The anodic dissolution of chalcocite in an ammoniacal environment

Presented is the proposed model for the mechanism of anodic oxidation of the semiconductor mineral chalcocite in an ammoniacal environment. The kinetic parameters of the process α_a, k_s, j₀⁰, the formal potential and the electrochemical order of the reaction in relation to ammonia are given.     

Relaxation kinetics of the current of hydrophilic metal dissolution activated by anodic pulses

Relaxation kinetics of the metal dissolution current after pulsed anodic activation are analyzed using a model of spatial separation of the dissolution and passivation of hydrophilic metals. The current rise is contributed to mainly by the formation of new step sources resulting from the desorption of blocking oxygen atoms from vertexes of trihedral pyramids that are formed in excess quantities during the activation pulse.Translated from Elektrokhimiya, Vol. 40, No. 12, 2004, pp. 1487–1493.Original Russian Text Copyright © 2004 by Lazorenko-Manevich, Sokolova.     

Kinetic calculations of the Ni anodic dissolution from EIS

Anodic nickel dissolution in acid media has been analyzed by means of electrochemical quartz crystal microbalance and electrochemical impedance spectroscopy techniques. The experimental impedance spectra have been fitted to an equivalent circuit which is related to a mechanism of two consecutive electron transfers followed by a Ni²⁺ mass transfer step. That way, an estimation for values of rate constants and surface concentrations of the Ni(0), Ni(I) and Ni(II) species has been obtained.     

On anodic dissolution of silver coatings deposited on base metals

Potentiodynamic polarization and potentiostatic electrolysis techniques were employed to study the anodic oxidation of silver and a number of other metals (copper, iron, nickel, and tin) in sulfite media, both individually and in Ag-M binary electrodes. The conditions in which silver is dissolved with a nearly 100% current efficiency were found.     

Electrochemical impedance spectroscopic studies on niobium anodic dissolution in HF

Journal of Solid State Electrochemistry - The dissolution of niobium electrode in anodic regime in hydrofluoric acid was studied using electrochemical techniques. In the active region, complex...     

Regularities of gold anodic dissolution in thiocarbamide solutions

It is shown that the gold dissolution in thiocarbamide electrolytes containing sulfide ions in the pH range from 1 to 4 proceeds with a current efficiently of almost 100%, and a change in solution acidity has a weak effect on the process. The oxidation of thiocarbamide to formamidine disulfide proceeds at the potentials around 1.1 V and depends on the pH of solution. When the pH value is raised, the thiocarbamide oxidation potential shifts in the negative direction and approaches the potential of gold dissolution. It is found that, in the absence of catalytically active species, the gold dissolution rate in thiocarbamide solutions in the pH range from 6 to 10 is vary low. At these pH values, as well as in the acidic solutions, an addition of less than 10⁻⁴ M sulfide ions to thiocarbamide electrolyte accelerates the gold dissolution at the potentials about 0.6 V. It is shown that sulfide ions in the concentration above 10⁻⁴ M inhibit the process. At pH 11, the gold dissolution proceeds also with no special addition of sulfide ions. This is associated with the formation of sulfide ions as a result of accelerated decomposition of thiocarbamide and formamidine disulfide with increasing pH value. It is found that in the pH range from 12 to 13, the processes of gold dissolution and thiocarbamide oxidation are inhibited as a result of the formation of passive film on the electrode surface. Probably, the film consists of elemental sulfur.     

Influence of the adsorption of N species on the anodic dissolution of Ni

The dissolution and passivation of Ni in nitrite-containing acid solutions are investigated by Auger spectroscopy, atomic force microscopy, and conventional electrochemical techniques. The dissolution/ passivation of the Ni surface is consistent with a competition between adsorbed OH- and nitrogen-containing species with a potential-dependent surface coverage. Nitrogen-containing species hinder the passivation of the Ni surface, shifting the formation of the complex nickel hydroxide/oxide film to more positive potential values. The dynamics of the dissolving interface, followed by atomic force microscopy, reflect first the competition of adsorbed species, leading to the development of protrusions and cavities, and finally the formation of the passive film that promotes surface smoothening by a preferential dissolution of the protrusion tips under ohmic control.     

Complex surface dynamics during anodic dissolution of Ni

The evolution of the surface roughness during the anodic dissolution of polycrystalline Ni was investigated by means of ex situ AFM in acid phosphate solutions. To characterize the time and spatial scaling behavior of surface roughness, the interface width and the power spectral density of the surface at different dissolution stages were analyzed in terms of dynamic scaling theories. The time dependence of global surface roughness, W(L,t), shows an unstable behavior characterized by a continuous increase without saturation following the relation W approximately t(beta), where beta > 0.5. The unstable behavior results from the development of wide grooves that originates a surface consisting of mounds. Two scaling regimes at scales shorter and larger than the mound dimensions (l(c)) were observed. For l < l(c), we found alpha approximately 1 consistent with mounds exhibiting smooth (faceted) walls, whereas an anomalous scaling behavior with a proper local roughness exponents (alpha(loc) < 1) dominates at l > l(c). The introduction of nitrite in the solution, a common additive used in phosphating baths, leads to some changes in the scaling behavior as a consequence of different generated chemical surface conditions during dissolution. The different dissolution rates of the exposed crystal orientations and surface diffusion of adatoms were identified as the physical processes that govern the interface dynamic for this system.     

Kinetics of zinc anodic dissolution from the EIS characteristic points

A possible faradaic impedance function for the complex mechanism of metals electrodissolution across two consecutive electrotransferences has been developed in this work. The analysis of this function provides some characteristics points from which it is possible to calculate kinetic parameters of these processes. The dependence of these parameters on the potential has been studied in the case of Zn. These ones have been interpreted in terms of changes in the controlling stages of the overall rate of reaction.     

Kinetics of silver anodic dissolution in thiosulfate electrolytes

The regularities of silver anodic dissolution are studied by using the voltammetry (at the potential scan rates from 5 to 1000 mV/s) on the electrode, which was renewed immediately in the solution by cutting-off a thin surface metal layer, and quartz microgravimetry, for various concentrations of sodium thiosulfate (0.05–0.2 M). It is shown that, in the potential range from 0 to 0.4 V (normal hydrogen electrode), the polarization curves reflect the silver dissolution, whereas the contribution of oxidation of S₂O₃²⁻ ions is insignificant. At low potential scan rates, the process kinetics is of mixed nature. The kinetics and mechanism of anodic process are studied by using the measurements at high potential scan rates (100–200 mV/s) and the calculations of equilibrium composition of near-electrode layer. It is found that the exchange current in the electrolytes studied is 5 × 10⁻⁵ A/cm², the transfer coefficient α is approximately 0.5, and both parameters are virtually independent of the concentration of S₂O₃²⁻ ions. The reaction order of silver dissolution with respect to the ligand $ \left. {\frac{{\partial logi}} {{\partial logc}}} \right|_E $ \left. {\frac{{\partial logi}} {{\partial logc}}} \right|_E is close to unity and is independent of potential. With regard for the literature data on the adsorption of thiosulfate ions on silver, this result is interpreted as the evidence for the involvement of one S₂O₃²⁻ ion from bulk solution, along with adsorbed ligands, in the elementary act of metal dissolution.     

The effect of water on the anodic dissolution of aluminum in non-aqueous electrolytes

The influence of water concentration on the electrochemical behavior of Al anodes in Al/active-non-aqueous electrolytes is investigated. Normally passive, Al exhibits facile electrochemical oxidation in both AlCl₃/γ-butyrolactone (AlCl₃/BLA) and (C₂H₅)₄NCl acetonitrile (TEAC/ACN) electrolytes. However, in these two electrolytes, the influence of water on Al oxidation shows opposite effects. Incremental increase from 0 to 1.5 M H₂O (0 to 3% water by volume) hinders Al oxidation in 1 M AlCl₃/BLA, increasing polarization loss from 100 to 400 mV cm² mA⁻¹. Yet in 0.3 M TEAC/ACN, Al is passive in the absence of water, exhibiting currents only in the μA cm⁻² domain, equivalent to oxidative polarization losses of over 1000 mV cm² mA⁻¹. This polarization loss is alleviated by water addition, and decreases from 20 to 7 mV cm² mA⁻¹ as water is increased from 0.3 to 1.5 M. FT-IR spectroscopy, linear voltammetry, galvanostatic reduction, surface microscopy and electrolytic conductivity measurements were conducted to probe competing water activation or water passivation effects on organic-phase Al electrochemistry.     

Characterization of the anodic growth and dissolution of oxide films on valve metals

Chemical dissolution processes coupled to anodic oxide growth taking place by a “high-field” conduction mechanism, are considered. The equation for the steady-state current density obtained during potentiodynamic polarization measurements is derived and the effect of the oxide dissolution rate on the overall potentiodynamic behaviour by applying repetitive scans with either fixed or increasing anodic switching potentials is discussed. The procedure for obtaining the current dissolution as well as the parameters that characterize the high-field growth is discussed.     

The influence of chloride on the initial anodic dissolution of Cu3Au(1 1 1)

We report a detailed in situ X-ray diffraction study of the influence of chloride on the atomic structure evolution at the solid-electrolyte interface during the selective dissolution of Cu from a Cu₃Au(1 1 1) surface immersed in 0.1 M H₂SO₄. We disclose that the formation of the initial ultrathin Au-rich (1 1 1) with an inverted stacking sequence, as recently observed at Cu₃Au(1 1 1) in contact with pure 0.1 M H₂SO₄, is strongly influenced by adding 5 mM HCl. The main finding is a negative shift of about 150 mV of the critical potential at which the ultra-thin Au-rich layer transforms into thicker Au islands. The presented results support the view that it is not a thermodynamic driving force, but rather the rate of surface diffusion that dominates the formation of the structures of the metallic layer.     

Electrochemical noise generated by anodic dissolution or diffusion processes

A model of the noise generated by electrochemical reactions and by diffusion is proposed. The elementary fluctuations are supposed to be the particle fluxes which are Poisson white noise. This model is successfully used to describe the experimental stochastic behaviour of two cases of non-equilibrium electrochemical interfaces: the noise generated by anodic dissolution of iron in acidic medium and that by diffusion of a reacting species in the bulk of the electrolyte.     

Effects of metal complexation on the accuracy of anodic stripping voltammetry

It is shown that the use of the method of standard additions for electrochemical quantitation, when complexation to form non-electroactive entities can occur, can lead to serious problems with accuracy. It is also shown that the errors can often be compensated through the use of correct calibration models.     

The anodic dissolution of chalcopyrite in water + acetonitrile solutions

The characteristics of chalcopyrite anodic electrodissolution in aqueous acetonitrile solutions have been studied. Experiments with a high-grade sample, of massive chalcopyrite have been carried out at 25°C in solutions containing 50 g l^?1 NaCl and different concentrations of sulphuric acid and acetonitrile. Galvanostatic and potentiostatic conditions were employed and the results obtained in solutions with and without acetonitrile compared.The characteristics of the mechanism involved in the chalcopyrite electrodissolution precluded acetonitrile having an influence at low potentials. However its influence is more noticeable at higher potentials where solvent decomposition reactions are involved. Chronopotentiometric experiments in acetonitrile aqueous solutions indicate the existence of diffusional (in the solid) and coulombic phenomena in originating the potential jump.     

Kinetics of anodic dissolution of Zr in acidic fluoride media

The kinetics of anodic dissolution of Zr in hydrofluoric acid (HF) was investigated using potentiodynamic polarization experiments. At lower potentials, an active region with a rapid increase in current with the potential was observed and at higher potentials, a large passivation current plateau was observed. The current decreased only slightly with potential in the passive region. Scanning electron micrographs confirmed that the passivation is incomplete in the region where current exhibits a plateau and x-ray photoelectron spectroscopic analysis showed that oxides and oxyfluorides are present on the surface. A four-step mechanism with two adsorbed intermediate species was evaluated and the model captures the essential characteristics of the polarization plots. The results suggest that \( {HF}_2^{-} \) species participates in the chemical dissolution step and actual HF participates in the electrochemical dissolution step.