Elemental Depth Analysis of Corroded Paint-Coated Steel by Confocal Micro-XRF Method

概要

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A confocal micro-XRF method combined with two individual polycapillary lenses was applied to steel sheets coated with anti-corrosive paint in order to nondestructively observe 3D elemental distribution of paint steels and corroded paint-coated steels. Nondestructive depth analysis and 3D elemental mapping of the painted steel sheets were demonstrated under the confocal XRF configuration. Three different painted steel sheets were prepared by cation electrodeposition coating for automotive onto flat steel sheets modified with a zinc phosphate conversion coating. These painted sheets were then caused to corrode by means of accelerated exposure to a salt bath (5 mass% NaCl) at 55°C for 240 hours. Depth elemental profiles of Ti, Zn, and Fe obtained by confocal micro-XRF measurements were in excellent agreement with that of the prepared sample. Elemental depth profiles and maps of the corroded painted sheets showed some blisters caused by crevice corrosion, which started from the site of a scratch. The distributions of Ti and Fe were approximately homogeneous in both the paint layer and the steel substrate, while the distributions of Zn, Mn, Ca, and Cl were heterogeneous.
The Iron and Steel Institute of Japanの論文