PASSIVITY BREAKDOWN AND EVOLUTION OF LOCALIZED CORROSION ON TYPE 316L STAINLESS STEEL
Passivity breakdown of 316L SS in the presence of aggressive Cl{sup -} and inhibitive NO{sub 3}{sup -} anions has been experimentally studied and the results have been interpreted in terms of the Point Defect Model (PDM). By introducing the competitive adsorption of Cl{sup -} and NO{sub 3}{sup -} into surface oxygen vacancies at the passive film/solution interface, the PDM yields a critical breakdown potential (V{sub c}) that is predicted to vary linearly with log[Cl{sup -}], or with log ([Cl{sup -}]/[NO{sub 3}{sup -}]) [1] when nitrate ions are present, which is shown in Fig. 1. The Point Defect Model also explains the fact that the slope of V{sub c} vs. log[Cl{sup -}] does not change in the presence of NO{sub 3}{sup -}, which is attributed to the quasi-equilibrium ejection of a cation from the barrier layer to form the vacancy pair V{sub M}V{sub O}{sup (2-{chi})} at the barrier layer/solution interface. The Point Defect Model predicts that measured V{sub c} increases linearly with the square root of voltage scan rate {nu}{sup 1/2} [1]. From this correlation, the critical, areal concentration of cation vacancies at the metal/barrier layer interface, {zeta}, has been estimated and found to be comparable to that calculated from the concentration of sites on the cation sublattice at the same location based on the presumed Cr{sub 2}O{sub 3} composition of the barrier layer. The Point Defect Model also explains the near normal distribution of V{sub c} in terms of a normal distribution of breakdown sites on the surface with respect to the vacancy diffusivity (D) [2]. The calculated distribution agrees with the experimental results very well and this agreement is used to estimate the cation vacancy diffusivity. Chronoamperometric studies have been performed on Type 316L SS at different voltages, [Cl{sup -}], [NO{sub 3}{sup -}] and temperatures to study the transition of metastable pits into stable pits. The survival probability for metastable pitting is determined and is used in Damage Function Analysis (DFA) to predict the accumulation of pitting damage on the surface, and is used in Deterministic Extreme Value Statistics (DEVS) to predict the distribution in the depth of the deepest pit in an ensemble of identical specimens.
- Research Organization:
- Yucca Mountain Project, Las Vegas, NV (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 883065
- Resource Relation:
- Conference: 210th ECS Conference, Cancun, Mexico, October 29-November 3, 2006
- Country of Publication:
- United States
- Language:
- English
Similar Records
Development and Integration of Light Water Reactor (LWR) Materials Corrosion Degradation Codes into Grizzly
Development of Advanced Electrochemical Emission Spectroscopy for Monitoring Corrosion in Simulated DOE Liquid Waste