الفهرس 
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Abstract
In this work the electrochemical behavior of different Cu alloys (Cu-Al, Cu-Al-Ni, Cu-Al-Zn and Cu-35Zn) was investigated in naturally aerated stagnant seawater solutions from the white Mediterranean Sea. It was noticed that, the addition of Al, Ni and Zn to Cu, decreases the corrosion rate of the alloy. The calculated values of the corrosion rate of the four different alloys in the same solution and under the same conditions show clearly that the Cu-Al-Zn and Cu-35Zn alloys are the most stable alloys in this medium. It seems that the presence of Al and Zn together in the copper alloy increases the corrosion resistance of the alloy. The behavior of the different materials was also studied in absence and presence of different concentrations of different surfactants (5-methyl-1H-benzotriazole (TTA), 5-methyle-1 dodecaethoxide-benzotriazole, (TTA(12), and 5-methyle-1 tetracosaethoxide-benzotriazole, TTA(24)) as corrosion inhibitors. These inhibitors were synthesized and their structures were confirmed using H1NMR and FTIR techniques. Conventional electrochemical techniques such as open-circuit potential measurements, polarization methods and electrochemical impedance spectroscopy (EIS) were used. The surface morphology and constituents of the surface components were analyzed by SEM/EDAX analysis.
The synthesized surfactants are applied as corrosion inhibitors for the same alloys. A selected concentration range of tolyltriazole compounds, TTAs, (from 50 to 400 ppm) were studied. The corrosion rate decreased as the inhibitor concentration increased and the inhibition efficiency reach its max value (96 %) in case of Cu-Al alloy in presence of 400 ppm of TTA(24). The Potentiodynamic polarization curves of pure Cu and Cu alloys after electrode immersion in stagnant naturally aerated seawater free and containing 400 ppm of the different inhibitors showed that the synthesized tolyltriazole compounds are very effective inhibitors for the selected Cu alloys in addition to the pure Cu. When the effect of the three inhibitors compared to each other at 400 ppm, it was noticed that TTA is more effective on the pure Cu surface than other inhibitors and TTA(24) has higher inhibition efficiency in case of Cu-Al. When the curves compared with each other, it was noticed that TTA is more efficient than TTA(12) and TTA(24) at 400 ppm in case of Cu-Al-Ni, Cu-Al-Zn and Cu-35Zn. The data obtained by electrochemical impedance measurements are in a good agreement with that obtained by potentiodynamic polarization measurements.
The variation of the corrosion resistance of the barrier layer on the Cu alloy with the time of immersion in stagnant naturally aerated seawater in presence of 300 ppm of different inhibitors were studied. The impedance semi-circle diameter increase with increasing time of immersion, implying the decrease in the corrosion rates with time. The charge transfer resistance, Rct, increases with the increase in the time of electrode immersion in case of Cu-Al and Cu-Al-Ni. The charge transfer resistance and the film resistance, Rf, of Cu-Al-Zn and Cu-35Zn increase with the increase in the time of electrode immersion time. Also, the effect of temperature on the inhibition efficiency of TTAs is investigated by polarization tests in the temperature range 298-333 K in presence of 300 ppm in sea water was studied. The data obtained showed that icorr value increases with increasing the temperature, indicating that the corrosion rate is accelerated by the rise in temperature. The activation energy was calculated for all alloys in presence of each inhibitor.
The mechanism of the corrosion inhibition process is based on the adsorption the tolyltriazole derivative molecules on the active sites on the alloy surface. The calculated free energy of adsorption of the three inhibitors on the different alloys reveals a strong physical adsorption process. The surface morphology was studied using SEM and EDX.