実験室系X線吸収分光分析装置を用いたクロメート皮膜中クロムの価数評価及びX線光電子スペクトルとの比較検討

概要

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We performed a nondestructive and in laboratory evaluation technique of hexavalent chromium (Cr(VI)) in chromate conversion coatings using a laboratory X-ray absorption fine structure (XAFS) spectrometer equipped with W anode X-ray tube. The recorded XANES spectrum of a chromate conversion coating sample with fluorescence mode possessed the Cr–K X-ray absorption edge. We have obtained calibration curves of the ratio of Cr(VI)/Cr(III) by the height of pre-edge peak and the Cr–K X-ray absorption edge energy of the reference samples prepared by Cr2O3 (Cr(III)) and CrO3 (Cr(VI)) particle reagents. The calibration curves showed the high correlation coefficients such as 1.00 for the height of pre-edge peak and 0.99 for the value of the energy on the Cr–K X-ray absorption edge. The ratio of Cr(VI)/Cr(III) in the chromate conversion coating has also been evaluated by the X-ray photoelectron spectroscopy (XPS) and 1,5-diphenyl-carbazide absorption spectrometry (DPC) methods. The ratio of Cr(VI)/Cr(III) evaluated by the laboratory XAFS spectrometer was almost identical to that by XPS method.