Pitting corrosion of stainless steels: Microanalytical studies of pitting corrosion and analysis of corrosion transients.
Item
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Title
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Pitting corrosion of stainless steels: Microanalytical studies of pitting corrosion and analysis of corrosion transients.
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Identifier
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AAI9304647
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identifier
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9304647
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Creator
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Cho, Jeong-Hwan.
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Contributor
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Adviser: Micha Tomkiewicz
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Date
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1992
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Physical | Chemistry, Analytical
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Abstract
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The chemical compositions of the highly concentrated solutions developed during pitting corrosion of a commercial stainless steel foil in a 0.5 M NaCl + 0.5 M HCl solution were investigated. The application of in situ x-ray fluorescence microscopy (XRM) to investigate the chemical compositions of the solutions within a one-dimensional artificial pit was discussed. The saturated concentration at the metal interface during anodic dissolution was obtained at approximately 4.7 {dollar}\pm{dollar} 0.1 M for the commercial stainless steel sample. The ratios of the relative metal ion concentrations along the pit were correlated with the diffusion coefficients of each species.;Video optical microscopy attached to the XRM beamline was applied to investigate the properties of salt films forming at metal interfaces during anodic dissolution of metals in acidic chloride solutions. The observation from the optical microscope showed that the thickness of the steady state salt film in the 1-2 mm deep artificial pit of the stainless steel foil at a constant potential of 600 mV (vs. SCE) was approximately 5-10 {dollar}\mu{dollar}m. A more precise results obtained from the XRM data analysis showed that the ratio of metallic elements in the salt layer is Fe: Cr: Ni = 88: 6: 6, which is quite different from the metal (69: 18: 13) and the solution of 67: 22: 11). Also, the thickness dependence on the applied potential and on the pit depth was observed.;AC impedance measurements on passive metal surfaces were investigated. The constant phase angle ({dollar}\theta{dollar}) of 80{dollar}\sp\circ{dollar} and the linear dependence of the magnitude on frequency in the range of 1-1000 Hz were the characteristic of the AC impedance with a uniform current density, Z{dollar}\sb{lcub}\rm i{rcub}{dollar}, of the stainless steel electrode in Na{dollar}\sb2{dollar}SO{dollar}\sb4{dollar} solutions. The magnitudes and the phase angles of the apparent impedance measured at different positions of electrode surfaces decreased exponentially depending upon the capacitance of electrode surface and the solution resistance. The effect of a local corrosion site along a transmission line on the apparent impedance measurements was investigated.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
