Anodic Linear Sweep Voltammetry Research Articles

The influence of Fe2+ concentration and deposition time on the corrosion resistance of the electrodeposited zinc–nickel–iron alloys

Electrodeposition operating conditions for Zn–Ni–Fe alloys from sulfate baths and the corrosion resistance of the electrodeposited alloys were studied. The comparison between Zn–Ni and Zn–Ni–Fe alloys co-deposition revealed that the remarkable inhibition of Ni and Fe deposition takes place due to the presence of Zn2+ in the plating bath. The electrodeposition was performed on the steel substrate, under galvanostatic conditions, for varying Fe2+ bath concentrations and at different times. X-ray diffraction studies of the deposit showed the presence of Fe3Ni2 phase and γ-phase with a composition of Ni2Zn11. The obtained data also exposed that the corrosion resistance increases as a result of increasing Fe2+ concentration and deposition time. Investigation was carried out using cyclic voltammetry and galvastatic techniques for electrodeposition, while linear polarization resistance and anodic linear sweeping voltammetry techniques were used for corrosion study.

Phase identification in electrodeposited Ag–Cd alloys by anodic linear sweep voltammetry and X-ray diffraction techniques

During electrodeposition of Ag–Cd alloy coatings phenomena of self-organization and formation of spatio-temporal structures can be observed. The difficulties in the determination of the local phase composition in the observed structures are mostly connected with the strong heterogeneity of the coatings consisting of several alloy phases. The results obtained with electrochemical techniques, such as anodic linear sweep voltammetry (ALSV) are compared with results obtained by X-ray analysis and SEM. In the proposed electrolyte for dissolution of Ag–Cd alloy coatings (12 M LiCl + 0.1 M HCl) the dissolution peaks of the pure metals, Ag and Cd, have a potential difference of about 700 mV. The peaks, corresponding to the alloy phases, are situated between the dissolution potentials of Ag and Cd, their height depending on the deposition current density, i.e. on the percentage content of the alloy. Different phases (Ag, Ag 3Cd, AgCd, AgCd 3 and pure Cd) are observed in the coatings deposited at different cathodic potentials. A good correlation between the XRD spectra of the Ag–Cd alloy coatings and the ALSV data obtained during their dissolution is established.

PtSnCo/C Anode Catalyst for Methanol Oxidation

A binary metallic catalyst(PtSn/C) and a ternary metallic catalyst(PtSnCo/C) with a metal mass fraction of 20% were prepared by borohydride reduction and subsequent hydrothermal treatment in a glycol liquid phase.The structure and composition of the as-prepared electrocatalysts were characterized by X-ray diffraction(XRD) and energy-dispersive spectrometry(EDS).Their activity and stability for the catalysis of methanol oxidation were evaluated by anodic linear sweep voltammetry(LSV),cyclic voltammetry(CV),and the anodic stripping of a pre-adsorbed CO monolayer.We found that the PtSnCo/C catalyst gave the best catalytic activity for the methanol oxidation of all the catalysts including the commercial JM-PtRu/C catalyst.After 100 cycles,the peak current of methanol oxidation for the PtSn/C catalyst rapidly decreased to 11% of its initial peak current but PtSnCo/C decreased to only 50%.This result suggests that the PtSnCo/C catalyst has better chemical stability for the catalysis of methanol oxidation compared to the PtSn/C catalyst.The more negative onset potential of methanol oxidation for the PtSnCo/C catalyst relative to pre-adsorbed CO oxidation implies that the intermediates of methanol oxidation on the PtSnCo/C catalyst may be ones,which can be more easily oxidized than CO,instead of CO.

Influence of Ni 2+ concentration and deposition potential on the characterization of thin electrodeposited Zn–Ni–Co coatings

The electrodeposition of Zn–Ni–Co alloys from sulphate electrolytes was studied on steel rod. In order to elucidate the characteristics of the layer formation, a complementary approach was used based on the combination of various electrochemical techniques. The cyclic voltammetry and galvanostatic techniques for electrodeposition, while potentiodynamic polarization resistance and anodic linear sweeping voltammetry techniques were used for corrosion study. Under the examined conditions, electrochemical and surface analysis indicate that the deposition has taken place with the formation of three structures have a composition corresponding to pure Zn, γ-Ni 5Zn 21 and pure Co phases. The influence of nickel concentration as well as the effect of potential on the surface appearance and the deposits composition was examined. Under these experimental conditions the electrodeposition of the alloys is of anomalous type. The results indicate that the addition of Ni to the Zn–Co alloy, Zn–Ni–Co alloy formed which is more corrosion resistance than Zn–Co alloy. Also, the amount of γ-phase increased and the amount of pure Zn decreased with the increase of nickel concentration in the bath. The corrosion resistance of the zinc–nickel–cobalt alloy had been improved with the more concentration of nickel. The Ni content in the deposition layer had been increased at high deposition potential, whereas, pure Zn deposition had been decreased.

Corrosion stability of Zn–Co alloys deposited from baths with high and low Co content — The influence of deposition current density

Electrochemically deposited Zn–Co alloys under various deposition conditions were investigated using atomic absorption spectroscopy (AAS) for determination of chemical composition, anodic linear sweep voltammetry (ALSV) and X-ray diffraction (XRD) for phase structure determination, SEM and AFM for surface morphology analysis, and polarization measurements for determination of corrosion properties. The influence of deposition current density and composition of deposition solution on the phase structure, morphology and corrosion properties of Zn–Co alloys were studied. The plating baths used were with low metal concentration, free of additives and deposition was carried out at room temperature, since the aim of the work was to investigate only the influence of different deposition current densities using economically favorable deposition parameters. It was shown that the ratio of cobalt to zinc ions in the plating bath strongly affects the chemical content and phase structure, as well as the morphology and corrosion stability, of Zn–Co alloys. The single-phased Zn–Co alloys showed the best corrosion stability. The alloys deposited at the highest current density from plating bath with the lower ratio of cobalt to zinc ions, as well as the one deposited at the intermediate current density from bath with higher ratio of cobalt to zinc ions, exhibited the lowest corrosion rates. It was also shown that the deposit having smaller crystallite grains (obtained at higher current density), among two alloy deposits having the same chemical content and phase structure, yielded lower corrosion rate.

Characterization of electrodeposited Cd–Co alloy coatings by anodic linear sweep voltammetry

The electrodeposited Cd–Co alloys were characterized by the anodic linear sweep voltammetry (ALSV) technique in the solution of 1 M NaCl (pH 2). It is shown that Cd–Co alloys could be deposited with high current efficiency (>90%) from the solution containing 0.2 M boric acid, low concentration of cadmium sulfate (0.01 M and 0.02 M) and high concentration of cobalt sulfate (0.2 M and 0.4 M) under the conditions of convective diffusion (RPM = 1000). The ALSVs were characterized by the presence of three peaks: one corresponding to the dissolution of pure Cd, one corresponding to the dissolution of pure Co and one corresponding to the dissolution of unknown phase formed in the system Cd–Co (since the phase diagram of the Cd–Co system does not exist in the literature). Depending on the charge and on the alloy composition (amount of Cd and Co) the peak of the unknown phase can either be hardly seen, or can prevail on the ALSV. This phase is formed mainly on the account of Co, but certain limiting amount of Cd must be deposited for the unknown phase to be formed and seen on the ALSV.

Electrodeposition behavior of zinc–nickel–iron alloys from sulfate bath

The present work is directed at collecting the properties of Zn–Ni and Zn–Fe alloys in one alloy via the electrodeposition of Zn–Ni–Fe ternary alloy. Electrodeposition of ternary Zn–Ni–Fe alloy was investigated and compared with the characteristics of Zn–Ni electrodeposits. The electrodeposition was performed from a sulfate bath onto a steel substrate. Structural analysis by X-ray diffraction (XRD) method revealed that the Zn–Ni–Fe alloys consisted of a mixture of zinc, and (γ-Ni2Zn11) and (Fe3Ni2) phases. The study was carried out using electrochemical methods such as cyclic voltammetry and galvanostatic for electrodeposition, while anodic linear polarization resistance and anodic linear sweeping voltammetry techniques were used for the corrosion study. Surface morphology and chemical composition of the deposits were also examined by using scanning electron microscopy and atomic absorption spectroscopy, respectively. It was found that the obtained Zn–Ni–Fe alloy exhibited more preferred surface appearance and better corrosion resistance without adding any organic brighteners to the plating bath in comparison to Zn–Ni alloy that electrodeposited at similar conditions. Results obtained revealed that the increase in corrosion resistance of ternary deposits is not only attributed to the formation of (γ-Ni2Zn11) phase, but also to iron codeposition and formation of (Fe3Ni2) phase.

Electrodeposition and characterization of zinc–nickel–iron alloy from sulfate bath: influence of plating bath temperature

The electrodeposition of ternary zinc–nickel–iron alloy was studied in acidic sulfate bath. The comparison between Zn, Ni, and Fe deposition and Zn–Ni and Zn–Ni–Fe co-deposition revealed that the remarkable inhibition of Ni and Fe deposition takes place due to the presence of Zn2+ in the plating bath. The increase in corrosion resistance of ternary deposits is not only attributed to the formation of γ-Ni2Zn11 phase but also to iron co-deposition and formation of iron phase. It was also found that the bath temperature has a great effect on the surface appearance and the deposit composition. The investigation was carried out using cyclic voltammetry and galvanostatic techniques for electrodeposition, while linear polarization resistance and anodic linear sweeping voltammetry techniques were used for corrosion study. Morphology and chemical composition of the deposits were characterized by means of scanning electron microscopy and atomic absorption spectroscopy.

Electrochemical deposition and corrosion stability of Zn–Co alloys

Electrochemically deposited Zn–Co alloys under various deposition conditions were investigated using anodic linear sweep voltammetry for phase structure determination, scanning electron microscopy for surface morphology analysis, atomic absorption spectroscopy for determination of chemical composition, and polarization measurements and open circuit potential measurements for determination of corrosion properties. The influence of deposition current density, temperature, and composition of deposition solution on the phase structure and corrosion properties of Zn–Co alloys was studied. It was shown that the ratio of cobalt to zinc ions in the plating bath strongly affects the chemical content and phase structure, as well as corrosion stability, of Zn–Co alloys. Zn–Co alloys deposited from plating baths with the lowest and the highest ratios of cobalt and zinc ions exhibited the lowest corrosion rate.

Electrochemical studies on the electrodeposited Zn–Ni–Co ternary alloy in different media

The electroplating of ternary Zn–Ni–Co alloy, surface morphology and corrosion resistance were investigated and contrasted with the characteristics of Zn–Ni electrodeposits. The investigation of electrodeposition was carried out using cyclic voltammetry and galvanostatic techniques, while potentiodynamic polarization resistance and anodic linear sweeping voltammetry techniques were used for corrosion study. Under the examined conditions, the electrodeposition of the alloy was of anomalous type. It was found that the obtained Zn–Ni–Co alloy exhibited more preferred surface appearance and better corrosion resistance compared to Zn–Ni alloy that electrodeposited at similar conditions. During the cathodic scan of cyclic voltammetry, a cathodic peak at − 574 mV is appeared and correlated with the deposition of sulfur liberated from the reduction of sulphate group in the presence of H +. Up to four anodic peaks were obtained by cyclic voltammetry technique, two correlated with zinc oxidation from pure deposited Zn and γ-Ni 5Zn 21 phases and two correlated with oxidation of cobalt and nickel, were observed. The phase structure, surface morphology and chemical composition of the deposits were characterized by means of X-ray diffraction analysis, scanning electron microscopy and atomic absorption spectroscopy, respectively.

Direct-Current Methods for the Estimation of Corrosion Rates in Aqueous Timber Preservatives

As part of a program to assess the durability of metals in timber preservatives, direct-current electrochemical analyses have been carried out using mild steel, American Iron and Steel Institute 316 stainless steel and galvanized steel immersed in three liquid timber preservatives containing dissolved copper as a biocide. The aqueous preservatives examined were copper–chrome–arsenate (Cu–Cr–As), copper azole (Cu-Tebucanazole), and alkaline copper quaternary (Cu-didecylthyl ammonium chloride). These preservatives are known commercially as CCA, CuAz, and ACQ-B, respectively. Despite previous assumptions, neither polarization resistance- nor Tafel slope-based analyses are suitable methodologies for the universal derivation of absolute values of corrosion rate. An alternative approach is suggested based on anodic linear sweep voltammetry. The results show that the hot-dipped zinc coating was found to be the most active material in terms of the polarization behaviour, especially within the CCA-based electrolyte. There is a strong qualitative correlation between the electrochemical data and corrosion rates estimated using the American Wood Preservers’ Association E-17 standard test for aqueous treatment solutions.

Electrodeposition of Zn–Cu coatings from alkaline sulphate bath containing glycine

A plating bath containing Zn sulphate, Cu sulphate, sodium sulphate and glycine is described for depositing smooth, bright and uniform Zn–Cu alloys containing 8–92%Zn. Cathodic polarisation, cathodic current efficiency and deposit composition were determined under different plating conditions. The results were consistent with the behaviour of a regular plating system with Cu being the preferentially depositable metal. The Zn content in the deposits increased with current density and concentration of Zn in the bath but decreased with increasing bath Cu concentration and temperature. X-ray diffraction, anodic linear sweep voltammetry and scanning electron microscope were used to examine the structure and morphology of the deposited alloys. The deposited alloys consisted of a single solid solution phase with a face centred cubic structure.

Double template electrochemical deposition and characterization of NiCo and NiCu alloys nanoparticles and nanofilms

The principle of double template deposition technique was developed to prepare NiCo and NiCu alloy nanomaterials. Ordered particles of about 800 nm high were obtained by reduction of ions from aqueous solution into the pores of anodic aluminum oxide (AAO) membrane with intact barrier layer. The size of the nanoparticles was significantly reduced by combination of AAO and the hexagonal phase of a lyotropic liquid crystal. The scanning tunneling microscopy (STM) micrograph of the material prepared in the presence of liquid crystal reveals the hexagonal array of cylindrical pores. The corrosion potential of the alloy nanofilm shifted to more negative values when the sizes of the particles decrease. The anodic linear sweep voltammetry shows, in each case, various current peaks characteristic of the dissolution of chemical elements in the film.

Electrochemical study on the inhibitory effect of the underpotential deposition of zinc on Zn–Co alloy electrodeposition

Zn–Co alloy electrodeposition from chloride baths containing different Zn 2+/Co 2+ ratios was investigated by cyclic voltammetry and anodic linear sweep voltammetry using a Pt electrode. The peaks were attributed by means of EDX analysis, SEM and TEM observations performed on some alloys potentiostatically deposited. In the range of potential where zinc deposits underpotential, cyclic voltammetry showed a complex cathodic peak with one maximum and two shoulders, correlated with the deposition of different cobalt rich alloys. Up to four anodic peaks, two correlated with zinc oxidation from η and γ phases and two correlated with oxidation of solid solutions of zinc in cobalt, were observed. ALSV and TEM indicated that the remarkable increase in Zn content of the alloy, which occurs with a strong inhibition of the process at potentials more negative than that of the cathodic peak and more positive than the bulk deposition potential of zinc, is due to the deposition of γ phase. No inhibition of the alloy deposition process was observed with very low concentrations of zinc (<0.015 M) in the bath containing 0.19 M Co 2+.

Electrochemical deposition and characterization of Zn-Fe alloys

Zn?Fe alloy electrochemically deposited on steel under various deposition conditions were investigated using anodic linear sweep voltammetry (ALSV) and X-ray diffraction (XRD) analysis for phase structure determination, energy dispersive X-ray (EDX) analysis for determination of chemical composition and polarization measurements and open circuit potential measurements for determination of corrosion properties. The influence of deposition current density on the chemical composition, phase structure and corrosion stability of Zn?Fe alloys was studied. It was shown that deposition current density strongly affects the corrosion stability of Zn?Fe alloys, while Zn?Fe alloy electrodeposited at 4Adm-2 exhibited the lowest corrosion rate.

Anodic linear sweep voltammetric analysis of Ni–Co alloys electrodeposited from dilute sulfate baths

Anodic linear sweep voltammetry was used to characterise electrodeposits of Ni, Co and five Ni–Co alloys (5:1, 2:1, 1:1, 1:2 and 1:5 ratios) obtained in a potentiodynamic mode on a vitreous carbon electrode from dilute sulfate baths. The voltammetric results showed a complex behaviour, with the deposits strongly dependent on the metal ion concentrations and less dependent on the final deposition potential. Probably due to simultaneous hydrogen evolution, the efficiency of the electrodeposition (in sulfate baths) and electrodissolution (in ammoniacal bath) processes of pure Co and Ni–Co alloys decreased with increasing final potential in all solutions, while that of pure Ni was enhanced with a shift to more negative potentials. Morphological information was acquired through investigations by techniques such as SEM, EDX and dot mapping. The voltammetric results revealed solid solution characteristics, with profiles varying from pure Ni to pure Co. The results of semi-quantitative EDX chemical analyses suggest a regular deposition mechanism instead of an anomalous one as is often observed in such binary systems.

ELECTROCHEMICAL DETECTION OF IONIC MERCURY AT BORON-DOPED DIAMOND ELECTRODES

ABSTRACT Boron-doped diamond (BDD) films were utilized for the first time to electrochemically detect mercury dissolved in solution via the initial deposition of metallic mercury, followed by anodic linear sweep voltammetry in the range from 10−10 to 10−5 M. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques were employed. The extremely low background current for BDD electrodes compared to glassy carbon (GC) provides a strong advantage in trace metal detection. CV peak currents showed good linearity in the micromolar range. A detection level of 6.8 × 10−10 M was achieved with DPV in 0.1 M KNO3 (pH = 1) for a deposition time of 20 min. Reproducible stripping peaks were obtained, even for the low concentration range. A comparison with GC shows that BDD is superior. Linear behavior was also obtained in the mercury concentration range from 10−10 to 10−9 M.

Galvanostatic Pulse Plating of Cu-Al Alloy in a Room-Temperature Chloroaluminate Molten Salt Rotating Ring-Disk Electrode Studies

The galvanostatic plating of Cu-Al alloy was examined at a platinum electrode in solutions of in the 60.0-40.0 mol % aluminum chloride-1-ethyl-3-methylimidazolium chloride room-temperature molten salt at 28°C using periodic-current plating techniques. The plating techniques that were investigated include pulse current, superimposed-pulse current, and reverse-pulse current. The composition of the electrodeposited alloy was determined by using rotating ring-disk anodic linear sweep voltammetry. The electrodeposition of Cu-Al is complicated by the instability of the alloy in solutions containing If alloy electrodeposits are removed from cathodic protection while immersed in the plating bath, a condition that occurs during the pulse plating “off-time,” in the plating solution oxidizes Al from the electrodeposits. The rate of this displacement reaction is greatest for small values of but decreases as becomes longer, suggesting that a copper-rich layer forms on the electrodeposits that blocks the displacement reaction. The displacement reaction can be minimized by lowering the concentration at the electrode surface through the application of a superimposed current during whose magnitude is comparable to that of the limiting current for © 2001 The Electrochemical Society. All rights reserved.

Electrochemical activation of the electroless deposition of Ni–P alloy and phase structure characterization of the deposit Part II: Single bath system

The process of electroless Ni plating (EP) was activated by the cathodic deposition of precursors of Ni in the same bath in which EP takes place. The current density (c.d.), duration of cathodic activation, as well as the duration of subsequent EP were varied and the effect of these parameters on the phase composition of the resulting Ni–P deposits was determined by anodic linear sweep voltammetry (ALSV). It was found that electrochemical activation can be achieved with relatively low c.d. and short current pulses, to run at rates comparable to EP activated in other ways. The rate of EP alone was found to be in the range between 1 and 5 mC cm−2 s−1, regardless of the activation c.d. or the amount of electrochemically deposited Ni precursors. A synergistic effect was obtained in cases when a little low c.d. cathodic current was passed simultaneously with the EP. The alloys were found to consist of a solid solution of P in Ni, as well as of some phosphide compounds and pure Ni (at increasing activation c.d.). During EP, however, only the solid solution was deposited. The phase structure of the deposit can be varied to a certain extent by the activation c.d.

Dissolution of tungsten carbide and tungsten carbide-cobalt in aqueous media

Scraps of cemented tungsten carbide were electrolyzed to dissolve their cobalt binder and recover tungsten carbide. Anodic passivation retards the acid dissolution of the cobalt. Anodic linear sweep and cyclic voltammetry were conducted for selecting adequate electrolytes, in which the passivation was diminished and thus the cobalt dissolution was enhanced. Anodic passivity of the scrap in acids was minimized in the presence of additives (e.g. 0.1 M citric acid in 1 M HCl). More effective electrolysis was carried out potentiostatically at 0.200–0.600 V (vs. SCE). A flowsheet to recover the tungsten carbide and cobalt from scraps of cemented tungsten carbide is suggested.