Morphology of rust phases formed on weathering steels in various laboratory corrosion tests

The morphology and growth characteristics of rust phases formed on ASTM A-588 weathering steel in three different types of laboratory tests—accelerated atmospheric exposure simulation tests (AAEST), salt fog test, and continuous immersion test in plain as well as salt water—are analyzed using microstructural information obtained from representative exposed specimens studied in a scanning electron microscope (SEM). The ultimate and most dominant phase in the AAEST was α-FeOOH whereas an amorphous phase designated as amorphous bulk (AB) appeared as “cotton bolls” in the adherent, sedimentary layer formed on the steel surface during continuous immersion. Crystalline phases α-, δ-, and γ-FeOOH as well as γ-Fe₂O₃.H₂O were found developed on top of the first-formed sedimentary amorphous layer, containing another amorphous phase designated as amorphous mix (AM). Magnetite was the dominant phase obtained in the salt fog test. It forms in layers and seems to transform to α-FeOOH through formation of whiskers and rods on its surface. Sandy grains of γ-Fe₂O₃.H₂O were also seen in the rusts obtained in this test.     

The atmospheric corrosion of iron as studied by Mössbauer spectroscopy

The composition of the rust on the surface of steel panels was determined after atmospheric exposure times of 2 weeks, 2 months and 6 months. The initial product is γ-FeOOH which converts in time to a mixture of α-FeOOH and γ-Fe₂O₃. Steel exposed for times of the order of 25 years is covered with corrosion product consisting largely of γ-Fe₂O₃. The similarity between the composition of the corrosion products and precipitates formed from FeSO₄ solution under mildly acidic conditions at 90°C suggests that the dominant anion in these atmospheric corrosion experiments is sulfate.     

Effect of SO<Subscript>4</Subscript> <Superscript>2-</Superscript>, Cl<Superscript>–</Superscript> and NO<Subscript>3</Subscript> <Superscript>-</Superscript> anions on the formation of iron oxide nanoparticles via microwave synthesis

In the present work iron oxide nanoparticles have been prepared by microwave assisted synthesis with the influence of different precursor salts and synthesis of magnetite, hematite, Iron oxide hydroxide and maghemite nanoparticles. Synthesized iron oxide nanoparticles were characterized with Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and Energy-dispersive X-ray Spectroscopy (EDX). XRD measurements show that the peaks of diffractogram are in agreement with the theoretical data of magnetite, hematite, FeO(OH) (Iron oxide hydroxide) and maghemite. Crystallite size of the particles was found to be 33, 45, 36 and 43.5 nm for Fe₃O₄, α-Fe₂O₃, FeO(OH) and γ-Fe₂O₃. FESEM studies indicated that size of the particles is observed in the range of about 19.4 to 46.7 nm (Fig. 2a, average 32 nm), 29.1 to 67.6 nm (Fig. 2b average 45 nm), 29.1 to 40.8 (Fig. 2c average 36.6 nm), 29.1 to 80 nm (Fig. 2d average 43.5) for Fe₃O₄, α-Fe₂O₃, FeO(OH) and γ-Fe₂O₃ respectively. EDX spectral analysis reveals the presence of carbon, oxygen, iron in the synthesized nanoparticles. The FTIR graphs indicated absorption bands due to O–H stretching, C–O bending, C–H stretching and Fe–O stretching vibrations.     

A Mössbauer spectroscopic study of rust formed during simulated atmospheric corrosion

Steel coupons were subjected to 100% relative humidity and were inoculated every day with 100 μl of 0.01 N solutions of NaCl, Na₂SO₄, LiCl or CsCl. The first solid rust constituent that formed contained significant amounts of both γ-FeOOH and ferrihydrite. In contrast, only γ-FeOOH was observed in the rust formed during atmospheric corrosion and during wet-dry cycling with distilled water in the laboratory. The ferrihydrite in time was converted to γ-FeOOH, α-FeOOH, and γ-Fe₂O₃. The fractions of ferrihydrite + γ-FeOOH in the rust formed as a function of time during atmospheric exposure and during rusting in the laboratory environment were the same in the two cases.     

Characterization of Atmospheric Corrosion of 2A12 Aluminum Alloy in Tropical Marine Environment

In this work, corrosion product formed on 2A12 aluminum (Al) alloy after 3 months of natural exposure in South China Sea atmosphere was characterized by various surface analysis techniques, including scanning electron microscopy, energy-dispersive x-ray analysis, x-ray photoelectron spectroscopy, and x-ray diffraction. The atmospheric corrosion mechanism of Al alloy in marine environment was derived. Results demonstrated that Al alloy specimen experiences serious general corrosion and pitting corrosion. Al and O are enriched in the product film, and Ca and Cl are also found in the film and corrosion pits in Al alloy substrate. The main component compounds existing in the film include Al₂O₃, Al(OH)₃, and AlOOH while AlCl₃ and CaCO₃ are also identified. Al alloy encounters corrosion under tropical marine atmosphere. Although somewhat protective, the formed surface film on Al alloy specimen is attacked by chloride ions, resulting in significant pitting corrosion of Al alloy.     

Effects of [SDS]/[H2O] molar ratio on the electromagnetic properties of polyaniline/maghemite nanocomposites

Polyaniline (PANI)/maghemite (γ-Fe₂O₃) nanocomposites were prepared by using the reverse micelle polymerization, where aniline, ferrous and ferric salts and sodium dodecyl sulfate (SDS) act as monomer, precursor of γ-Fe₂O₃ and surfactant, respectively. The effect of the molar ratio of [SDS]/[H₂O] on the electromagnetic properties of PANI/γ-Fe₂O₃ nanocomposites was investigated by Fourier transform spectroscopy (FTIR), UV–visible spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS), wide angle X-ray diffraction diffractometer (WAXD), impedance analysis analyzer, micro-ohmetry and superconductor quantum interference device (SQUID). The nanostructure of the PANI/γ-Fe₂O₃ nanocomposites was characterized by micrographs of transmission electron microscopy (TEM). Results showed that both the γ-Fe₂O₃ content and particle size in the nanocomposites decreased with molar ratio of [SDS]/[H₂O]. The γ-Fe₂O₃ phase is non-uniformly distributed in the PANI matrix, and exhibits a broader size distribution at higher [SDS]/[H₂O] molar ratio due to the reduced strength of PANI–γ-Fe₂O₃ interactions. In the presence of γ-Fe₂O₃, the growth rate of quinoid ring is markedly retarded. The retard effect is significantly reduced by increasing the [SDS]/[H₂O] molar ratio, leading to the improvement of crystallinity, conductivity and dielectric properties (i.e., permittivity and loss factor) of nanocomposites. Simultaneously, the ionic polarization relaxation time is shortened from 2.61 × 10^?9 to 1.04 × 10^?9 s. For SQUID analysis at room temperature, the typical superparamagnetic behavior is found with the saturation magnetization decreased with the [SDS]/[H₂O] molar ratio, resulting from the reduced γ-Fe₂O₃ content, smaller γ-Fe₂O₃ particle size, and the wider particle size distribution.     

Untersuchung der Struktur und der Phasenzusammensetzung einer Schutzschicht auf Kohlenstoffstahl nach einer Behandlung in 15%iger,mit CO2 gesättigter MEA-Lösung mit und ohne Zugabe von NaVO3 als Inhibitor

Investigation of the structure and phase composition of a protective layer on carbon steel after treatment with a 15 % SO₂-saturated MEA solution with and without NaVO₃ as inhibitor Anodic passivation in inhibitor-free solution yields a surface layer containing Fe₂O₃, γ-Fe₂O₃·H₂O and β-Fe₂O₃·H₂O; when NaVO₃ is added, Fe₃O₄ and V₂O₄·3SO₃·16H₂O are found additionally. The crystal lattice of this protective layer is free from dislocations and is characterized by good protective properties.     

The effects of air pollution and climatic factors on atmospheric corrosion of marble under field exposure

The atmospheric corrosion of marble was evaluated in terms of SO₂ concentration as air pollution and climatic factors such as rainfall, relative humidity, temperature and so on under the field exposure. Marble of calcite type (CaCO₃) was exposed to outdoor atmospheric environment with and without a rain shelter at four test sites in the southern part of Vietnam for 3-month, 1- and 2-year periods from July 2001 to September 2003. The thickness loss of marble was investigated gravimetrically. X-ray diffraction and X-ray fluorescent methods were applied to study corrosion products on marble. The corrosion product of marble was only gypsum (CaSO₄ · 2H₂O) and was washed out by rain under the unsheltered exposure condition. It was found that the most substantial factors influencing the corrosion of marble were rainfall, SO₂ concentration in the air and relative humidity. Based on the results obtained, we estimated the dose-response functions for the atmospheric corrosion of marble in the southern part of Vietnam.     

Oxidation of 310 steel in H2O/O2 mixtures at 600 °C: the effect of water-vapour-enhanced chromium evaporation

The oxidation of type 310 stainless steel was investigated at 600 °C in the presence of O₂ and O₂+10% and 40% H₂O. The effect of gas velocity was studied. The oxidized samples were investigated by grazing angle X-ray diffraction, SEM/EDX and SAM. The addition of H₂O to O₂ resulted in a change of oxidation behaviour. A strong dependence on flow rate was observed in O₂/H₂O mixtures. At low flow rates a thin (30-50 nm) protective α-(Cr,Fe)₂O₃ formed, the outer part being depleted in chromium. When the flow rate was increased beyond a critical value the protective oxide failed. Under these conditions ?5 μm thick α-Fe₂O₃/(Cr,Fe)₃O₄, oxide islands formed on the part of the surface corresponding to the centre of the alloy grains. The effect of water vapour is attributed to the water-vapour-assisted evaporation of chromium from the oxide, in the form of a chromium oxide hydroxide, probably CrO₂(OH)₂. The oxidation behaviour is rationalized using a qualitative mechanism proposed previously and parallels that of the 304L alloy.     

Long term corrosion of X70 steel and iron in humid supercritical CO2 with SO2 and O2 impurities

Abstract

The corrosion of X70 steel and iron in supercritical CO₂/SO₂/O₂/H₂O environment were investigated after a 454 h exposure. Optical microscopy was applied to observe the morphology of etch pits and synthesise the three-dimensional morphology. X-ray diffraction and X-ray photoelectron spectroscopy were employed to detect the composition of product scales. Experimental results verified that the localised corrosion occurred on the X70 steel sample under corrosion product deposits. Ferrous sulphate, sulphur and iron sulphide were detected as the corrosion products.     

Field sludge characterization obtained from inner of pipelines

Physicochemical characterization of sludge obtained from refined hydrocarbons transmission pipeline was carried out through Mössbauer spectroscopy and X-ray diffraction. The Mössbauer and X-ray patterns indicate the presence of corrosion products composed of different iron oxide and sulfide phases. Hematite (α-Fe₂O₃), magnetite (Fe₃O₄), maghemite (γ-Fe₂O₃), magnetic and superparamagnetic goethite (α-FeOOH), pyrrhotite (Fe_1−xS), akaganeite (β-FeOOH), and lepidocrocite (γ-FeOOH) were identified as corrosion products in samples obtained from pipeline transporting Magna and Premium gasoline. For diesel transmission pipeline, hematite, magnetite, and magnetic goethite were identified. Corrosion products follow a simple reaction mechanism of steel dissolution in aerated aqueous media at a near-neutral pH. Chemical composition of the corrosion products depends on H₂O and sulfur inherent in fluids (traces). These results can be useful for decision-making with regard to pipeline corrosion control.     

Influence of Water Vapor on the Cyclic-Oxidation Behavior of a Low-Pressure Plasma-Sprayed NiCrAlY Coating

The oxidation of a low-pressure plasma-sprayed (LPPS) NiCrAlY coating on a nickel-base superalloy was studied at 1050 °C in flows of O₂, and mixture of O₂ and 5% H₂O under atmospheric pressure. Water vapor has an obvious effect on the cyclic oxidation of the NiCrAlY coating. There is more decrease in weight gain when exposure to O₂ is replaced by exposure to O₂ + 5% H₂O. The oxide formed on the LPPS NiCrAlY coating after cyclic oxidation in pure oxygen is composed mainly of Cr₂O₃, and a thin Al₂O₃-rich layer is formed at the interface between the Cr₂O₃-rich layer and the coating. The oxide formed on the LPPS NiCrAlY coating after cyclic oxidation in a mixture of O₂ + H₂O is composed of NiCr₂O₄, NiO and Cr₂O₃. The effect of water vapor on the oxidation of the NiCrAlY coating may be attributed to an increase in Ni and Cr cation transport, stress-corrosion cracking of Al₂O₃ and moisture-enhanced volatility of the Cr₂O₃ scale.     

Atmospheric corrosion of ordinary mild steel in the Arabian Gulf environment

Atmospheric corrosion tests were carried out on mild steel to study its corrosion behaviour in the Arabian Gulf environment. Results of exposure tests indicate that the atmospheric attack proceeds in a paralinear fashion during the first year of exposure. S.E.M. examination of the oxide scale showed extensive porosity, spallation and cracking with the appearance of platelike structures close to pitted sites. X-ray diffraction analysis revealed the presence of γFeOOH, αFeOOH, αFe₂O₃ and Fe₃O₄. EDX analysis disclosed that specimen surface contaminants are primarily constituents of sea spray.     

A study of the corrosion properties of plasma nitrocarburized and oxidized AISI 1020 steels

Plasma nitrocarburized AISI 1020 steels were oxidized for 15, 30 and 60 min to evaluate their corrosion and microstructural properties. After plasma nitrocarburizing for 3 h at 570°C in a gas mixture comprising 85 vol.% N₂, 12vol.% H₂ and 3 vol.% CH₄, the compound layer composed of ɛ-Fe_2–3(N,C) and γ’-Fe₄(N,C) phases and the diffusion layer above the matrix were observed. The top oxide layer, consisting mainly of magnetite (Fe₂O₄) and hematite (Fe₂O₃) phases, forms after post-oxidation treatment at 500°C. However, the oxide layer was severely degraded by spallation as a result of increases in post-oxidizing time. The difference in corrosion resistance should be attributed to the thickness of the top oxide layer, which was governed by post-oxidizing time.     

Identification of corrosion products resulting from accelerated oxidation process

Abstract

Scanning electron microscopy analysis, X-ray powder diffraction and room temperature ⁵⁷Fe Mössbauer spectroscopy were used to identify the corrosion products of uncoated and coated low alloy steels (LAS) and low carbon steels (LCS) resulting from an accelerated steam oxidation test for 180 h at 660°C. From the Mössbauer spectral analysis, it was shown that in all cases, a series of iron compounds such as α-Fe₂O₃, Fe₃O₄, γ-Fe₂O₃, δ-FeOOH, α-FeOOH, Fe(OH)₂ and Fe(OH)₃ were formed, while XRD measurements revealed only the α-Fe₂O₃ and/or Fe₃O₄/γ-Fe₂O₃ phases. In the LAS uncoated sample, an amorphous phase with magnetic features is found. In the spectra of the borided samples and of the uncoated LCS, an additional doublet was observed, which reveals the presence of a superparamagnetic phase. From the relative areas of the subspectra, it is concluded that the boron aluminised sample underwent the lowest degradation. The mechanism proposed for corrosion products formation is based on the dissociation process.     

Hydrogen permeation and corrosion behavior of high strength steel MCM 430 in cyclic wet-dry SO2 environment

Hydrogen permeation caused by corrosion under a cyclic wet (2 h)-dry (10 h) SO₂ condition was investigated for a high strength steel of MCM 430 by using an electrochemical technique in addition to the corrosion behavior obtained from weight loss measurement and the determination of corrosion products by using X-ray diffraction method. The hydrogen content converted from hydrogen permeation current density was observed in both wet and dry periods. The origin of proton was estimated to be from (1) the hydrolysis of ferrous ions, (2) the oxidation of ferrous ions and ferrous hydroxide, and (3) hydrolysis of SO₂ and formation of FeSO₄, but not from the dissociation of H₂O. With respect to the determination of the corrosion products consisting of inner (adherent) and outer (not adherent) layers, the outer layer is composed of α-FeOOH, amorphous phase and γ-FeOOH, where α-FeOOH increases with the increase in the wet-dry cycle, and amorphous phase shows the reverse trend. The corrosion product in the inner layer is mainly Fe₃O₄ with them. On the basis of the results obtained, the role of the dry or wet period, the effect of SO₂ and the corrosion process during the cyclic wet-dry periods were discussed.     

Influence of tensile stress on corrosion behaviour of high‐strength galvanized steel bridge wires in simulated acid rain

Corrosion behaviour of the high‐strength galvanized steel wires under tensile stress was researched by electrochemical polarization and salt spray test (SST) using simulated acid rain as electrolyte. Electrochemical polarization and SST results showed corrosion rate rose significantly with increasing tensile stress; white grains were observed by SEM after polarization, while cellular and dendritic crystals appeared on the rust layer after SST. XRD and TG‐DTA results revealed (Zn(OH)₂)₃ · ZnSO₄ · 5H₂O was the main corrosion product, and traces of Fe₂(SO₄)₂O · 7H₂O, Fe₂(SO₄)₃, Fe₂O₃ · H₂O were also detected. A three‐stage corrosion process for the galvanized steel wires during SST was proposed.     

XPS study of oxides on carbon steel in LiOH at 250°C

Using X-ray photo-electron spectroscopy (XPS), the compositions of the oxides formed at 250°C on carbon steel in 10.5 pH LiOH solution containing 0.05 ppm and 3.5 ppm dissolved oxygen were studied. Magnetite (Fe₃O₄) was found to be bulk oxide in both cases. A layer of γ-Fe₂O₃ was found on the outer surface of the sample exposed to the low oxygen environment, while α-Fe₂O₃ in small amounts, together with bulk Fe₃O₄, was found for the case of the high oxygen environment. Chemisorption of water molecules on the outer surface was observed in both the environments with the additional possibility of formation of FeOOH. Weak signals of Li 1s peak indicated the formation of small amounts of LiFeO₂ in both cases.     

Corrosion mechanism of copper in palm biodiesel

Biodiesel is a promising alternative fuel. However, it causes enhanced corrosion of automotive materials, especially of copper based components. In the present study, corrosion mechanism of copper was investigated by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Compositional change of biodiesel due to the exposure of copper was also investigated. Corrosion patina on copper is found to be composed of Cu₂O, CuO, Cu(OH)₂ and CuCO_3. Dissolved O₂, H₂O, CO₂ and RCOO⁻ radical in biodiesel seem to be the leading factors in enhancing the corrosiveness of biodiesel.     

Influence of heat treatment on phase transformation of clay-iron oxide composite

Magnetic clay composite prepared by the method of precipitation of iron oxide onto the clay surface was subjected to a heat treatment. The presence of iron oxide phase in composite before the heating was determined by the Mössbauer spectroscopy method as γ-Fe₂O₃. Structural changes of maghemite in clay composite after heating at selected temperatures in N₂ and Ar/H₂ atmosphere were studied using Mössbauer spectroscopy, X-ray diffraction, TG/DSC and SEM methods. It was shown the full transformation of γ-Fe₂O₃ to α-Fe₂O₃ in the inert atmosphere at temperature 650 °C and only a partial transformation to Fe₃O₄ in the reductive atmosphere at 300 °C.