Experimental and Theoretical Study of Inclusions During Initiation of Crevice Corrosion
Lott, Stephen Elder
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https://hdl.handle.net/2142/69787
Description
Title
Experimental and Theoretical Study of Inclusions During Initiation of Crevice Corrosion
Author(s)
Lott, Stephen Elder
Issue Date
1987
Doctoral Committee Chair(s)
Alkire, Richard C.
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Abstract
The initiation sites of crevice corrosion on stainless steel are generally recognized to be sulfide inclusions (MnS), although the mechanism by which the initiation occurs remains unknown. Controlled solution experiments showed that the products of the MnS electrochemical oxidation reaction were elemental sulfur and thiosulfate. Spectroelectrochemical cell experiments on MnS quantified the electrochemical production of thiosulfate. This finding linked the metallurgical and solution phases and suggested a depassivation mechanism based on a critical crevice solution composition. The range of thiosulfate and chloride ion concentrations in which the stainless steel oxide film remained passive was determined. All other species present in the crevice were shown not to influence depassivation. From the proposed mechanism a mathematical model was developed to determine the position and time of breakdown in the crevice based on transport of species by migration and diffusion, electrochemical kinetics, and potential field theory. Instrumented artificial crevice cell experiments were conducted to test the validity of the model and the proposed mechanism. The crevice cell geometry had a variable crevice height of 2.7 to 9.2 $\pm$ 0.2 $\mu$m and a depth of 1.27 cm; very good agreement between the experiments and the model was found for the conditions for avoiding crevice corrosion. The model was inverted in order to suggest the design criteria for achieving corrosion free crevices.
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