Confocal micro-XRF analysis of light elements with Rh X-ray tube and its application for painted steel sheet

A confocal micro-X-ray fluorescence (XRF) instrument with a vacuum chamber was applied for analysis of light elements for painted steel sheet. Because this instrument is equipped with a Rh-anode X-ray tube, light elements are excited more effectively by the Rh-L lines. However, it was difficult to analyze Cl, because the energies of the Cl-K lines are close to those of the Rh-L lines. Thus, we applied an Al thin film as a primary X-ray filter to eliminate the Rh-L lines and confirmed the feasibility of Cl analysis using a Rh X-ray tube. Rh-L scattered X-rays were observed by using an acrylic plate as a sample. The Rh-L scattered X-rays were completely absorbed by a 24 mu m thick Al filter. A calibration curve of Cl was prepared by using certified reference materials with different Cl concentrations. The limit of detection for Cl was 11.9ppm as estimated from the calibration curve. Confocal micro-XRF with a Rh X-ray tube enables the analysis of low Z elements including Cl by applying an Al filter. This technique was applied for a practical painted steel sheet sample. The elemental image of Cl was successfully observed after corrosion in NaCl solution as well as other light elemental maps. Copyright (c) 2015 John Wiley & Sons, Ltd.