Abstract
The kinetics of passivity and pitting corrosion of copper in borate-boric acid buffer containing potassium thiocyanate is studied at 25°C by means of potentiostatic transients recorded at different constant potential values. Three different potential regions are distinguished. Region I, as the applied potential is increased, implies the successive formation of cuprous thiocyanate, cuprous and cupric oxide. This corresponds to the formation of a composite anodic layer. Region II extends from the potential of the third anodic voltammetric peak up to the breakdown potential. Region III involves the breakdown of the passive layer caused by thiocyanate ions, and the formation of different copper salts in the pits. The kinetics of the various stages is discussed in terms of an extension of the nucleation and growth mechanism following an approach which was earlier applied for explaining the initiation and growth of pitting corrosion of metals.
Highlights
EXPERIMENTALThe influence of anions in the electrochemical behaviour of copper in nearly neutral buffered and alkaline solutions has been studied over a wide range of experimental conditions [l-3]; generally implying an electrode surface initially covered by a protective layer consisting of an inner Cu20 layer and an outer CuO hydrated layer, as revealed by ESCA and ISS[4]
Region III extends beyond the passivity b breakdown potential (E,) which is associated with pitting corrosion of copper
The voltammetric response of copper in borate-boric acid buffer containing potassium thiocyanate involves the appearance of different new phases at the electrode surface along the potential scan
Summary
Instituto de Investigaciones Fisicoquimicas Te6ricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, Universidad National de La Plata, Casilla de Correo 16, Sucursal 4, (1900) La Plats, Argentina (Receioerl 20 January 1986; in revised form 7 April 1986). Abstract-The kinetics of passivity and pitting corrosion of copper in borate-boric acid buffer containing potassium thiocyanate is studied at 25°C by means ofpotentiostatic transients recorded at different constant potential v@ues: Three different potential regions are distinguished. Region I, as the applied potential is Increased, rmphes the successive formation of cuprous thiocyanate, cuprous and cupric oxide. This corresponds to the formation of a composite anodic layer. Region II extends from the potential of the third anodic voltammetric peak up to the breakdown potential. Region III involves the breakdown of the passive layer caused by thiocyanate ions, and the formation of different copper salts in the pits. The kinetics of the various stages is discussed in terms of an extension of the nucleation and growth mechanism following an approach which was earlier applied for explaining the initiation and growth of pitting corrosion of metals
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