Mössbauer Studies on Particle Volume Distribution of α-FeOOH in Rust Formed on Weathering Steel

Abstract

Rust formed on weathering steel and that on mild steel were studied by Mössbauer spectroscopy at various temperatures from room temperature to 12 K. The observed spectra were decomposed into the contribution of fine antiferromagnetic particles of α-FeOOH (85 at.%, T N=403 K) and that of γ-FeOOH (15 at.%, T N=73 K). Volume distributions of α-FeOOH particles obtained by analyzing the superparamagnetic relaxation effect on Mössbauer spectra show the following distinct characteristics: While 83 vol% of α-FeOOH particles in the rust on mild steel are larger than 7.5×10-24 m3 and the rest of them (17 vol%) are smaller than 3.0×10-24 m3, the rust on weathering steel shows a continuous and wide volume distribution down to the ultrafine particle region (smaller than 3.0×10-24 m3) without a missing region, and 53 vol% of particles are smaller than 7.5×10-24 m3. It is understood that this continuous volume distribution of α-FeOOH particles in the rust on weathering steel is favorable for accommodating a closely packed structure in the protective rust layer on weathering steel.

Chlorine Occupancy Dependence of Crystal Structure of Pure β-Phase of Iron-Oxyhydroxide

“…In previous works, the fraction and volume distributions of rust particles formed on conventional and advanced weathering steel were estimated by analyzing temperature dependence of Mössbauer absorption spectra. 4,5) It is known that the spin of Fe 3þ ions in b-phase exhibits anti-ferromagnetic ordering with uniaxial anisotropy parallel to the crystalline b-axis.…”

“…The Debye-Waller factors, T j , is written by eq. (4) in which the isotropic atomic displacement parameters, B j were fixed to 0.5 for Fe, 0.8 for O and 2.0 for Cl sites.…”

Atomic-Scale Structure and Morphology of Ferric Oxyhydroxides Formed by Corrosion of an Iron–Silicon Alloy

“…2,3) The corrosion rate of steel is influenced by the properties of corrosion products formed on the steel surface, as seen a protective rust layer on weathering steel. [4][5][6] Thus, the structure and properties of corrosion products are of great importance.…”

<I>In-situ</I> X-ray Diffraction of Corrosion Products Formed on Iron Surfaces

“…14,15) The other analytical methods, such as electron probe microanalysis, transmission electron microscopy, infrared spectroscopy and Raman spectroscopy, are also applied for analyzing corrosion products formed on the steel surface. These results provide interesting information on the composition, morphology and structure of corrosion products.…”