Synchrotron far‐infrared spectroscopy of corroded steel surfaces using a variable angle of incidence

Far‐infrared spectroscopy, using a synchrotron source, has been used to study carbon steel corroded in CO₂‐saturated brine in the presence and absence of the corrosion inhibitor 2‐mercaptopyrimidine (MPY), which allowed the steel surface roughness to be modified. The effect of the angle of incidence (θ_i, 30–80°) on the band intensity and observed bands of the spectra from these surfaces has been determined. For the MPY‐treated steel (low surface roughness) the highest band intensity is observed at high θ_i (80°) and different bands were observed at different θ_i. In contrast, for the MPY‐free steel (high surface roughness) the highest band intensity is observed at low θ_i (30°) and spectral content changes were not observed. The results are explained in terms of the roughness of the MPY‐treated and MPY‐free steels, and their effect on the level of diffusely reflected light of the incident infrared beam.     

Changes in the state of iron atoms in Zr alloys during corrosion tests in an autoclave

Mössbauerinvestigations were carried out on oxide films formed on specimens of zirconium alloys Zr-1.0 %wtFe-1.2 %wtSn-0.5 %wtCr subjected to corrosion in steam-water environment at a temperature of 360 °C and at a pressure of 16.8 MPa with lithium and boron additions, and on Zr-1.4 %wtFe-0.7 %wtCr corroded in steam-water environment at 350 °C and 16.8 MPa as well as in steam-water environment at 500 °C and 10 MPa. In the metal part of the samples, under the oxide film, the iron atoms are in form of intermetallic precipitates of Zr(Fe, Cr)₂. The corrosion process decomposes the intermetallic precipitates and particles are formed of metallic iron with inclusions of chromium atoms –Fe(Cr), α–Fe₂O₃ and Fe₃O₄ compounds. Part of the iron ions are in divalent and part in trivalent paramagnetic states. It is proposed that some part of the iron containing oxide precipitates in the oxide film may be in the form of nanoparticles which pass from the superparamagnetic to the ferromagnetic state with decreasing temperature.     

Characteristics of CO2 corrosion scale formed on N80 steel in stratum water with saturated CO2

The component and structure of CO₂ corrosion scale formed on N80 tubing steel were studied by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM); the electrochemical property of N80 steel covered by corrosion scale was investigated by electrochemical impedance spectroscopy (EIS). The results shows a double-layer structure of the corrosion scale, in which the principal component of the outer layer is FeCO₃ with a limited amount of ∂-FeOOH; while for the inner scale, FeCO₃ is still the major component, but some Fe positions in FeCO₃ lattice are substituted by Ca, and form a composite compound of (Fe,Ca)CO₃ in the inner scale. EIS study shows that the anodic impedance spectrum has three time constants, i.e., the capacitance at high frequency, Warburg impedance at middle frequency and capacitance at low frequency.     

Microstructure and properties of high chrome steel roller after laser surface melting

Laser surface melting of high chrome steels was achieved by a 5 kW continuous wave CO₂ laser. The microstructure of the laser surface-melted steels was investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffractometry, and the hardness profiles were determined by a Vickers hardness tester. The corrosion behavior in 3.5% NaCl solution was studied by electrochemical corrosion equipment. The large carbides of high chrome steels are completely dissolved and ultrafine dendrites of austenite with submicroscopic M₂₃C₆ carbides precipitation are formed in the melted zone. The austenite in the melted zone has a high tempering stability. The corrosion resistance of the laser surface-melted steels is significantly improved due to the dissolution of carbides and the increase of the alloying elements in the solid solution as well as the large amount of austenite.     

利用电化学微分质谱在燃料电池的阴极研究碳载体的氧化

利用电化学微分质谱,在双薄层流动电解池中,通过检测二氧化碳产物的信号研究氧气与铂纳米粒子对碳载体氧化机理与动力学的影响．研究发现,碳载体可以在不同的电位区间内被氧化;氧气可以加速碳的氧化,在相同的电位下碳氧化生成二氧化碳产物的速率在氧气饱和溶液中是在氮气饱和溶液中的两倍;铂纳米粒子可以催化碳的氧化,在碳电极上,担载的铂纳米粒子可以大大降低碳氧化的过电势．讨论了铂与氧气促进碳氧化的机理．     

Corrosion behavior of X-70 pipe steel in near-neutral pH solution

The mechanism of near-neutral pH stress corrosion cracking (SCC) of natural gas pipelines has not been well-established since the first accident was found in the 1980s. In particular, the role of hydrogen in near-neutral pH SCC has remained unknown. In this work, cyclic voltammetry was used to comprehensively investigate the fundamentals of the electrochemical corrosion reactions occurring at the steel/solution interface in diluted, 5% CO₂/N₂-purged, near-neutral pH bicarbonate solutions. It is shown that there is no stable oxide film formed on the steel surface in near-neutral pH solution. The dissolution-based cracking mechanism does not apply for near-neutral pH SCC of pipelines. The formation of a metastable Fe(OH)₂ deposit layer shows a catalytic activity on hydrogen evolution reaction, indicating that a significant amount of hydrogen could be generated under near-neutral pH condition. The presence of corrosive anions in the soil electrolyte enhances both the anodic polarization of the steel and the cathodic hydrogen evolution reaction, resulting in an increased hydrogen evolution rate. The introduction of oxygen could form a stable oxide film on the surface of steel, resulting in the loss of the surface catalytic effect on hydrogen evolution reaction. Thus, a hydrogen-based mechanism does not apply for SCC in the presence of oxygen.     

Mössbauer and XRD analysis of corrosion products on weathering steel treated by wet-dry cycles using various solutions

Weathering steels (COR-TEN) were corroded by wet-dry cycles using a splay of various solutions in a laboratory. Corrosion products on weathering steel were characterized by X-ray diffractometry and Mössbauer spectrometry at room and low temperatures. Fine α-FeOOH, γ-FeOOH and γ-Fe ₂ O ₃ are fundamentally formed in various atmospheric conditions. β-FeOOH is additionally formed under the existence of chloride ions, but not formed when sulfate ions are coexisting. Spraying a NaF solution prevents the progress of corrosion.     

Inhibition performance of 2-mercaptobenzothiazole derivatives in CO2 saturated solution and its adsorption behavior at Fe surface

Two 2-mercaptobenzothiazole derivatives, N,N′-bis-(2-thionobenzothiazolin-3-yl-methyl)-n-dodecylamine (BTBMDA) and N,N′-bis-(2-thionobenzothiazolin-3-yl-methyl)-n-octadecylamine (BTBMOA), were synthesized under microwave irradiation. Their inhibition performance for N80 steel in CO₂ saturated solution at 90 °C were tested by weight loss method and the surface analysis was performed by SEM. The adsorption behavior of two inhibitors at the Fe surface was studied by the molecular dynamics simulation method and the quantum chemistry calculations. Results showed that the two inhibitors could inhibit the corrosion of N80 steel in simulated solution significantly. There were two types of end configurations for two inhibitors at the Fe surface in the molecular dynamics simulation, and the two inhibitors adsorbed at the surface mainly through one of the two types.     

Photoemission study of the chromium(111) surface interacting with oxygen

The interaction of the Cr(111) surface with O₂ was studied by means of X-ray and UV photoemission and also work function measurements. A strong oxygen adsorption was found even at very low exposures, suggesting a high sticking coefficient. Previous treatments of the clean surface such as argon-ion bombardment or annealing result in significant changes of the surface structure reflected on work function and adsorption kinetics. No work function change was observed in the initial stage of adsorption, ruling out a model of chemisorption on top. In this range the sticking coefficient remains also constant, supporting a model of rapid regeneration of the genuine surface sites and incorporation of oxygen into the lattice. But in contrast with non transition metals like Cs or Sr, oxygen absorbed at room temperature in Cr, remains essentially in the topmost layers of the surface. At room temperature this initial stage of oxygen incorporation is followed by chemisorption on the corrosion film obtained when the uppermost layers are saturated with oxygen. The oxide layer has a stoichiometry close to Cr₂O₃ at saturation, but the detailed electronic structure depends on previous thermal treatments. Exposures at room temperature lead to a thin (about 9 Å), probably amorphous corrosion layer with a maximum work function change Δφ = +0.9 eV. Adsorption followed by heating at 500° C results in a much thicker corrosion film with a limiting work function decrease of Δφ = ?1.2 eV. The XP and UP spectra differ significantly in both cases and suggest a Fermi level shift of nearly 1 eV connected with oxygen adsorption on the Cr₂O₃ surface. The thickness of the corrosion film may be further increased by heating at 500°C in oxygen. The usual XPS spectra of bulk chromium sesquioxide are then clearly observed.     

Diffusion of nickel in single- and polycrystalline Cr2O3

Chromia protective layers are formed on many industrial alloys to prevent corrosion by oxidation. Their role is to limit the inward diffusion of oxygen and the outward diffusion of cations. A number of chromia-forming alloys contain nickel as a component, such as steels, FeNiCr and NiCr alloys. To ascertain if chromia is a barrier to outward diffusion, nickel diffusion in chromia was studied in both single crystals and polycrystals in the temperature range 900–1100°C at an oxygen pressure of 10^?4 atm (argon + 100 ppm O₂). A nickel film of ～35 nm thick was deposited on the chromia surface and, after diffusing treatment, nickel penetration profiles were established by secondary ion mass spectrometry (SIMS). Two diffusion domains appear in polycrystals, the first domain is assigned to bulk diffusion and the second is due to diffusion along grain boundaries. For the bulk diffusion domain and diffusion in single crystals, using a solution of Fick's second law for diffusion from a thick film, bulk diffusion coefficients were determined at 900 and 1000°C. At the higher temperature, a solution of Fick's second law for diffusion from a thin film could be used. For the second domain in polycrystals, Le Claire's model allowed the grain boundary diffusion parameter (αD _gb δ) to be established. Nickel bulk diffusion does not vary significantly according to the microstructure of chromia. The activation energy of grain boundary diffusion is slightly greater than the activation energy of bulk diffusion, probably on account of segregation phenomena. Nickel diffusion was compared with cationic self-diffusion and with literature data on Fe and Mn heterodiffusion in the bulk and along grain boundaries. All results were analyzed in relation to the oxidation process of stainless steel.     

Magnetic properties of corrosion products investigated by CEMS at low temperatures near 4.2 K

Conversion electron Mössbauer measurements with a proportional counter at 6.3, 78 and 300 K have been done to investigate the magnetic properties of the corrosion products formed on the surface of iron foils, which consist of small particles of γ-Fe₂O₃. The growing period of the corroded layer formed in a solution of low oxygen concentration has insignificant influence on the size of particles composing the layer, however, when the corroded layer is grown in a solution of comparatively high oxygen concentration, the particle size becomes large with growing period of the layer.     

An XPS and UPS study of the kinetics of carbon monoxide oxidation over Ag(111)

The oxidation of carbon monoxide over a Ag(111) catalyst has been studied by XPS and UPS. The kinetics have been determined over the temperature range of 180 to 400 K and found to be of the Langmuir-Hinshelwood type, although the Eley-Rideal mechanism is mimicked. A negative activation energy, ?1.7 kcal/mole, and a preexponential, 6 × 10^?18 cm², are found. The former corresponds to the difference in the activation energies for carbon monoxide desorption and for carbon monoxide oxidation (leading to CO₂ desorption). At 90 K, upon carbon monoxide exposure to the active oxygen precovered surface, the O ls and C ls spectral regions show the formation of CO₂-like and carbonate species; the latter is stable to at least room temperature. That is, at 90 K, the residence time and mobility of CO₂ formed at the surface permits a new surface reaction — the formation of stable surface carbonate. The identifications are based on C and O coverages and on line positions from the literature for Cu/CO₂ and several bulk carbonates. With UPS, the 1π_g, the unresolved doublet 1π_u and 3σ_g, and the 4σ_g molecular orbitals of adsorbed CO₂-like species are identified, as well as the unresolved triplet 1α′₂, 1e″ and 4e′ and the unresolved triplet 3e′, 1α″₂ and 4a′ molecular orbitals of the carbonate species. Surface CO₂-like species formed by surface oxidation of CO seem to be more strongly bound than reversibly adsorbed CO₂.     

Low-nickel stainless steel passive film in simulated concrete pore solution: A SIMS study

Low-nickel and AISI 304 austenitic stainless steel (SS) passive films were studied using secondary ion mass spectrometry (SIMS). An alkaline Ca(OH)₂ saturated test solution containing different chloride additions was used at room temperature. The passive film formed consists mainly of an inner chromium-rich oxide layer and an outer iron-rich oxide layer. The chemistry of the passive film depends strongly on the chloride content in the alkaline solution. Under these exposure conditions nickel was detected in the outer part of the oxide, whereas chloride ions were not found in the passive film for either the low-nickel or AISI 304 SS alloys.     

Synchrotron infrared reflectance microspectroscopy study of film formation and breakdown on copper

This work demonstrates the utility of synchrotron infrared reflectance microspectroscopy in the far‐ and mid‐IR for the determination of the composition of electrogenerated surface films formed during the general and localized corrosion of copper in alkaline and bicarbonate solutions. Back‐reflection geometry has been employed to identify the anodic film formed on copper in 0.1 M NaOH solution at 0.3 V (versus a Ag/AgCl reference) to be mainly CuO. In 0.01 M NaHCO₃ solution general corrosion occurs with passive film formation below 0.2 V. The surface film at 0.2 V consisted mainly of bicarbonate, copper carbonate dihydroxide or malachite [CuCO₃·Cu(OH)₂], Cu(OH)₂ and possibly some CuO. At higher potentials the passive film breaks down and localized corrosion occurs leading to the formation of pits. The composition of the surface films inside the pits formed at 0.6 V was found to be essentially the same as that outside but the relative amount of Cu(OH)₂ appears to be higher.     

Raman spectroscopic studies of the corrosion of model iron electrodes in sodium chloride solution

We have explored the un‐enhanced Raman spectra of both single and twin electrodes in 3.5% NaCl solution (at ambient temperatures) over a range of applied potentials (between 20 and 200 mV) and times (between 0 and 5 h). Under these conditions, we observed the initial formation of ‘green rust’ (hydroxychlorides and/or hydroxycarbonates), followed by the formation of magnetite (Fe₃O₄) and then a mixture of the α‐ and γ‐FeOOH (goethite and lepidocrocite, respectively). These data are consistent with a model for corrosion during which the initially formed magnetite is either covered, or replaced, by layers of the FeOOH oxidation products. Fitting of the data as a function of time and potential shows that, although the product range is independent of potential, the relative kinetics of formation of magnetite and its subsequent conversion to the γ‐FeOOH were potential and time dependent. Analysis by mapping of the dry corroded surface showed a variety of species, including green rust, some Fe(OH)₃, as well as the γ‐FeOOH, and possibly some β‐FeOOH. But no surface magnetite was found, indicating that this material had been either covered up or converted to FeOOH. We noted several complications during this work, including the interference of resonance effects (on the Raman intensities) and the heterogeneity of the corrosion process (and hence distribution of species on the corroded surface). However, we believe that the use of un‐enhanced Raman methods has led to conclusions more likely to be relevant to ‘real’ corrosion processes. Copyright © 2007 John Wiley & Sons, Ltd.     

The effect of chloride ions on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation

The effects of Cl⁻ on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation in chloride solutions were investigated using nanoindentation in conjunction with XRD and XPS. The results demonstrate that Cl⁻ had a strong effect on the nano-mechanical properties of the corroded surface layer under cavitation, and there was a threshold Cl⁻ concentration. Furthermore, a close relationship between the nano-mechanical properties and the cavitation corrosion resistance of 00Cr22Ni5Mo3N duplex stainless steel was observed. The degradation of the nano-mechanical properties of the corroded surface layer was accelerated by the synergistic effect between cavitation erosion and corrosion. A key factor was the adsorption of Cl⁻, which caused a preferential dissolution of the ferrous oxides in the passive film layer on the corroded surface layer. Cavitation further promoted the preferential dissolution of the ferrous oxides in the passive film layer. Simultaneously, cavitation accelerated the erosion of the ferrite in the corroded surface layer, resulting in the degradation of the nano-mechanical properties of the corroded surface layer on 00Cr22Ni5Mo3N duplex stainless steel under cavitation.     

Emission and Transmission Mössbauer Spectroscopic (EMS and TMS) Study of Perovskite Oxides, (Ba, Ca)(Fe, Co)O3-δ, Absorbed with CO2

Perovskite oxides, (Ba_0.95,Ca_0.05) (Co_1-x,Fe_x) O_3-δ, are prominent materials for CO₂ absorption at high temperature. The substitution of Ba sites with Ca ion, and the mixed valence states of Fe and Co ions due to the formation of oxygen vacancies at high temperatures are effective for CO₂ absorption. Especially Co ions are more active for CO absorption than Fe ions. These oxides were analyzed by EMS and TMS before and after treatment in CO₂ atmospheres. The difference between EMS and TMS spectra is found to be observed not only due to the oxygen affinity, but also to the different reactivity of Co and Fe ions in the B site towards CO₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mössbauer study of oxide films of Fe-, Sn-, Cr- doped zirconium alloys during corrosion in autoclave

Mössbauer investigations were used to compare iron atom states in oxide films of binary Zr-Fe, ternary Zr-Fe-Cu and quaternary Zr-Fe-Cr-Sn alloys. Oxide films are received in an autoclave at a temperature of 350–360 °C and at pressure of 16.8 MPa. The corrosion process decomposes the intermetallic precipitates in alloys and forms metallic iron with inclusions of chromium atoms α–Fe(Cr), α–Fe(Cu), α–Fe ₂O₃ and Fe ₃O₄ compounds. Some iron ions are formed in divalent and in trivalent paramagnetic states. The additional doping influences on corrosion kinetics and concentration of iron compounds and phases formed in oxide films. It was shown the correlation between concentration of iron in different chemical states and corrosion resistance of alloys.     

Mössbauer Study of Discoloration of Synthetic Resin Covered Electric Switches

⁵⁷Fe Mössbauer spectroscopy and X-ray diffractometry were used to investigate brown discoloration and sediments formed on the surface of synthetic resin product covered electronic switches. The Mössbauer measurement revealed that alloyed steels and iron-containing corrosion products are associated with the discolored layers. Iron, and iron corrosion products were shown by both MS and XRD in the sediments formed eventually during the finishing of the synthetic resin products after machining and washing with water solution.     

Electrochemical behaviors of the magnesium alloy substrates in various pretreatment solutions

Interface reactions and film features of AZ91D magnesium alloy in pickling, activation and zinc immersion solutions have been investigated. The surface morphologies of the specimens were observed with scanning electron microscope (SEM). Electrochemical behaviors of AZ91D magnesium alloy in the baths of pickling, activation and zinc immersion were analyzed based on the open circuit potential (OCP) - time curves in various solutions. The results show that the corrosive rate in HNO₃ + CrO₃ or HNO₃ + H₃PO₄ pickling solution was more rapid than in KMnO₄ pickling-activation solution. Both α phase and β phase of the substrates were uniformly corroded in HNO₃ + CrO₃ or HNO₃ + H₃PO₄ pickling solution, the coarse surface can augment the mechanical occlusive force between the subsequent coatings and the substrates, so coatings with good adhesion can be obtained. In HF activation solution, the chromic compound formed via HNO₃ + CrO₃ pickling was removed and a compact MgF₂ film was formed on the substrate surface. In K₄P₂O₇ activation solution, the corrosion products formed via HNO₃ + H₃PO₄ pickling were removed, a new thin film of oxides and hydroxides was formed on the substrate surface. In KMnO₄ pickling-activation solution, a film of manganic oxides and phosphates was adhered on the substrate surface. Zinc film was symmetrically produced via K₄P₂O₇ activation or KMnO₄ pickling-activation, so it was good interlayer for Ni or Cu electroplating. Asymmetrical zinc film was produced because the MgF₂ film obtained in the HF activation solution had strong adhesive attraction and it was not suitable for interlayer for electroplating. However, the substrate containing compact MgF₂ film without zinc immersion was fit for direct electroless Ni-P plating.