Anodic Linear Sweep Voltammetry Research Articles

Effect of heat treatment on the anodic oxidation of Ti–0.2 Pd alloys in chloride solutions

The effect of heat treatment of Ti and Ti–0.2 Pd alloys on their anodic oxidation was studied in deaerated 1% NaCl by means of anodic linear sweep voltammetry, SEM, TEM, EDS, optical microscopy and microhardness measurements. The specimens, as fabricated, consisted of α-phase only. The β-phase, intergranular or with a Widmansttaten type growth, was produced by heat treatment of the Ti–0.2 Pd alloys at the temperature range from 750 to 850 ∘C. The β-phase was transformed into the α′-phase during quenching. The current density against voltage curves for pure Ti and Ti–0.2 Pd, as fabricated or heat-treated, presented an initial plateau at about 1.5 V vs Ag/AgCl/KCl (3 M), an anodic peak at about 4.5 V and a current increase due to the pitting attack at about 10 V. The anodic peak was related to an oxide growth together with a solution electrolysis. Current spikes appeared at random from potentials about 8.3 V, which were related to film breakdown and repair events. The passive films of the alloys oxidized up to about 10 V presented oxidation bands parallel to the surface, with different oxygen content and microhardness, together with a structural transformation of the α′-phase under the titanium oxide layer. The similar behaviour of pure Ti and Ti–0.2 Pd alloys in front of pitting corrosion in chloride was due to such a structural transformation.

Corrosion behaviour of epoxy coatings electrodeposited on steel electrochemically modified by Zn–Ni alloy

The corrosion behaviour and thermal stability of epoxy coatings electrodeposited on steel, phosphatised steel and steel previously modified by electrodeposited Zn–Ni alloy was investigated during exposure to 3% NaCl. The electrochemical impedance spectroscopy (EIS), gravimetric liquid sorption experiments, thermogravimetric analysis (TGA) and anodic linear sweep voltammetry (ALSV) were used. Epoxy topcoat was formed by cathodic electrodeposition of an epoxy resin using constant voltage method. From the results obtained from EIS (pore resistance, coating capacitance), gravimetric liquid sorption experiment (diffusion coefficient) and TGA (water content inside the coating and thermal resistance), it can be concluded that electrochemical, transport and thermal properties of epoxy coatings are strongly affected by surface modification of the substrate. The better protective properties of epoxy coating on Zn–Ni sublayer can be explained by its less porous structure, caused by lower rate of H 2 evolution on Zn–Ni alloy, while the increased corrosion protection is due to the passive film of ZnO on the alloy surface. The mechanism of electrolyte penetration through an organic coating was also given.

Determination of the zinc and cadmium contents in low-alloyed tin

The method of anodic linear sweep voltammetry (ALSV) has been used to determine the content of Zn and Cd (up to 4% w/w) in eutectic type binary alloys with Sn. The alloy samples were prepared by casting. The effect of the type and the pH of the electrolyte, as well as of the sweep-rate on the dissolution of Zn and Cd from the alloy during an anodic potentinal-sweep was investigated. It was shown that ALSV is sensitive to low concentrations of both Zn and Cd in the investigated alloys, as well-defined peaks of the dissolution of the two metals were recorded before the massive dissolution of Sn commenced. Well-defined linear dependencies between the quantities of electricity under the dissolution peaks of Zn (QZn) or Cd (QCd) and the respective contents of the metals in the alloys were found. Intercepts at the abscissa were found in both investigated systems indicating the formation of solid solutions from which neither Zn norCd could be eluted. In both alloys, the smallest amount of the alloying component which could be detected was 0.25% (w/w). The application of the ALSV method has several advantages over other analytical methods: it is non-destructive as the dissolution involves only a very thin layer of the alloy; it requires simple and cheap instrumentation; it is fast and relatively sensitive. These make it suitable for routine analysis.

Dependence of coating characteristics on deposition potential for electrodeposited Zn–Ni alloys

The electrodeposition of zinc–nickel alloys from ammonium chloride baths was studied on different substrates under potentiostatic and galvanostatic conditions, from low potentials/current densities where the codeposition was normal to the conditions where anomalous deposition took place. Anodic linear sweep voltammetry (ALSV) and ex situ techniques were used to characterize the coatings obtained in each condition. The results indicated that three deposition potential zones could be defined corresponding to practically pure nickel, α- and γ-phase domains. It was observed that the abrupt change in alloy composition and current efficiency that occurred during potentiostatic deposition did not correspond to the transition from normal to anomalous codeposition. In our conditions, this change always coincided with the appearance of γ-phase in the coatings.

Intermediate layers in electrodeposited CMA coatings

Abstract The existence of an intermediate layer in electrodeposited CMA coatings composed of a Ni+Cd alloy layer and a pure Cd layer has been investigated by the anodic linear sweep voltammetry technique. It was shown that the voltammogram of a single layer of the pure Ni+Cd alloy differs from that representing the dissolution of a two-layer deposit composed of a Ni+Cd alloy layer and a pure Cd layer on top of it. This difference is ascribed to the formation of an intermediate layer. It was found that the contribution of β and γ phases in the intermediate layer depends on the alloy layer composition as well as on the composition of the plating bath. From the charges corresponding to the contribution of these two phases, assuming a homogeneous distribution of phases, the thickness of the intermediate layer has been estimated. The maximum thickness of the intermediate layer was found to be about 40 nm.

Determination of the amount of Zn in electrochemically deposited Zn + Cd alloys by anodic linear sweep voltammetry

A detailed qualitative and quantitative analysis of the anodic linear sweep voltammograms of the dissolution of electrodeposited Zn + Cd alloys of different compositions has been performed in order to obtain the data about the solubility (miscibility) of solid Zn in solid Cd. It was shown that up to about 5 at.% of solid Zn dissolves in electrodeposited Zn + Cd alloys and that this amount of Zn dissolves in the peak corresponding to dissolution of pure Cd. The conclusion rests on the quantitative analysis of the charge under the peaks of Zn and Cd dissolution. A precise quantitative analysis can be performed only in sulphate electrolyte where dissolved Zn forms simple Zn 2+ cations, while in chloride electrolyte the presence of different complexes of Zn with Cl − anions influences the kinetics of the dissolution of pure Zn from the alloy.

Qualitative and quantitative assessment of phases in electrodeposited Ni + Cd alloys by the ALSV technique

During the last decade the anodic linear sweep voltammetry technique (ALSV) has frequently been used for qualitative assessment of phases in electrodeposited alloys. In the case of the Ni + Cd alloy it is shown that, as well as the qualitative, the quantitative assessment of phases in electrodeposited alloys can also be achieved by taking into account all relevant parameters of alloy electrodeposition. This is practically the first attempt of successful application of the ALSV technique for this purpose. It is shown, by the comparison between the phase distribution obtained by the analysis of the ALSV results and the phase distribution corresponding to the phase diagram, that the phase distribution in electrodeposited alloys is slightly different from the one predicted by the phase diagram. The values of the standard chemical potentials of β and γ phases are also estimated. A high negative value for μ o( γ) indicates a strong interaction between Cd and Ni in order to form this phase, which is in a good accordance with the fact that the γ phase is present in the alloy at all alloy compositions.

Catalytic electrodeposition of silver on glassy carbon electrodes modified with films of cobalt phthalocyanine

Glassy carbon electrodes were modified with thin films of unsubstituted cobalt phthalocyanine (CoPc), prepared at the surface of an aqueous NaOH solution by spreading a CoPc solution in CCl3COOH + CHCl3. This simple procedure allows a reproducible and homogeneous modification of the electrodes with a film thickness of the order of a monolayer. Cyclic voltammetry of the modified electrodes and UV-visible spectroscopy of the film and spreading solution is provided. Furthermore, silver electrodeposition on modified and unmodified glassy carbon electrodes from low-concentrated silver solutions in NaCl was studied, using relatively long deposition times up to 100 s at an overpotential of −0.3 V. The charge corresponding to the deposited silver was measured by anodic linear sweep voltammetry. For both electrodes, linear plots of Q23 vs. t were obtained, which is according to an instantaneous nucleation and three-dimensional growth mechanism.

Selective dissolution of the cobalt binder from scraps of cemented tungsten carbide in acids containing additives

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.

Identification of phases in Ag + Pd alloys electrodeposited by the electrochemical ALSV technique

The well-established anodic linear sweep voltammetry (ALSV) technique has been used to identify the phases present in electrodeposited thin layers of Ag+Pd alloys. Alloys were deposited both potentiostatically and galvanostatically on glassy carbon and gold rotating-disc electrodes from a chloride-containing electrolyte at elevated temperatures. It is shown that electrodeposited Ag+Pd alloys appear in two different phases (ordered structures) depending on the chemical composition and the amount (thickness) of electrodeposited alloy. It is also found that the temperature of the electrolyte for alloy deposition and/or dissolution has a slight effect on the ALSV peak potentials but has no influence on the phase composition of the alloy. The concentration of chloride ions in the electrolyte for alloy dissolution (characterization) was found to be a limiting factor in successful and complete dissolution of Ag+Pd alloys.

Investigation of phase-transformation kinetics in electrodeposited Cu + Cd alloys using anodic linear sweep voltammetry

The anodic linear sweep voltammetry technique was used for a quantitative assessment of the phase composition of Cu + Cd alloys obtained by electrochemical deposition. Current peaks obtained in the voltammograms were attributed to the presence of particular intermetallic compounds known to exist in this system. It was found that alloys deposited by current densities exceeding the diffusion limiting current of Cu by several fold contain all the compounds recorded in the phase diagrams at an excess of pure Cd. The most dominant phase was found to be Cu 5Cd 8. It was observed that the voltammograms change with time, indicating that the freshly deposited alloys are unstable. Stabilization was found to take times in the range of 2 h. It is likely to occur in such a way that the excess Cd reacts with Cu-rich compounds to form CuCd 3. The method was found to be very sensitive to the presence of any particular phase. Thus CuCd 3, for example, could be detected at a level as low as 0.5%. The kinetics of the solid state reaction can be interpreted using the Johnson-Mehl equation. High values of the coefficient n indicate that nucleation of the new phase is a probable rate-determining step.

Phase-structure analysis of brass by anodic linear-sweep voltammetry

Anodic linear-sweep voltammetry (ALSV) was applied to electrodeposited alloy layers and to metallurgically obtained Cu−Zn alloys of different composition and structure. Metallurgically obtained samples covered the range of composition in which α, (α+β), β and (β+γ) intermediate phases were detected by X-ray. The ALSV of samples containing less than 30 wt % Zn exhibited a single peak at −0.08 to −0.1 V/SCE before massive dissolution, starting at about −0.05 V/SCE. The presence of the γ-phase gave another peak at a significantly more negative potential (−0.25 to −0.35 V/SCE). The ALSV of electrodeposited alloys were significantly more complex than the former, depending on the deposition potentials, with peaks attributable to pure Zn, to the e-phase, to the η-phase as well as to the α-phase, present in most cases and dissolving at potentials similar to that of pure Cu. ALSV was shown to be a reliable and practical method for a fast determination of both the composition and the phase structure of electrodeposited brass.

Identification of intermetallic compounds in thin layers of electrodeposited Cu–Cd alloys using electrochemical techniques

AbstractAn attempt was made to analyse the phase structure of thin layers of electrodeposited Cu–Cd alloys using anodic linear sweep voltammetry combined with a potentiostatic pulse technique (ALSV–PPT). The results were compared with data obtained using conventional techniques for phase structure analysis. It was found that application of the conventional X-ray technique (Guinier analysis) is limited, because the grain size of the alloy constituents is too small for compounds to be revealed by X-ray peaks. Electrodeposited alloys could be successfully analysed using that method only after subsequent thermal treatment. Diffraction patterns from transmission electron micrographs of very thin foils (of the order of 20–50 nm) of electrodeposited 75Cd–25Cu (at.-%) alloy revealed the presence of CuCd3 intermetallic compound having a grain size of ~20 nm. By comparing all the results, the distribution of the various intermetallic compounds present at various stages in the electrodeposition of thin (up to 10 μm)...

ChemInform Abstract: Identification of Intermetallic Compounds in Electrodeposited Copper‐Cadmium Alloys by Electrochemical Techniques.

AbstractIt is demonstrated that anodic linear sweep voltammetry (ALSV) can be used to detect the presence of different phases in binary alloys.

Kinetics of oxidation of polypyrrole-coated transparent electrodes by in situ linear sweep voltammetry and spectroscopy

In situ measurements of absorption spectra combined with anodic linear sweep voltammetry are made at polypyrrole-coated optically transparent electrodes by varying the potential sweep rates and the thickness of the polypyrrole film. Voltammograms are decomposed into the Faradaic and capacitive components. The peak current of the Faradaic component is proportional to the product of the sweep rate and the thickness. The variation of the peak potential with this product falls on a common convex curve. These variations are supported by the propagation theory for conductive polymers. The time dependences of the three absorption bands are not inconsistent with the prediction of the reported band assignment. The band at ≈1000 nm corresponds to signals of oxidized species. Curves of intensity of the band versus the potential are sigmoidal and similar to the integral curves of the Faradaic component. The former curve is shifted positively from the latter by 0.1 V, indicating the delay of generation of species relevant to the band. The kinetics probably involve slow conversion of the radical cation into the dication.