Corrosion behavior was evaluated by cyclic potentiodynamic polarization method using a potentiostat Metrohm model Autolab/PGSTART302 connected to a typical electrochemical cell with a saturated calomel electrode (SCE) used as a reference electrode, a platinum plate employed as counter- electrode and the working electrode made from thesteels studied. Electrochemical measurements were performed in triplicate for each condition. An aerated solution of synthetic marine medium with a concentration of 60,000 ppm at room temperature Cl, prepared according to ASTM D1141-98, was used. After immersion inthe solution, the samples were subjected to conditions of open circuit potential (OCP). The potentiodynamic curves were measured at a potential scan rate of 1 mV/s with direction reversal when impacted the anodic current density of 10 -3 A/cm 2 .
bulk metallic glass (BMG) (Fe 41 Co 7 Cr 15 Mo 14 C 15 B 6 Y 2 ) with a diameter of 5mm exhibits high corrosionresistancein simulated body luids. However, the commercial application of Fe-based bulk metallic glass with a high Mo content is expensive. Therefore it is important to carry out studies to analyze the effect of Mo substitution with other elements for corrosionresistance and glass forming ability. BMG with the greatest corrosionresistance should have a high glass forming ability (GFA), because it has to have a big enough diameter for use in applications such as medical implants. Therefore a study of these alloys should analyze the effect of alloying elements onthe GFA.
Nickel is the most important alloying element to stabilize the aus- tenite phase in 300 series austenitic stainless steel, but its price has shown considerable luctuations over the last decades. Onthe other hand, manganese (another austenite stabilizer element) has presented a more stable price over the same period. In this sense, Mn has been used to partially replace Niin some grades of austenitic stainless steels (Charles, 2005). Prior investigations reported that Mn addition promoted a negative effect onthe general corro- sion resistance of austenitic stainless steels (Murgulescu and Radovici, 1960, Knyazheva et al., 1965, Condylis et al., 1970, Shams et al,. 1973, Lunarska et al,. 1975). All of these investigations did not propose any mechanism to explain the deleterious role of Mn addition onthe general corrosionresistance of austenitic stainless steels. Kemp (Kemp et al., 1995) studied the effect of Mn on general and pittingcorrosion of Cr-Mn duplex stainless steels (with 3 to 10 wt.% Mn). Electrochemical tests (cyclic polarization) in 0.025N NaCl and anodic polarization in 0.1N H 2 SO 4 revealed that Mn addition reduced both general and pittingcorrosionresistance.
The aim of the present work was to study the passive ilm stability and pittingcorrosion behavior of the AISI 409 stainless steel. The electrochemical tests were carried out in 0.1 M NaCl solution at room temperature. The general electrochemical behavior was assessed using electrochemical impedance spectroscopy (EIS) measurements whereas the semiconducting properties of the passive ilm were evaluated by the Mott-Schottky approach. Pittingcorrosion was investigated using potentiodynamic and potentiostatic polarization tests. Surface morphology was examined using confocal laser scanning microscopy and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDS) analyses were carried out to identify the composition of precipitates that could act as preferential sites for the onset of pittingcorrosion. The results showed that the passive ilm presents n-type semiconductive behavior. Grain boundaries played an important role as pitting initiation sites for the AISI 409 stainless steel.
Although it is clear that the purpose of building codes is to provide adequate safety inthe design and construction of structures, the level of safety cannot be measured quantitatively basedonthe codes alone, since they hide a myriad of safety margins and conservative approximations. The two Brazilian codes mentioned, in particular, have been subject to major revisions just recently. NBR8681 has been extensively updated in 2003, and NBR 8800 is currently under revision. None of the codes has been around long enough for a practical verification of the safety of structures designed to comply with them.
A large part of the world’s trans- port and energy infrastructures rely on reinforced concrete. Its durability is due tothe excellent chemical stability of hydrated Portland cement and the pas- sivity of steel inthe alkaline pore solution of concrete with a pH from 10 to 13.5. Corrosion of the reinforcement steels, induced by chloride ions penetrating into the concrete, is the main cause of early damage, loss of serviceability and safety of reinforced concrete structures (Addari et al., 2008). In order to prevent reinforce- ment steel corrosionin highly aggressive environments, the use of stainless steels (SS) is becoming increasingly popular as they exhibit much higher pittingcorrosionresistance than plain carbon steel and a higher chloride content is required to de- passivate them (Abbott et al., 1997). The localized corrosion and generalized attack onthesteels are associated with chlorides and carbonation ions, respectively (Blanco et al., 2006). Thus, these reinforcements suffer severe corrosion problems when the reinforced concrete structure is exposed to chloride contaminated environments and when the concrete cover is carbonated.
Some issues that need to be established prior to a simulation include: (1) chemical kinetics on batch melting and reactions inthe glass, chemical equilibrium, solubility data, and chemical kinetics during refining; (2) the thermophysical properties of glass compositions; (3) coupling of combustion-heat transfer models to glass bath models; (4) data for predicting melting and refining kinetics of silica dissolution, bubble dynamics, and glass quality; (5) analysis and synthesis between numerical predictions and operating data; (6) complete understanding of physico-chemical processes to improve models and provide more accurate predictions. Little has been published onthe thermodynamic aspects of thecorrosion reaction of ceramic oxides by silicate melts. This is an area that can be expanded. Other important areas of research encompass: (1) development of new refractories or compositions with improved properties (i.e., ); and (2) understanding of the glass melting process, by developing relations expressing the influence of temperature, glass composition, batch granulometry, and glass convection, in order to demonstrate the significance of the dissolution phenomena in glass melting [i.e.,40].
2007; Toshiyasu, 2007). This element pro- motes the formation of an internal nano- sized oxide layer enriched in Si, compact and adherent. In addition tothe function as a physical barrier, hindering the access of water and corrosive agents tothe steel substrate, this Si- substituted layer, similar to that Ni- substituted and Cr-substituted oxide layer, has cationic permeability and prevents that corrosive anions such as chlorides reach the substrate (Nishimura, 2007; Toshiyasu, 2007). The addition of silicon inFe alloys enhances the protec- tion and densification of rust layers in Si- bearing steels, increasing its atmospheric corrosionresistance (Chen et al., 2005).
the severity of induced mechanical wear. It implies that the phenomenon could become additive. It means, that the corrosive electrochemical phenomenon would be the dominant inthe marine environment. This aggressive effect of the environment is attributable tothe action of the chloride ion which promotes further corrosionpittingonthe material surface to propagate by the incessant impact of the particles ranging in size from 210 µm and 300 µm causing the release of the material inthe non passivated areas, transfer inthe hardened layers of the surface. This phenomenon is more evident in AFe2 and AFe3 materials. In general and as expected, the materials under study have an increase inthe activity, especially of thecorrosion current density when it is subjected to an environment under dynamic conditions in particular under the action of erosive particles. It is observed that the modification of the mechanical condition of the environment, such as the fluid impact and the erosive particles at certain attack angles, leading to a slight change of corrosion potential for the AFe1 steel, because the effect of the agitation of the environment by the dissipation of energy in it, while at the same time it shows an increase inthecorrosion current density effect of the particles attack and the subsequent generation of widespread corrosion points. It should be mentioned that stainless steel in notable for its very stable corrosion potentials as environmental conditions change, it is an effect that is not apparent in fermanal alloys, which show an evident thermodynamic increased of the activity inthe dynamic environments, not however, AFe1 fermanal steel generates a density and corrosion rate in narrow ranges similar to those shown by the stainless steel which is an important aspect in engineering applications where the changing environmental conditions of work require that the material is sufficiently stable thermodynamically to compensate these changes without incurring in loss of resistant area of the material which is closely related tothe applied stress.
Carbon distribution inFe-Cr-C alloys with a variety of Cr concentrations is studied basedon internal friction, optical and transmission-electron microscopy. It is found that the carbon distribution strongly depends on initial microstructure, being ferritic or ferritic/martensitic, which is determined by the thermal treatment, and Cr and carbon concentrations. Inthe quenched alloys, carbon is observed inthe form of small carbon-vacancy complexes, most probably two carbon - single vacancy cluster, 2CV, that dissolve at about 500 K. In tempered alloys, the carbon atoms are observed to be uniformly distributed only inFe-2.5Cr-C alloy, which is fully ferrite. Inthe alloys with 5-12% of Cr, with ferritic/martensitic microstructure, carbon-Snoek relaxation peak is not observed due tothe carbon precipitation, as well as due to atomic carbon being trapped at dislocations and grain boundaries. In both quenched and tempered alloys, the plastic deformation causes the appearance of the broad relaxation peak close to 300 K which could be assigned to dissolution of single carbon - single vacancy, CV, complexes.
Armando Ortiz-Prado. Se graduó como inge niero mecá nico elec tri cista por la Facultad de Inge niería de la UNAM en 1980, poste rior mente obtuvo la maes tría y el docto rado en inge niería mecá nica. Es profesor desde hace 28 años impar tiendo cátedra prin ci pal mente en las áreas de procesos de manu fac tura y ciencia de mate riales. Es profesor titular “C” de tiempo completo defi ni tivo y tutor doctoral de los posgrados de ciencia e inge niería de mate riales y de inge niería. Sus líneas de inves ti ga ción son mode lado de procesos de confor mado mecá nico, análisis de falla, compor ta miento mecá nico de bioma te riales y corro sión en equipo elec tró nico. Ha desa rro llado proyectos y estu dios para dife rentes empresas privadas y enti dades guber na men tales, orien tados al desa rrollo y mejora de métodos de manu fac tura, desa rrollo de mate riales, corro sión y análisis de falla; lo cual se traduce en más de 50 estu dios y aseso rías para la indus tria, 12 proyectos de inves ti ga ción y desa rrollo tecno ló gico. A la fecha, suma más de 90 tesis de licen cia tura concluidas, así como 12 de maes tría y una de docto rado. Su expe riencia se ha trans mi tido a través de 7 textos para licen cia tura en las áreas de manu fac tura, mate riales y corro sión. Asimismo, su produc ti vidad incluye más de 15 artículos en congresos inter na cio - nales, más de 80 artículos en congresos nacio nales y más de 15 artículos en revistas arbi tradas. Fue galar do nado por la UNAM con la Distin ción Univer sidad Nacional para Jóvenes Acadé micos (Docencia en cien cias exactas) en 1989. Su produc ti vidad acadé mica y cien tí fica ha sido reco no cida por la UNAM, a través del otor ga miento del nivel D del PRIDE y por el CONACYT con el nombra miento de Inves ti gador Nacional Nivel I.
Thepittingcorrosion susceptibility of the oxide ilms formed onthe stainless-steel samples inthe three situations (as received and grown inthe presence and absence of chromic acid) was evaluated by potentiodynamic polarization curves carried out in a borate buffer solution pH 9.2, containing chloride ions (Figure 4). After these measurements, the visual colour of all steel samples was practically unchanged. As already pointed out in Figure 1, the values of current density are also higher for coloured (near one order of magnitude) than non-coloured samples for the same overpotential inthe passive region. The values of E cor , E pit and (E pit − E cor ) extracted from the potentiodynamic polarization curves of Figure 4 for steel samples non-coloured and previously coloured using the triangular current scan method are listed in Table 1. All coloured steel samples present similar values of E pit but they are higher than those for non-coloured ones. By the other hand, the values of (E pit − E cor ) are inthe range of 0.45 V-0.57 V, 0.78 V-0.92 V and 0.98 V-1.12 V for native ilms (very thin ilms) and ilms grown (thicker ilms) inthe presence and absence of chromic acid, respectively. These
The application of thermal spray coatings has been effective in preventing corrosion of steel and iron products. It has been used in a wide range of applications spreading from the petroleum tothe food industry. In this work, the performance and effectiveness of a two-layered aluminum-based thermal spray coating applied to an ASTM A387 G11 steel was evaluated. The coating structure was comprised of an inner Al-Fe-Cr layer and an outer layer of aluminum. Coated samples were tested inthe reactor zone of a fluid catalytic cracking unit (FCCU) of a petrochemical plant for 2.5 years. The reactor zone temperature was about 793 K (520 °C) and the environment was a mixed gas containing sulfur, oxygen and carbon. Laboratory-scale tests were also conducted onthe coated samples in order to gain a better understanding of the corrosive effect of the gaseous species present inthe FCCU atmosphere. Porosity present inthe thermal spray coatings allowed the penetration of the atmosphere corrodents, which instigated intergranular corrosion of the steel substrate. The presence of an inner Al-Fe-Cr layer did not prevent coating spallation, which further contributed tothe internal corrosion process.
To determine the distribution of friction in micro scale and its impact onthe extrusion forces, roughness numerical model surfaces of container 1mm in diameter and right-angled die with diameter reduction 1/2, for rod forward extrusion has been created (fig. 2). This model is the triangular wave in two variants. Inthe first case its height h = 10µm and length λ = 40µm represents the average height of roughness achieved during initial polishing. Inthe second, height h = 5µm and length λ = 20µm simulates the surface layer after the finish polishing (fig. 3).
___________________________________________________________________________ 55 Com o propósito de comparar a fracção de precipitados “brancos”, fora e dentro do cordão, recorreu-se ao software de domínio público, Image J (versão 1.41) desenvolvido por Wayne Rasband do National Institute of Health, USA. A tabela seguinte (tabela 3.1) resume os resultados obtidos. Verifica-se que a fracção de precipitados “brancos” no material base, comparativamente à região do cordão, é muito superior, apresentando-se também no material base com maiores dimensões e maior variabilidade de dimensões. As imagens para a região do material base mostram que os precipitados a “branco” devem ter sido fragmentados segundo a direcção aplicada durante a última operação de polimento (perpendicular ao plano de laminagem da chapa de alumínio), deste modo, por esta análise só poderá concluir-se que a região fora do cordão apresenta uma precipitação de Al(Fe,Mn,Cr) muito mais grosseira do que a observada para o cordão de soldadura.
The stainless steel, before and after coloration, was cut to 20×20×0.8 mm sized samples for the elec- trochemical characterization essays in an aqueous 0.5 mol/L NaCl solution. The electrochemical measure- ments were performed using an AUTOLAB PGSTAT 302N potentiostat/galvanostat. The analysis was con- ducted on a conventional three-electrode cell, using platinum as a counter electrode and Ag/AgCl as the ref- erence electrode, and stainless steel, before and after coloration, as the working electrode. The steel samples were covered with artificial wax (Fluka), leaving an exposed area of 2 cm 2 . Before performing the assays, the samples were cleaned with water, purified by reverse osmosis, and acetone. All tests were performed in aer- ated solutions at room temperature. First, measurements of the open circuit potential (OCP) were taken over a 2 hour period. For the EIS measurements, an AC disturbance of 10 mV was applied around the open circuit potential. The frequency range used was of 10 4 to 10 –2 Hz . All impedance data were adjusted to equiva- lent circuits that were appropriate for use in Zview software. The quality of the adjustments was evaluated by chi-squared (χ2) values. Anodic polarization experiments were carried out in 0.5 mol/L NaCl solution at a scanning rate of 0.167 mV/s until a potential higher than thepitting potential .
magnetite were identified basedonthe XRD pattern. The presence of goethite agrees with Olowe & Genin (1991) who showed that goethite and lepidocrocite are expected GR2 oxidation products, depending on initial conditions. Magnetite was identified inthe precipitation of the fresh GR2 sample prior to oxidation. Onthe contrary, samples with higher Ni content, P = 80/20, 70/30, 60/40 and 30/70, remained greenish. For these samples the three most intense peaks typifying green rust can be easily seen. As was shown for Ni(II)- GR2 (Refait et al., 1990) all Fe(II) is transformed toFe(III) and the oxidized LDHs contain only Ni(II) and Fe(III). In addition tothe reference Ni(II)-Fe(III) LDH isomorphous with green rust (c-value ~ 1.09 nm) additional peaks are seen indicating the presence of other minerals. For P = 80/20 a peak appears at 2θ = 9.85 corresponding to a d-value of 0.926 nm. This peak is still present for P = 70/30 but appears as a shoulder. It was not possible to detect the mineral inducing this peak. For samples P = 60/40 and 30/70 the peak at 2θ = 9.85° was no longer present and three peaks appeared, each of which had shifted tothe right of one of the main peaks associated with the reference Ni(II)-Fe(III) LDH with c-value of 1.09 nm. These peaks are marked with asterisks and correspond to an additional LDH with c-value 1.013 nm and a-value 0.3094 nm. The reduction inc-value on exposure to air is probably due to dehydration. This is consistent with the fact that the LDHs honessite (c-value 0.89 nm) and hydrohonessite (c-value 1.09 nm) only differ inthe amount of water inthe interlayer (Nickel & Wildman, 1981). This suggests the sample is a mixture of two Ni-Fe(III) LDHs which differ inthe extent of dehydration. With further increase inNi content (P = 20/80, 10/90 and 0/100) the oxidized samples become poorly crystalline LDH phases.
Amostras com massas entre 1 g e 5 g das Fe-28%Ni e Fe-31Ni-0,02 (%mássica) foram fundidas em atmosfera inerte num forno a arco, utilizando correntes entre 5 e 100 A, a partir dos elementos puros (pureza comercial). Posteriormente, foi necessário promover a substituição da estrutura dendrítica característica da solidificação fora de equilíbrio, como mostrado na Figura 2.1, por grãos austeníticos equiaxiais, com composição mais uniforme. Na Figura 2.1, ainda é possível verificar regiões pretas na microestrutura da liga, exceto a região inferior, correspondente à resina fenólica. Estas regiões são martensita, as quais não deveriam ocorrer numa liga Fe-31Ni-0,02C (%p). A formação deste microconstituinte é atribuída à composição não uniforme da liga, possibilitando o aparecimento da martensita em regiões contendo menos carbono e níquel.
varying sliding distances ranging from 200m-4600m. All the tests were carried out in ambient air (humidity 70%) under dry sliding condition (without lubrication). After completion of wear tests, samples were cleaned with acetone. At least three tests were done for each type of material. The sliding distances were calculated by knowing the track diameter and speed of rotation of the disc. Wear rates were calculated from average values of weight-loss measurements. Wear rate (WR) was estimated by measuring the mass loss (ΔW) after each test. It is calculated as the ratio of ΔW to sliding distance (SD) and applied load L 16,22 :
II.4.1. Langmuir Adsorption isotherm model The Langmuir model was developed basedon assumption of the formation of a monolayer of the metal ion solution onto the surface of the phthalic acid, It has also been assumed that surface sites are completely heterogeneous. The study of Langmuir isotherm is essential in assessing the adsorption efficiency of the phthalic acid. In this regard the Langmuir isotherm is important, through the restriction and the limitation if this model has been well recognized.