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Wednesday, March 19, 2008 - 9:05 AM
Convention Center, Second Level, 210 (Ernest N. Morial Convention Center)
08578
Effect of the Addition of Organic Acids to the General and Crevice Corrosion Behavior of Alloy 22 in Chloride Solutions
Alloy 22 (N06022) is a nickel based alloy containing alloying elements such as chromium, molybdenum and tungsten. It is highly corrosion resistant both under reducing and under oxidizing conditions. This is why Alloy 22 is the current candidate alloy to fabricate the external container of the high level nuclear waste containers for the Yucca Mountain repository.
Electrochemical studies such as cyclic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were performed to determine the corrosion behaviour of Alloy 22 in 1M NaCl solutions at various pH values from acidic to neutral at90ºC . All the tested material was wrought Mill Annealed (MA). The specimens were prismatic specimens for corrosion rate measurements. For crevice corrosion susceptibility tests, prism crevice assemblies (PCA) were used, which were fabricated based on the washer for crevice forming described in ASTM G 48. Tests were also carried out in NaCl solutions containing weak organic acids like oxalic, acetic, citric and picric acids.
The results showed that the corrosion rate of Alloy 22 was significantly higher in solutions containing oxalic acid than in solutions of pure NaCl at the same pH. Citric and Picric acids showed a slightly higher corrosion rate, and Acetic acid maintained the corrosion rate of pure chloride solutions at the same pH. With respect to localized corrosion, organic acids revealed to be weak inhibitors. High concentration ratios, compared to nitrate ions, were needed to completely inhibit crevice corrosion in chloride containing solutions. Repassivation potentials in Picric acid could not be detected due to reduction of the acid at that potential range.
Electrochemical studies such as cyclic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were performed to determine the corrosion behaviour of Alloy 22 in 1M NaCl solutions at various pH values from acidic to neutral at
The results showed that the corrosion rate of Alloy 22 was significantly higher in solutions containing oxalic acid than in solutions of pure NaCl at the same pH. Citric and Picric acids showed a slightly higher corrosion rate, and Acetic acid maintained the corrosion rate of pure chloride solutions at the same pH. With respect to localized corrosion, organic acids revealed to be weak inhibitors. High concentration ratios, compared to nitrate ions, were needed to completely inhibit crevice corrosion in chloride containing solutions. Repassivation potentials in Picric acid could not be detected due to reduction of the acid at that potential range.
The results were discussed considering acidity constants, buffer capacity and complex formation constants of the different weak acids.
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See more of The CORROSION 2008 Conference and Expo (March 16-20, 2008)