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Tuesday, March 16, 2010: 10:10 AM
214 D (Henry B. Gonzales Convention Center)
The composition and the electronic properties of the passive films formed on Alloy 690 in various environments including a neutral aqueous solution, high-temperature air, and a PWR (pressurized water reactor) simulated condition at 325 °C were investigated.
The passive film formed on Alloy 690 at high potential (0.3 VSCE) in pH 8.5 buffer solution and that in air at 400 °C were highly enriched with Cr from the XPS concentration profiles. However, the passive film formed at low potential (-0.3 VSCE) in pH 8.5 buffer solution and that in PWR simulated environment showed relatively low content of Cr. The photocurrent spectra for the passive films comprised spectral components originated from Cr2O3, NiO, Ni(OH)2, Cr(OH)3, and γ-Fe2O3, with variations of intensity and flat band potential for each of them depending on the film formation condition. Mott-Schottky plots for the passive film of Alloy 690 exhibited n-type semiconducting property, demonstrating that the capacitance behavior of the passive film is controlled by n-type γ-Fe2O3. The XPS and Mott-Schottky analyses suggest that the high Cr content in the passive film presumably reduces the defect density in the passive film of Alloy 690.
The passive film formed on Alloy 690 at high potential (0.3 VSCE) in pH 8.5 buffer solution and that in air at 400 °C were highly enriched with Cr from the XPS concentration profiles. However, the passive film formed at low potential (-0.3 VSCE) in pH 8.5 buffer solution and that in PWR simulated environment showed relatively low content of Cr. The photocurrent spectra for the passive films comprised spectral components originated from Cr2O3, NiO, Ni(OH)2, Cr(OH)3, and γ-Fe2O3, with variations of intensity and flat band potential for each of them depending on the film formation condition. Mott-Schottky plots for the passive film of Alloy 690 exhibited n-type semiconducting property, demonstrating that the capacitance behavior of the passive film is controlled by n-type γ-Fe2O3. The XPS and Mott-Schottky analyses suggest that the high Cr content in the passive film presumably reduces the defect density in the passive film of Alloy 690.