The Open Circuit Potential Versus Time Curves And Self Corrosion Rate Of Al

1504 Words Aug 2nd, 2016 7 Pages
Fig. 2 and Table 1 present the open circuit potential versus time curves and self-corrosion rate of Al, Alloy 1 and Alloy 2 electrodes in 2 M NaCl electrolyte, respectively. Corrosion rates were obtained by weight loss measurements in 2 M NaCl solution after 60 min. As seen in Table 1, the corrosion rate increases in the following order: Al <Alloy 1 < Alloy 2. Fig. 2 indicates that open circuit potential of Alloy 1, 2 (especially Alloy2) is more negative than that of Al. It can be seen that the potential of the Al electrode shifts in the positive direction and achieves a stable value of about -0.82 V. This is due to the formation of natural oxide layer on the Al surface which is stable in saline environments and leads to ennoblement of the potential of aluminum electrode (see Fig. 3A). This oxide film is Al2O3 and Al(OH)3, in neutral solution, based on Pourbaix diagram [20]. The alloy 1 presents OCP value of about -1.30 V whereas that of Alloy 2 was -1.44 V, which are more negative than that of Al in the same medium. The presence of tin and gallium in aluminum matrix as alloying elements increases the adsorption of Cl- ions at the values of negative potential which leads to the alloy dissolution [10]. The surface morphologies of Al, Alloy 1 and Alloy 2 after immersion in 2 M NaCl solution for 1 h were obtained by scanning electron microscopy (SEM) (Fig. 3). The morphology of Alloy 2 (Fig. 3C) in 2 M NaCl solution have large pits, which probably is due to the presence of…

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