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摘要
The study focuses on the passivation behavior of single-gamma-phase titanium aluminide in acidic solutions with a particular emphasis on the role of oxidizing strength in characteristics of passive layer. The report includes potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies along with Mott-Schottky analysis in order to determine the corrosion behavior of the alloy and the semiconducting properties of the scale formed during exposure to acidic environment. Passive current density measured from potentiodynamic polarization curve, polarization resistance (R (p)) estimated by EIS, defect density, and flatband potential drawn from Mott-Schottky analysis are mainly used in estimating the ability of passive film formed on alloy in protecting it against high corrosion rates in Sulfuric acid (a non-oxidizing acid), perchloric acid, and nitric acid (oxidizing acid with different oxidizing strength). The results show that passive current density (i (pass)) in Sulfuric acid is 2.67 x 10(-5) A cm(-2), which is 2.5 and 3 times greater than the values obtained in perchloric acid (i (pass) = 9.91 x 10(-6)) and nitric acid (i (pass) = 7.98 x 10(-6)), respectively. EIS data reveal that the value of R (p) in sulfuric acid (20 k Omega cm(2)) is about three and five times smaller than that its value in perchloric acid and Nitric acid, respectively. Mott-Schottky analysis shows that the passive layer exhibits an n-type semiconducting characteristics irrespective of acidic environment. The greatest and the smallest values of donor density (N (D)) are obtained for the passive scale formed in sulfuric acid (N (D, H2SO4) = 18.36 x 10(19)) and nitric acid (N (D, HNO3) = 13.13 x 10(19)), respectively. The report concludes that characteristics of the passive scale are directly affected by reduction potential of the acid, which is the criterion of its oxidizing strength. An increase in the oxidizing strength of the acidic solution results in formation of more protective and less conductive layer on gamma phase titanium aluminide.
- 出版日期2014-3
