Fig. 3 shows Nyquist plots of AA5052 aluminium alloy in 4 M
sodium hydroxide-ethylene glycol solution without and with
additives.
The whole figure shows a similar shape. The EIS diagram consists
of three loops, (i) a big capacitive loop at high frequencies, (ii) a
small inductive loop at medium frequencies, and (iii) a second
capacitive loop at low frequencies. Approximate impedance results
were reported for aluminium in alkaline solution [21] and in
alkaline methanol solution [31]. The proposed equivalent circuit in
Fig. 4(a) is used to analyse the impedance spectra. As shown in