Electrochemical behavior of Cu in the (NaCl-KCl-CuCl) molten salt

The electrochemical reaction mechanism and electrocrystallization process of Cu on copper electrode in the eutectic NaCl-KCl-CuCl molten salt were investigated by means of cyclic voltammetry, chronopotentiometry and chronoamperometry technique at 710 C. The results show that the electrochemical reaction process of Cu is a quasi-reversible process mix-controlled by Cu + diffusion rate and electron transport rate; the electrochemical reduction mechanism is Cu + +e→Cu; the electrocry stallization process of co...     

Electrochemical reduction and electrocrystallization process of B（Ⅲ） in the LiF-NaF-KF-KBF4 molten salt

The mechanisms of the electrochemical reduction and nucleation process of B（Ⅲ） on the platinum electrode in the LiF-NaF-KF-KBF4 molten salt at 700℃ were first investigated using cyclic voltammetry and chronoamperometry techniques. It was found that the electrochemical reduction of B（Ⅲ） occurs in single-step charge transfer： B（Ⅲ） ＋ 3e → B, and the cathode process is reversible. The electrocrystallization process of B（Ⅲ） is instantaneous.     

Electrochemical preparation of titanium and titanium–copper alloys with K_2Ti_6O_(13) in KF–KCl melts

To investigate the electrodeposition mechanism of Ti~(4+), electrochemistry experiments were conducted using a KF–KCl–K_2Ti_6O_(13) molten salt at a Cu electrode at 950 ℃. Transient electrochemical techniques such as cyclic voltammetry(CV) and square-wave voltammetry were used in this study. The main phases and compositions of the product were analyzed by X-ray diffraction(XRD), scanning electron microscopy(SEM), and energy-dispersive spectrometry(EDS). The resulting product has the structure of metallic Ti. The results indicate that Ti~(4+) is reduced to metallic Ti by a two-step mechanism, corresponding to the reduction pathway: Ti~(4+)→ Ti~(2+)→ Ti. Moreover, Cu–Ti alloy could be obtained by the potentiostatic electrolysis at a Cu electrode.     

Electrochemical behavior of zirconium in molten NaCl-KCl-K<Subscript>2</Subscript>ZrF<Subscript>6</Subscript> system

The electrochemical reduction of Zr4+(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 Zr4+/Zr2+ and Zr2+/Zr steps were observed in the cyclic voltammograms.The result was also confirmed by square wave voltammetry.The diffusion coefficient of Zr4+(complex) ions at 1023 K in NaCl-KCl-K2ZrF6 melt,measured by cyclic voltammetry,is about 4.22×10-6 cm2/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 Zr4+(complex) ions.     

Electrochemical behavior of tungsten in （NaCI-KCI-NaF-W03） molten salt

Abstract The electrochemical reaction mechanism and electrocrystaUization process of tungsten in the NaCl- KCl-NaF-WO3 molten salt were investigated at 973 K （700℃） by means of cyclic voltammetry, chronopotentiometry, and chronoamperometry techniques. The results show that the electrochemical reaction process of tungsten in the NaCl-KCl-NaF-WO3 molten salt system is a quasireversible process mix-controlled by ion diffusion rate and electron transport rate. Tungsten ion in this system is reduced to W（0） in two steps. The electrocrystallization process of tungsten is found to be an instantaneous, hemispheroid three-dimensional nucleation process and the tungsten ion diffusion coefficient of 2.361 × 10^-4 cm2.s^-1 is obtained at experimental conditions.     

STUDY THE INFLUENCE OF H3BO3 ON THE ZINC ELECTROPLATING USING ELECTROCHEMICAL NOISE TECHNIQUE

The influence of H3BO3 on the zinc electroplating was studied using electrochemical noise technique, cyclic voltammetry and steady-state polarization method. The results showed that,under the experimental conditions, the deposition of zinc followed the mechanism of two-dimensional nucleation and subsequent grain growth. The addition of H3BO3 into the electroplating solution prominently changes the nucleation and growth kinetics of zinc deposits, which is directly related to the features of electrocrystallization noise and the corresponding structure of the electrodeposits. The results also shown that the electrochemical noise (EN) technique can give more information about the electrodeposits structure and electroplating mechanism than other normal electrochemical measurements can give, such as steady-state polarization method and cyclic voltammetry technique.     

Electrodeposition mechanism of ZnSe thin film in aqueous solution

ZnSe is one of the important and excellent Ⅱ-Ⅵsemiconductor materials, which has direct transition band structure. In this paper, ZnSe thin films were prepared by an electrochemical deposition method, and the formation mechanism of ZnSe was studied systematically. Voltammetry and chronoamperometry combined with X-ray diffraction(XRD) and Raman techniques were used to analyze the deposition processes. It is found that the substrate and deposition potentials have a great influence on the phase composition of deposited thin film, and Zn substrate is beneficial to the preparation ZnSe films. Strong selenium-substrate interaction results in the formation of selenium compounds involving electrode materials. The addition of Zn(Ⅱ) source can affect the reduction potential of Se, and results in the change of reducing mechanism of Se(0) from Se(Ⅳ). Se(0) formed from H_2Se because the formation of H_2Se is more active than forming Se(0)directly from Se(Ⅳ), and H_2Se can recombine with the substrate material, forming selenium-substrate compounds more quickly.     

Catalytic mechanism of Cu（p-OTs）2／ethanolamine as mimetic enzyme

The electrochemical behaviors of various copper salts complexes coordinated with equal molar ethanolamine were studied, and those of Cu(p-OTs)2 and Cu(p-OTs)2/ethanolamine(1：1) complex in CH3OH or DMF were characterized. The results show that the reduction of Cu(Ⅱ) in Cu(p-OTs)2 is via one two-electron step mechanism both in CH3 OH and DMF. The reduction mechanism transforms to two one-electron steps in the case of Cu (p-OTs)2/ethanolamine(1：1) in DMF. However, it does not change in CH3OH. All the Cu(Ⅱ)/ethanolamine(1:1) with the electrochemical reactions are through two one-electron steps, and can act as mimetic enzyme to oxidize 1, l‘-bi-2-naphthol. The Cu(Ⅱ)/ethanolamine(1:1) with electrochemical reactions through one two-electron step could not act as mimetic enzyme. It is concluded that the transformation between centre Cu(Ⅱ) and Cu(Ⅰ) is the crucial condition for the catalytic activity of copper-amine complex.     

Corrosion behavior of thermal-sprayed WC cermet coatings in SO4 2− environment

A series of the electrochemical and long-term corrosion tests was carried out in a 3.5 wt% Na2SO4 solution on thermal-sprayed WC-17Co and WC-10Co-4Cr cermet coatings in order to examine the effect of composition of binder materials on the corrosion behavior. The results reveal that the overall corrosion resistance of the WC-17Co coating is inferior to that of the WC–Co–Cr coatings due to the corrosion of binder materials which induce WC particles to fall off. CoO and WO3 oxide films form on the surface of WC-17Co coating in Na2SO4 solution electrochemical corrosion process, which will protect the coating in the process of corrosion. Cr2O3 oxide film formed on the WC-10Co-4Cr coating surface has a strong hindered role to corrosion. The corrosion mechanism of WC-17Co coating in Na2SO4 solution is entire corrosion of Co matrix, while it is film-hole corrosion mechanism for WC-10Co-4Cr coating.     

Electrochemical behavior of Nd in its pyrometallurgical recovery from waste magnet

High-purity Nd metal was recovered from waste Nd–Fe–B magnet by the molten salt electrowinning process with chemical pretreatment. X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), cyclic voltammetry(CV),chronopotentiometry(CP), and inductively coupled plasma-atomic emission spectrometer(ICP/AES) were used to characterize the deposit and electrochemical behaviors. The results show that NdF3 is effectively synthesized from the Nd–Fe–B magnet using HCl solution and NH4F. During the chemical treatment of the waste magnet,iron impurity is eliminated as a soluble [NH4]3[FeF6]complex. Electrowinning using NdF3 in LiF molten salt shows that Nd metal is deposited from the electrolyte onthe cathode at the reduction potentials ranging from-1.48to-1.35 V(vs. W) with the concentration change of NdF3.The final purity of Nd metal deposit is higher than99.78 %.     

Non-isothermal kinetics of synthesizing vanadium nitride by one-step method

Vanadium nitride was synthesized by one-step method using V2O5 and carbon black as raw materials in nitrogen atmosphere. The phases of different reaction products prepared in different reaction temperatures were analyzed by X-ray diffraction(XRD), and the dynamic behavior of the process of synthesizing vanadium nitride(VN) by one-step method was studied with non-isothermal thermogravimetry. The mechanism function and kinetic parameters of reaction process were calculated by thermal gravimetric analyses(TGA), and the reaction rate equation was established. The XRD results show that for the samples tested with minimal VN after holding for 4 h at 1273 K, the main phase of products is VN at 1476 K, while some vanadium nitrides transform into vanadium carbides again over 1573 K. It is found that N2 is beneficial to stimulate reduction and proceed carbonization reaction,and the reduction and nitridation reaction can occur simultaneously. The activation energy of preparing VN by one-step method is 104.005 kJ·mol-1, and the frequency factor is 470.52 at 1280–1358 K, and 150.052 kJ·mol-1 and 2.35 9 104 at 1358–1426 K, respectively.     

Composite corrosion inhibitors for secondary alkaline zinc anodes

The corrosion inhibition property of PEG600 and In(OH)3 as composite corrosion inhibitors for secondary alkaline zinc electrodes was studied, and the inhibition efficiency was determined as 81.9%. The research focused on the mechanism by the methods of electrochemical impedance spectroscopy, polarization curves and IR spectroscopy. The results indicate that the corrosion inhibition effectiveness is attributed to the joint inhibition of anodic zinc dissolution and cathodic hydrogen evolution. And the anodic process is depressed to a greater extent than the cathodic process. The synergistic mechanism of the composite inhinbitors proves to be the enhancement of adsorption of PEG600 by In(OH)3. Potentiostatic experiment results and SEM images verify the inhibition of dendritic growth by the composite inhibitors.     

Process of producing magnesium by thermal vacuum reduction using silicocalcium as reductant

A new process of producing magnesium by thermal vacuum reduction using dolomite and magnesite as materials and silicocalcium as reductant was studied in this study. The reduction process of MgO by silicocalcium was analyzed by phases analysis of reduction slag through X-ray diffraction(XRD) and the factors influencing the reduction ratio of MgO were investigated. The experimental results show that when using silicocalcium as reductant, the reduction ratio of MgO can be over 93%. In the reduction process, calcium in silicocalcium takes part in the reduction reaction of MgO firstly below 1,000 ℃ and it makes CaSi_2 decompose. It also releases elemental silicon which has more reactive activity and improves the reduction reaction of MgO. That is the main cause that the reduction ratio of MgO using silicocalcium as reductant is 8%–10% higher than that by Pidgeon process using ferrosilicon as reductant under the same conditions.     

Electrocatalytic performance of Pd–Ni nanowire arrays electrode for methanol electrooxidation in alkaline media

A successful approach to prepare the Pd–Ni nanowire arrays electrode without carbon supports was reported. The morphology and crystallinity of nanowire were characterized by transmission electron microscopy, selected-area electron diffraction(SAED), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS) analyses, respectively. The results show that the diameters of the nanowire are in the range of 65–75 nm, and the polycrystalline binary solid solution alloy is formed in the Pd–Ni nanowire. Cyclic voltammograms, chronoamperograms, and electrochemical impedance spectroscopy demonstrate that the Pd–Ni nanowire arrays electrodes show excellent electrocatalytic performance for methanol oxidation in alkaline media. The catalytic activity of Pd–Ni nanowire arrays electrode is *1.39 times higher than that of the Pd nanowire arrays electrode and *2.28 times higher than that of the commercial Pd/C catalyst. This is mostly owing to the transfer of electron density from Ni to Pd. These results indicate that Pd–Ni nanowire arrays electrode is very promising in an alkaline direct methanol fuel cell.     

ELECTROCHEMICAL NOISE ANALYSIS OF THE INFLUENCE OF THE Zn^2＋ IONS CONCENTRATION ON ZINC ELECTROPLATING

The influence of the concentration of Zn^2 ions on zinc electroplating process was investigated by means of electrochemical noise (EN) and cyclic voltammetry methods in conjunction with the scanning electron microscopy (SEM) technique. It was found that the EN generated during the electroplating of dentritic or large polymeric zinc deposit has large potential oscillation amplitude and positive potential drift while the compact zinc deposit possesses small noise amplitude and little potential drift. With the change of rate determining step from diffusion-control through mixed-contro! to activation-control, the maximum relative energy obtained from wavelet analysis defined from the region with larger scales to those with smaller scales, and the EDP (relative energy distribution plot) can be us, as “fingerprints” of EN to characterize the electroplating process and the deposit structure. The results also showed that electrochemical noise technique can give more information about the electrodeposit structure than other normal electrochemical measurements, such as linear potential sweep method and cyclic voltammetry, technique.     

Formation behavior of CaTiO_3 during electrochemical deoxidation of ilmenite concentrate to prepare Fe–Ti alloy

The formation behavior of CaTiO_3 during electro-deoxidization of ilmenite concentrate to prepare Fe–Ti alloy was investigated by experiments and simulation.The results indicate that the formation and decomposition of intermediate products,CaTiO_3,are inevitable steps during electro-deoxidization of ilmenite concentrate.CaTiO_3 can be generated through the hydrolyzation of molten salt and electrochemistry reaction during electrochemical process.The main reason for the generation of CaTiO_3 is the electrochemistry reaction between Ca~(2+) from molten salt and TiO_2 in the cathode.With the proceeding of the electro-deoxidization,CaTiO_3 is further electrolyzed to form titanium sub-oxide.The current efficiency can be improved when CaTiO_3 forms in the cathode by adding CaCO_3 during sintering process.     

Reduction roasting–magnetic separation of vanadium tailings in presence of sodium sulfate and its mechanisms

Reduction roasting with sodium sulfate followed by magnetic separation was investigated to utilize vanadium tailings with total iron grade of 54.90 wt% and TiO_2 content of 17.40 wt%. The results show that after reduction roasting–magnetic separation with sodium sulfate dosage of 2 wt% at roasting temperature of 1150 °C for roasting time of 120 min, metallic iron concentrate with total iron grade of 90.20 wt%, iron recovery rate of 97.56 % and TiO_2 content of 4.85 wt% is obtained and high-titanium slag with TiO_2 content of 57.31 wt% and TiO_2 recovery rate of 80.27 % is also obtained. The results show that sodium sulfate has a catalytic effect on the reduction of tailings in the novel process by thermodynamics, scanning electron microscopy(SEM) and X-ray diffraction(XRD) and reacts with silica and alumina in the tailings to form sodium silicate and sodium aluminosilicate. Migration of elements and chemical reactions destroy the crystal structures of minerals and promote the reduction of vanadium tailings, resulting in that iron grains grow to large size so that metallic iron concentrate with high total iron grade and low TiO_2 content is obtained.     

Hydrothermal conversion of Ti-containing minerals in system of Na_2O–Al_2O_3–SiO_2–CaO–TiO_2–H_2O

Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution.Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na_2O–Al_2O_3–Si O_2–Ca O–Ti O_2–H_2O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to Al_4Ti_2 SiO_(12) at low temperatures(60–120 °C), which is similar to anatase in crystal structure. As the temperature continues to rise, Al4Ti2 Si O12decomposes gradually and converts to Ca_3 Ti Si_2(Al_2Si_(0.5)Ti_(0.5)O_(14) at 200 °C. When the temperature reaches 260 °C, Ca Ti O_3 forms as the most stable titanate species for its hexagonal closest packing with O_2-and Ca_2?. The findings enhance the understanding of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.     

A Multi-step Thermodynamic Model for Alumina Formation during Aluminum Deoxidation in Fe–O–Al Melt

Based on the two-step nucleation mechanism, a multi-step thermodynamic model for alumina inclusion formation during aluminum deoxidation process was proposed in Fe–O–Al melt. Thermodynamic properties of metastable intermediates including(Al2O3)nclusters for prenucleation and a-Al2O3 nanoparticle for growth process were calculated using density functional theory. Furthermore, Gibbs free energy change of forming the intermediate by reaction between the dissolved aluminum(Al) and oxygen(O) in the melt was calculated. The results indicated that the thermodynamics of(Al2O3)nat steelmaking temperature are dependent on their structures, while that of a-Al2O3 nanoparticle are dependent on their size. The nuclei of a-Al2O3 which was originated from(Al2O3)naggregated under a high supersaturation ratio of Al and O(Rs) in the melt. There existing excess oxygen because of the low Rs, but the secondary inclusions will be formed during the cooling process due to the excess oxygen. The nuclei lager than 20 nm can grow up spontaneously and instantaneously into primary inclusions because of thermodynamic drive. It is difficult to control the size of a-Al2O3 to be less than 20 nm, in the aluminum deoxidation process of the current conditions of steelmaking.     

Formation of black nickel in leaching solution containing ammonia and chloride

The black nickel formation process in leaching solution containing ammonia and chloride was investigated in terms of cyclic voltammetric and galvanostatic reduction techniques. The structure of black nickel was examined by means of X-ray diffraction technique. The results show that in the scanning region, two oxidization current peaks are observed during the positive sweep, one of which is attributed to a valence state transformation of Ni(OH)2 to high valence nickel compound(black nickel), and the other is caused by nitrogen evolution. During the formation process of black nickel, γ-NiOOH probably tends to self-discharge with water to form a-Ni(OH)2. As a result, it is observed that Ipa/Ipc (Ipc-anodic peak current; Ipc-cathodic peak current) maintains at a constant with the scanning rate increasing. Two reduction current peaks in cyclic vohammogram and two potential plateaus in galvanostatic reduction curve for black nickel are ascribed to the reduction of various oxidization states of nickel oxide. The potential plateaus at about 0.75 V reach the maximum in galvanostatic reduction curves. Black nickel presents amorphous structure.