Oswaldo E. Barcia

Mass‐Transport Study for the Electrodissolution of Copper in 1M Hydrochloric Acid Solution by Impedance

The dissolution of copper in 1M chloride solution was studied by steady-state (current-voltage curves for various disk rotation rates) and transient [frequency analysis of the electrochemical and electrohydrodynamical (EHD) impedance] measurements. The anodic polarization curves have presented one region of mixed kinetic and another of mass-transport control characterized by a current plateau. The limiting current is a Ω 1/2 function throughout the whole range of rotation rates. From the EHD impedance diagrams observed below the anodic plateau, it was shown that the limitation by mass transport is due to CuCl 2 - . 0n the current plateau, the presence of two time constants on the EHD impedance diagram and the reductibility of the curves have been attributed to the existence of a salt layer covering the surface, the rate of formation of this layer being identical to the rate of dissolution. A layer model has been developed

Application of the impedance model of de Levie for the characterization of porous electrodes

From the de Levies theory for a porous electrode, the impedance can be expressed in function of the cylindrical pore characteristics: the pore length, the pore radius and the number of pores. If the pores have a finite length, these parameters can be regressed from the experimental impedance diagrams. In the case of a semi-infinite pore length, only the product r3/2n can be obtained. In this paper, two practical examples of porous electrodes were presented: the corrosion of cast iron in drinking water and the electrodissolution of copper in 1 M hydrochloric acid solution. In each case, the pore parameters were assessed.

Reaction model simulating the role of sulphate and chloride in anodic dissolution of iron

Abstract The role of chloride and sulphate anions on anodic dissolution of iron was studied. A gradual transition from sulphate to chloride system was found. Based on a previously proposed model it was possible to take into account this experimental result. The role of anions was explained by a numerical parameter representing the loss of the self-catalytic characteristic of electrochemical reactions.

High‐Rate Copper Dissolution in Hydrochloric Acid Solution

The dissolution of copper in 1 M chloride solution was studied by steady-state (current-potential curves for various disk rotation rates) and transient measurements [frequency analysis of the electrochemical and electrohydrodynamical (EHD) impedance]. The anodic polarization curves present four regions according to the potential : one region of mixed kinetics followed by another of mass-transport control characterized by one plateau, followed by a second mixed kinetics region and a second plateau. The results obtained for the first domain of mixed kinetics and for the first plateau were previously published. In this work, the second mixed kinetics region is considered. From the analysis of the ac and EHD impedance measurements, it was shown that a transition between the presence and the absence of a CuCl salt layer occurs at a critical potential. The value of this critical potential depends on the rotation rate ; the higher the rotation rate, the higher the potential value. A model of kinetic dissolution for this transition is presented, and a coupling between the currents corresponding to the two reactions is demonstrated.

ZnFe anomalous electrodeposition: stationaries and local pH measurements

Abstract The kinetics of ZnFe codeposition was investigated in acid solutions. The effects of solution composition and pH were analyzed. Inhibition of H + reduction and Fe deposition occurs with increasing Zn ++ concentration in sulfate solution. An activation of Zn deposition is also observed. Increasing pH causes Zn deposition activation during ZnFe codeposition. The anomalous codeposition is also favored in chloride medium. When alloy deposition becomes the main process, the interfacial pH is governed by the individual metal deposition that controls the kinetic behavior. The interfacial pH increases during separate Fe deposition, meaning that it occurs with simultaneous consumption of H + . Individual Zn deposition brings about an H + inhibition. A correlation between the codeposition behavior of ZnFe and ZnNi in sulfate and chloride solutions suggests that the prevailing cathodic reaction governs the interfacial pH. Anomalous codeposition process does not seem to be associated with a saturation of any thermodynamic species at the electrode surface. It can only be described by kinetic arguments.

Electrodeposition of Zn-Ni alloys in sulfate electrolytes

Abstract The electrodeposition of Zn-Ni in sulfate solutions has been investigated by means of polarization curves, morphological analysis and electrochemical impedance using a rotating disc electrode. The polarization curves showed two parts, the first one related to the Zn-Ni normal codeposition and the second one to the Zn-Ni anomalous codeposition. The mass transport influenced only the Zn-Ni normal codeposition and had no influence on the anomalous codeposition. The temperature showed a great influence on the Zn-Ni alloy deposition and affected both parts of polarization curves. The electrolyte composition had no influence on the Zn-Ni anomalous codeposition, but it affected the transition current density between normal codeposition and anomalous codeposition. The impedance diagrams were obtained in sulfate electrolytes and showed four loops at low frequency domain at the beginning of anomalous codeposition : three capacitive loops and one inductive. For the high polarizations, one of the capacitive loops disappears. These results were discussed comparatively to those previously obtained for chloride electrolyte, in view of establishing a kinetic model for the sulfate electrolyte.

Copper electrodissolution mechanism in a 1M sulphate medium

A model with two adsorbed species at the electrode surface is proposed for describing the copper electrodissolution in sulphate medium in a pH range 0–5. No a priori hypothesis was assumed for the relative rate values of each step present in the mechanism. A good agreement was found between the experimental and simulated results.

Anodic Dissolution of Iron in Acid Sulfate Under Mass Transport Control

The dissolution of iron in 1 and 1.8M of sulfate at pH=0 was studied by steady-state and electrohydrodynamical impedance. The experimental results were simulated by integration of the diffusionequation with the migration term together with an empirical viscosity profile from the electrode surface to the bulk solution. This model could be explained either by the presence of a porous and thin FeSO 4 film or by a colloidal dispersion of FeSO 4

The role of chloride and sulphate anions in the iron dissolution mechanism studied by impedance measurements

Abstract Impedance measurements were performed on iron in sulphate and chloride media with varying additions of chloride and sulphate respectively. These experiments were performed within pH 0–4 and current density up to 0.2 A cm −2 . The impedance diagrams showed a gradual transition from the iron—chloride to iron—sulphate systems. These results were interpreted on the basis of the previously proposed iron dissolution mechanism.

Rotating disc and hemispherical electrodes for copper dissolution study in hydrochloric solution in the presence of benzotriazole

The effect of benzotriazole (BTAH) on the anodic dissolution of copper in 1 M HCl solution was investigated by using a rotating disc electrode (RDE) and a rotating hemispherical electrode (RHSE). It was shown that the presence of Cu(I) (CuCl or CuCl2−) on the copper surface is necessary to have the inhibitive effect of BTAH. Just below the current plateau, the effect of BTAH depends on the electrode geometry: for the RDE, the electrode surface remained partially active, the protection by BTAH occurred only on a ring at the edge of the electrode, whereas for the RHSE the surface is uniformly covered by a protective BTAH complex. For both electrodes without the presence of BTAH, a surface roughness develops during the copper electrodissolution that can be kinetically interpreted as a porous-like electrode with pores of finite size. In the presence of BTAH and for the RSHE, the size of the pores becomes semi-infinite.