The pitting corrosion of copper in borate buffer containing sodium chloride is studied by using potentiostatic and potentiodynamic techniques complemented mth scanning electron microscopy and EDAX. The breakdown potential shifts towards more negative values as the sodium chloride concentration increases. During pitting both soluble Cu(I) and Cu(I1) species are detected. The first stage of pitting is explained through the competition between the passive layer formation and the nucleation and growth of the CuCl layer in equilibrium with Cu(I)-chloride complexes in solution. When salt nuclei reach the metal surface, pit growth under charge-transfer control is found. In the following stage the kinetics of pit growth changes to a diffusion controlled process when the thick CuCl layer is completed. Secondary breakdown of the salt layer results in copper dissolution through Cu(II) soluble species. The corresponding overall process is discussed in terms of a sum of nucleation and growth processes. The reaction model reproduces the potentiostatic current transients of copper in weakly alkaline borate buffer containing sodium chloride.

The electrochemical behaviour of copper electrodes in NaOH solutions with the addition of Na,S was studied through the analysis of current transients under constant potential and complementary voltammetric and scanning electron microscopy data including energy dispersive X-ray analysis.The overall process can be described by the following three stages. The First stage corresponds to the nucleation and growth of a complex copper sulphide layer at potential values close to the equilibrium potentials of the Cu/Cu2S and Cu/CuS reversible electrodes. The second stage is related to the rupture of the copper sulphide film at potentials more positive than a certain critical value leading to pitting corrosion of copper metal and yielding a poorly protective copper sulphide layer. The third stage occurs in the copper oxide electroformation range, where the presence of copper sulphide accelerates the electrodissolution of the base metal and copper oxide hinders the sulphidization processes. The current transients of each stage are interpreted through a model based on the nucleation and growth mechanism.

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Passive film growth, electrodissolution and pitting corrosion of prepassivated carbon steel in dilute NaOH solutions containing Na,SO, are studied by using potentiostatic and potentiodynamic techniques. Two kinetic reaction models implying different passive IiIm growth mechanisms are proposed to describe the passive Iilm growth, the electrodissolution process through the passive film and pitting corrosion. Current transients at constant potential recorded in the passive and pitting region can be satisfactorily reproduced by assuming the occurrence of simultaneous processes. The physical interpretation of adjusting parameters derived from the two models is consistent with a duplex structure for the passive film and with the nucleation and growth of pits when the applied potential exceeds the breakdown potential although both mechanisms for the passive layer growth seem to be equally probable.

The pitting corrosion of nickel in different electrolytes containing chloride ions was studied by using potentiostatic and potentiodynamic techniques complemented with scanning electron microscopy. The breakdown potential depends linearly on the logarithm of the chloride ion concentration. The logarithm of the induction time for pit initiation decreases linearly with the reciprocal of the applied potential. The overall process can be described by two stages. The first stage of pitting is explained through the formation of the passive layer in competition with the nucleation and growth of a chloride layer. The second stage, which is diffusion controlled, occurs when the salt precipitation conditions is reached. The proposed reaction model reproduces the potentiostatic current transients of nickel pitting by chloride in near-neutral buffered and alkaline solutions.

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Die Korrosion von Ni in verschiedenen CF‐haltigen Elektrolyten erfolgt in 2 Stufen.

Die lokalisierte Korrosion des untersuchten 1020 SAE‐Stahls in NaF enthaltender gepufferter (pH 8) Lösung ist mit der in Gegenwart anderer agressiver Anionen vergleichbar.