Measurement of the ac impedance of aluminum samples by holographic interferometry

In the present investigation, holographic interferometry was utilized for the first time to measure the alternating current (A.C.) impedance of aluminum samples during the initial stage of anodization processes in aqueous solution without any physical contact. The anodization process (oxidation) of the aluminum samples was carried out chemically in different acid sulpheric acid concentrations (0.5 - 3.125% H2SO4) at room temperature. In the mean time, a method of holographic interferometric was used to measure the thickness of anodization (oxide film) of the aluminum samples in aqueous solutions. Along with the holographic measurement, a mathematical model was derived in order to correlate the A.C. impedance of the aluminum samples in solutions to the thickness of the oxide film of the aluminum samples which forms due to the chemical oxidation. The thickness of the oxide film of the aluminum samples were measured by the real time-holographic interferometry. 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 thickness of the anodized film as well as the A.C. impedance of the aluminum samples can be determined in situ. In addition, a comparison was made between the obtained data of the A.C. impedance from the holographic measurements and A.C. impedance data obtained from measurements of electrochemical impedance spectroscopy. The comparison indicates that there is good agreement between the data from both techniques.