Performance Study of Aluminium–Zinc Anode using Noise Resistance, Pitting Index and Recurrence Plots from Electrochemical Noise Data

Abstract

Electrochemical noise technique allows the simultaneous measurement of voltage and current on a material in a process stream. Useful information regarding the state of the sample, initiation, type and growth of corrosion can be obtained. To this end, time domain and recurrence plots have been used to study the electrochemical noise data obtained for an Al–Zn sacrificial anode immersed in NaCl solution over 7 days to understand various corrosion mechanisms occurring on the anode surface. The noise resistance, pitting index and recurrence plots were correlated with scanning electron microscopy (SEM). The results revealed that PI and Rn for the non-heat-treated and heat-treated aluminium–zinc anodes decreased progressively with immersion time. This can be attributed to increasing dissolution activity on the anode surfaces. The obtained Rn for non-heat-treated anodes were greater than 105 Ω cm2 and the Rn for heat-treated anodes were less than 105 Ω cm2. Heat treating the Al–Zn anodes helped to reduce the noise resistance values to a maximum of 12,000 Ω cm2. The recurrence plots showed distinct butterfly-like structures that indicated progressive dissolution activity on the anode surfaces. Lower noise resistance and pitting index as immersion time progressed signified improved electrochemical performance of the anodes.