1. National Science Foundation Grants DMR-9119304
This research takes a new approach to understanding the changes occurring in solution chemistry during localized corrosion. Ion chromatography is employed to probe the progression of solution chemistry within occluded cells. Ion chromatography is capable of detecting nanogram quantities of a wide variety of ions in solution volumes as low as 10 microliters. This technique permits the analysis of changes in solution chemistry at localized corrosion sites such as in crevices. New insights can be obtained into the fundamental processes that control corrosion pit formation and propagation. Surface analysis techniques (Auger spectroscopy and X-ray photoelectron spectroscopy) are used to examine the composition of passive films and surface corrosion layers that form before and after the onset of corrosion. %%% Localized corrosion of metals and alloys in aqueous environments is an especially damaging form of environmental attack. It has generally been accepted that the cause of the initiation and propagation of a localized corrosion site is the formation of a highly aggressive environment in an occluded cell that comprises the area of attack. Understanding obtained from the approach described in this study could have a significant impact on the development of strategies for mitigating pitting and crevice corrosion.
2. National Science Foundation Grants DMR-9811412 (PDF) "Microfabrication Methods Applied to the Development of Rigorously Defined Occluded Region Corrosion Samples"
Crevice corrosion occurs as a result of aggressive conditions inside small occluded regions on metal surfaces. One of the primary stumbling blocks to the comparison of modeling and experimental results in crevice corrosion has been the extraordinary difficulty involved in experimentally producing a crevice sample that is directly equivalent to a geometry that is amenable to computational modeling. In this work, both sides of the crevice are constructed on silicon wafer substrates. The metal side of the crevice is formed by patterning, etching, and oxidizing the silicon before deposition of the metal. A highly planar surface is produced. The metal surface is segmented to allow measurement of current distribution within the crevice. The crevice-former side of the crevice (formed by patterning and depositing SiO2) contains precisely grown spacers that control the gap between the crevice-former surface and the metal electrode to a uniform, preselected level. The crevice former contains microsensors for pH, chloride concentration, and electrochemical potential. Using these samples, measurements are made that directly relate to computational results from a recently developed two dimensional occluded region mass transport model. In this way, the phenomena controlling crevice corrosion initiation and propagation are probed. %%% The work investigates issues that have prevented the development of effective crevice corrosion mitigation strategies as well as life prediction methodologies. The research has impact on other forms of corrosion because the critical structures and processes that control many types of corrosion operate on the micron to sub-mm size scale. For example, the chemistry and electrochemistry associated with corrosion due to inclusions in stainless steel, constituent particles in aluminum alloys, droplets in atmospheric corrosion, and defects in organic coatings occur on the 1-micron to several mm size scales. The size scale and dimensionality of the controlling structures make experimental and computational studies very challenging, requiring compromises and approximations in order to make the problem tractable. This new approach permits improved quantitative assessments.
3. Dissertations and Thesis
4. CREVICER Related Papers
Several papers have been published that center on or at least reference CREVICER.
R. G. Kelly, K. C. Stewart, Passivity of Metals and Semiconductors VIII , M. B. Ives, B. R. MacDougall, J. A. Bardwell, eds. PV 99-42, The Electrochemical Society, Princeton, p. 546-554 (1999).
L. A. DeJong, R. G. Kelly, "The Demonstration of the Microfabrication of Rigorously Defined Crevices for the Investigation of Crevice Corrosion Scaling Laws," in Critical Factors in Localized Corrosion IIII, R. G. Kelly, G. S. Frankel, P. M. Natishan, R. C. Newman, eds., PV 98-17, The Electrochemical Society, Inc., Pennington, NJ, pp. 678-89 (1999).
J. S. Lee, M. L. Reed, R. G. Kelly, in Corrosion and Corrosion Protection, J. D. Sinclair, E. Kalman, M. W. Kendig, W. Plieth, W. H. Smyrl, PV 2001- 22, The Electrochemical Society, Princeton, pp. 279-90 (2001).
Last modified: June 25, 2002 David Wang