MEASUREMENT OF THE DOUBLE-LAYER CAPACITANCE OF ALUMINUM SAMPLES BY HOLOGRAPHIC-INTERFEROMETRY

In the present investigation, holographic interferometry was utilized for the first time to measure the double layer capacitance of aluminiu m samples during the initial stage of anodization processes in an aque ous solution without any physical contact. The anodization process (ox idation) of the aluminium samples was carried out chemically in differ ent sulphuric acid concentrations (0.5-3.125% H2SO4) at room temperatu re. In the meantime, a method of holographic interferometry was used t o measure the thickness of anodization (oxide film) of the aluminium s amples in aqueous solutions. Along with the holographic measurement, a mathematical model was derived in order to correlate the double layer capacitance of the aluminium samples in solutions to the thickness of the oxide film of the aluminium samples which forms due to the chemic al oxidation. The thickness of the oxide film of the aluminium samples was measured by real-time holographic interferometry. Consequently, h olographic interferometry is found to be very useful for surface finis h industries, especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film as w ell as the double layer capacitance of the aluminium samples can be de termined in situ. In addition, a comparison was made between the obtai ned data of the double layer capacitance from the holographic measurem ents and the double layer capacitance data obtained from measurements of electrochemical impedance spectroscopy. The comparison indicates th at there is good agreement between the data from both techniques. Copy right (C) 1996 Elsevier Science Ltd.