Aluminum assisted electrodeposition of europium in LiCl-KCl molten salt

Cyclic voltammetry (CV), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were employed to investigate the electrodeposition of Eu and Al in an LiCl-KCl eutectic melt containing Eu²⁺ and Al³⁺ at 450 °C. In order to deposit a pure Eu and Al alloy, the stoichiometrically lower concentration of Al³⁺ than that of Eu²⁺ and Al wires as a counter electrode was introduced into the bath of LiCl-KCl melt for the electrodeposition. The electrodeposition takes place at a potential more negative than −1.95 V vs. Ag|Ag⁺ while the deposit is oxidized at more positive potential than −1.92 V. Two new reduction peaks and an anodic peak on a W working electrode were observed at −2.39 V, −2.42 V, and −2.1 V, vs. Ag|Ag⁺, respectively, suggesting that the potential window of the Al system in LiCl-KCl melt can be extended to −2.43 V vs. Ag|Ag⁺. The EDS analysis indicated that AlEu can be deposited at the potential more negative than −2.37 V.     

Co-deposition of Al-Zn on AZ91D magnesium alloy in AlCl3-1-ethyl-3-methylimidazolium chloride ionic liquid

The co-deposition of Al and Zn on AZ91D magnesium alloy from a Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl₃-EMIC, with a molar ratio of 60:40) ionic liquid containing 1 wt% ZnCl₂ at room temperature was studied. The effect of potential on the deposition rate, the microstructure and the chemical composition of the deposit was explored. The experimental results show that the simultaneous deposition of Al and Zn on Mg alloy can be achieved under properly controlled potential conditions. The deposition rate increased while the amount of Zn existing in the coating decreased with increasing negative deposition potential. In the ionic liquid studied, a uniform chemical composition of the coating was obtained when the deposition was performed at −0.2 V (vs. Al).     

Electrodeposition of Sb, Bi, Te, and their alloys in AlCl3-NaCl-KCl molten salt

The Electrochemistry of Sb, Bi, and Te in AlCl₃-NaCl-KCl molten salt containing SbCl₃, BiCl₃, and/or TeCl₄ at 423 K was investigated by voltammetry, and electrodeposition of the three metals was performed under constant potential control in the melt. The voltammogram on a glassy carbon (GC) electrode in a melt containing 0.025 mol dm⁻³ [M] SbCl₃ showed a couple of redox peak corresponding to the Sb/Sb(III) redox reaction, and a stable layer of pure Sb was deposited under the constant potential control. The voltammograms in the melt containing 0.025 M BiCl₃ or 0.025 M TeCl₄ showed several redox couples. Stable deposit layers of pure Bi and Te were not obtained under the constant potential control, as the deposited layers detached from the electrode and immediately dissolved into the molten salt. Binary alloy deposition was possible in a melt containing BiCl₃ and SbCl₃, and also with BiCl₃ and TeCl₄. A stable Bi-Sb alloy deposit of metallic Sb and Bi-Sb solid solution was obtained at 0.8 and 0.9 V versus Al/Al(III) in the melt containing BiCl₃ and SbCl₃. The atomic ratio of Bi in the deposit was 37% at 0.9 V and 57% at 0.8 V. A stable Bi-Te alloy deposit was also obtained with the molten salt containing BiCl₃ and TeCl₄. The deposited Bi-Te alloy consisted of a mixture of Bi₂Te₃, BiTe, and Bi₂Te. The alloy deposit had good crystallinity and the preferential orientation was the (1 1 0) plane.     

Effect of interfacial-active elements addition on the incorporation of micron-sized SiC particles in molten pure aluminum

Ceramic particles generally have poor wettability by liquid metal, leading to a major drawback in fabrication of cast metal matrix composites (MMCs). In this work,  the effect of 1 wt. % of Ca, Mg, Si, Ti, Zn and Zr interfacial-active alloying elements was studied on the incorporation of micron-sized SiC particles into the molten pure aluminum using the vortex casting method at 680 °C. The results indicated that Ti, Zr, Zn and Si were not positively effective in improving particulate incorporation, while Ca and especially Mg were very efficient at increasing the incorporation of ceramic particles into the molten Al. Also, it was revealed that Al₃Ti, and Al₃Zr intermetallic phases were formed for samples containing Ti and Zr, making hybrid MMCs with a higher amount of hardness. Finally, it was found that a reaction layer between Al and SiC particles was formed at the Al/SiC interface for all of the samples, expect for the ones containing Si and Ti, indicating that for most of the samples at 680 °C an exothermic reaction took place between the Al and SiC particles.     

Fabrication of Pd-Ni alloy nanowire arrays on HOPG surface by electrodeposition

Pd-Ni alloy nanowires with diameters 50-300 nm and lengths of over 250 μm have been obtained by electrochemical step edge decoration (ESED). The fabrication by ESED is accomplished on highly oriented pyrolytic graphite by applying three potential pulses in succession: an oxidizing “activation” pulse, a reducing “nucleation” pulse, and a reducing “growth” pulse. The alloy composition is controlled by adjusting the ion concentration ratio of palladium and nickel, and the deposition processes. The scanning electron microscopy (SEM) images reveal that the alloy nanowires fabricated by this procedure are separate, parallel, and continuous. The composition of alloy nanowires can be controlled in the range of 8-15 wt.% Ni when the ion concentration ratio of palladium and nickel is 7:3 in the solution containing 70 mmol dm⁻³ Pd(NH₃)₄Cl₂. The reaction mechanism involves nucleation at potential of −1.1 V_SCE to −2.0 V_SCE and growth at potential of −0.3 V_SCE to −0.5 V_SCE.     

A direct electrochemical route from oxide precursors to the terbium-nickel intermetallic compound TbNi5

Successful direct electrochemical reduction of mixed powders of terbium oxide (Tb₄O₇) and nickel oxide (NiO) to the intermetallic compound, TbNi₅, is demonstrated in molten CaCl₂ at 850 °C by constant voltage (2.4-3.2 V) electrolysis. The reduction mechanism was investigated by cyclic voltammetry using a molybdenum cavity electrode in conjunction with characterisations of the products from both constant voltage and potentiostatic electrolysis under different conditions by XRD, SEM and EDX. It was found that the reduction started from NiO to Ni, followed by that of Tb₂O₃ (resulting from Tb₄O₇ decomposition) on the pre-formed Ni to form the intermetallic compound. The reduction speed increased with increasing the cell voltage, but the speed gain was counterbalanced by decreased current efficiency and increased electric energy consumption. At 2.4 V, the current efficiency reached 63.2%, and the energy consumption by electrolysis was as low as 3.2 kWh/kg TbNi₅ when the oxide phase was converted fully to the metal phase (XRD) in 4 h. The oxygen level in the produced TbNi₅ could readily reach 1800 ppm by electrolysis at 3.2 V for 12 h with the energy consumption being 18.9 kWh/kg TbNi₅.     

CoFeRh alloys: Part 2. Electrodeposition of CoFeRh alloys with high saturation magnetic flux density and high corrosion resistance

A Co₃₈Fe₆₁Rh₁ alloy with high saturation magnetic flux density, Bs, of 2.4 T was produced by electrodeposition from a solution containing RhCl₃, NH₄Cl, H₃BO₃, CoSO₄, FeSO₄, saccharin, NaLS (Na-lauryl sulfate) at pH 2.0. This alloy showed excellent corrosion resistance, which was comparable to sputtered 2.4 T Co₄₀Fe₆₀ alloy. It has been demonstrated that CoFeRh films with Bs = 2.3-2.4 T can be obtained at lower current density and lower concentration of RhCl₃ in the plating solution. The increase of current density and RhCl₃ concentration brings about increase of Rh-content in CoFeRh films with higher corrosion resistance, but lower Bs value. The co-electrodeposition of Co and Fe at the controlled potential occurs at more positive potentials (−0.6 to −0.8 V vs. SCE) in the presence of RhCl₃ in the plating solution. This phenomenon is possibly driven by the negative enthalpy of CoFeRh formation and/or through induced co-deposition of CoFeRh from a mixed-metal complex as an electroactive intermediate. It is also demonstrated that the decrease of the Bs value of CoFeRh alloys from 2.4 to 1.2 T is linked to the increase of nonmagnetic elements, i.e. Rh, O, H, S, C, N, and Cl, in the CoFeRh deposit.     

Voltammetric and differential pulse determination of roxithromycin

The oxidative behavior of antibiotic roxithromycin standard was studied at a gold electrode in 0.05 M NaHCO₃ using cyclic linear sweep voltammetry and differential pulse voltammetry. It was found that the value of the oxidative peak of pure roxithromycin at 0.81 V vs. SCE in 0.05 M NaHCO₃ at a scan rate of 50 mV s⁻¹ is a linear function of the concentration in a range 0.10006-0.654 mg cm⁻³. It was also found that peak current density at 0.75 V vs. SCE at a scan rate of 2 mV s⁻¹, pulse amplitude of 25 mV and pulse time of 0.1 s exhibits linear dependence on the concentration of roxithromycin from 0.1006 to 0.476 mg cm⁻³. Roxithromycin as a content of solid dosage form and urine was quantitatively determined and the obtained results were checked by HPLC.     

Investigation on electrochemical reduction process of Nb2O5 powder in molten CaCl2 with metallic cavity electrode

The direct electrochemical reduction process of Nb₂O₅ powder was investigated by cyclic voltammetry and constant potential electrolysis with a novel metallic cavity electrode in molten calcium chloride at 850 °C. The products of both constant potential and constant voltage electrolysis were characterized by XRD, SEM and EDX. CaNb₂O₆ was formed upon addition of solid Nb₂O₅ into molten CaCl₂ when CaO was present. During the electrolysis solid Nb₂O₅ was reduced to various niobium oxides of lower oxidation states, including some composite oxides, and then was converted completely to metallic niobium near −0.35 V (vs. Ag/AgCl), which was more positive than the reduction potential of Ca²⁺. Constant potential electrolysis was applied at the potentials near the reduction current peaks derived from the cyclic voltammetry curves, and cell voltages were monitored. The voltage was near 2.4 V when the oxide was metallized at −0.35 V (vs. Ag/AgCl). Nb₂O₅ pellet could be used to prepared metallic niobium at cell voltage 2.4 V in a larger electrolysis bath filled with calcium chloride at 850 °C. The experiment results further demonstrated the direct electrochemical reduction mechanism of Nb₂O₅ powder in a molten system.     

Room temperature electrodeposition of aluminum antimonide compound semiconductor

AlSb is a group III-V compound semiconductor material that is conventionally grown by high temperature processes such as Czochralski and Bridgman methods. Development of a method to synthesize AlSb at room temperature will be more economical to help modulate the electronic properties. In this investigation, a pulsed potential electrodeposition method using a room temperature molten salt system (aluminum trichloride, AlCl₃/1-methyl-3-ethylimidazolium chloride, EMIC) with an addition of SbCl₃ is discussed. The potential pulse parameters were established by carrying out cyclic voltammetry at different concentrations of SbCl₃ and with varying molar ratios of AlCl₃/EMIC. Stoichiometric AlSb deposits were obtained from an acidic AlCl₃/EMIC (1.5:1 molar ratio) melt containing 4 × 10⁻³ mol/l of SbCl₃ onto an ordered TiO₂ nanotubular template. The AlSb compound was predominantly amorphous in as-deposited condition and annealing at 350 °C for 2 h in argon transformed into crystalline phase. The AlSb deposit showed a high resistivity in the order of 10⁹ Ω-cm and a defect concentration of 10¹⁶ cm⁻³ which was attributed to presence of carbon. The deposits obtained from a basic melt (0.67:1 molar ratio of AlCl₃/EMIC) were enriched with antimony.     

Comparative study of Li[Co1−zAlz]O2 prepared by solid-state and co-precipitation methods

Li[Co_1−zAl_z]O₂ (0 ≤ z ≤ 0.5) samples were prepared by co-precipitation and solid-state methods. The lattice constants varied smoothly with z for the co-precipitated samples but deviated for the solid-state samples above z = 0.2. The solid-state method may not produce materials with a uniform cation distribution when the aluminum content is large or when the duration of heating is too brief. Non-stoichiometric Li_x[Co_0.9Al_0.1]O₂ samples were synthesized by the co-precipitation method at various nominal compositions x = Li/(Co + Al) = 0.95, 1.0, 1.1, 1.2, 1.3. XRD patterns of the Li_x[Co_0.9Al_0.1]O₂ samples suggest the solid solution limit is between Li/(Co + Al) = 1.1 and 1.2. Electrochemical studies of the Li[Co_1−zAl_z]O₂ samples were used to measure the rate of capacity reduction with Al content, found to be about −250 ± 30 (mAh/g)/(z = 1). Literature work on Li[Ni_1/3Mn_1/3Co_1/3−zAl_z]O₂, Li[Ni_1−zAl_z]O₂ and Li[Mn_2−yAl_y]O₄ demonstrates the same rate of capacity reduction with Al/(Al + M) ratio. These studies serve as baseline characterization of samples to be used to determine the impact of Al content on the thermal stability of delithiated Li[Co_1−zAl_z]O₂ in electrolyte.     

The underpotential deposition of Bi2Te3−ySey thin films by an electrochemical co-deposition method

Bi₂Te_3−ySe_y thin films were grown on Au(1 1 1) substrates using an electrochemical co-deposition method at 25 °C. The appropriate co-deposition potentials based on the underpotential deposition (upd) potentials of Bi, Te and Se have been determined by the cyclic voltammetric studies. The films were grown from an electrolyte of 2.5 mM Bi(NO₃)₃, 2 mM TeO₂, and 0.3 mM SeO₂ in 0.1 M HNO₃ at a potential of −0.02 V vs. Ag|AgCl (3 M NaCl). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were employed to characterize the thin films. XRD and EDS results revealed that the films are single phase with approximate composition of Bi₂Te_2.7Se_0.3. SEM studies showed that the films are homogeneous and have micronsized granular crystallites.     

Study on the electrochemical behaviour of Al3+ in LiCl-KCl-AlCl3 melt

The electrochemical behaviour of Al³⁺ reduction on a tungsten electrode in LiCl-KCl-AlCl₃ molten salt was investigated by electrochemical techniques. Using cyclic voltammetry (CV) and square wave voltammetry (SWV), Al³⁺ was reduced to Al in one step, and Li was deposited on Al to form Al-Li alloys of different compositions. According to chronoamperometry (CA), co-deposition of Li-Al alloys can be obtained at cathode current densities greater than 0.045 A cm⁻² or cathode potentials lower than −2.28 V (vs. Ag/AgCl). The apparent standard potential was calculated using the equilibrium electrode potential obtained from the open-circuit chronopotentiometry. Al³⁺ diffusion coefficient calculated by CV at 703 K is 0.82 × 10⁻⁵ cm²/s. In addition, the diffusion activation energy of Al³⁺ in LiCl-KCl-AlCl₃ molten salt was also obtained using the Arrhenius equation. The linear polarization was used to calculate exchange current density at different temperatures. Based on the theoretical model of metal nucleation deposition developed by Scharifker and Hills, the nucleation process of Al³⁺ involves instantaneous nucleation in the range of 673~763 K.     

Quantitative study of pH change during LaNi5−xAlx (x = 0, 0.3) discharge process by SECM

Oxygen reduction reaction (ORR) on Pt microelectrode was used for developing a micro pH sensor for scanning electrochemical microscopy (SECM) study in this work. When the potential of Pt microelectrode was held constant in ORR region, the ORR current (cathodic current) increased with decreasing solution pH and vice versa. The response time of the ORR current to pH changes was measured to be ca. 30 ms which implies that the pH response is fast enough for monitoring the temporal pH changes. Furthermore, a fine linear relationship was found to exist between the half wave potential of ORR (E_1/2) and the solution pH value, and the slope is −46 mV/pH. The Pt micro pH sensor was located 1 μm above the LaNi_5−xAl_x (x = 0, 0.3) substrate electrode surface in pH = 9 KOH solution to perform the tip-substrate voltammetry of SECM. In tip voltammogram, the ORR tip current qualitatively reflects the transit solution pH changes during LaNi_5−xAl_x discharge reaction. Also, the minimum values of the solution pH near LaNi₅ and LaNi_4.7Al_0.3 surface during the discharge reaction were quantitatively detected; they were 7.17 and 7.57, respectively. The result indicates that Al partial substitution for Ni degrades the maximum discharge ability of the alloy and decreases the hydrogen diffusion coefficient in alloy bulk.     

Electrochemical performances of Al-based composites as anode materials for Li-ion batteries

Al-C, Al-Fe and Al-Fe-C composite materials have been prepared by high-energy ball milling technique. The electrochemical measurements demonstrated that the Al-Fe-C composites have greatly improved electrochemical performances in comparison with Al, Al-C and Al-Fe anode. For example, Al₇₁Fe₉C₂₀ can deliver the reversible capacity of 436 mAh g⁻¹ at first cycle and 255 mAh g⁻¹ at 15th cycle. This improved electrochemical performance could be attributed to the alloying formation of Al with Fe and the buffering effect by the graphite matrix. This suggests that the Al-Fe-C composite has a potential possibility to be developed as an anode material for lithium-ion batteries.     

Effect of polymerization potential on the actuation of free standing poly-3,4-ethylenedioxythiophene films in a propylene carbonate electrolyte

The linear actuation of poly-3,4-ethylenedioxythiophene (PEDOT) films polymerized at different potentials (0.8-1.3 V) at −27 °C in propylene carbonate (PC) solutions of TBACF₃SO₃ (tetrabutylammonium trifluoromethanesulfonate) was examined under isotonic (constant force) and isometric (constant length) conditions. The actuation properties were evaluated by electrochemomechanical deformation measurements (ECDM) during cyclic voltammetry, square wave potential steps and long term cycling. The ECDM response revealed mixed ion actuation behaviour for PEDOT films polymerized at the potential extremes of 0.8 and 1.3 V. At intermediate polymerization potentials from 0.9 to 1.2 V, cation-driven actuation was observed involving immobilized triflate anions (CF₃SO₃⁻). Long term experiments (50 cycles) showed that films prepared at polymerization potentials of 0.8 V exhibited mainly anion-driven actuation, during potential steps to and from 1.0 V; conversely PEDOT prepared at a polymerization potential of 1.1 V showed exclusively cation-driven actuation. PEDOT films prepared at a polymerization potential of 1.1 V showed the maximum cation-driven actuation during cyclic voltammetry experiments including long term cycling. SEM images showed an open porous structure in all of the PEDOT films.     

Preparation of ZnO/Eu mixed films by electrochemical precipitation

The electrochemical preparation of europium doped zinc oxide and europium oxide/hydroxide as thin films is investigated. First, a thermodynamic study of the Eu-Cl-H₂O system has been carried out at 25 and 70 °C in order to predict the electrochemical behaviour of Eu(III) dissolved in aqueous solution containing chloride ions. A comparison of the Eu-Cl-H₂O and Zn-Cl-H₂O systems indicates the possible coprecipitation of ZnO and Eu(OH)₃ from deposition solutions containing well-adjusted Eu(III)/Zn(II) concentrations ratio. The thermodynamic predictions have been confirmed experimentally by the electrochemical co-deposition of ZnO/Eu thin films on conducting electrode substrates at −1.4 V versus MSE. The presence of europium in the film is detected for Eu(III)/Zn(II) concentration ratio at (0.6 mM/5 mM) which is lower than the predicted value. Increasing Eu(III) concentration leads to the rapid appearance of two phases: dispersed zinc oxide nanorods and, at the bottom of the rods, a covering layer containing Eu(OH)₃ and zinc. The density of ZnO rods decreases and the rod size increases with increasing Eu(III) concentration in the bath. Above 1 mM EuCl₃, a dramatic fall in the current density is observed with the formation of a less conducting ZnO/Eu mixed deposit.     

A three-step metal fractionation scheme for fly ashes collected in an Argentine thermal power plant

A new three-step fractionation scheme was applied to study the distribution of Al, As, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, S, Sb, Ti, V and Zn in fly ashes collected in the electrostatic precipitator of a thermal power plant in the city of San Nicolás (Argentina). Seven samples were collected during one week of operation in 2005. For the fractionation, the scheme applied consisted of extracting the elements in three fractions: (i) soluble and exchangeable elements, (ii) carbonates, oxides and reducible elements and (iii) residual elements. Metals and metalloids at μg g⁻¹ level were determined in each fraction by plasma based techniques namely, inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS). For validation, a certified reference materials NIST SRM 2711 (Montana soil) was subject to the same chemical sequential extraction procedure. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the major minerals present in the matrix. The predominant phases found in the total samples were mullite, quartz, iron oxides and lime. Total analyte concentration varied (in μg g⁻¹) from 1.54 for Cd to 30 600 for Al. The leachability of the 15 elements under study proved to be different. All the elements (except Cd and Pb) were detected in the soluble fraction in the order: Cu (0.10%) ∼ Mn (0.13%) < Ni (0.17%) ∼ Ti (0.19%) ∼ Fe (0.20%) ∼ As (0.21%) < Zn (0.86%) < Al (1.3%) < Cr (2.9%) < V (3.9%) < Sb (6.9%) < Mo (45.1%) < S (58.0%). Percentages higher than 20% of S (24.1%) < V (27.5%) < Mn (29.0%) were detected in the second fraction. Al, As, Cr, Cd, Cu, Fe, Ni, Pb, Sb and Zn were mostly associated to the residual fraction. Recoveries of the overall procedure varied between 106% (Mo) and 72% (Cr).     

Electrochemical synthesis and characterization of mixed molybdenum-rhenium oxides

The electrodeposition of Mo_xRe_1−xO_y films (0.6 ≤ x ≤ 1) on indium-tin oxide (ITO) coated glass substrates from acidic peroxo-polymolybdo-perrhenate solutions is described. Trends in film growth were established as a function of potential from +0.4 V to −0.7 V vs Ag/AgCl by analyzing the composition and stoichiometry of the deposit using inductively coupled plasma mass spectrometry (ICPMS) and X-ray photoelectron spectroscopy (XPS). These experiments show that the concentration of rhenium increases linearly with the deposition potential and that the deposits are mixed-valent containing up to five different metal oxidation states (i.e., Mo^IV, Mo^V, Mo^VI, Re⁰, Re^IV). Electroanalytical techniques were used to explore the deposition mechanism, including chronocoulometry, cyclic voltammetry, spectroelectrochemistry, and electrochemical quartz crystal nanogravimetry (EQCN). At potentials positive to −0.26 V, perrhenate (Re^VIIO₄⁻) behaves as a redox mediator to accelerate the deposition of a mixed-valent molybdenum oxide, but at more negative potentials mixed molybdenum-rhenium oxides are produced.     

Heavy metals contribution of non-aqueous fluids used in offshore oil drilling

A monitoring program was performed to investigate heavy metal content alteration due to exploratory drilling for oil using non-aqueous fluids (NAFs) in Brazilian offshore, 900 m deep. Fourteen elements were monitored in 54 sites and it was verified that after drilling activities the average Ba concentration was remarkably increased with respect to background level, even 1 year after the activity. A minor increase in Mn and a moderate increase in Al concentrations were verified. The Cd, Cr, Ni, As, Co, Cu, Pb, V, and Zn concentrations were at the background levels, ca. 1 year after the NAFs drilling materials deposition on the seafloor. The Al, Ba, Cd, Cr, Cu, Ni and Zn mean concentrations were significantly different (P<0.05) between the three sampling operations (cruises) performed, while As, Cd, Fe and Pb presented different mean values according to the distance of the oil well, independent of the sampling operation. Interaction between sampling operation and distance was observed for Mn. In all sediment samples the Hg concentration was below the detection limit (0.07 μg g⁻¹).