In the present investigation, holographic interferometry was utilized for the first time to
measure in situ the thickness of the oxide film, alternating current (A.C.) impedance, and double
layer capacitance of aluminium samples during anodization processes in aqueous solution without
any physical contact. The anodization process (oxidation) of the aluminium samples was carried out
by the electrochemical impedance spectroscopy (EIS), in different concentrations of sulphuric acid
(0.5-2.5 % H2SO4) at room temperature. In the mean time, the real-time holographic interferometric
was used to measure the thickness of anodized (oxide) film of the aluminium samples in aqueous
solutions. Also, mathematical models were applied to measure the alternating current (A.C.)
impedance, and double layer capacitance of aluminium samples by holographic interferometry,
during anodization processes in aqueous solution. 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, the A.C. impedance,
and the double layer capacitance of the aluminium samples in sulphuric acid (0.5-2.5 % H2SO4) can
be determined in situ. Futhermore, a comparison was made between the electrochemical values
obtained from the holographic interferometry measurements and from measurements of
electrochemical impedance spectroscopy(EIS) on aluminium samples in sulphuric acid (0.5-2.5 %
H2SO4). The comparison indicates that there is good agreement between the obtained
electrochemical data from both techniques. However, there is a drastic difference between the
measurement of the oxide film thickness by both techniques. The oxide film thickness of the
aluminium samples in 0, 0.5, 1.0, 1.5, 2.0, 2.5% H2SO4 by the optical interferometry is in a
micrometer scale. However, the oxide film thickness of the aluminium samples in 0, 0.5, 1.0, 1.5,
2.0, 2.5% H2SO4 by the E.I.Spectroscopy in a nanometer scale. This can be explained due to the fact
that the E.I.Spectroscopy is useful technique to measure the electrochemical parameters and the
thickness of the barrier (compact) oxide films. In contrast, the optical interferometry is found useful
technique to characterize and measure the thickness of the porous oxide layer. Also, the optimum
thickness of the oxide barrier film was detected to be equivalent to 0.612nm in sulphuric acid
concentration of 2.5% H2SO4 by E.I. spectroscopy.
In-situ determination of thickness and electrochemical properties of barrier oxide film on impure aluminium in aqueous solution