D.L. capacitance-emission spectroscopy of determining the electrochemical behavior of anodized aluminium in aqueous solutions

Abstract

In the present investigation, holographic interferometry was utilized for the first time to determine the rate change of the Double layer (D.L) capacitance of aluminium samples during the initial stage of anodization processes in aqueous solution without any physical contact. In fact, because the D.L. capacitance values in this investigation, were obtained by holographic interferometry, electromagnetic method rather than electronic method, the abrupt rate change of the D.L. capacitance was called D.L. capacitance-emission spectroscopy. The anodization process (oxidation) of the aluminium samples was carried out chemically in different sulfuric 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 of the D.L. capacitance of two subsequent values, dC, 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 D.L. capacitance-emission spectra of the present investigation represent a detail picture of not only the rate change of the D.L. capacitance throughout the anodization 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 interferometric is found very useful for surface finish industries especially for monitoring the early stage of anodization processes of metals, in which the rate change of D.L. capacitance of the aluminium samples can be determined in situ.