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07586 In Situ Investigation of the Passivation of Alloy C22 and of the Passive Films Formed on Alloy C22 in Acidic Electrolytes at Room Temperature and at 90 C

Picture for 07586 In Situ Investigation of the Passivation of Alloy C22 and of the Passive Films Formed on Alloy
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Product Number: 51300-07586-SG
ISBN: 07586 2007 CP
Author: Thomas M. Devine, Marcela Miyagusuku, and Scott Harrington
Publication Date: 2007
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The passive film that forms on Alloy C22 was investigated by comparing/contrasting the results of electrochemical tests conducted on Alloy C22 and chromium. A combination of cyclic polarization, electrochemical impedance spectroscopy and Mott-Schottky analyses were used to (1) investigate the passivation of Alloy C22 and (2) identify the passive films formed on Alloy C22 in 1 M NaCl + 0.1 M H2SO4 at room temperature and at 90°C. The results indicate that the passive films formed on Alloy C22 exhibit semiconductor-like behavior. In particular, the passive films have n-type behavior and form an inversion layer at their free surface at potentials above approximately +0.45V vs Ag/AgCl. Measurements of capacitance suggest the passive films at room temperature and 90°C of both Alloy C22 and chromium are very thin (approximately = 1nm), even at potentials as high as +0.8V vs SCE. Mott- Schottky analyses indicate the passive films of Alloy C22 and chromium behave as n-type semiconductors, although both films’ carrier densities are high (~1x1021/cc). The Mott-Schottky plots are functions of the frequency of the measurement but the frequency dependence can be minimized/eliminated by replacing the capacitor in the sample’s equivalent circuit with a constant phase element (CPE). The flatband potential of Alloy C22’s passive films is significantly higher (-0.10V) than the flatband potential of chromium’s passive films (-0.70V), which correlates with the much faster kinetics of H+ reduction on Alloy C22 than on chromium.
The passive film that forms on Alloy C22 was investigated by comparing/contrasting the results of electrochemical tests conducted on Alloy C22 and chromium. A combination of cyclic polarization, electrochemical impedance spectroscopy and Mott-Schottky analyses were used to (1) investigate the passivation of Alloy C22 and (2) identify the passive films formed on Alloy C22 in 1 M NaCl + 0.1 M H2SO4 at room temperature and at 90°C. The results indicate that the passive films formed on Alloy C22 exhibit semiconductor-like behavior. In particular, the passive films have n-type behavior and form an inversion layer at their free surface at potentials above approximately +0.45V vs Ag/AgCl. Measurements of capacitance suggest the passive films at room temperature and 90°C of both Alloy C22 and chromium are very thin (approximately = 1nm), even at potentials as high as +0.8V vs SCE. Mott- Schottky analyses indicate the passive films of Alloy C22 and chromium behave as n-type semiconductors, although both films’ carrier densities are high (~1x1021/cc). The Mott-Schottky plots are functions of the frequency of the measurement but the frequency dependence can be minimized/eliminated by replacing the capacitor in the sample’s equivalent circuit with a constant phase element (CPE). The flatband potential of Alloy C22’s passive films is significantly higher (-0.10V) than the flatband potential of chromium’s passive films (-0.70V), which correlates with the much faster kinetics of H+ reduction on Alloy C22 than on chromium.
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