Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

9A, 27B/2003G051

Characterization of Rust Layers on Fe-Based Binary Alloys Exposed to Cl-Rich
Atmosphere by XANES measurements
Hiroyuki KONISHI*1 and Masato YAMASHITA2
1Japan Atomic Energy Agency, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan2
Univ. of Hyogo, Shosya, Himeji, Hyogo 671-2201, Japan

Results and Discussion
Figure 1 shows Cl K-edge XANES spectra of somerust samples. That of akaganéite is also shown in Fig. 1for comparison. All spectra show a strong absorption peak(A) in the region of 2825.9-2827.4eV. The result indicatesthat all the rust samples contain large amount ofakaganéite. The spectra of Fe-3Cr, Fe-5Cr and Fe-3Ni
exhibit a shoulder peak (B) on the main absorption edgeat almost the same photon energy, 2823.5eV. Therefore,
some kinds of chloride other than akaganéite arecontained in the rust layers on the alloys having relatively
high corrosion rate.
We previously found by X-ray diffraction that the rustsamples are mainly composed of goethite, akaganéite,lepidocrocite, magnetite and a so-called X-ray amorphous
substance, which does not give a well-defined Bragg peak.
The X-ray amorphous substance must be the fine particlesof the above iron oxides. In order to obtain the mole ratio

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Users' Report

AAkaganeite
AFe
Normalized Absorbance (arb. units)Experimental
The rust samples were provided from The National
Institute for Materials Science. The atmospheric exposure
tests of Fe, Fe-Cr alloys and Fe-Ni alloys were performedat Miyakojima, Japan. The specimens were supported
horizontally under a roof during the exposure period of2-3 years. In order to obtain the samples for XANES
measurements, we scraped off the rust layer with a razor.
XANES spectra at Cl and Fe K-edge were measured influorescence mode at the BL-9A and in transmission
mode at the BL-27B, respectively.

composition of the rust samples, we performed thepattern-fitting calculation, in which the Fe K-edge
XANES spectrum of the rust sample is approximated tothe superposition of those of the iron oxides. The result
indicates that akaganéite is the major component of any
rust layers as shown in Fig. 2.

AFe-3Ni

BAFe-5NiABFe-3Cr

AFe-5Cr

B

2810

2820

2830

2840

2850

Photon Energy (eV)Fig. 1 Cl K-edge XANES spectra of akaganéite and therust samples formed on Fe and Fe-based binary alloys.
10080

Mole Ratio (%)

Introduction
Weathering steel has strong resistance to atmosphericcorrosion. This feature is responsible for the so-called“protective” rust layer spontaneously formed on thesurface of weathering steel. The properties of Cr-goethitesuch as cation selectivity contribute to the protective
ability of the rust layer. However, the corrosion resistanceof weathering steel considerably reduces in anenvironment of a large amount of chloride deposition.
Some studies have shown that Ni is a very effective
anticorrosive alloying element in a Cl-rich environment.
We have examined the XANES spectra of rust layers
on Fe, Fe-Cr alloys and Fe-Ni alloys exposed to a Cl-richenvironment in order to clarify the relation between thestructural properties of the rust layer on weathering steel
and anticorrosive alloying elements and/or chloride ions.

Magnetite
Lepidocrosite
Goethite
Akaganeite

6040200FeFe-3Ni Fe-5Ni Fe-9Ni Fe-3Cr Fe-5Cr Fe-9Cr

Rust Sample

Fig. 2 Comparison of mole ratios of iron oxides in therust samples obtained by pattern-fitting calculations of
the Fe K-edge XANES spectra.
References[1] H. Konishi et al., Mater. Trans. 46, 329 (2005).
* konishi@spring8.or,jp