Papers by Author: F. Al-Sabti

Abstract: The technique of electrochemical impedance spectroscopy (EIS) is widely used in laboratories and industries for materials evaluation. The aim of this investigation is to monitor the thickness of the anodized (oxide) aluminium sheets (samples) by using the EIS in a laboratory and a field study at a predetermined exposure duration in the field, i.e., 0, 1, 3, 6, 9, 12 months, in 0-10 % sulphuric acid. Four experimental stations were built out of KISR in order to monitor the thickness of the anodized (oxide) layer and the electrochemical parameters of anodized aluminium sheets by using the EIS. The zero state results at 0 exposure duration, indicating that as the concentration of the sulphuric acid increased from 0-10% H₂SO₄, the polarization resistance was observed to decrease from 3.15E+05 to 9.80E+03 Ohms, except at a concentration of 4% H₂SO₄, where the polarization resistance was observed to increase from 5.20E+03 to 2.90E+04 Ohms. On the contrary, the value of the solution resistance was observed to vary several times between 1.33E+04 to 1.53E+00 Ohms as a function of the increase of the sulphuric acid concentration from 0-10% H₂SO₄. In similar fashion to the polarization resistance, as the concentration of the sulphuric acid increased from 0-10% H₂SO₄, values of the alternating current impedance were found to vary several times between 1.94E+09 to 3.95E+05 Ohms, in a non-linear fashion. A similar behavior was observed on the values of the double layer capacitance as a function of the sulphuric acid increased, from 0-10% H₂SO₄, in which the values of the double layer capacitance was observed to change several times from 2.24E-09 to 2.53E-06 μF. The optimum thickness of the oxide film was detected (26.5 nm) at 8% H₂SO₄ of the sulphuric acid concentration. In order to determine the performance of the anodized aluminium-sheet in surrounding areas of Kuwait, a plan was arranged for such a field study. The field study consists of setting up four racks of sample panels in different locations in Kuwait. The racks were installed in the main field of Kuwait Institute for Scientific Research (KISR) in Shuwaikh area, in a residential area of South Sura area, in the main field of the Petroleum Research Department and Studies Center (PRSC) of Kuwait Institute for Scientific Research (KISR), in an industrial area of Ahmadi city, and in the main field of the fishery department of Kuwait Institute for Scientific Research (KISR) in a marine area of Salmia. The investigation planned to take a sheet each three months, for a 12 months duration, in order to determine the electrochemical parameters and the oxide film thickness of the sheets by the EIS technique in the field and to compare the data with those obtained in this report, at zero state.

Abstract: 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.

Abstract: In the present work, the electrochemical behavior and the oxide barrier-film thickness of anodized aluminum-magnesium (Al-Mg) alloy were determined in the as-received and annealed conditions by using electrochemical techniques. Electrochemical parameters such as the polarization resistance, solution resistance, alternating-current (AC) impedance, and the doublelayer capacitance of the anodized Al-Mg alloy were determined in boric acid solutions, with 0 to 10%H3BO3, by using electrochemical impedance spectroscopic (EIS) methods. The oxide barrierfilm thickness of the anodized Al-Mg alloy was then deduced, from the electrochemical parameters obtained, as a function of the boric acid concentration (0 to 10%H3BO3). The optimum thickness of the oxide barrier-film was detected for as received samples (1.17nm) and for annealed samples (1.22nm) at a boric acid concentration of 4%H3BO3.