AC impedance–emission spectroscopy for determining the electrochemical behaviour of anodised aluminium in aqueous solutions

In the present investigation, holographic interferometry was utilised for the first time to determine the rate change of the alternating current (AC) impedance of aluminium samples during the initial stage of anodisation processes in aqueous solution without any physical contact. In fact, because the AC impedance values in this investigation were obtained by holographic interferometry, electromagnetic method rather than electronic method, the abrupt rate change of the AC impedance was called AC impedance–emission spectroscopy. The anodisation process (oxidation) of the aluminium samples was carried out chemically in different sulphuric acid concentrations (0.5–3.125% H2SO4) at room temperature. In the mean time, the real time holographic interferometry was used to determine the difference in the AC impedance of two subsequent values, dZ, as a function of the elapsed time of the experiment for the aluminium samples in 0. 5, 1.0, 1.5 and 3.125% H2SO4 solutions. The AC impedance–emission spectra of the present investigation represent a detailed picture of not only the rate change of the AC impedance throughout the anodisation processes but also the spectra represent the rate change of the growth of the oxide films on the aluminium samples in different solutions. Consequently, holographic interferometry is found to be very useful for surface finish industries, especially for monitoring the early stage of anodisation processes of metals, in which the rate change of AC impedance of the aluminium samples can be determined in situ.