In-Situ Observation on Localized Corrosion of Corrosion - Resistant Alloys by Using Micro-Electrode / Raman Scattering / Ion Chromatography System

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The research results were obtained from the following three kinds of standpoints.(1) Two kinds of pH micro-sensors of an iridium (Ir) thin wire oxidized by alternating current electrolysis and platinum (Pt) thin wire casted with H^+ iono-fore were at first prepared for measuring localized pH and as a tip of scanning electrochemical microscopy (SECM) on the alloy electrode surface.(2) Localized pH observed on the anodic dissolved alloy electrodes of Fe-(0-9 mass %)Cr-(B, N) in Na_2SO_4 aqueous solution of pH 8.9 fell down to about 3.9 by acidification of Cr hydrolysis product in Fe-Cr alloy and the addition of B or N in 9Cr steel suppressed the acidification by buffer action. In-situ micro-Raman scattering spectra showed an initial corrosive products of Fe(OH)_2 and Green Rust II on the alloy surfaces.(3) Localized pH distribution in electrolyte and in-situ micro-Raman scattering investigation under H_2 atmosphere for La-Ni_5 metal hydride were performed to get microscopic information. The results indicates that the catalytic fresh surface area created by cracking plays an important role in the hydride formation.