Atmospheric Rust Formation Process on Fe–Cr and Fe–Ni Alloys under Wet/Dry Cycles Observed by Synchrotron Radiation X-ray Diffraction

Abstract

In situ observation of initial process of rust formation on Fe-5 mass%Cr and Fe-9 mass%Ni alloys using SPring-8 synchrotron radiation was carried out under wet/dry cycling with 3.5% Na 2 SO 4 and NaCl solution films. It was shown that the rust constituents detected during the quite initial wet/dry cycles were Fe(OH) 2 and Fe(OH) 3 independent of alloying elements. Most characteristic X-ray diffraction peaks obtained under the Na 2 SO 4 solution film are indexed as those from goethite, -FeOOH, both in the Fe-Cr and Fe-Ni alloys. In the case of the Fe-Cr alloy, coexistence of Cr 3þ ion in the Na 2 SO 4 film weakened the -FeOOH diffraction peaks probably due to formation of ultrafine goethite crystals. Akaganéite, -FeOOH, appears only under the NaCl solution film. Especially, the Fe-Ni alloy forms a considerable amount of akaganéite, which can be interpreted in terms of formation of the monoclinic akaganéite.

Structure of Corrosion Product Formed on Carbon Steel Covered with NiSO₄-Added Resin Coating under Sulfuric Acid Mist Environment Containing Chloride

“…Due to these two different types of binding, akaganeite possesses a tunnel in its structure. The structure of akaganeite stabilizes if the center of the tunnel is occupied with Cl ¹ , 16,17) indicating that akaganeite can be formed under the simulated sulfuric acid mist environment containing chlorides. However, peaks derived from akaganeite were smaller than those from goethite and magnetite.…”

X-ray Diffraction Analysis of Rust Layer on a Weathering Steel Bridge with Surface Treatment Using Synchrotron Radiation

“…tion of 0.1 kmol/m 3 . Yamashita et al 15) observed rust formation processes using synchrotron radiation X-rays and showed that -FeOOH was preferentially formed under the effect of SO 4 2À ion. Moreover, it was pointed out that Cr become a nucleus for the growth of -FeOOH 16) because Cr is less soluble in -FeOOH than in -FeOOH.…”