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

9A,12C/2005C010

Fe(O,OH)6 Network Nanostructure of Rusts Formed on Weathering Steel (IV)
Masao KIMURA*1, Noriaki OHTA 2, Hiroshi KIHIRA3, Yasuhiro NIWA4, Yasuhiro INADA4,and Masaharu NOMURA4
1
Adv. Tech. Res. Lab., Nippon Steel Corp., Futtsu, Chiba, 293-8511, Japan
2
Nippon Steel Technoresearch, Chiba 293-8500, Japan
3
Steel Res. Lab., Nippon Steel Corp., Futtsu, Chiba, 293-8511, Japan
4
Photon Factory, KEK, Tsukuba, Ibaraki, 305-0801, Japan
Introduction
Improvement of corrosion resistance of steels without
coating is important from the viewpoint of life-cycle
assessments of structures. Weathering steel (WS) has
been developed for such applications especially to bridges.
WS, containing a 0.3-0.7 mass% Cr and Cu, forms aprotective rust after a few years of exposure toatmosphere to show good corrosion resistance [1,2].
However, a conventional WS shows a good corrosion
resistance only when it is exposed to atmosphere
containing little air born salt. Thus advanced WS wasdeveloped; the addition of 3 mass% Ni increases thecorrosion resistance to a large extent [3]. The mechanism
has been investigated by in situ observation techniques
using synchrotron radiation [4-6]. In this study, effects ofcopper addition on the formation of rust on WS is studied.

Fig.1 XAFS spectra of rusts and reference materials.

Experiments
Conventional WS (0.3Ni-0.3Cu-0.5Cr-Fe in mass%)
and advanced WS (3.0Ni-0.4Cu-Fe in mass%) were
exposed to atmosphere in a rural area for 5 years and in a
costal area for 9 years, respectively. The rusts on bothsteels were investigated by X-ray absorption finestructure (XAFS) in the florescence geometry using a 19element SSD [7] and Bent Crystal Laue Analyzer. Cu-K
edge XAFS measurements were carried out at BL-9A and12C at PF, KEK, Tsukuba, Japan.
Results and Discussion
Before corrosion begins, Cu atoms are in a solid
solution in an alloy. As corrosion progressed, XAFS
spectra showed significant change. Figure1 shows XAFS
spectra of rusts formed after atmospheric corrosion. Edge
energies of the rusts are higher than that of mother metal,
showing formation of oxide. However near-edgestructures of the rusts are different from those of Cu2O orCuO. Microstructure analysis with TEM showed no clear
indication of formation of copper oxides. These results
show that copper atoms in the rusts form Cu-O bonding
which is different from Cu2O and CuO. These spectra
indicate that copper atoms are expected to occupy aunique sites in the Fe(O,OH)6 [1,2] in the rust. This mayalter the evolution of the atomic scale network of rust(Fig. 2), resulting in formation of fine grain rust, which
can be attributed to the good corrosion resistance of WS.

154

Users' Report

Fig. 2 Schematic diagram of the evolution of the Fe(O,OH)6
nano-network of the rust formed on the advanced weathering
steel in an atmosphere containing relatively high air-bornsalinity (top), conventional weathering steel in milder condition(middle), and mild steel in milder condition (bottom) [1,2,5].

References[1] M. Kimura et al: J. Japan Inst. Metals, 66, 166 (2002).
[2] M. Kimura et al: ISIJ International, 42, 1534 (2002).
[3] H. Kihira et al: Zairyo-to-Kankyo, 49, 30 (2000).
[4] M. Kimura et al: PF Act. Rep. #20 Part B, p.200 and p.201(2003); #21 Part B, p.183, 184 and p.185 (2004); #22 Part B,p.140, 141 and p.142 (2005).
[5] M. Kimura et al: Corrosion Sci., 47, 2499 (2005).
[6] T. Mizoguchi et al: Corrosion Sci., 47, 2477 (2005).
[7] M. Nomura: J. Synchrotron Rad., 5, 851 (1998).

* kimura@re.nsc.co.jp