Electrical Resistance-Emission Spectroscopy for Determining the Electrochemical Behavior of Anodized Aluminum in Aqueous Solutions

Holographic interferometry was utilized for the first time to determine the rate change of the electrical resistance of aluminum samples during the initial processes of anodization of the samples in aqueous solution without any physical contact. In fact, because the electrical resistance values in this investigation were obtained by holographic interferometry, electromagnetic method rather than electronic method, the abrupt rate change of the electrical resistance was called the electrical resistance –emission spectroscopy. The anodization process of the aluminum samples was carried out by the electrochemical impedance spectroscopy (EIS) test in different sulfuric acid concentrations (1.0–2.5% H₂SO₄) at room temperature. In the meantime, the real time holographic interferometry was used to determine the difference in the electrical resistance of two subsequent values, dR, as a function of the elapsed time of the EIS test for the aluminum samples in 1. 0, 1.5, 2.0 and 2.5% H₂SO₄ solutions. The electrical resistance–emission spectra of the present investigation represent a detailed picture of not only the rate change of the electrical resistance throughout the anodization processes but also the spectra represent the rate change of the growth of the oxide films on the aluminum samples in different solutions. Consequently, holographic interferometry is found to be very useful for surface finish industries, especially for monitoring the early stage of anodization processes of metals, in which the rate change of electrical resistance of the aluminum samples can be determined in situ.

Keywords: holographic interferometry; electrochemical impedance spectroscopy (EIS); anodization process; oxide film thickness; sulfuric acid; aluminum.