Electrochemical Oscillations During Anodic Dissolution Of Metals

In this paper, techniques such as, microelectrode, scanning reference electrode technique, holograph and nonlinear dynamic analysis methods are used to investigate the current oscillations during anodic dissolution processes of metallic materials. New oscillatory system is developed, and current oscillations induced by pitting corrosion are studied. The electrochemical oscillations are typical nonlinear dynamic behavior. During the oscillatory electrodissolution of metallic materials, the oscillatory behavior is sensitive to the chemical and physical environment at the electrode/electrolyte interface. Effects of chloride ions perturbation and oxidation of hydrogen at the electrode/electrolyte interface on the current oscillations are studied, and thus how the chloride ions and hydrogen affect the anodic dissolution of metallic materials can be known better. The main result of this paper is summarized as follows:1. Investigation of current oscillations of Cu/CCI3COOH system with holographic photography and copper microelectrodeOscillatory electrodissolution of Cu/CCI3COOH system is investigated with holographic photography and microelectrode technique. The CU/CCI3COOH system shows a rich dynamical behaviour on two controllable parameters: the trichloroaceticacid concentration (Ccci3cooh) and the imposed potential (E). Phase trajectories werereconstructed from time series using time delay methods in order that the complex oscillations could be analyzed. The film formed on the surface of the copper electrode may contain more than one material. As the result of energy dispersive spectroscopy (EDS) analysis is considered, the amount of chloride is rich in the surface film on the copper electrode after its electrodissolution in CCI3COOH solutions. It is known that insoluble salt film can be formed. During the current oscillations of copper, holographic photography is used to observe the electrode/electrolyte interface in situ, and the result show that the concentration gradient at the electrode/electrolyte interface changesperiodically during the current oscillations of copper electrode in CCI3COOH solutions. Copper microelectrode is used to study the current oscillations. The basis of this work was to apply microelectrode to study oscillatory electrodissolution of metallic materials for the purpose of avoiding the IR potential drop between working electrode and reference electrode. The phase trajectories were reconstructed from the corresponding time series to show that the chaotic current oscillations could occur at copper microelectrode in trichloroacetic acid solutions as conventional copper electrode did. It is shown that microelectrode can be used as a counterpart of conventional electrode to study the oscillatory dissolution of metallic materials.2. Pitting corrosion induced current oscillations during electrodissolution of Al in HCIO4 solutionsIt is the first time that a new electrochemical oscillatory system Al/HClO4 is studied. The following features of Al/HClO4 system are quite different from the other systems, such as a typical Fe/H2SO4 system:(i). There is gas evolution from the anode during the current oscillations; (ii). The average oscillatory period decreases with the increase in potential; (iii). Neither passive potential region nor upper oscillatory potential is observedin large range of HClO4 concentrations.There is evidence that when aluminium dissolves anodically, both the Al3+ and Al+ are formed initially, then the univalent aluminium reducing water to hydrogen. Hence, when aluminium is anodized, a surface oxide film is formed and hydrogen is evolved at the anode.The ClO4- ions may reduce to Cl~ ions at Al/electrolyte interface in acid medium. According to point defect model (PDM) model, it seems impossible that an anion the size of hydrated or even unhydrated Cl~ could move through a metal oxide lattice initially. So, the Cl- ions were presumed to occupy oxygen vacancies first. It is unlikely that the ClO4- ions occupy the oxygen vacancies for its large size. The oxide film is formed with defect...