Comparison of electrochemical current noise signals arising from symmetrical and asymmetrical electrodes made of Al alloys at different pH values using statistical and wavelet analysis. Part II: Alkaline solutions

• Asymmetrical (As) electrodes retained their essential advantages at pH 9 and lost them partly at pH 12.
• Statistical data made it possible to differentiate between small and large symmetrical (SS & LS) configurations.
• SS and LS configurations were preferable for measuring ECN in solutions of pH 6 and 9, respectively.
• Electrochemical behavior of intermetallic particles can affect the true time scale of ECN transients.
• All results obtained in neutral, acidic and alkaline solutions have been interpreted by a recently proposed model.

In this paper, the electrochemical current noise (ECN) signals arising from the symmetrical (both small and large) and asymmetrical electrodes made of AA6061 and AA2024 in 1.0 M NaCl electrolyte adjusted to pH 9 and 12 were analyzed by statistical and wavelet methods. The asymmetrical electrodes (1–100 mm2) retained their essential advantages in weak alkaline solutions as well as in the near-neutral solutions. However, their advantages were partly lost in the strong alkaline solutions. The use of statistical data made it possible to differentiate between the two symmetrical configurations. The statistical analysis of ECN signals arising from the symmetrical electrodes revealed that the small symmetrical electrodes (1–1 mm2) were preferable for measuring ECN in near-neutral solutions, while the large symmetrical electrodes (100–100 mm2) were preferable for measuring ECN in weak alkaline solutions. However, in strong alkaline solutions the large symmetrical electrodes were preferable for measuring ECN on AA6061, but the small symmetrical electrodes were preferable for measuring ECN on AA2024. The electrochemical behavior of intermetallic particles as a function of pH along with an earlier modeling of ECN transients were employed to interpret the ECN data of AA2024 asymmetrical electrodes at pH 9 in comparison with near-neutral pH. The SDPS values of the true timescale crystals of the ECN signals arising from asymmetrical electrodes increased with increasing pH value from 9 to 12 due to the enhanced corrosion severity. A recently presented model describing the process of EN generation has been employed to interpret all results obtained in near-neutral, acidic and alkaline solutions.