Influence of Silver Content on Corrosion Resistance of Lead Anodes During Potential Decay by Electrochemical Noise Measurements

Abstract

The electrochemical behaviour of different Pb-Ag (0.5, 0.6 and 0.7%) anodes during zinc electro winning has been studied in acid zinc sulphate electrolyte containing Mn2+ at 38 °C, and 50 mA/cm2 by electrochemical noise measurements “ENM” using the zero resistance ammeter set-up (ZRA). During 16 h decay period after 24 h of electrolysis, Pb-0.5% Ag anode had the highest corrosion rate among the three anodes, followed by Pb-0.6%Ag anode and Pb-0.7% Ag anode. It can be observed that at the end of 16 h decay, the 0.7% Ag lead anode had the lowest potential (the most active) followed by 0.6% and 0.5% Ag lead anodes. Also, 0.5% Ag lead anode had the longest first plateau as compared to 0.6% and 0.7% Ag lead anodes. This plateau had higher corrosion rate “1/Rn”, higher slope of ratio “Sr” than that in its following decay period. In addition, at the end of 16 h potential decay, the potential-time record shows that Pb-0.7% Ag anode had several high amplitude and high frequency oscillations with several peak transients; while Pb-0.5% Ag anode had more frequent repetition of fluctuations with smoother potential. Moreover, at the end of 16 h decay, it was also obtained that the absolute magnitudes of the slopes of potential of power spectral densities (PSD) of 0.7% Ag lead anode are also lower than that of 0.5% Ag lead anode. Finally, it can be admitted that 0.5% Ag-Pb anode has more corrosion rate during polarization and this is shown by important plateau at the average value of 1.61 V/SHE for the longest time (45 min); while 0.7% Ag lead anode showed more active galvanic cells at the end of decay (11-16 h) that can correspond to more localized corrosion because of more abundant silver containing phases. Keywords: Corrosion rates, electrochemical noise measurements, Pb-Ag alloy anodes, plateau, potential decay.