions in the melt to produce AlN particles (1-5 μm of diameter) of wurtzite structure.     

Electrochemical formation and control of chromium nitride films in molten LiCl-KCl-Li3N systems

Electrochemical formation and control of chromium nitride films have been investigated in molten LiCl-KCl-Li₃N systems at 723 K. Chromium nitride films were obtained by means of potentiostatic electrolysis of chromium electrodes in the melts. From XPS and XRD analyses, it was confirmed that all obtained films consisted of Cr₂N and CrN, and the composition of each nitride layer was effected by the applied potential value. For instance, a nitride layer consists mostly of Cr₂N on a chromium specimen after potentiostatic electrolysis at 1.0 V (vs. Li⁺/Li), and it consists mostly of CrN at 1.5 V. At the potential range from 1.0-1.5 V, the ratio of CrN-Cr₂N in the nitride layer increases, as the applied potential is more positive. Furthermore, the thickness of the nitride layer increases with increasing the electrolysis time. The obtained results suggest that compositions and thickness of nitride films can be controled by electrolytic conditions, e.g. applied potential and electrolysis time.     

Internal cation mobility in molten LiCl-NdCl3 system

Internal mobilities of Li⁺ and Nd³⁺ cations have been investigated in binary unsymmetrical molten LiCl-NdCl₃ system by countercurrent electromigration method (so-called Klemm method). The results have been presented as isotherms of cation internal mobilities versus equivalent fraction of NdCl₃ for 1023, 1073 and 1123 K and have been compared with corresponding relationships for NaCl-NdCl₃ and KCl-NdCl₃ systems. It has been found that internal mobility of Nd³⁺ ions (as well as Li⁺) increases with decreasing concentration of NdCl₃, contrary to KCl-NdCl₃ and NaCl-NdCl₃ systems for which Nd³⁺ internal mobility decreases or is nearly constant, respectively. The tendency that smaller alkali metal cation enhances internal mobility of trivalent ion (b_Ln) has been described with a simple equation: , where is the internal mobility of Ln³⁺ in molten LnCl₃, yLnCl₃ the equivalent fraction of LnCl₃ and a parameter is the difference between internal mobility of Ln³⁺ cation in molten LnCl₃ and internal mobility of this cation in infinitely diluted solution of LnCl₃ in alkali metal chloride.     

Study on the preparation of Mg-Li-Zn alloys by electrochemical codeposition from LiCl-KCl-MgCl2-ZnCl2 melts

Electrochemical codeposition of Mg, Li, and Zn on a molybdenum electrode in LiCl-KCl-MgCl₂-ZnCl₂ melts at 943 K to form Mg-Li-Zn alloys was investigated. Cyclic voltammograms (CVs) showed that the potential of Li metal deposition, after the addition of MgCl₂ and ZnCl₂, is more positive than the one of Li metal deposition before the addition. Chronopotentiometry measurements indicated that the codeposition of Mg, Li, and Zn occurs at current densities lower than −0.78 A cm⁻² in LiCl-KCl-MgCl₂ (8 wt.%) melts containing 1 wt.% ZnCl₂. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li, and Zn is −2.000 V, and the codeposition of Mg, Li, and Zn is formed when the applied potentials are more negative than −2.000 V. X-ray diffraction (XRD) indicated that Mg-Li-Zn alloys with different phases were prepared via galvanostatic electrolysis. The microstructure of typical α + β phase of Mg-Li-Zn alloy was characterized by optical microscope (OM) and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) showed that the elements of Mg and Zn distribute homogeneously in the Mg-Li-Zn alloy. The results of inductively coupled plasma analysis showed that the chemical compositions of Mg-Li-Zn alloys are consistent with the phase structures of the XRD patterns, and that the lithium and zincum contents of Mg-Li-Zn alloys depend on the concentrations of MgCl₂ and ZnCl₂.     

Electrochemical synthesis of Ni-Sn alloys in molten LiCl-KCl

The electrochemical formation of Ni-Sn was investigated in molten LiCl-KCl in the temperature range 380-580 °C. Before, an electrochemical study of the Ni²⁺/Ni⁰, Sn⁴⁺/Sn²⁺ and Sn²⁺/Sn⁰ redox couples was performed by cyclic voltametry and chronopotentiometry in a wide temperature range. It had been pointed out that in the case of the Sn⁴⁺/Sn²⁺ redox couple, an insoluble compound is probably formed for T < 460 °C. For higher temperature, this compound becomes soluble and then, the shape of the cyclic voltammogram is analogue to the one usually observed when a diffusion-controlled process is involved. The diffusion coefficient values of Ni²⁺ and Sn²⁺ ions were determined. For instance, D_Ni(II) and D_Sn(II) values deduced from chronopotentiometry were about 2.1 × 10⁻⁵ and 2.7 × 10⁻⁵ cm² s⁻¹ at 440 °C, respectively. Then, Ni-Sn alloys have been formed in potentiostatic mode. The electrochemical route proposed in this paper leads to the formation of crystallized alloys with a well-defined composition depending on the operating conditions.     

Template formation of magnesium aluminate (MgAl2O4) spinel microplatelets in molten salt

Magnesium aluminate, MgAl₂O₄ (MA), microplatelets were synthesized using a molten salt technique. -Alumina platelets partially decomposed from aluminium sulphate were reacted with either commercial magnesium oxide or magnesium nitrate in the molar ratio 1:1 to synthesize spinel platelets. Molten salts such as chloride, MCl (M = Li, Na, and K) and potassium sulphate were used for MA synthesis and the salt to oxide ratio was kept at 3:1 for all compositions. Reactants and molten salt mixes were fired in an alumina crucible for 3 h at from 800 to 1150 °C. XRD revealed complete MA without formation of any secondary phase for powders fired for 3 h at 1100 °C. Electron microscopy revealed the MA platelet morphology and size was the same as the -alumina platelets indicating a ‘template process’ during molten salt synthesis.     

Bi(Ⅲ)在NaCl-KC1熔盐体系中的电化学行为

为开发环境友好型铋提取技术,在700℃下采用循环伏安、方波伏安和计时电位等方法研究了NaCl?KCl熔盐体系中Bi(III)在玻碳电极上的电化学行为。在–0.3 V (vs. Ag/AgCl)电位下以玻碳电极为工作电极对NaCl?KCl?BiCl3进行恒电位电解。结果表明,Bi(III)在NaCl?KCl熔盐体系中的还原反应是一步得到3个电子的准可逆反应Bi3++3e?=Bi,起始还原电位为0.05 V (vs. Ag/AgCl),该反应受扩散控制。Berzins-Delahay方程和Sand方程计算的700℃下Bi(III)在熔盐中的扩散系数分别为0.83×10–5和1.0×10–5 cm2/s。阴极产物为致密纯金属Bi,不含杂质。     

Electrolytic reduction behavior of U3O8 in a molten LiCl-Li2O salt

An electrolytic reduction of U₃O₈ in a molten LiCl-Li₂O salt was investigated using the electrochemical techniques of cyclic voltammetry (CV) and chronopotentiommetry (CP). The electrolytic reduction of U₃O₈ powder exhibited a different behavior when the initial current density was higher than for 10 g U₃O₈/batch run. Two kinds of reduction mechanisms, an electro-metallothermic reduction (EMR) and a direct electrochemical reduction (DER) were adopted to explain the resultant behavior. Current efficiencies and reduction products were obtained by a series of constant current runs. Current efficiencies, evaluated for a reduction side, were estimated to be more than 75% throughout a series of constant current runs and lithium uranium oxides (lithium uranates) were detected during the U₃O₈ reduction to metallic uranium.     

Internal cation mobility in molten CsCl-NdCl3 system at 1073 K

CsCl-NdCl₃ is the next of binary MCl-NdCl₃ systems (M: alkali metal) investigated for determination of relative internal mobilities of cations (b_Cs, b_Nd) by countercurrent electromigration method (Klemm's method). The results have been presented as isotherms of internal mobilities of Cs⁺ and Nd³⁺ ions on NdCl₃ equivalent fraction (y_Nd). It has been found that internal mobility of cesium cations is higher than neodymium ones in the entire composition range (what is typical for nonsymmetrical MCl-LnCl₃ systems (M: Li, Na, K; Ln: La, Nd, Dy)) and decreases with increase of NdCl₃ concentration in the melt. Generally, dependence of internal mobility of lanthanide cations in melts with alkali metal chlorides on lanthanide (i.e. its atomic number and concentration) seems strongly related to stability of chloride complex anions of lanthanides in the melt. Investigated systems may be divided into two classes. The first class includes MCl-NdCl₃ systems (M: Li, Na) characterized by decrease of b_Nd with increase of NdCl₃ concentration. The second includes KCl-LnCl₃ systems (Ln: La, Nd, Dy) and presented here CsCl-NdCl₃ system, and is characterized by increase of b_Ln with concentration of Ln³⁺ cation. The dependence of b_Nd on NdCl₃ concentration at 1073 K was fitted (as for other systems) by a simple equation of the form: , where is the internal mobility of Ln³⁺ cations in pure molten LnCl₃, a the difference between internal mobility of Ln³⁺ cations in pure molten LnCl₃ and infinitely diluted LnCl₃ in molten alkali metal chloride (extrapolated), and yLnCl₃ is the equivalent fraction of LnCl₃.     

Synthesis of CoAl2O4 by double decomposition reaction between LiAlO2 and molten KCoCl3

Submicronic CoAl₂O₄ powders were prepared by double decomposition reaction between solid LiAlO₂ and molten KCoCl₃ at 500 °C for 24 h. The reaction mechanism involves the dissolution of LiAlO₂ shifted by the precipitation of CoAl₂O₄ until complete transformation and the reaction leads to powders with a very homogeneous chemical composition. The powders obtained were mainly characterized by XRD, FTIR, ICP, X.EDS, electron microscopy and diffraction and diffuse reflexion. The blue pigments obtained exhibit a high thermic stability allowing their use for the colouring of ceramic tiles.     

Synthesis of NiWO4 nano-particles in low-temperature molten salt medium

Nickel tungstate (NiWO₄) nano-particles were successfully synthesized at low temperatures by a molten salt method, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet visible spectra techniques (UV–vis), respectively. The effects of calcining temperature and salt quantity on the crystallization and development of NiWO₄ crystallites were studied. Experimental results showed that the well-crystallized NiWO₄ nano-particles with about 30 nm in diameter could be prepared at 270 °C with 6:1 mass ratio of the salt to NiWO₄ precursor. XRD analysis confirmed that the product was a pure monoclinic phase of NiWO₄ with wolframite structure. UV–vis spectrum revealed that NiWO₄ nano-particles had good light absorption properties in both ultraviolet and visible light region.     

Preparation of Co-Sn alloys by electroreduction of Co(II) and Sn(II) in molten LiCl-KCl

Co-Sn alloys were prepared by an electrochemical route in molten LiCl-KCl between 400 and 550 °C. The Sn(IV)/Sn(II), Sn(II)/Sn(0) and Co(II)/Co(0) redox couples were studied by cyclic voltammetry and/or chronopotentiometry over the temperature range. The diffusion coefficient values of Co(II) ions were measured. For example, it was found that the D_Co(II) values deduced from chronopotentiometry range from D_Co(II) = 1.65 × 10⁻⁵ cm² s⁻¹ at 400 °C to 4.95 × 10⁻⁵ cm² s⁻¹ at 550 °C. The standard potential of the Co(II)/Co(0) redox couple in molten LiCl-KCl was measured at 400 °C: vs Cl₂/Cl⁻. Finally, Co-Sn alloys were prepared in potentiostatic mode. The influence of the temperature of molten LiCl-KCl, the applied potential and the deposition time on the morphology and the composition of the Co-Sn alloys were also investigated. For T > 450 °C, the following tendency has been observed: the more negative the potential, the higher the Sn content in the deposited alloy. Thus, depending on the operating conditions, pure CoSn or CoSn₂ can be prepared.     

Preparation and electrochemical studies of electrospun TiO2 nanofibers and molten salt method nanoparticles

The TiO₂ nanofibers and nanoparticles are prepared by electrospinning and molten salt method, respectively. The materials are characterized by X-ray diffraction scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and a thermal analysis. The SEM and TEM studies showed that fibers were of average diameter ∼100 nm and composed of nanocrystallites of size 10-20 nm. Electrochemical properties of the materials are evaluated using cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. Cyclic voltammetric studies show a hysteresis (ΔV) between the cathodic and the anodic peak potentials for TiO₂ nanofibers and nanoparticles (sizes ∼15-30 nm) are in the range, 0.23-0.30 V and a redox couple Ti^4+/3+ around ∼1.74/2.0 V. Electrochemical cycling results revealed that the TiO₂ nanofibers have lower capacity fading compared to that of the nanoparticles. The capacity fading for 2-50 cycles was ∼23% for nanofibers, which was nearly one-third of that of corresponding nanoparticles (∼63%). We discussed the effect of particle size on hysteresis and cycling performance of TiO₂ nanoparticles. Impedance analysis of TiO₂ nanofibers and nanoparticles during first discharge cycle is analyzed and interpreted.     

Effect of LiF dosage on morphology of ZrO2 prepared by the molten salt method

Zirconia nanorods and polyhedral particles were prepared using the molten-salt method. The effects of the LiF dosage on the ZrO₂ crystal morphology were studied using XRD combined with Rietveld refinement, FE-SEM combined with EDS, FTIR, Raman spectroscopy, and high-temperature microscopy. The results show that the ZrO₂ obtained with LiF is in the monoclinic phase. ZrO₂ nanorods were synthesized at low LiF dosages. Polyhedral ZrO₂ particles were synthesized, and the ZrO₂ crystal planes (100) and (200) were exposed to a high LiF dosage. LiF promoted the dissolution of ZrO₂ and was adsorbed onto the ZrO₂ crystal surface. This work provides a new strategy for controlling morphology and crystal surface exposure.     

In-situ formation of Ti3SiC2 interphase in SiCf/SiC composites by molten salt synthesis

Titanium silicon carbide (Ti₃SiC₂) film was synthesized by molten salt synthesis route of titanium and silicon powder based on polymer-derived SiC fibre substrate. The pre-deposited pyrolytic carbon (PyC) coating on the fibre was utilized as the template and a reactant for Ti₃SiC₂ film. The morphology, microstructure and composition of the film product were characterized. Two Ti₃SiC₂ layers form the whole film, where the Ti₃SiC₂ grains have different features. The synthesis mechanism has been discussed from the thickness of PyC and the batching ratio of mixed powder respectively. Finally, the obtained Ti₃SiC₂ film was utilized as interphase to prepare the SiC fibre reinforced SiC matrix composites (SiC_f/Ti₃SiC₂/SiC composites). The flexural strength (σ_F) and fracture toughness (K_IC) of the SiC_f/Ti₃SiC₂/SiC composite is 460 ± 20 MPa and 16.8 ± 2.4 MPa?m^1/2 respectively.