Electrochemical Behavior and Thickness of Aluminium Oxide Films Studied by EIS: Laboratory and Field Studies

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.