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The AA 2198-T851 is a third-generation Al-Li alloy developed for use in the aircraft industry. Al-Li alloys are susceptible to localized corrosion due to their complex microstructure resulting from the used thermomechanical treatment. In order to prevent localized corrosion, these alloys are usually protected by anodizing in order to avoid a corrosive environment. Subsequently, for anodizing, a sealing treatment is usually performed for parts. Some sealing treatments use hexavalent-chromium-ion-containing solutions. In this investigation, a chromium-free sealing treatment in a solution with cerium ions has been carried out, and the effect on the corrosion resistance of the AA2198-T851 alloy was investigated. Hydrothermally sealed or unsealed samples were also tested for corrosion resistance for comparison reasons. The corrosion resistance of the anodized aluminum alloy, either hydrothermally sealed or in a cerium-ion-containing solution, was evaluated in a sodium chloride solution by electrochemical impedance spectroscopy as a function of immersion time. The samples sealed in a cerium-containing solution increased their corrosion resistance when compared to the hydrothermally sealed. The effectiveness of the sealing process with cerium that was observed in the electrochemical tests indicated that after the corrosive attack of the barrier layer, there was a “sealing” process of the sample surface.

In this work, the local electrochemical activity of the zones coupled by Friction Stir Welding (FSW) of an Al-Cu-Li alloy was studied and the results were correlated to the microstructural characteristics of each zone. Electrochemical studies were carried out in the zones affected by welding using cyclic voltammetry (CV) and scanning electrochemical techniques (namely, SECM - Scanning Electrochemical Microscopy and LEIS - Local electrochemical impedance spectroscopy). The results showed that the welding joint (WJ) is predominantly cathodic relatively to the heat affected zones (HAZ). The HAZ was always anodic and showed the highest electrochemical activities among the tested ones. The high electrochemical activity of the HAZ was associated with the effect of galvanic coupling between the cathodic region (WJ) and the anodic region (HAZ). In addition, the advancing side (AS) presented increased electrochemical activity compared to the retreating one (RS).

In this study, the corrosion mechanism of an Al-Cu-Li alloy manufactured by two different treatment routes (T3 and T851) was evaluated by immersion and electrochemical tests in solutions containing chloride ions (Cl-). For both alloys, the formation of cavities on the surface was associated with micrometer-sized intermetallics (IM’s), however, in addition to this attack, the alloy submitted to T851 treatment also presented an attack called severe localized corrosion (SLC), caused by the preferential attack to the nanometric T1 (Al2CuLi) phase. The electrochemical concepts involved in these two types of attacks were discussed. During the IM’s corrosive process, whereas the O2 reduction occurred over the IM’s, the Al dissolution is favored around the particle, forming trenching and cavities (with 2 and 6 μm of depth). On the other hand, the mechanism associated with the SLC is related to the formation of a differential aeration cell followed by the evolution of H2, with greater depth of attack penetration (8 and 35 μm). Additionally, by the use of the Scanning Vibrating Electrode Technique (SVET), it was concluded that the higher anodic currents observed for the T851 temper were related to the relation between the anodic area (Aa) and the cathodic area (Ac).

Magnesium-based alloys have been proposed for used in temporary biomaterials in the applications that request their biocompatibility and degradability. Analyses of these alloys are of great interest to verify if their element composition is within the product specification and also to evaluate the impurities that may cause toxic effects to the human health or influence in their corrosion processes. In this study, nuclear techniques of neutron activation analysis (NAA) and wavelength dispersive X ray fluorescence spectrometry (WD XRFS) were applied in the analyses of two magnesium-based alloys: commercially pure magnesium (CP-Mg) and AZ31 alloy. The NAA procedure consisted of irradiating aliquots of sample and synthetic element standards followed by measurements using a HGe detector and the WD XFRS was carried out using the Model RIX 3000 X-ray spectrometer. In the CP-Mg sample several element impurities were quantified. In the AZ31 alloy, the alloying element mass fractions were within the product specification and the impurities of As, La, Na and Sb were also quantified. Nickel and sulfur were quantified only by WD XFRS. The Horwitz method was a good parameter to evaluate the repeatability of the results in Al, Mg, Mn and Zn determinations. In conclusion, the results indicated the viability of using NAA and WD XFRS in the analyses of magnesium-based materials mainly due its multielement determinations, precision of the results, quantification of elements in a wide range of mass fractions and the lack of need for sample dissolution.

THE ANODIZING PROCESS OF ALUMINUM AND ITS ALLOYS: A HISTORICAL AND ELECTROCHEMICAL APPROACH. Al and its alloys are found in several industrial applications. However, like most metals, this material is not immune to corrosion, being necessary to be protected against corrosion. One of the methods most commonly employed to improve the corrosion resistance of Al alloys is the anodizing process, which consists of thickening of the natural oxide (Al2O3) presents in Al through anodic oxidation. The anodizing process is accomplished by immersion of the Al alloy into an acid bath and passing an electric current through it. This process produces two layers: a barrier layer thicker than the natural oxide and a layer with regular arrangement of nanopores (porous layer). This duplex structure forms the anodized layer with a large specific surface area. With the advent of nanotechnology, this layer has been applied in other areas due to its low cost, stability, absence of toxicity, and biocompatibility. In this context, this paper addresses a historical and electrochemical review of the anodizing process of Al and its alloys, presenting the main events that culminated in the development of the current processes and the understanding of the relationship between the chemical reactions and the mechanisms that occur during nucleation and development of the oxide layer.

Abstract Aluminum alloys are the state-of-art materials for structural components of aircrafts. As they are susceptible to localized corrosion, this kind of damage can become a major threat for its safe use in aircraft components. Therefore, surface protection of aluminum alloys against corrosion is a core issue in these applications. In this work, an alternative eco-friendly cerium-based surface pretreatment was developed and applied on the AA1230 clad of the AA2024-T3 alloy for corrosion protection. The corrosion resistance evaluation of this modified surface was evaluated by several techniques. The results were compared to chromium based conventional treatments and revealed that the coating layer, composed of spherical nodular nanostructures of cerium, obtained with the proposed eco-friendly treatment, improved the corrosion resistance of the alloy. Moreover, it was comparable to the corrosion behavior of chromate-treated alloy, showing that this treatment is a promising alternative to replace chromate based surface treatments.

The galvanic interactions within and between the friction stir weld zones of the AA2198-T851 alloy have been investigated using electrochemical and microscopy techniques. The parent material (PM) was the most anodic region and exhibited pronounced severe localized corrosion (SLC) both when coupled and isolated. The stir zone was the most resistant to corrosion and exhibited no SLC when coupled, but exhibited SLC when isolated. Profiles associated with dissolved oxygen consumption and hydrogen generation currents across the weldment were inversely related because the anodic (PM) region produced higher hydrogen bubbles and, interestingly, consumed more dissolved oxygen compared with the other regions. Keywords: Aluminium, Polarization, SEM, Pitting corrosion, Oxygen reduction, Friction stir welding

Friction stir welding has been considered as an alternative to fusion welding processes of stainless steels. A lean duplex stainless steel, grade UNS S82441, has been recently developed and is prone to localized corrosion, such as pitting when exposed to harsh conditions during use. However, pitting resistance of UNS S82441 has not been previously investigated. In this study, UNS S82441 lean duplex stainless steel was friction stir welded, and its microstructure and localized corrosion resistance were investigated by phase volumetric fraction, scanning electron microscopy, transmission electron microscopy and electrochemical tests. The pitting resistance of each zone was investigated by polarization tests and by determining the critical pitting temperature. The results indicated that microstructural changes promoted by friction stir welding affected the pitting resistance of the lean duplex stainless steel. Keywords: Electrochemical tests, Electron microscopy, Duplex stainless steel, FSW

Over the last decades there was an increasing interest in using magnesium alloys for medical applications due to their biodegradability in the human body, providing a temporary mechanical support and corroding completely after the tissue healing. Although magnesium is a non-toxic element, it is of great importance to evaluate the element concentration, as well as the impurities present in both, pure magnesium and magnesium alloys, as the AZ31. The purpose of this study was to analyze the element composition of these materials using the method of neutron activation analysis (NAA). Standard Reference Materials (SRMs) acquired from National Institute of Standards and Technology (NIST) were analyzed for analytical quality control. Short and long term irradiations were carried out at the IEA-R1 nuclear research reactor and gamma-ray activities induced to the samples and element standard were measured using HPGe detector coupled to a Digital Spectrum Analyzer. The radioisotopes were identified by gamma ray energies and half-life. Concentrations of the elements As, Cr, Cd, Co, Fe, In, La, Mg, Mn, Mo, Na, Sb, V, W and Zn were determined in pure magnesium sample and the Al, As, La, Mg, Mn, Na, Sb and Zn in the AZ31 alloy, calculated by comparative method. The SRMs were analyzed by applying the same experimental conditions used for magnesium-based materials and their results presented good accuracy and precision. Thus, from the measurements obtained in this study it can be concluded that NAA is a suitable method for element determinations in magnesium-based materials providing reliable results.

Austenitic stainless steel alloys, mainly those produced according to ISO 5832-1, have received much attention due to their promising characteristics to be used as biomaterials. The aim of this study was to establish the proper conditions of neutron activation analysis (NAA) in order to determine chemical elements in a sample of ISO 5832-1 stainless steel. These determinations are of great interest for further evaluation of its corrosion resistance and of cytotoxicity of corrosion products. For the analyses, chips of ISO 5832-1 austenitic stainless steel were obtained. Aliquots of this material were weighed in polyethylene involucres and irradiated together with synthetic element standards at the IEA-R1 nuclear research reactor. Short and long irradiations were carried out using thermal neutron flux of about 4.5 x 1012 n cm-2 s-1. Quality control of the results was performed by analyzing two certified reference materials (CRMs). The elements concentrations of Cr, Cu, Mn, Mo and Ni obtained in the ISO 5832-1 austenitic alloy are within the specification values of this material. Besides, the elements As, Co, V and W were determined in this alloy. The sensitivity of the technique was verified by the determination of detection and quantification limits. In the case of CRMs, their results presented precision and accuracy for most of elements with relative standard deviations and relative errors lower than 15 %. Results obtained in this study demonstrated the viability of applying NAA in the analysis of the ISO 5832-1 stainless steel alloy.

In the present work, the microstructure, electrochemical behavior and localized corrosion of the AA2198-T851 Al-Cu-Li alloy were studied. The microstructure was correlated with corrosion results obtained by immersion, gel visualization and scanning electrochemical microscopy (SECM) tests. Immersion and gel visualization tests showed high kinetics of corrosion attack during the first hours of immersion. SECM analyzes by means of surface generation/tip collection (SG/TC) mode detected hydrogen evolution generated during spontaneous corrosion from severe localized corrosion (SLC) sites on the metal surface. SECM results revealed sites of intense hydrogen evolution after 2 h of immersion and increased amounts of corrosion products after 4 h of immersion. Hydrogen evolution sites detected by SECM were associated with severe localized corrosion (SLC).

Carmakers must achieve the worldwide targets for lightweight materials, safety and reducing the fuel consumption. The use of press-hardened steel (PHS), in vehicle structures has been contributing with these requirements. This type of steel is widely used for the hot-stamping which consists in heating the steel blank to total austenitization temperature and then transferring it from the furnace into the die tool where the steel is formed and quenched at the same time. PHS is usually protect with metallic coatings in order to avoid both steel oxidation and decarburization. Hot-dip Al-Si coating is currently the main used in this application. However, alternative coatings, like zinc-based, are under investigation. This work aims at evaluating the corrosion resistance of the 22MnB5 grade PHS, electroplated with Zn-Ni, before and after hot stamping, using the scanning vibrating electrode technique (SVET). Results from SVET showed that samples prior to hot stamping, the corrosion mechanism was uniform over the exposed surface, and was mainly related to selective dissolution of zinc from the coating. On the other hand, hot stamped samples showed localized corrosion mechanism with decrease in current with time of immersion due to the formation of corrosion products on the exposed surface.

The 2XXX Al alloys are characterized by their superior mechanical properties resulting from alloying elements and precipitation hardening treatments. The AA2524-T3 alloy was developed to replace the AA2024-T3 alloy in the aerospace industry. However, both alloys present many intermetallic particles (IMCs) in their microstructure, and this is the main reason for their high susceptibility to localized corrosion (such as pitting and stress corrosion cracking). Despite the similarities between these alloys (e.g., chemical composition and type of intermetallics) the literature comparing their properties is scarce and focuses mainly on their mechanical properties, not their corrosion resistances. In this investigation, the corrosion resistance of the AA2524-T3 alloy was compared to the AA2024-T3 alloy. The microstructure of both alloys was analyzed by Scanning Electron Microscopy before and after immersion in the test electrolyte, and the number and area fraction of intermetallics of each alloy was determined. The corrosion resistance of both alloys was monitored as a function of exposure time by electrochemical impedance spectroscopy and the results were fitted using electrical equivalent circuits. The AA2524-T3 alloy presented not only higher impedance values but also less corroded areas than the AA2024-T3 alloy.

Amperometric and potentiometric probes were employed for the detection and characterization of reactive sites on the 2098-T351 Al-alloy (AA2098-T351) using scanning electrochemical microscopy (SECM). Firstly, the probe of concept was performed on a model Mg-Al galvanic pair system using SECM in the amperometric and potentiometric operation modes, in order to address the responsiveness of the probes for the characterization of this galvanic pair system. Next, these sensing probes were employed to characterize the 2098-T351 alloy surface immersed in a saline aqueous solution at ambient temperature. The distribution of reactive sites and the local pH changes associated with severe localized corrosion (SLC) on the alloy surface were imaged and subsequently studied. Higher hydrogen evolution, lower oxygen depletion and acidification occurred at the SLC sites developed on the 2098-T351 Al-alloy.

BackgroundTitanium (Ti) and its alloys possess high biocompatibility and corrosion resistance due to Ti ability to form a passive oxide film, i.e. TiO2, immediately after contact with oxygen. This passive layer is considered stable during function in the oral cavity, however, emerging information associate inflammatory peri-implantitis to vast increases in Ti corrosion products around diseased implants as compared to healthy ones. Thus, it is imperative to identify which factors in the peri-implant micro-environment may reduce Ti corrosion resistance.MethodsThe aim of this work is to simulate peri-implant inflammatory conditions in vitro to determine which factors affect corrosion susceptibility of Ti-6Al-4V dental implants. The effects of hydrogen peroxide (surrogate for reactive oxygen species, ROS, found during inflammation), albumin (a protein typical of physiological fluids), deaeration (to simulate reduced pO2 conditions during inflammation), in an acidic environment (pH 3), which is typical of inflammation condition, were investigated. Corrosion resistance of Ti-6Al-4V clinically-relevant acid etched surfaces was investigated by electrochemical techniques: Open Circuit Potential; Electrochemical Impedance Spectroscopy; and Anodic Polarization.ResultsElectrochemical tests confirmed that most aggressive conditions to the Ti-6Al-4V alloy were those typical of occluded cells, i.e. oxidizing conditions (H2O2), in the presence of protein and deaeration of the physiological medium.ConclusionsOur results provide evidence that titanium's corrosion resistance can be reduced by intense inflammatory conditions. This observation indicates that the micro-environment to which the implant is exposed during peri-implant inflammation is highly aggressive and may lead to TiO2 passive layer attack. Further investigation of the effect of these aggressive conditions on titanium dissolution is warranted.

[This corrects the article DOI: 10.1371/journal.pone.0210530.].

The corrosion of engine components of the combustion chamber is usually related to the formation of acids such as sulfuric and nitric. These acids are generated by the condensation of combustion gases that usually occur in vehicle exhaust systems. However, with the development of new technologies to reduce emissions, condensation is also being promoted in vehicle combustion chambers. This fact is associated with high exhaust gas recirculation rates, known as EGR (English term for Exhaust Gas Recirculation). Consequently, corrosion problems in the engine components are increasing, especially in cylinder liners alloy manufactured using cast iron. In this study, the corrosion resistance of two cast iron alloys, one with a pearlitic microstructure and the other with a bainite microstructure in a solution simulating the composition of the condensate obtained from the combustion gases. It was found that the microstructure of the cast iron is an important factor affecting the corrosion behavior. The results showed that none of the two materials investigated is resistant to corrosion in the test medium, and the small difference observed between the behavior of the two cast iron was related to its microstructure, which are dependent on their chemical compositions. The cast iron with a pearlitic microstructure showed less formation of corrosion products than the bainitic cast iron. This result is related to the presence of steadite phase, highly stable and resistant to corrosion in pearlitic microstructure. This phase (steadite) anchors the corrosion products formed on the surface and act as a partial barrier slowing the progress of the corrosion process, that was more pronounced in the bainitic cast iron.

Corrosion control of electrogalvanized steel employing Cr VI based treatments is widely known and studied. However, researchers have been trying to find out alternatives to replace these salts once they must be banned in accord to environmental and industrial guidelines. Cr III – based conversion coatings have shown performance compatible to Cr VI – based treatments. In this work, EIS measurements are performed in NaCl 0,05 mol/L and Na2 SO4 0,1 mol/L, during the immersion time, to evaluate the corrosion resistance of electrogalvanized steel passivated with Cr III – based conversion treatment and painted with three different organic coatings. The organic coatings are characterized by their adherence. The results show a similar behavior for the three coatings and, despite a second constant time has been pointed by the EIS fitting, the R2 values indicate a low corrosion rate. The system Zn – Cr III – organic coating is compatible to the system Zn – Cr VI – organic coating, for the immersion period considered.

Austenitic stainless steels, titanium and cobalt alloys are widely used as biomaterials. However, new medical devices require innovative materials with specific properties, depending on their application. The magnetic properties are among the properties of interest for some biomedical applications. However, due to the interaction of magnetic materials with Magnetic Resonance Image equipments they might used only as not fixed implants or for medical devices. The ferromagnetic superalloys, Incoloy MA 956 and PM 2000, produced by mechanical alloying, have similar chemical composition, high corrosion resistance and are used in high temperature applications. In this study, the corrosion resistance of these two ferritic superalloys was compared in a phosphate buffer solution. The electrochemical results showed that both superalloys are passive in this solution and the PM 2000 present a more protective passive film on it associated to higher impedances than the MA 956.

The effect of potentiostatic polarisation on the electrochemical behavior of the Ti-13Nb-13Zr alloy was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation curves in Hanks' solution at 37 °C. Potentiodynamic polarisation curves show a passive behavior with a slight current increase as potentials around 1300 mV(SCE). Based on these curves, different potentials were chosen to perform potentiostatic EIS experiments. EIS experimental data were interpreted using different equivalent circuits associated with the duplex nature of the oxide layer. The fitting procedure evidenced the thickening of a defective oxide layer with the applied potentials, corresponding to key points in the potentiodynamic polarisation curves.

Titanium alloys are largely used for biomedical applications mainly due to their high corrosion resistance resulting from the protective oxide film formed on their surface. The literature, however, has pointed out discrepancies between in vitro tests and in vivo tests. These discrepancies have been ascribed to hydrogen peroxide (H2O2) generated by inflammatory reactions. In this investigation the electrochemical behaviour of a Ti-13Nb-13Zr alloy, which was developed as material for implants, has been evaluated in Hanks' solution, with and without H2O2. The evolution of the electrochemical behavior was monitored by electrochemical impedance spectroscopy (EIS) and the results were fitted to an equivalent circuit that simulates an oxide film as a duplex layer structure composed of an inner barrier layer and an outer porous layer. In the solution without H2O2, the oxide film was very stable during the whole test period. On the other hand, in the solution with H2O2, the EIS results varied significantly, indicating a progressive decrease in the barrier layer resistance until 35 days which was followed by the restoration of the barrier layer protective characteristics against corrosion, either due to its growth or to its self-healing after partial consumption of the oxidant agent. The oxide film formed on the Ti alloy samples after 125 days of immersion in Hanks' solution, either with or without H2O2 was analyzed by XPS. The XPS results revealed the presence of TiO and TiO2 on the samples immersed in the two electrolytes, however, Ti2O3 was only found on the samples exposed to the H2O2 containing solution.

The resistance to localised corrosion of the full austenitic 15%Cr-15%Ni-1.2%Mo titanium stabilized stainless steel (DIN W. Nr. 1.4970) was investigated by electrochemical methods including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and potentiostatic polarization measurements in a phosphate-buffered solution (PBS). The low carbon and non-stabilized austenitic stainless steel, AISI 316L (ASTM F-138), widely used for surgical implants, was also tested for comparison. The tests were conducted at room temperature after a stable potential had been reached. After the electrochemical measurements, the surfaces of the specimens were observed using SEM to evaluate the presence of pits. Potentiodynamic polarization results showed that both steels are prone to localized corrosion. Larger pits were found on the surface of AISI 316L specimens after the electrochemical tests. EIS response has indicated the duplex structure of the passive oxides. The results showed that the electrochemical behaviour of the DIN W. Nr. 1.4970 is better than of AISI 316L steel. Therefore, their application as an implant material may be considered.

Nd-Fe-B magnets are highly susceptible to corrosion and need protection against environment attack. The use of organic coatings is one of the main methods of corrosion protection of these materials. Data related to the effect of conversion coatings, such as phosphating, on corrosion performance of these magnets is still scarce. Studies about the effect of phosphating on the corrosion resistance of a commercial Nd-Fe-B sintered magnet indicated that it increases the corrosion resistance of these magnets, compared to non-phosphated magnets. In this study, the solution chemistry of a phosphating bath was altered with the addition of molybdate and its effect on the corrosion resistance of magnets investigated. Sintered magnet specimens were phosphated in solutions of 10 g/L NaH2PO4 (pH 3.8), either with or without molybdate [10-3 M MoO4(2-)], to improve their corrosion resistance. The effect of phosphating time was also evaluated, and specimens were phosphated for 4 and 18 hours. To evaluate the corrosion performance of phosphated and unphosphated specimens, a corrosion test based on monitoring hydrogen evolution on the surface of the magnets was used. This technique revealed that the addition of molybdate to the phosphating solution improved the corrosion resistance of the magnets phosphated by immersion for short periods but had no beneficial effect if phosphated by immersion for longer periods.

Aluminium-silicon alloys have been wide accepted in the automotive, electric and aerospace industries. Preferred orientation is a very common condition for metals and alloys. Particularly, aluminium induces texture during the forming process. The preparation of an aggregate with completely random crystal orientation is a difficult task. The present work was undertaken to analyse the texture by X-ray diffraction techniques, of three spray formed hypereutectic Al-Si alloys. Samples were taken from a billet of an experimental alloy (alloy 1) and were subsequently hot-rolled and cold-rolled (height reduction), 72% and 70%, respectively. The other used samples, alloys 2 and 3, were taken from cylinders liners. The results from the Laue camera showed texture just in the axial direction of alloy 3. The pole figures also indicated the presence of a typical low intensity deformation texture, especially for alloy 3. The spray formed microstructure, which is very fine, hinders the Al-Si texture formation during mechanical work.

In this investigation the corrosion resistance of four Al-Si hypereutectic alloys in a solution typical of condensate from automotive fuel combustion products, and referred to here as synthetic condensed automotive solution, has been studied. Three commercial alloys that are used for cylinder liners, and a laboratory made alloy, were studied by electrochemical impedance spectroscopy and measurements were taken after increasing times of immersion in this solution. Comparison of the electrochemical response of the four alloys in the corrosive solution was carried out. Although the mechanisms by which the four alloys corroded were similar, the results indicated differences in corrosion resistances of these alloys, and these differences could be related to their microstructures. The laboratory prepared alloy showed increased susceptibility to pitting corrosion compared to the commercial alloys. The surfaces of the alloys were examined, before and after the corrosion test, by scanning electron microscopy and analyzed by energy dispersive spectroscopy. The results indicated preferential attack of the aluminium matrix phase in all the alloys. The alloy with higher copper content and prepared by spray forming was more susceptible to pitting compared to the other alloys. The EIS response at low frequencies indicated a diffusion-controlled process, probably that of oxygen to the alloy interface.

In this investigation, the corrosion resistance of AISI 316 SS filters prepared with powders in the size ranges 74-44 µm and 210-105 µm and compacted with pressures of 300 MPa and 400 MPa has been evaluated in naturally aerated 0.5 M H2SO4 solution at 25 °C. Weight loss of filters manufactured with compacting pressure of 400 MPa were significantly higher than that of filters compacted at 300 MPa. The filter compacted at 400 MPa had higher carbon and nitrogen contents compared to those compacted at 300 MPa. The former also had chromium rich precipitates and oxides in the grain boundaries. The pores in filters compacted at 400 MPa were smaller than in filters compacted at 300 MPa. Smaller pores favor the formation of concentration cells and consequently, increased crevice corrosion.

The corrosion products of carbon steel and weathering steel exposed to three different types of atmospheres, at times ranging from one to three months, have been identified. The steels were exposed in an industrial site, an urban site (São Paulo City, Brazil), and a humid site. The effect of the steel type on the corrosion products formed in the early stages of atmospheric corrosion has been evaluated. The corrosion products formed at the various exposure locations were characterized by Raman microscopy, X-Ray diffraction (XRD) and their morphology was observed by Scanning Electron Microscopy (SEM). Three regions of different colours (yellow, black and red) have been identified over the steel coupons by Raman microscopy. Analysis carried out on each of these areas led to the characterization of the correspondent oxide/hydroxide phases. The main phases present were lepidocrocite (g-FeOOH) and goethite (a-FeOOH). Small amounts of magnetite (Fe3O4) were also eventually encountered.

The aim of this work was to compare the corrosion products formed on carbon steel plates submitted to atmospheric corrosion in urban and industrial atmospheres with those formed after accelerated corrosion tests. The corrosion products were characterized by X-ray diffraction, Mössbauer spectroscopy, and Raman spectroscopy. The specimens were exposed to natural weathering in both atmospheres for nine months. The morphologies of the corrosion products were evaluated using scanning electron microscopy. The main product found was lepidocrocite. Goethite and magnetite were also found on the corroded specimens but in lower concentrations. The results showed that the accelerated test based on the ASTM B117 procedure presented poor correlation with the atmospheric corrosion tests whereas an alternated fog/dry cycle combined with UV radiation exposure provided better correlation.