Investigation on the Effect of Lead (Pb) on the Degradation Behavior of Passive Films on Alloy 800
Alloy 800 has been demonstrated to be susceptible to Pb-induced degradation such as stress corrosion cracking (SCC) in laboratory experiments. Pb has been proposed to cause such degradation by affecting the formation of protective oxides comprising the passive films on the alloys. To understand the detrimental effects of Pb, Alloy 800 samples pre-passivated under all volatile treatment (AVT) conditions were exposed to alkaline environment of pH280 °C 9.5 at 280 °C in the absence and presence of Pb. The Pb-free and Pb-containing passivated surfaces, along with bare surfaces as control samples, were characterized using electrochemical and surface analytical techniques. The results contrast the susceptibility of Alloy 800 to Pb-induced degradation reported in literature, where experiments are usually performed on bare surfaces with excess Pb, typically as PbO, present in the aqueous solutions; suggesting that the effect of Pb depends on whether it is present in solution or incorporated in the film.
KeywordsAlloy 800 Passive film Pb Cyclic polarization Mott-schottky analysis Atom probe tomography
Many thanks are due to colleagues at CNL, especially A. Audet and H. Chaudhry for performing the room temperature and high temperature electrochemical measurements; C. Mayhew, H. Rudzinski, and B. Payne for the AES and XPS characterization; and J. Smith for review and technical discussion. APT was performed and analyzed by B. Langelier at the Canadian Center for Electron Microscopy, Hamilton.
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