Effect of Addition of Sulphide Ions on the Electrochemical Behaviour and Corrosion of Cu-Ag Alloys in Alkaline Solutions

Abstract

The electrochemical behaviour of copper-silver alloys was studied in 0.5 M NaOH containing sulphide ions using cyclic voltammetric and potentiodynamic anodic polarization techniques between the hydrogen and the oxygen evolution reactions under the effect of different variables such as reversal potential, scan rate, sulphide ion concentration, temperature and number of repeated cycles. The anodic sweep of potential was characterized by the appearance of three potential regions: sulphide attack potential region, copper dissolution potential region and silver dissolution potential region, prior to the oxygen evolution reaction. The first potential region was characterized by the appearance of three anodic peaks A 1 , A 2 and A 3 , which were related to the formation of Cu x S, Ag 2 S and sulphur on the electrode surface. The formation of Cu x S and Ag 2 S was associated with the formation of pits on the electrode surface. Scanning electron microscope was used to examine the electrode surface for pitting corrosion. In the copper dissolution potential region, copper dissolved selectively that was associated with the appearance of three anodic peaks A 4 , A 5 and A 6 , which are related to the formation of Cu 2 O, Cu(OH) 2 and CuO, respectively. In the third potential region, silver dissolves, which was associated with the appearance of two anodic peaks A 8 and A 9 , which were related to the formation of Ag 2 O and both of Ag 2 O 2 and soluble SO 4 2¯ compounds, respectively. X-ray diffraction analysis confirmed the existence of Ag 2 S, Cu x S, Ag 2 O and CuO on alloy I potentiodynamically polarized to 400 mV. The reverse sweep was characterized by the appearance of one activation peak A 10 and eight cathodic peaks