Effect of pH on corrosion behavior of CuCrZr in solution without and ...

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gradient is determined by the electrode potential [15-17]. As the potential is further increased, the anodic curves exhibit small peaks consistent with the formation <strong>of</strong> a CuCl film [16, 17] at a potential <strong>of</strong> about -0.05 V. Beyond the peaks, limiting-current behavior is observed and the rate <strong>of</strong> anodic reaction is controlled by the formation and dissolution <strong>of</strong> CuCl film [16]. The rate <strong>of</strong> the reaction is probably driven by the cathodic reduction <strong>of</strong> oxygen in neutral solution: O 2 2H 2 O 4e 4( OH ) (7) In chloride solution at <strong>pH</strong> 7, the I corr <strong>of</strong> Cu and CuCrZr are the lowest (Fig. 11). It seems their polarization behaviors in chloride solutions are dominated by the dissolution <strong>of</strong> copper to soluble cuprous chloride ion complex CuCl 2 - . For CuCrZr in solution without chloride at <strong>pH</strong> 10, passivation is observed and the passive range (-0.1 to 0.25 V) is wider than that <strong>of</strong> CuCrZr at <strong>pH</strong> 7 and Cu at <strong>pH</strong> 10 (Fig. 10). Their passive current densities are <strong>of</strong> the order <strong>of</strong> A/cm 2 . A thin and dense Cu 2 O layer formed on the surface <strong>of</strong> CuCrZr and Cu results in spontaneous passivation. Whereas, the polarization curves <strong>of</strong> CuCrZr and Cu show active behavior in choride solution at <strong>pH</strong> 10 and are similar to those at <strong>pH</strong> 7 (Fig. 11). The curves for CuCrZr and Cu in 0.6 M NaCl start with similar active regions followed by active–passive transition that occurs at comparable potentials. The sudden increase <strong>of</strong> anodic currents at higher potentials is due to film breakdown, being accompanied by corrosion. It has been shown that the potentiodynamic behavior <strong>of</strong> copper in slightly alkaline solution exhibits anodic peak associated with the electro-formation <strong>of</strong> Cu 2 O and CuO. Formation <strong>of</strong> Cu 2 O occurs through: 2Cu + H 2 O → Cu 2 O + 2H + + 2e - (9) 10
and subsequent oxidation <strong>of</strong> Cu 2 O to CuO film at higher potentials, according to: Cu 2 O + H 2 O → 2CuO + 2H + + 2e - (10) Thus, passivity breakdown at <strong>pH</strong> 10 occurs with the formation <strong>of</strong> Cu 2 O for CuCrZr at lower potential and with the growth <strong>of</strong> CuO film for Cu at higher potential. This is attributed primarily to the generation <strong>of</strong> H + ions at the electrode surface [18]. For CuCrZr and Cu in the solution without chloride at <strong>pH</strong> 12, the behavior at the active region appears to be influenced by high alkalinity. The noticeable Tafel region shows a large slope and wide passive range. The CuO layer formed and its thickness increases rapidly due to high alkalinity. The polarization curves (Fig. 10) exhibit a passive region with an anodic peak which corresponds to the formation <strong>of</strong> Cu(OH) / Cu 2 O layer [19, 20] through the following reactions: 2Cu + 2OH - → Cu 2 O + H 2 O + 2e - (10) and subsequent oxidation <strong>of</strong> Cu 2 O to Cu(OH) 2 film at higher potentials, according to: Cu 2 O + 2OH - + H 2 O → Cu(OH) 2 + 2e - (11) In chloride solution, the film stability <strong>of</strong> CuCrZr and Cu is lower but the curves still show considerable passive ranges (Fig. 11). As the potential is increased above the pitting potential, breakdown becomes evident. The polarization curves show two passive regions with two anodic peaks. The first peak corresponds to the formation <strong>of</strong> the Cu(OH) / Cu 2 O layer. The second peak is more complex and involves the formation <strong>of</strong> Cu(OH) / Cu 2 O and Cu(OH) 2 / CuO [21]. 3.5 <strong>Effect</strong> <strong>of</strong> <strong>pH</strong> on I corr 11
Page 1 and 2: Manuscript Click here to view linke
Page 3 and 4: In the literature, some studies wer
Page 5 and 6: the potential was increased at a ra
Page 7 and 8: preferential dissolution of
Page 9: Moreover, copper oxidizes to cuprou
Page 13 and 14: 3.7. SEM and EDX analyses The SEM m
Page 15 and 16: [4] V. Belous, G. Kalinin, P. Loren
Page 17 and 18: Table and Figure captions Table 1.
Page 19 and 20: Designation UNS number Hardness (Hv
Page 22 and 23: Fig. 1 Fig. 1. SEM micrograph <stro
Page 24 and 25: Fig. 3 (a) (b) Fig. 3. Plots <stron
Page 26 and 27: Fig. 5 (a) (b) Fig. 5. Plots <stron
Page 28 and 29: Fig. 7 (a) (b)
Page 30 and 31: Fig. 8 (a) (b) Fig. 8. Potentiodyna
Page 32 and 33: Fig. 10 (a) (b) Fig. 10. Potentiody
Page 34 and 35: Fig. 12 (a) (b) Fig. 12. Ef
Page 36: Fig. 14 Element O K Cl K Cr K Cu K

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