Noah D. Budiansky

Origins of Persistent Interaction among Localized Corrosion Sites on Stainless Steel

The origins of persistent interactions among localized corrosion sites were investigated using multielectrode arrays (MEA). MEAs consisted of one hundred 250 μm diam AISI 316 stainless steel wires configured into 5 X 20 close-packed rectangle and 5 X 5 far-spaced configurations. Experiments were conducted in dilute chloride solutions and elevated temperatures to accentuate interactions. Interactions between early dominating pits and the adjacent electrode surface were found to develop as regions of enhanced or suppressed pitting susceptibility triggered by concentration and potential fields developed during growth of large pits, respectively. Transient aggressive species accumulation around active pits was also found to cause surface damage to electrodes that persisted for long periods after primary pits were repassivated and solutions extensively stirred. Oxide film alteration, mixed metal sulfide inclusion damage, and surface contamination were all considered to be possible origins of persistent interactions. Mn(Fe,Cr)S inclusions were implicated to be the origin of such persistent interactions. Persistent interactions were completely suppressed by nitric acid treatment, which is believed to remove or modify susceptible Mn(Fe,Cr)S inclusions.

Use of Coupled Multi-Electrode Arrays to Advance the Understanding of Selected Corrosion Phenomena

The use of multi-coupled electrode arrays in various corrosion applications is discussed with the main goal of advancing the understanding of various corrosion phenomena. Both close-packed and far-spaced electrode configurations are discussed. Far-spaced electrode arrays are optimized for high-throughput experiments capable of elucidating the effects of various variables on corrosion properties. For instance, the effects of a statistical distribution of flaws on corrosion properties can be examined. Close-packed arrays enable unprecedented spatial and temporal information on the behavior of local anodes and cathodes. Interactions between corrosion sites can trigger or inhibit corrosion phenomena and affect corrosion damage evolution.

Detection of Interactions among Localized Pitting Sites on Stainless Steel Using Spatial Statistics

Spatial point pattern analysis methods @A Population Perspective-Statistical Ecology , Kluwer Academic Publishers, Boston ~1998!; Statistics for Spatial Data, Wiley-Interscience Publications, New York ~1993!; Statistical Analysis of Spatial Point Patterns, 2nd ed., Arnold Publishers, London ~2003!; Spatial Statistics, John Wiley & Sons, New York ~1981!# were used to characterize the spatial patterns of pitting sites on AISI 316 stainless steel. Populations of artificial pitting sites were generated ~e.g., clustered, anti-clustered, random, or periodic ! to test the ability of the selected spatial statistics methods to characterize these patterns. Experimental pitting patterns on AISI 316 stainless steel analyzed by the same methods indicated that interactions occur between micrometer scale pits over multiple micrometer distances. Spatial statistics results indicated that positive ~e.g., clustering of pit sites! occur between pitting sites when they are grown potentiodynamically. Processes associated with the acid/halide pitting mechanism have been shown to promote interactions between pit sites that give rise to such spatial patterns @J. Electrochem. Soc., 151, B233 ~2004!; Paper presented at The Electrochemical Society Meeting, Salt Lake City, UT, Oct 20-25, 2002; Electrochem. Solid-State Lett., 3 ,2 71~2000!; J. Electrochem. Soc., 149, B163 ~2002!; Science, 305, 1133 ~2004!#. Positive interactions were eliminated by stirring, indicating that local acid/halide accumulation was the source of positive interactions.

Coupled Multielectrode Investigation of Crevice Corrosion of AISI 316 Stainless Steel

Close packed coupled multielectrode arrays simulating a planar electrode were used to measure the current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel. Scaling laws derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCI at 50°C was found to initiate close to the crevice mouth and to spread inward and outward with time. The local crevice current density increased dramatically over a short period to reach a limiting value.