51312-01678-Nanoscale Polarizations that Enable Stress Corrosion Cracking

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Product Number: 51312-01678-SG

ISBN: 01678 2012 CP

Author: David J. Quesnel

Publication Date: 2012

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This paper addresses fundamental mechanisms of stress corrosion cracking by simulating the 3D distribution of electrical charge at the tip of a stress corrosion crack. Ledges and steps on freshly created surfaces interact with electrons that move about on that surface in an effort to maintain a net negative equipotential. Excess electrons stick to the ledges creating nanoscale variations in electrical polarization of the metal-electrolyte interface. The excess electrons responsible for the negative free corrosion potential have a spatially varying density that supports local variations in the dissolution and replating rates of the near-surface metallic ions comprising the electrical double layer. In essence the electrical double layer has an as-yet unexplored lateral structure owing to the presence of geometric features on the fracture surface which promotes mass transfer from the crack tip region to the atomic sites just a few lattice spacings away minimizing the need for diffusion and allowing for rapid crack advance via short-circuit exchange currents. At larger stresses slip steps from dislocations introduce features that concentrate the excess electrons promoting cathodic (electron consuming) processes while regions of reduced electron concentration such as at the symmetric crack tip favor anodic (electron producing) processes such as metallic ionization and dissolution. Implications of the temporally and spatially varying electron distribution with charged ions in the solution that create local anodes and cathodes are also discussed.