Study on Micro-corrosion Mechanism for Low Alloy Steel by Scanning Tunneling Microscope

概要

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The scanning tunneling microscope (STM) can be used not only in vacuum but also in air and in aqueous solution. There has been no device which can detect sub-micron range of the surface morphology change by electrochemical reaction. Therefore study on the possibility of in-situ quantitative evaluation of micro-corrosion around micron range was carried out by using the STM. The corrosion behavior of the low alloy steel in 1% NaCl and 0.1% HNO3 aqueous solution was studied by the STM. The local corrosion rate was obtained by the subtraction between STM images. The average corrosion rate was also obtained by averaging all data after subtraction between STM images. The obtained average corrosion rate was well coincident with the corrosion rate calculated from Faraday's conversion of the anode current density, while the local corrosion rate was more than 3 times larger than the average corrosion rate. From these results, it is concluded that the local corrosion behavior can be studied very accurately by the STM.
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