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 aluminium samples during the initial stage of anodization processe s in aqueous solution without any physical contact. The anodization pr ocess (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, a method of holographic interferometric was used to measure the thickness of anodization (oxide film) of the aluminium samples in aqueous solutions. Along with the holographic mea surement, a mathematical model was derived in order to correlate the a .c. impedance of the aluminium samples in solutions to the thickness o f the oxide film of the aluminium samples which forms due to the chemi cal oxidation. The thickness of the oxide film of the aluminium sample s was measured by the real-time holographic interferometry. Consequent ly, holographic interferometry is found very useful for surface finish industries especially for monitoring the early stage of anodization p rocesses of metals, in which the thickness of the anodized film as wel l as the a.c. impedance of the aluminium samples can be determined in situ. In addition, a comparison was made between the a.c. impedance va lues obtained from the holographic interferometry measurements and fro m measurements of electrochemical impedance spectroscopy. The comparis on indicates that there is good agreement between the data from both t echniques. (C) 1997 Elsevier Science Ltd.