Atomic-scale Structure of Ferric Oxyhydroxide Formed from Fe–Si Alloy in Aqueous Solutions Containing Different Salts

Abstract

Quantitative X-ray structural analysis coupled with reverse Monte Carlo (RMC) simulation was performed for characterizing the atomic-scale structure of g-FeOOH (lepidocrocite) particles. These particles were formed by dipping pure iron or Fe-2mass%Si alloy into aqueous solutions containing Na 2 SO 4 or NaCl. The realistic atomic-scale structures of g-FeOOH particles were estimated by fitting ordinary interference functions through the RMC simulation technique. The results revealed that the fundamental FeO 6 octahedral structural units and their linkages were distorted in the g-FeOOH particles formed from the Fe-Si alloy. This distortion was considered to be caused by the incorporation of silicate species into these particles. Transmission electron microscopy and Fourier-transform infrared (FT-IR) spectroscopy were employed for observing the morphology of the particles and for characterizing their bonding structure, respectively. Further, the amount of g-FeOOH particles formed was measured in order to investigate their formation processes. The changes in the pH and oxidation-reduction potential (ORP) of the solutions were monitored during the formation of g-FeOOH particles. Inductively coupled plasma analyses were also performed for determining the amounts of iron and silicon in supernatant solutions. The results indicated that the formation process of gFeOOH particles in the solutions was influenced by the addition of silicon to iron.KEY WORDS: ferric oxyhydroxide; lepidocrocite; X-ray diffraction; atomic-scale structure.

In situ structural analysis of corrosion products formed on the surfaces of iron‐based alloys

“…Intermediate iron oxides such as GRs containing ferrous ions are considered to be formed in the inner rust layer, and they are oxidized in final corrosion products, in which alloying elements may influence the formation of different constituent species formed in corrosion products. [3,4] In practice, it has been shown that in an aqueous solution, GR is transformed to Fe 3 O 4 with a spinel structure or ferric oxyhydroxides such as γ -FeOOH and α-FeOOH by oxidation, [13] and the amounts of these products depend on the reaction conditions. [13,14] These studies showed that the formation of the species depends on the temperature, partial pressure of oxygen, and reaction rates.…”

“…[3,4] In practice, it has been shown that in an aqueous solution, GR is transformed to Fe 3 O 4 with a spinel structure or ferric oxyhydroxides such as γ -FeOOH and α-FeOOH by oxidation, [13] and the amounts of these products depend on the reaction conditions. [13,14] These studies showed that the formation of the species depends on the temperature, partial pressure of oxygen, and reaction rates. As these reaction conditions are important to control the constituent species in the corrosion products of iron and iron-based alloys, further in situ X-ray diffraction experiments for clarifying the formation process of corrosion products must be useful.…”