X-ray microprobe characterization of corrosion at the buried polymer-steel interface

Soft X‐ray spectromicroscopy studies of pitting corrosion of reinforcing steel bar

“…The extent of corrosion detected by analysis of the Fe L 3 -edge μ-XANES spectra from the two areas can be further confirmed by comparing these results to the Fe XRF maps (Figure 2D,E). Figure 2D indicates a higher Fe fluorescent intensity than that in Figure 2E when comparing the spots from the uncorroded regions (spots [15][16][17][18][19][20]. Comparing the Fe XRF maps from the heavily corroded regions from Areas 1 and 2 (spots 1-5) shows the difficulty in using just these XRF maps to determine which area is more corroded because both regions have similar Fe fluorescent counts (~1500 counts).…”

“…The reason why the spectra from spots 1 to 4 in Area 2 have a higher Fe (III) contribution may be due to exposure to O 2 (g) during the corrosion test or The comparison of the fitted TEY and PFY Fe L 3 -edge μ-XANES spectra from Area 1 and Area 2 demonstrates that Area 1 was less corroded than Area 2 due to the higher ratio of iron metal to iron oxides (Fe (II/III) + Fe (III)) detected in the spectra from Area 1. For example, from the TEY LCF fitting results, the ratio of rebar to Fe (II/ III) from the spots located in the uncorroded region (spots [15][16][17][18][19][20] in Area 1 was between 0.96 and 1.27 (Table S1), while this ratio ranged from 0.25 to 0.75 (Table S3) for spots from Area 2 corresponding to the uncorroded regions (spots [15][16][17][18][19][20]. For the PFY fitting results from spots 15 to 20, the rebar to iron oxides ratio in Area 1 was either 19.00 or 24.00 (Table S2), while this ratio decreased to 13.29 to 19.00 (Table S4) when the spectra from Area 2 were studied, which is consistent when compared with the analysis of the TEY μ-XANES spectra.…”

“…52,53 In addition, 30% to 40% of the Mn phases present were determined to be Mn (III) phases when both the PFY and TEY μ-XANES spectra were fitted, which can be explained by the further oxidation of Mn (II) to Mn cations migrate to the cathode site. 16,52,53 4 | CONCLUSIONS Soft X-ray XRF microprobe and μ-XANES were used in this study to investigate the corrosion products formed at the polymer-steel interface of polymer-coated rebar after corrosion tests in highly saline and alkaline environments. The distribution of metallic iron and iron oxides was differentiated by collection of Fe Lα 1 XRF maps using an excitation energy just above the metal absorption edge (707 eV) because of the large absorption cross-section differences between Fe metal and Fe oxides at this specific energy.…”

“…12 Although X-ray microprobe has been previously applied in many research areas including geosciences, 13 biosciences, 14 and material science, 15 most microprobe images were either generated using hard X-rays or in transmission mode when using soft X-rays (ie, scanning transmission X-ray microscopy; STXM). [16][17][18][19][20][21][22] The authors have previously demonstrated the application of hard X-ray XRF microprobe to the study of the corrosion of materials. [16][17][18] However, the soft X-ray-based methodology discussed herein possesses the advantages of faster XRF map collection times and the ability to probe multiple depths of a sample with the trade-off being the need to remove the polymer film prior to analysis.…”

“…[16][17][18][19][20][21][22] The authors have previously demonstrated the application of hard X-ray XRF microprobe to the study of the corrosion of materials. [16][17][18] However, the soft X-ray-based methodology discussed herein possesses the advantages of faster XRF map collection times and the ability to probe multiple depths of a sample with the trade-off being the need to remove the polymer film prior to analysis. The objective of the present study was to demonstrate how the combination of soft X-ray XRF microprobe and μ-XANES can be used to map the corrosion products on corroded rebar surfaces and to identify the corrosion products at various depths by collection of TEY and PFY μ-XANES spectra.…”