Physicochemical properties of DMI–LiNO3 solvated ionic liquid and its application in electrodeposition of neodymium at room temperature

The density, conductivity, and viscosity of the 1,3-dimethyl-2-imidazolinone and lithium nitrate (DMI– LiNO₃) solvated ionic liquid were measured as a function of temperature. Additionally, the electrochemical mechanism and electrodeposition of neodymium from the DMI–LiNO₃ solvated ionic liquid were investigated. Cyclic voltammetry results indicate that the electrochemical reduction of Nd(III) is irreversible and proceeds via one-step with three-electron transfer, which is controlled by diffusion with a diffusion coefficient of 5.08×10⁻⁸ cm²/s. Energy- dispersive X-ray spectrometry and X-ray photoelectron spectroscopy data confirm that the electrodeposit obtained after electrodeposition at −4 V (vs Ag) using the DMI–LiNO₃–Nd(CF₃SO₃)₃ solvated ionic liquid contains metallic neodymium.     

Doping mechanism of PPy/LiDS film in aqueous solutions

We studied electrochemical redox reaction of polypyrrole (PPy) films prepared in an aqueous lithium dodecylsulfate (LiDS) solution by means of cyclic voltammetry, Auger electron spectroscopy, electrochemical quartz crystal microbalance and atomic force microscope, and presented a new doping–dedoping mechanism of PPy/LiDS film associated with the movement of DS⁻. During a potentiodynamic polymerization of PPy/LiDS, an additional small cathodic peak appeared at −0.37 V in addition to the main redox peaks at −0.81 V. PPy/LiDS film prepared under a galvanostatic condition also showed the additional cathodic peak, too. EQCM results indicated that the main redox peaks were due to the fast movement of small Li⁺ while the additional peaks were associated with the movement of DS⁻ despite of its large molecular size. In potentiostatic condition the movement of DS⁻ could be found even in negative potential region (−0.8 V) where the movement of Li⁺ is dominant for potentiodynamic condition. Thus, both cations and anions were involved in the redox process of PPy/LiDS film but the mobility of DS⁻ was controlled by scan rate of potential due to its bulkiness.     

Electrochemical behaviour of polypyridazine and o-, m-, p-diazines

The electrochemical behaviours of polypyridazine (PPd), an electrical conducting polymer, its monomer, pyridazine, and isomers, pyrazine and pyrimidine, have been studied by cyclic voltammetry (CV). When the electrochemical behaviours of the three diazines in acetonitrile (MeCN) solution with different supporting electrolytes (such as LiClO₄, NH₄BF₄, KPF₆, KAsF₆) are compared, it is found that under each of the above conditions the oxidation peak potential of pyridazine is the lowest, but its peak current is the highest. When LiClO₄ or NH₄BF₄ is used as the supporting electrolyte, pyridazine can be polymerized to form a dark greenish-blue PPd film on the anode, while pyrimidine or pyrazine is oxidized only to produce a yellowish powdery precipitate.A pair of redox peaks in the cyclic voltammogram of PPd film, generated in 0.2 mol l⁻¹ LiClO₄ or NH₄BF₄/MeCN solution at 2.0 V by potentiostatic electrolysis, are found at ≈0.40 V and −0.25 V, respectively. The changes of the acidity of the solution during the electrolysis and the effects of the experimental conditions on the electrochemical and other properties of PPd film have been studied. The oxidized PPd film contains para-linked pyridazine rings and ClO₄⁻ or BF₄⁻ counterion, the mole ratio of which is 2:1. PPd film can act like a metal, showing rapid electron transfer, while it is oxidized.     

Electrochemical synthesis and characterization of tantalum alkoxides

Tantalum(V) propoxide (Ta(OPrⁿ)₅), isopropoxide (Ta(OPrⁱ)₅) and butoxide(Ta(OBuⁿ)₅) were synthesized by electrochemical reactions of corresponding alcohol at sacrificial tantalum anode in the presence of tetraethylammonium chloride as a conductive additive. The pure products were isolated by reduced pressure distillation under 5 kPa. The crystal of Ta(OPrⁱ)₅ was obtained by recrystallization from hexane at ?10 °C. These samples were characterized by Fourier transform infrared spectra (FT-IR), Raman spectra, nuclear magnetic resonance spectra (NMR), TG/DTA and ICP-MS. The results show that direct electrochemical synthesis of metal alkoxides has a high current efficiency and electrolysis yield. These alkoxides have a high purity of 99.97% and can be directly used as the precursor of Ta₂O₅ films.     

Erosion–corrosion behavior of aluminum in a 50°C ethylene glycol aqueous solution simulating cooling water in HVDC transmission

The erosion–corrosion of aluminum in a 50 °C ethylene glycol aqueous solution (EGAS) was studied. Compared with that in deionized water, the corrosion of aluminum in an EGAS was inhibited to a certain extent. The corrosion potential, corrosion current, and charge transfer impedance of aluminum changed from −1.5776 V, 380.4 nA cm⁻², and 1.924 × 10⁻⁴ Ω cm⁻² in deionized water to −1.3127 V, 285.5 nA cm⁻², and 4.041 × 10⁻⁴ Ω cm⁻² in a 45.3 vt% EGAS, respectively. Ethylene glycol did not ionize in deionized water and the ionic conductivity of the EGAS was low, effectively restraining the corrosion of aluminum. However, a test with aluminum in an EGAS after long-term storage (9 days) showed that ethylene glycol gradually oxidized to glycolic acid, oxalic acid, and other substances, which slowly corroded the aluminum surface. Analysis results showed that the corrosion products on the surface of aluminum were Al(OH)₃ and Al₂O₃. The pitting hole formation mechanism of aluminum occurs via an aluminum–alcohol phase formed on the aluminum surface, which can inhibit the dissolution of the oxide film. Therefore, a suitably concentrated EGAS with a high heat capacity and low ionic conductivity similar to that of deionized water can be used as a coolant in airtight valve cooling systems for high-voltage direct-current transmission.     

Spectroelectrochemical studies of polyaniline

The structural change and electrode reaction mechanism of polyaniline with counter anion NO⁻₃ were investigated on the basis of vis-n.i.r. absorption spectra at different potentials in 1 M NaNO₃ aqueous solution at pH 1.5, with and without alkali treatment of the polyaniline film. Three redox stages were found in the spectra and the cyclic voltammogram in the potential range −0.4 V to 0.8 V (versus SCE). The equilibrium electrode potential of as-prepared polyaniline film is ≈0.3 V (versus SCE) in 1 M NaNO₃ aqueous solution at pH 1.5. The spectral changes with time after removing the polarization potential show that the stable state in the solution is in the potential range 0.2 –0.4 V; the over-oxidized state at higher than 0.5 V and the reduction state at lower than 0.1 V are both unstable.     

Studies on the chemical compensation of conducting polypyrrole by NaOH solution

The ‘chemical compensation’ of conducting polypyrrole (PPy) film by NaOH solution has been studied by cyclic voltammetry and vis-n.i.r. spectrometry. Strong evidence has been obtained to consider the process as a counter anion exchange between the intercalated anion and OH⁻ in solution. The NaOH-treated PPy film, PPy (OH⁻), was found to be capable of being further electrochemically reduced to PPy⁰. PPy(OH⁻) in NaOH solution is electrochemically reversible in the potential range −0.2 to −1.0 V versus SCE. When the potential scan went more positive than −0.2 V, irreversible oxidation of the PPy chain took place. PPy(OH⁻) has mid-gap electronic states lying at 1.6 and 1.0 eV above the valence band, the band gap being 3.0 eV.     

Electrochemical deposition of aluminum on W electrode from AlCl_3-NaCl melts

Electrochemical deposition of aluminum on W electrode from AlCl3-NaCl melts was studied by cyclic voltammetry and chronopotentiometry. The results show that Al ( Ⅲ) is reduced in two consecutive steps, i.e., 4Al2Cl7-+3e-→Al+7AlCl4- and then AlCl4-+3e-→Al+4Cl-. The electrochemical reaction of 4Al2Cl7-+3e-→Al+7AlCl4- is reversible. Certain nucleation overpotential is required during the deposition of aluminum on W electrode. Chronopotentiometry analysis also shows that Al (Ⅲ ) is reduced in two consecutive steps under certain current density, which is in reasonable agreement with cyclic voltammograms. By using constant current deposition, the electrodeposits on Al substrate obtained at between 50 and 100 mA/cm2 are quite dense and well adherent to the Al substrate. The electrochemical deposition of aluminum on Cu substrate in AlCl3-NaCl melts indicates that the intermetallic compounds are formed. The intermetallic compounds are AlCu and Al2Cu.     

The corrosion behavior of amorphous nickel base alloys in a hot concentrated phosphoric acid

The corrosion behavior of more than 50 melt-spun alloys was examined in an 87 wt% H₃PO₄ solution at 433 K. Ni-(30–50)Ta alloys possess the highest corrosion resistance due to the formation of a hydrated tantalum(V) oxyhydroxide film containing a small amount of phosphate. Corrosion rates of Ni-(1–10)Ta-P, Ni-(15–20)Cr-P and Ni-(10–20)Mo-P alloys are comparable to that of crystalline tantalum metal. The corrosion resistance of the former two alloy families is based on the formation of tantalum(V) phosphate and chromium(III) phosphate, respectively. The surface film on the Ni-Mo-P alloys consists of molybdenum(VI) and Ni(II) oxyhydroxides and phosphates, and nickel oxyhydroxide seems more protective than molybdenum oxyhydroxide.     

Electrochemical characteristics of titanium based biomaterials in artificial saliva

In the last decade, new titanium alloys have been developed in different areas of dentistry, such as Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, and Ti5Al2.5Fe. The aim of this study was to compare the Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, Ti5Al2.5Fe, and Ti6Al4V alloys with the commercial titanium, regarding the corrosion resistance in artificial saliva. In the electrochemical estimations the polarization data are converted into instantaneous corrosion rate values (I_corr). The passivation properties were comparable for the four alloys. The EIS spectra are best fitted using an equivalent circuit (EC), which corresponds to the model of a two‐layer structure for the passive film. High impedance values (in the order of 10⁶ Ω cm²) were obtained from medium to low frequencies for all materials suggesting high corrosion resistance in artificial saliva. The electrochemical and corrosion behavior of Ti6Al4V is not affected on substituting vanadium with niobium, iron, molybdenum, and tantalum.     

The electrochemical polymerization of methylene blue and properties of polymethylene blue

The electrochemical polymerization of methylene blue in the aqueous solutions has been carried out using repeated potential cycling. The scan potential was controlled at the region of −0.40 and 1.10 V, and the region of −0.40 and 0.92 V (vs. saturated calomel electrode, SCE). A blue film, i.e., polymethylene blue was formed on the platinum foil, and had a good electrochemical activity and reversibility in the pH region of 2.0 and 8.0. There are an anodic peak and a cathodic peak on the cyclic voltammograms. The currents of both anodic and cathodic peaks are proportional to υ^1/2 at the scan rate (υ) region of 25 and 600 mV s⁻¹. The electrochemical property of polymethylene blue polymerized on the platinum foil is different from that polymerized on the glassy carbon electrode. The visible spectra of polymethylene blue indicate that the wavelengths of absorption peaks are independent of potential at the range between 0.50 and −0.30 V (vs. Ag/AgCl with saturated KCl solution) and change a little with pH at the range between 3.0 and 8.0. The UV–Visible spectra and Raman spectra of polymethylene blue are different from those of methylene blue.     

Anodic process on Cu−Al alloy in KF−AlF3−Al2O3 melts and suspensions

Anodic processes on Cu−10Al electrode in molten KF−AlF₃−Al₂O₃ (saturated) and suspensions were characterized using chronopotentiometric and cyclic voltammetric techniques. Effects of cryolite ratio (CR= x(KF)/x(AlF₃)), temperature and particle volume fraction (ϕ) on the electrochemical behaviour of the anode were demonstrated. Initially, the anode was polarised in the galvanostatic mode in melt and suspensions (ϕ=0.12, 0.15) at 750 °C with 0.4 A/cm² current density. The anode potential in melt varied between 2.5 and 3.2 V and in suspensions (ϕ= 0.12) between 3.3 and 3.4 V. XRD analysis was conducted to study the oxide phases on the anode surface. Anode limiting current densities and mass transfer coefficients drastically decreased with the increase of ϕ in the suspension. The results suggest that the Cu−10Al electrode works better in suspensions with CR of 1.4 and particle volume fraction of 0.09 at 800 °C.     

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 formation of holmium-copper alloys on copper cathode in molten KCl-HoCl3

1 Introduction Alloys of rare earth Ho with other metals (Fe, Co, Ni, Cu, etc) possess electrical, magnetic and other properties important for modern technology[1- 4]. LI and ZHU[5] proposed a new processing technology for high property permanent magnets.…     

Redox behavior of indium in molten chlorides

An electrochemical study on the redox behavior of indium in the eutectic LiCl-KCl system at 450 °C was carried out with the transient techniques of cyclic voltammetry and chronopotentiometry on an inert molybdenum electrode. The reduction of In(III) was found to be a two-step process involving In(III)/In(I) and In(I)/In couples at the potentials of about ?0.4 and ?0.8 V versus Ag/AgCl, respectively. The redox mechanism was further confirmed by the theoretical evaluation of the number of transferred electrons based on cyclic voltammetry and characterizations of the precipitates generated by the potentiostatic electrolysis. The diffusion coefficients of indium ions in the eutectic LiCl-KCl melt at 450 °C were estimated by cyclic voltammetry and chronopotentiometry. The results obtained through the two methods are in fair agreement, delivering an average diffusion coefficient of approximately 1.8×10^?5 cm²/s for In(III), and 1.4×10^?4 cm²/s for In(I).     

Thermoelectric properties of ternary transition metal antimonides

Novel compounds T₆MBi₂, where T=Zr, Hf; M=Fe, Co, Ni, were synthesised by arc melting elemental combinations. Isotypism of these compounds with the ordered Fe₂P-type was established from Rietveld X-ray powder data. Physical properties (electrical resistivity and thermoelectric power) were investigated for a series of ternary transition metal compounds with stoichiometries such as TM_1−xX and T₆MX₂, where T is an electropositive transition metal (Zr, Hf and Nb), M is a metal from the iron group (Fe, Co, Ni) and X is Sb or Bi. Resistivities reveal a general metallic behaviour except for ZrCoSb and NbFeSb which are characterized by variable range hopping conductivity in a substantial temperature region. Thermoelectric power of these materials does not exceed 100 μV K⁻¹.     

In-situ synthesis of silicide coatings on molybdenum substrates by electrodeposition in chloride-fluoride molten salts

Silicide coatings including MoSi₂ and Si-MoSi₂ were prepared on molybdenum substrates by electrodeposition in NaCl-KCl-NaF-K₂SiF₆ molten salt. The experimental was conducted under different cathodic current densities at the temperature of 1073 K. The effect of the current density on the microstructure, phase composition, cross-section morphologies and elemental distribution of the as-prepared coatings were investigated by means of SEM, XRD and EDX. The results revealed that the type of the silicide coatings was strongly dependent on the current density and the relevant deposition mechanism was discussed. Besides, the electrochemical behavior of silicon ion in the chloride-fluoride molten salts was also studied using cyclic voltammetry and chronopotentiometry to reveal the electroreduction mechanism. The reduction of Si(IV) to Si was proved to be a quasi-reversible or irreversible diffusion-controlled single-step reaction and the diffusion coefficient of Si(IV) calculated from chronopotentiograms was (1.28 ± 0.25) × 10⁻⁵ cm²·s⁻¹.     

Preparation and characterization of a polypyrrole hybrid film with [Ni(dmit)2]2−, bis(1,3-dithiole-2-thione-4,5-dithiolate)nickellate(II)

The synthesis of a hybrid material obtained by electropolymerization of a solution of pyrrole and [NEt₄]₂[Ni(dmit)₂] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in acetonitrile solution is reported. The material was characterized by cyclic voltammetry, UV–vis and infrared spectroscopies, scanning electron microscopy (SEM), atomic force microscopy (AFM) and thermal gravimetric analysis (TGA). The FTIR spectroscopy showed that the [Ni(dmit)₂]²⁻ anion has been inserted in the polypyrrole framework and was not destroyed or modified during the polymerization process. The voltammetric analysis indicated that the material has electroactivity and undergoes redox processes associated with the conducting polymer and the counteranion. The cyclic voltammetry results also suggest that the counteranion is not trapped in the PPy matrix undergoing anion exchange during the redox cycle of PPy. The PPy/[Ni(dmit)₂]²⁻ exhibits good thermal stability and a intrinsic conductivity value in the range of semiconductors (10⁻³ S cm⁻¹).     

Factors affecting the corrosion behaviour of aluminium in acid solutions. II. Inorganic additives as corrosion inhibitors for Al in HCl solutions

CrO₄²⁻, WO₄²⁻ and HPO₄²⁻ ions affect on the corrosion behaviour of Al in 2 M HCl. The inhibition efficiencies of the additives depend on their type and increase with increasing concentration. Oxide film destruction and/or repair follow a direct logarithmic law. The inhibitive action of these anions is discussed in terms of competitive adsorption with Cl⁻ ions on the electrode surface followed by a reduction mechanism to form metal oxides. The calculated values of ΔG°_ads of the inhibition process reveal a physical adsorption of the inhibitors. The inhibition efficiency is found to decrease in the order: CrO₄²⁻ > WO₄²⁻ > HPO₄²⁻.     

AlCl3-assisted formation of charge-transfer complexes between polyacetylene and tetracyanoethylene,TCNE

Polyacetylene, (CH)_x, the simplest conjugated polymer, can be converted into a conducting materials (8 Ω⁻¹ cm⁻¹) by treating it with TCNE/ AlCl₃/benzene solution. An electron transfer π-complex was obtained, as shown by EPR and XPS spectroscopies.