Artigos Científicos

Resumo: The main goal of this work is two‐fold: (1) to compare three different excitation conditions in x‐ray fluorescence microtomography (XRFCT) in the analysis of reference samples, and (2) to determine the elemental distribution map for breast tissue samples, in order to verify concentrations of certain elements correlated with characteristics and pathology, using x‐ray transmission microtomography (CT). The experiments were performed at the X‐Ray Fluorescence Facility (D09B‐XRF) of the Brazilian Synchrotron Light Laboratory (LNLS), Campinas, Brazil. In this work, a multilayer monochromator with photon energies near 12 keV, a monochromatic beam at 9.8 keV using a Si (111) crystal, and the white beam were used for elements excitation of elements inside the sample. The sample was placed on a high‐precision goniometer and translation stages, which allowed for rotation as well as translation perpendicular to the beam. Fluorescence photons were collected by means of an energy dispersive HPGe detector placed at 90° to the incident beam, while transmitted photons were detected with a fast Na(Tl) scintillation counter, placed behind the sample, in the direction of the incoming beam. Transmission CT images were reconstructed using a filtered back‐projection algorithm, and XRFCT images were reconstructed using a filtered back‐projection algorithm with absorption correction. Copyright © 2009 John Wiley & Sons, Ltd.

Resumo: Density measurements were made for binary aqueous solutions of polyethylene glycol at seven temperatures: 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, and 313.15K. Polyethylene glycol samples with nominal average molar masses of 3000g⋅mol−1 (PEG 3000), 6000g⋅mol−1 (PEG 6000), 10000g⋅mol−1 (PEG 10000) and 20000g⋅mol−1 (PEG 20000) were used. These results were used to determine the specific volumes of solutions with solute-to-solvent mass ratios (mass of the solute/mass of the solvent) in the range 0.0546 to 1.4932 for PEG 3000, from 0.0553 to 1.4986 for PEG 6000, from 0.0552 to 1.2241 for PEG 10000, and from 0.0530 to 1.2264 for PEG 20000. The differences between the specific volume of a solution and the specific volume of the pure solvent, at a given temperature, were represented by a virial-type equation in terms of solute concentration. The first-order coefficient of the expansion is the partial specific volume of the solute at infinite dilution. The higher-order coefficients are related to the contribution of pairs, triplets, and higher-order solute aggregates, according to the Constant-Pressure Solution Theory. The functional dependence of the virial coefficients upon temperature is discussed in terms of solute-solute and solute-solvent interactions. The effect of the PEG molar mass on the partial specific volume of solute at infinite dilution, as well as the contributions of pairs of solute molecules to the solution volume, are also investigated. The apparent specific volume, apparent specific expansibility, apparent specific expansibility at infinite dilution and virial coefficients of the apparent specific expansibility are also presented.

Resumo: We present in this paper very interesting vibrational data for formamide (FA) complexes with Mg and Ca ions. The νCO and νCN modes of FA are shifted to lower (45 cm−1) and higher (30 cm−1) wavenumbers, respectively, in the presence of Mg(II), whereas both modes are upshifted (∼15 cm−1) as Ca(II) is present. The shifts observed for the system containing Mg(II) indicate that the HC−ON+H2 form is majority due to the coordination through the O atom. On the other hand, the HCONH2 form is dominant because of the coordination to Ca(II) via both O and N atoms. Such differences may be explained based on the ionic radii of Mg and Ca, which lead to the formation of FA complexes with coordination numbers equal to 6 and 8, respectively. The results here presented may help us for a better understanding about amide bond hydrolysis reactions catalyzed by metal ions, since the ionic and molecular FA forms have been recognized as active and inactive intermediates, respectively, in the hydrolysis mechanisms proposed so far.

Resumo: Developing a sustainable and environmentally friendly inhibitor remains an essential and challenging goal for corrosion control. Here, different extracts from the same biomass (Juçara - Euterpe edulis) were applied as a new inhibitor for mild steel in different corrosive medium: 1 mol L−1 HCl (pH 0) and simulated CO2-saturated formation water (pH 5). Depending on the extraction process, the anticorrosive capacity of extracts may increase, a fact verified in gravimetric tests, reaching 94.4% maximum inhibition efficiency for the acidic medium (1000 mg L−1 of Juçara pulp in 48 h of immersion) and 86.1% inhibition efficiency for the saline medium (600 mg L−1 of Juçara pulp extract assisted by ultrasound in 24 h of immersion). Gravimetric tests, electrochemical tests, and surface and biochemical characterization analyses were carried out to better understand these extracts' performance. This work provides an interesting application of the same biomass effectively acting in different corrosive medium, depending on the extraction method.

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Resumo: The aim of this work is presenting results of uncertainty of measurement calculations applied to both a low temperature PEMFC (proton exchange membrane fuel cell) and a high temperature SOFC (solid oxide fuel cell) by using Monte Carlo method simulations. The intention is correlating electric voltage, obtained in the technical literature, and energetic efficiency of the fuel cells studied in this work. In order to validate the Monte Carlo results achieved a comparison with the procedure for the evaluation of the uncertainty of measurement existing in the GUM 95 ”Guide to the Expression of Uncertainty in Measurement” (by BIPM, IEC, IFCC, ISO, IUPAC, IUPAP and OIML) is made. A reasoning of the balancing of the sources of uncertainty is presented as well. In last, it is discussed why the calibration process and traceability of the voltmeter are key factors in providing reliable metrological results in the production of electricity by fuel cell technology. This work is the first part of a broader study from which the next steps will be the validation of these presented simulations by fuel cell bench tests and the planning and development of Brazilian Conformity Assessment programs for PEMFC and SOFC fuel cells afterwards.

Resumo: The use of composite materials has been an option increasingly used in various industry sectors. However, the degradation process by which these materials are subjected due to operational conditions is a reality that makes monitoring a challenge. In this work, conventional ultrasonic technique was used to analyse the behaviour of GFRP pipes under different aging conditions (temperature and pressure). The pipes were submitted to aging for 2, 6 and 18 months and acoustic measurements were performed in certain areas of each pipe in order to monitor the relevant locations, both in circumference and in length. The gathering of these signals was carried out periodically throughout the aging process. Through the methodology presented in this work regarding ultrasonic inspection, it was possible to correlate the acoustic properties obtained with the mechanical properties of the material during aging. Additionally, after the end of the aging process and occasional failures, some samples were extracted to perform tensile tests, which were able to indicate residual Young Modulus in the axial direction. Sound testing for mechanical characterization were also performed and their results were compared to the ones calculated by ultrasonic results. Microstructure of the material and its manufacturing process were also found to be important parameters that must be considered. The experimental database obtained were analysed using statistical tools to evaluate the feasibility of a trend model in the behaviour of material properties during aging.

Resumo: Ballistic helmets are individual pieces of armor equipment designed to protect a soldier’s head from projectiles and fragments. Although very common, these helmets are responsible for several casualties due to their significant back face deformation and low ballistic resistance to projectiles. Therefore, to enhance helmet performance, studies have focused on the development of new materials and new ballistic protection solutions. The purpose of this study was to develop and evaluate a new ballistic solution using thermoplastic-based matrices. The first matrix was based on high-density polyethylene (HDPE). The second matrix was based on HDPE modified with exfoliated montmorillonite (MMT). The main manufacturing processes of a thermoplastic-based ballistic helmet are presented, along with its ballistic performance, according to the National Institute of Justice (NIJ) standard 0106.01 and an investigation of its failure mechanisms via a non-destructive technique. All the helmets resulted in level III-A ballistic protection. The postimpact helmets were scanned to evaluate the back face deformation dimensions, which revealed that the global cone deformation was deeper in the HDPE than in the HDPE/MMT helmet. The failure analysis revealed an overall larger deformation area in the HDPE and HDPE/MMT helmet delamination zones in the regions with a large radius of curvature than in the zones with the lowest radius, which is in accordance with previous simulations reported in the literature.

Resumo: This work presents a study of the influence of the molecular weight on the thermodynamic modeling of the viscosity of non-newtonian polymer solutions. The employed model is based on the absolute rate theory of Eyring and on the solution theory of McMillan-Mayer. The Soave-Redlich-Kwong equation of state was adopted for the calculation of the excess molar McMillan-Mayer free energy derived from the osmotic pressure of the solution. The model presents parameters that take account separately the different possibilities of interaction in the macromolecular environment. As the tertiary structure of a polymer molecule can be affected by applied shear stress, only the parameters related with the intramolecular interactions are dependent of the shear stress. The experimental rheological curves for different molecular weights of polyethylene glycol aqueous solutions have been measured at several concentrations, within the whole polymer solubility range, at 298.15 K and 0.1 MPa. The dependence on the molecular weight for all parameters of the model was analyzed and characterized. The dependence of the shear sensitive parameters on the shear stress was also studied.

Resumo: An eddy current method was applied to evaluate amount of sigma phase in duplex stainless steel. In the preliminary experiments several transducers configuration were considered. The performance of the transducers were verified utilizing samples having different amount of sigma phase. The configurations presenting the greatest possibility of evaluation of sigma phase were chosen for further experiments. In this paper a dedicated transducer operating in differential mode will be presented. The results will be shown and discussed.

Resumo: The molybdate–zinc conversion process was investigated by means of different techniques such as EIS, interfacial pH measurements, QCM and SECM. SEM and XPS complemented the electrochemical measurements. EIS results have shown different behaviour as function of the pH of the solution. Interfacial pH measurements have evidenced that the coatings were formed after about 200 s. The QCM measurements have exhibited three main characteristic regions and have shown that the formation kinetics was pH-dependent. The surface characterization has shown the presence of Mo5+ inside the coatings. The Mo and P amounts did not markedly change when the conversion time was increased.

Resumo: The corrosion resistance of the nickel-based alloy 718 in chloride environment depends on its microstructure and the influence of the different phases is still uncertain in the literature. In this study, the effect of heat treatments on the corrosion behaviour of alloy 718 in aerated 25% NaCl solution at room temperature was investigated, using chronoamperometric method applying 1.3 V anodic potential. The alloy was solubilized and aged in different conditions in order to obtain different grain sizes and δ phase volume fractions. The microstructure and the surface of the samples were characterized using scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The microstructure was also observed by transmission electron microscopy. This work showed that the presence of a passive Al-rich oxide film at the surface increases the pitting corrosion resistance of alloy 718 after aging heat treatment. This Al-rich oxide layer results from the dissolution of γ’ precipitates formed during aging.

Resumo: Interstitial free steels (IF steels) find wide application in the automotive industry, due to their excellent drawability. This work aims to study the microstructural and mechanical properties variations that might occur in an IF steel, when amounts of titanium, niobium and phosphorus are added to a specific alloy composition. The goal is to address how the insertion of such elements could provide excellent deep drawing applications without compromising the steel mechanical strength. Mechanical testing was performed in different samples to determine the steel anisotropy and compare those to the calculated crystallographic texture obtained by X-ray diffraction analysis. Scanning transmission electron microscopy (STEM) was also performed to correlate the properties achieved by the alloying elements to the microstructure of the steel rolled sheets.

Resumo: Serial numbers are marks present on several day-to-day objects, created by manufacturers for purposes such as quality control, product tracking and to prevent counterfeiting. In the case of firearms, these characters can be obliterated or damaged by natural processes or intentionally by criminals to prevent positive identification of stolen property. One non-destructive method employed by crime laboratories for the restoration of obliterated characters is the magnetic particle method. The present work aims to study the synthesis and application of waste-made magnetic nanoparticles in the recovery of adulterated markings. A set of analytical-grade materials and metallic waste magnetic nanoparticles were synthesized for comparison purposes. Chemical characterization tests by X-ray fluorescence, morphological tests by scanning electron microscopy (SEM), and magnetization tests by vibrating sample magnetometer (VSM) were performed. The efficacy of the synthesized nanoparticles was tested on 1020 steel plates previously engraved and adulterated by sanding. Both homemade magnetic nanoparticles demonstrated superior performance compared to commercial magnetic particles. The application of homemade magnetic particles, especially using waste as the source of production, decreases the cost of the material and is environmentally friendly. The development of this material makes magnetic serial number restoration a better option for widespread use in forensic procedures.

Resumo: Synchrotron X-ray imaging systems with fluorescence techniques was developed for biomedical researches in Brazilian Synchrotron Laboratory. An X-ray fluorescence microtomography system was implemented to analyse human prostate and breast samples and an X-ray microfluorescence system was implemented to study bone sites of human and animal samples with and without bone disorders.

Resumo: The adsorption dynamics of Imidazol (Imid) and Imidazolium (ImidH+) on copper was investigated by Surface-Enhanced Raman Scattering (SERS) as a function of the applied potential and pH. Although both species adsorb on metal surfaces the neutral molecule changes the orientation from tilted to perpendicular as the potential is made more negative. On the other hand, the cation remains parallel over the whole studied potential window. Imid is the major species on copper electrode, although ImidH+ can be identified even in alkaline solutions. Cyclic voltammetry and chronoamperometry measurements show good correlation with SERS data in terms of CuCl (CuCl2− as well) and Cu2O formation. Initially, a chemisorption mechanism is proposed at cathodic potentials, which changes to physisorption near the copper corrosion potential and finally a soluble complex is formed at more positive potentials. Such findings indicate that Imid is a good cathodic inhibitor, but its inhibition efficiency is very low at anodic potentials.

Resumo: In this paper the detection limit of lack of adhesive defects in GFRP adhesive composite joints was evaluated through a computational simulation model of active pulsed thermography technique. In this study, several simulations were carried out in order to evaluate the influence of the thickness of the collar, heating time and excitation energy on the detection limit of defects. In addition to these analyzes, it was also evaluated the reduction of the thermal contrast of the defects as a function of the thickness of the collar (depth of the defects) and thus it was possible to estimate mathematically the limit value of the thickness of the collar that allows the detection of the defects for each heating time. The results obtained showed that the pulsed thermography technique would be able to detect defects of lack of adhesive that are located up to 8.5 mm deep in this type of composite joint.

Resumo: The kinetics of oxygen reduction was studied on copper in tartarate solutions using a rotating disc electrode. The effect of pH on the cathodic reduction was examined. AC impedance and cathodic polarization curves showed that the reaction is partially controlled by mass transport. At high current densities, the limiting current values showed that O2 is reduced mainly through the four electron pathway. From measurements of density and viscosity and data taken from Levich and Tafel plots, diffusion coefficients for oxygen in tartarate medium were calculated. Peroxidase-mediated oxidation of methylene blue (MB) results using electrogenerated H2O2 on copper electrode showed that O2 reduction reaction occurs in two steps producing the adsorbed intermediate species H2O2 by k 2. In the absence of peroxidase, the hydrogen peroxide elimination has to be rapid with k 3≫k M. The MB oxidation by lignin peroxidase using electrogenerated H2O2 was studied. After 24h LiP is able to oxide the MB, producing different oxidized forms: azure C and thionine, with yield of 23% and 66%, respectively.

Resumo: The anticorrosive activity of furfural derivatives, by ex-situ and in-situ syntheses, on mild steel immersed in CO2-saturated formation water solution was evaluated using mass loss measurements, polarization curves, X-ray photoelectron spectroscopy, quantum chemical calculation, and electrochemical impedance. Furfural thiosemicarbazone presented inhibition efficiency reaching 90.2% for 72 h in immersion. The same molecule, synthesized in-situ by the mixture of the precursors in the corrosive medium, also produced good efficiency, 82.2% for 24 h of immersion, but it decreased over the time due to incomplete conversion of the precursors in furfural thiosemicarbazone.

Resumo: In the petrochemical industry, steam reforming furnaces play a crucial role in large-scale hydrogen production. These furnaces are equipped with centrifugal cast HP-modified austenitic stainless-steel tubes, which are exposed to temperatures ranging from 600 to 1000ºC for extended periods. As a result, the wall temperature profile of these tubes exhibits a vertical gradient of distinct aging states, labelled as state I to VI in the literature, each characterized by specific microstructures. Given that the reformer tubes are expensive components of the furnace assembly, it is imperative to monitor their service life. Non-destructive testing is a vital tool for evaluating the structural integrity of industrial components. Hence, the objective of this study is to establish a real-time classification system for determining the aging states of HP-modified stainless-steel tubes using a non-destructive magnetic system and the machine learning technique Support Vector Machine (SVM). Two tubes, each measuring 12.6 meters in length, were removed from the same steam reforming furnace after 160,000 hours of service. The inspection was conducted using an eddy current hybrid probe adapted to an inspection vehicle, allowing for real-time data acquisition. The results demonstrated that the developed classification system was capable of accurately identifying the different aging states present along the studied tubes.

Resumo: Reliability of non-destructive (NDT) procedures is usually assessed using probability of detection (POD). However, the reliability of the POD is rarely questioned. A POD usually produces a curve that relates the size of a defect to the likelihood that it will be detected by the NDT procedure. PODs are often used in conjunction with fracture mechanics that can relate the severity of a flaw to the service life of a component (Fitness for Service or FFS). To this end, it is the flaw vertical extent relative to the component thickness that is important. Closely related to the concern for flaw height is how close the flaw is relative to the surface of the component. Proximity to a surface can increase the stresses raised by the flaw and make it more critical to the fitness for service. Use of full matrix capture (FMC) techniques in ultrasonic testing, in conjunction with the postprocessing use of Total Focussing Method (TFM), has shown good potential to provide accurate flaw sizing. This paper examines the results of a round-robin trial using CIVA simulated data that were configured to assess flaw height and ligament in simulated welds. Results suggest that FMC with TFM post-processing can provide sizing estimates as good or better than manufacture estimates and can be used as the actual measured values for POD assessments.

Resumo: Slow Strain Rate Tests (SSRT) is a methodology to assess the influence of hydrogen in stress corrosion cracking. However, additional information correlating SSRT and hydrogen permeation might provide a better understanding of the influence of hydrogen on susceptibility to failure of materials. This paper presents a new methodology connecting SSRT with hydrogen permeation tests in the presence of hydrogen. The internal part of an SSRT specimen was used for hydrogen generation, whereas its external surface was used to detect hydrogen permeation during SSRT. The results showed a good correlation between the hydrogen permeation with parameters of SSRT.

Resumo: Computational simulations and reliability analysis were used to optimize an automated ultrasonic system used in pipe inspections in a manufacture plant in operation. Through the application of these tools the quality of the final product could be improved from more efficiency inspections. The main purpose was to establish the influence of each variable involved in the capacity of the ultrasonic system in detecting flaws. Tests were conducted considering a calibration API X65 steel pipe in which fitted reflectors were inserted artificially according to the DNV-OS-F101 standard. Experimental variables such as index, probe angle and gate position showed an important effect on the efficiency of the system and statistical analyses proved to be a powerful tool to validate the simulated and experimental results.

Resumo: In this study, we investigate artifacts arising from electric charges present in magnetic force microscopy images. Therefore, we use two austenitic steel samples with different microstructural conditions. Furthermore, we examine the influence of the surface preparation, like etching, in magnetic force images. Using Kelvin probe force microscopy we can quantify the charges present on the surface. Our results show that electrical charges give rise to a signature in the magnetic force microscopy, which is indistinguishable from a magnetic signal. Our results on two differently aged steel samples demonstrate that the magnetic force microscopy images need to be interpreted with care and must be corrected due to the influence of electrical charges present. We discuss three approaches, how to identify these artifacts – parallel acquisition of magnetic force and electric force images on the same position, sample surface preparation to decrease the presence of charges and inversion of the magnetic polarization in two succeeding measurement.

Resumo: Duplex stainless steel (DSS) presents a good combination of mechanical properties and high corrosion resistance. Its microstructure is composed of two phases with different physical properties: delta ferrite and gamma austenite. The best properties of DSS for in service applications are achieved when these phases are in equal proportions. However, exposition to high temperatures, may entail undesired consequences impairing the mechanical and corrosion properties of the material. Eddy current testing (ECT) has already been used for DSS inspection and microstructure characterization, mainly to detect the presence of deleterious phases, such as sigma. However, conventional ECT was not able to quantify different amounts of austenite and ferrite in the absence of deleterious phases. The present study focuses on the experimental and computational problem of DSS inspection using ECT in saturated magnetic conditions in order to identify different amounts of austenite and ferrite within the DSS microstructure. Samples containing ferrite to austenite ratio equal to 50/50, 70/30 and 80/20 respectively were brought to saturation as designed in the simulations and the ECT was applied presenting a very good result. Saturated low frequency ECT condition proved to be a reliable methodology in quantifying delta ferrite and gamma austenite phases in DSS.

Resumo: The use of anticorrosive coatings has been a powerful method to be applied on the surface of metallic materials to mitigate the corrosive process. In this study, the focus is composite coatings that are commonly used on the internal surface of storage tanks in petrochemical industries. The development of non-destructive methods for inspection of faults in this field is desired due to unhealthy access and mainly because undercoating corrosion is difficult to detect by visual inspection. Pulsed thermography (PT) was employed to detect undercoating corrosion and adhesion loss of anticorrosive composite coatings defects. Additionally, a computational simulation model was developed to complement the PT tests. According to the experimental results, PT was able to detect all types of defects evaluated. The results obtained by computational simulation were compared with experimental ones. Good correlation (similarity) was verified, regarding both the defect detection and thermal behavior, validating the developed model. Additionally, by reconstructing the thermal behavior according to the defect parameters evaluated in the study, it was estimated the limit of the remaining thickness of the defect for which it would be possible to obtain its detection using the pulsed modality.

Resumo: We developed a computer simulation model using finite elements for the reproduction of physical phenomena found in active pulsed thermography of GFRP adhesive tubular joints. During the manufacture of the joint, defects such as the lack of adhesive were included in order to evaluate the ability of the active pulsed thermography technique to detect this type of material and joint configuration. The experimental results obtained with the thermographic camera were compared with a numerical approximation obtained through the simulation model developed in this study using the Comsol Multiphysics® software and, because of their similarity; it was possible to validate the computer simulation model. In both methods assessed in this study, it was only possible to detect the lack of adhesive when the thermographic test was performed from inside the joint, as, on the outer side of the joint, the defects' surfaces are at a depth greater than on the inner side.

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Resumo: The petrochemical industry heavily relies on steam reforming furnaces for large-scale hydrogen production. Centrifugally cast HP stainless-steel tubes constitute the majority of components in these furnaces, enduring temperatures ranging from 600 to 1000 ºC for extended periods. These tubes manifest distinct aging states, characterized by specific microstructural markers linked to the exposed wall temperature. Given their significant cost and importance, monitoring the service life of these tubes is crucial. The current aging state is particularly relevant due to the correlation between creep damage and advanced aging stages. Hence, this study aims to assist in assessing the remaining life of HP stainless-steel tubes by employing a portable Eddy Current Testing (ECT) inspection system, coupled with real-time Support Vector Machine (SVM) classification of aging states. Two 12.6-meter-long tubes, aged for 160,000 hours, underwent inspection using the portable ECT inspection system to evaluate the progression of aging states along their height, considering the expected vertical temperature gradient. Results underscore the efficacy of the SVM classification in identifying the various aging states present along the studied tubes, highlighting promising in situ applications.

Resumo: Glass Fiber Reinforced Polymers (GFRP) laminated joints combine properties such as high mechanical resistance, low specific weight and high corrosion resistance, features that allow their application in harsh environments. The structural integrity of these components must be ensured; therefore, their inspection through non-destructive methods capable of certifying such integrity is necessary. This work evaluates the phased array inspection of GFRP laminated joints, in order to detect defects frequently found in this material. For the development of the study, artificial flaws representing interply delamination were inserted in the material. The experiments were conducted with a 32 elements matrix probe (500 kHz frequency). Two focal laws were applied aiming the detection of the existing defects. Results indicated that the proposed methodology is adequate for the detection of the flaws, highlighting the performance of focal laws with focal spots in the back wall of the joint.

Resumo: Surface enhanced raman scattering (SERS) spectra of 4‐methylimidazole (4‐MeImid) are shown for the first time on a copper electrode and in the presence of chloride. The potential dependence on the spectra reveals that the N1H tautomer is majority close to the open circuit, but the N3H tautomer predominates at more cathodic polarizations. At these latter conditions, 4‐MeImid orientation changes from tilted to perpendicular, and such a behavior is similar to the one of Imid at natural pH. Interesting issues are observed at pH = 2.0: (a) 4‐MeImidH+ is not identified on the metal surface for the whole applied potential range and must be either adsorbed as an ion pair with chloride or in the bulk solution; (b) at open circuit and anodic polarization, its neutral form is the unique azole species present, in contrast to the ImidH+ behavior, which is easily observed in the surface spectra. SERS spectra of 4‐methylimidazole (1) and its cation (2), on a copper electrode, are presented for the first time in the literature as well as the classic equilibrium involving the neutral tautomers, which has been only observed in solution. The data support electrochemical results reported by other authors about the better copper corrosion inhibition efficiency of (1) as compared with imidazole at acidic media.

Resumo: Most non-destructive techniques can be well represented in a virtual environment, in particular, eddy current testing (ECT) simulation is a useful and well-established tool to predict and represent real inspection situations permitting testing customization in a fast, cheap and efficient way. Conventional ECT generally works with low-intensity magnetic fields, however, for advanced variations of the technique, where external DC magnetic fields can be applied to locally decrease the magnetic permeability, there is no Finite Element Method (FEM) packages available to deal with such nonstandard model. Many authors [1] and [2] have presented this ECT solution for different industrial applications using external DC magnetization to carry nonlinear ferromagnetic materials to the saturation level of the magnetization curve to increase the ECT depth penetration. In general, ECT modelling calculation is benefited by properties of steady-state regime where all magnetic fields are oscillating at the same frequency not permitting through multi-frequency calculation. The present work proposes a simulation solution for such a case where DC magnetic field is associated with ECT. A theoretical model is presented together with experimental results validation.

Resumo: This paper presents a numerical analysis of the chemical-electrochemical (CE) mechanism of a rotating disk electrode at steady-state. Two sets of kinetic constants (denominated "fast kinetics" and "slow kinetics") were used to evaluate how they alter the original concentration profiles and the current response. Comparing the results obtained with those in the literature allows concluding that the range of validity of the reaction layer hypothesis, although able to accurately predict the current density in some cases, is intrinsically limited, because it will always fail for sufficiently high rotation speeds. Hence, a system with "fast kinetics" is merely one in which the hypothesis is applicable for all the rotation speeds that were studied. It was also observed that the range of validity of the reaction layer hypothesis is independent of the equilibrium constant of the chemical process and is determined solely by the absolute values of the kinetic constants.

Resumo: This paper presents a numerical analysis of the effect of different parameters (rotation speed, equilibrium constant and Schmidt numbers) on the diffusion (ZD) and electro-hydrodynamic (ZEHD) impedances of chemical-electrochemical (CE) systems in a rotating disk electrode (RDE) configuration. For this purpose, we used a finite difference algorithm to discretize and solve the governing equations. Our results show that the separation between convection-diffusion and reaction impedance loops depends on the ratio between diffusion layer thickness ( ) and reaction layer thickness ( ). Also, we have demonstrated that the characteristic frequency of the reaction impedance loop is a function of As for ZEHD data, we found that, for slow kinetics, the plots do not overlap for different rotation speeds. Further, the upper limit of the negative phase is different for both, slow and fast kinetics, from the usual 180° value found for single charge transfer systems. The increment of the equilibrium constant, obtained via increasing the reaction rate constant of the electroactive species, caused the magnitude ZD to decrease and that of ZEHD to increase. Lastly, we found that changing ScA mainly affects the concentration gradient at the surface while the effect of ScB will depend on the kinetic regime.

Resumo: We have built a scanning dc-susceptometer for magnetic characterization of millimeter-scale samples. Using samples with few millimeter-thick slabs, the setup used is able to apply perpendicularly to the sample uniform dc magnetic fields up to 500 mT. It has a scanning range of 100 mm × 100 mm with micrometer resolution. In the present configuration, the dc-susceptometer is equipped with a pair of commercial Hall effect sensors forming an axial gradiometer. The measured output noise at 6.0 Hz is about 1.0 µTrms/√Hz in an unshielded environment and the magnetic moment sensitivity is 8.8 × 10−11 Am2. In particular, we used it to characterize heat-resistant steels, used as radiant tubes in steam reformer furnaces. We measured the cross-section of tube samples with progressing states of aging from as-cast to state VI. Measuring their susceptibilities, we detected a ferromagnetic layer at the external tube wall on aged samples. We were able to establish a relation between the magnetic response and the microstructural change of the steel.

Resumo: This paper describes the development of an original eddy current method for the characterization and classification of different aging states of heat resistant austenitic steel tubes, commonly used in petrochemical industry to produce oil derivatives. These tubes are exposed to high temperatures causing microstructural transformations. They are also under oxidizing environments leading on the formation of an external surface with ferromagnetic behavior. An eddy current testing (with a Hall sensor) was used in order to observe magnetic changes in the specimen. The amplitude and phase-shift of the eddy current signals are calculated and used as features for the samples characterization. An electromagnet was implemented in order to overpass the ferromagnetic external surface and measure the base metal response. A finite element simulation was also developed in order to estimate the skin depth of the eddy currents in samples with different aging states. A machine learning algorithm has been used to classify the test specimen based on the extracted features. Results suggest that the proposed method is a potential non-destructive technique for the characterization and classification of heat-resistant austenitic steel tubes with different aging states.

Resumo: The objective of the present study is to apply digital radiography (DR) and computed microtomography (microCT) techniques to the inspection of laminated pipe Joints in polymeric composite material reinforced by fiberglass. The study comprises a structural assessment, defect characterization and void distribution of each sample. Non-destructive X-ray testing is increasingly present in composite material analyses and has advantages over other laboratory techniques since it is non-invasive and allows for the 2D/3D visualization of the inner structures without previous preparation. The results showed that the techniques detected the defects inserted. The digital radiography made an extension defect measurement possible. The microCT volumetrically quantified these defects as well as the reinforcement and matrix layers.

Resumo: CO2 corrosion is an important process affecting oil and gas industries. Understanding the role of CO2 in the mechanism of carbon steel dissolution may contribute to better predict corrosion rate. Impedance, local pH and weight loss tests were measured using X65 carbon steel at pH 4 in the presence and absence of CO2, including high CO2 pressure experimental conditions. The results did not evidence a direct reaction of CO2 on the free iron surface.

Resumo: Different types of montmorilonites (MMTs) were studied for a survey of properties which may contribute for corrosion control, while they are employed as pigments in corrosion protective organic coatings. Experimental methodology involves epoxy novolac paints specially formulated with iron oxide plus 1 or 5 wt.% MMTs, long term corrosion tests, gravimetric tests, titrations of MMTs filtrates and suspensions. The emphasis in literature is that MMTs improve barrier properties. Nevertheless, results revealed that MMTs are not inert pigments. They have two important properties hardly considered: active corrosion inhibition and control of H+ permeation which depend on MMTs affinity by water.

Resumo: Hydrogen bonding between pyridazine (PRD) and formamide (FA) molecules has been investigated both experimentally by Raman spectroscopy on their binary mixtures and theoretically by DFT calculations on various gas-phase PRD:FA clusters. The band at 1160 cm−1 of PRD was used for the first time as a marker for monitoring the degree of complexation. Upon dilution with FA, a new band at 1169 cm−1 is observed and attributed to hydrogen-bonded PRD. The Raman experiments were complemented by DFT calculations and the corresponding structures, vibrational spectra and binding energies were determined. The most stable species were found to be the 1:2 PRD:FA complexes and such stoichiometry is in excellent agreement with the experimental determination. The shift to higher frequency observed to the prominent modes of PRD may be related to a shortening of the NC and CC bonds, upon complexation, which causes a decrease in the electron delocalization in PRD ring.

Resumo: Hydrogen evolution reaction (HER), occurring on platinum rotating disc electrode (RDE) in aqueous solutions containing dissolved CO2 in different pressures was investigated. This system was modeled by taking into account the two dissociation reactions of CO2 and using a numeric finite difference method (FDM). Moreover, in the high potential range where the current plateau starts to increase, a new reaction (water reduction) was proposed. A satisfactory agreement between the experimental data and the model was obtained. The model-building article did not take into account any additional cathodic reactions attributed to CO2.

Resumo: A previous work has shown that a modified HP-NbTi heat-resistant stainless steel exhibited a different magnetic behavior after 90,000 hours of operation in a steam reformer furnace exposed to temperatures between 500 °C and 550 °C or between 950 °C and 1000 °C. In this work, in the sample exposed to the lower temperature range, a thin ferromagnetic layer was detected by magnetic force microscopy in the matrix around the chromium and niobium carbides. However, for the sample exposed to the higher temperature range, no ferromagnetic response was detected whatsoever. The understanding of the influence of microstructure on magnetic behavior is important for the development of non-destructive inspection test methodologies. For this reason, the aim of this study is to perform a microstructural analysis to assess the different magnetic responses. Transmission electron microscopy allowed identifying a Cr-depleted zone in austenite at the Cr23C6-matrix and (NbTi)C-matrix interfaces in the sample exposed to the lower temperature range. Therefore, the austenitic region, with a lower Cr content, becomes ferromagnetic. In the sample exposed to the higher temperature range, the chemical composition of the austenitic matrix was homogenous, and the sample was completely paramagnetic.

Resumo: Duplex stainless steels are high strength and corrosion resistant alloys extensively used in chemical and petrochemical industries. However, exposition to temperatures in the range 300–1000 °C leads to precipitation of different phases having a detrimental effect on the mechanical properties and on the corrosion resistance of the alloy. In this work, the microstructural evolution during aging of a UNS S32304 lean duplex stainless steel was investigated by scanning electron microscopy, transmission electron microscopy and magnetic force microscopy. Formation of secondary austenite as well as Cr2N and Cr23C6 precipitation and, consequently, a decrease of ferrite volume fraction were observed. EDX analysis indicated that secondary austenite is depleted in chromium which is detrimental to the corrosion resistance of the alloy. A variation of magnetic properties and Eddy current measurement parameters during aging was simultaneously detected and can be explained by the decrease of ferrite volume content. Therefore, Eddy current non-destructive testing can be successfully applied to detect the formation of deleterious phases during aging.

Resumo: The demand for high strength materials with improved corrosion resistance boosted the development of supermartensitic steels from conventional martensitic stainless steels The first alloys were designed with 11-13%Cr, extra-low carbon and nickel addition. More recently, experimental alloys with higher Cr (15-17%) and other ferritizing elements (Mo, W, Nb,…) were developed with the aim of obtain higher corrosion resistance in high chloride environments. In this work, the microstructure features of a new 17%Cr stainless steel were investigated.

Resumo: Composite materials are created by combining different substances, each contributing specific properties that enhance the material's overall performance. Given the diversity of composite types, a range of Non-Destructive Testing (NDT) techniques has been developed for their inspection, each offering unique benefits. Among these, Computed Microtomography (micro-CT) emerges as a particularly powerful method for volumetric analysis, providing highly detailed three-dimensional (3D) imaging of internal structures. This study aims to develop a methodology for analyzing the joints of polymer composite tubes. To achieve this, the volumes of the matrix, reinforcement, and any defects within the selected samples were meticulously evaluated. The findings reveal that the micro-CT technique, when integrated with advanced image processing tools, is highly effective for detecting, locating, and quantifying defects.

Resumo: Heat-resistant austenitic stainless steels have become the principal alloys for use in steam reformer tubes in the petrochemical industry due to its mechanical properties. These tubes are typically exposed to severe operational conditions leading to microstructural transformations such as the aging phenomenon. The combination of high temperatures and moderate stresses causes creep damages, being necessary to monitor its structural condition by non-destructive techniques. The tube external wall is also subjected to oxidizing atmospheres, favoring the formation of an external surface, composed by an oxide scale and a chromium depleted zone. This external surface is usually not taken into account in the tube evaluation, which can lead to erroneous estimations of the service life of these components. In order to observe the magnetic influence of this layer, two samples, exposed to different operational temperatures, were characterized by non-destructive eddy current testing (ECT), scanning DC-susceptometer and magnetic force microscopy (MFM). It was found that the external surface thickness influences directly in the magnetic response of the samples.

Resumo: The development of techniques to detect deleterious phases in duplex and super duplex stainless steel has a great technical-scientific appeal. However, establishing a quality control of these steels using a unique technique of inspection requires an attentive analysis about its limits and sensibility of detections. Thus, the current work compares magnetic techniques based on eddy current methods and electrochemical potentiokinetic reactivation with double loop to detect deleterious phases in duplex stainless steel. The limitations and advantages of each technique are discussed mainly concerning the viability to detect sigma phase and chromium nitride.

Resumo: Pipelines for fuel transportation range in length from hundreds to thousands of kilometers, with part of their length underground. Due to the high cost of the fluids and products transported an increasing number of criminal activities are taking place all over the world. In addition to causing great economic and environmental losses the illegal activity brings risks to the surrounding population. For example, the accident in Tlahuelilpan, Mexico, due to illegal tapping, resulted in the tragedy of hundreds of deaths. In order to combat such activities, many efforts have been employed to early detect and locate illegal tapping in pipelines. The great challenge of such inspections is the unpredictable activity of the clandestine taps, requiring frequent inspections. Usual pipeline inspection tools, such as ultrasound or MFL (Magnetic Flux Leakage) PIG’s, are sensitive for detecting and positioning the anomalies, however, the high operating costs make the recurring application of such tools unfeasible. Focusing on these challenges, a low-cost inspection tool embedded with a minimalist eddy current instrumentation was developed. The results achieved show the capability to detect and differentiate the components existing in the pipeline and illegal taps of different diameters as well as, in a complementary way, the detection of corrosion on the internal surface of the pipelines.

Resumo: Aiming to reducing the gas emissions in the steel mill, in the present study the kinetic behavior of self-reducing pellets containing elephant grass coal and iron ore was investigated through kinetic isotherms for different temperatures. The pellets were isothermally treated in different time intervals for X-Ray diffraction and SEM analyzes. The results obtained by XRD showed that the higher mass of iron in the sample was achieved until the first 24 min. The SEM analysis allowed visualizing the presence of a metallic porous structure closer to edge and whiskers in the center of sample.

Resumo: The objective is to study the influence of Mg–Al layered double hydroxides (LDHs) reconstruction processes on inhibitor release kinetics and anion exchange properties, emphasizing the importance of the knowledge of these physicochemical properties to manage and optimize intelligent corrosion protective action. LDHs were prepared using two reconstruction methods after hydrotalcite (HT) calcination: i) reconstruction in terephthalic acid (HTCTe), followed by substitution of terephthalate by imidazole (HTCTe-Im) and ii) direct reconstruction in imidazole solution (HTC-Im). Imidazole (Im) is a film-forming corrosion inhibitor that was selected due to its molecule features. XRD showed that terephthalate and Im did not influence network parameters of reconstructed LDHs, but HTC-Im presented better crystallinity. Such difference strongly influence the kinetics of Im release and anion exchange process of the two LDHs. Similar corrosion inhibition efficiencies were measured for both particles by weight loss. However, localized corrosion was evidenced for HTC-Im. It was notable the synergistic effect of HTC-Im and HTCTe-Im mixtures due to the large amount of imidazole released by HTCTe-Im and removal of chloride from solution by HTC-Im. Results also suggested an active role of LDH itself on corrosion inhibition, attributed to pH and solubilization of structural components other than Im.

Resumo: This article undertakes a critical evaluation of the literature regarding the use of the Langmuir isotherm, specifically in the context of inhibitor research. The Langmuir isotherm is frequently employed to derive thermodynamic and kinetic parameters, which are then used to gauge inhibitor performance. However, the validity of the Langmuir isotherm has been challenged, particularly by Walczak et al. (2019), whose work has served as a basis for others to reject its use as inadequate. Imposing limitations on the Langmuir isotherm would involve restrictions on heterogeneous kinetics, impedance interpretation, and other transient techniques. These aspects will be subjected to a more in-depth analysis in this discussion paper.

Resumo: This paper presents experimental and theoretical results concerning the corrosion inhibitor effect of imidazole and five of its derivatives on iron surface. Gravimetric methods and polarization curves were the experimental techniques used in this study. The polarization curves showed that the inhibitors have an anodic role on the electrochemical process. Weight-loss measurements indicated that the adsorption process obeys Langmuir's isotherm. The theoretical study was done using ab initio calculations for the organic molecules and complexes formed between imidazoles and a Fe atom, a Fe2+ ion, and a Fe3+ ion. Correlations between structural properties of the compounds and their experimental inhibitor efficiencies were analyzed. A satisfactory correlation between quantum-mechanical parameters and inhibition efficiency was found.

Resumo: In this study, cellular spacing, porosity and corrosion of 1050 aluminum alloy subjected to the different levels of Gamma radiation was examined using a Gammacell Co-60 type irradiator, with activity of 16.13 TBq and dose rate around 6.98 Gy/min. Samples were extracted from an aluminum ingot, which was obtained with directional solidification apparatus. This upward directional solidification technique allowed obtaining of aluminum samples under different conditions of cooling rates. Firstly, cooling rates were determined during solidification experiment and then correlated to the cellular spacings and porosity content. The experimental results pointed out that cooling rates exerts a strong effect on the microstructural patterns and porosity formation. Laws have been determined, indicating that increase in cooling rates favored a refinement effect on as-cast microstructure and a decrease in porosity content. Furthermore, measurable effects of different levels of the Gamma radiation on the microstructure, porosity and corrosion for samples of 1050 aluminum alloy, were determined. The experimental results show that Gamma radiation has favored changes in cellular spacings, porosity formation and corrosion behavior. From this results, one can conclude that coarser microstructures, porosity formation and corrosion are favored by prolonged thermal annealing caused by temperature field generated during Gamma radiation exposure. On the other hand, even after the exposure to different levels of Gamma radiation, the microstructure and porosity observed in as-cast samples are still strongly dependent of the cooling conditions.

Resumo: Surface cleaning tools made of copper alloys are widely employed when sparks have to be avoided. On the other hand, copper residues may be left on the surface. It is not known whether such copper incrustation interferes with the performance of a painting system. Therefore, the aim of this paper is to evaluate the effect of steel surface treatment with copper-containing tools on the performance of a painting system. Painted samples pretreated with ferrous and copper-containing tools were submitted to corrosion tests. The performance was monitored by visual inspection and electrochemical impedance. The surfaces of unpainted samples were analyzed by energy dispersion spectroscopy (EDS) and the open circuit potentials were measured. It is shown that the residues left on the metallic surface due to the mechanical action of the cleaning tools did not interfere significantly with the performance of the painting system.

Resumo: Metastable β-Ti alloys have become one of the most attractive implant materials due to their high biocorrosion resistance, biocompatibility, and mechanical properties, including lower Young’s modulus values. Mechanical properties of these alloys are strongly dependent on the final microstructure, which is controlled by thermomechanical treatment processing, in particular the Young’s modulus and hardness. The aim of this work was to analyze the influence of phase precipitations in heat-treated Ti-12Mo-xNb (x = 0, 3, 8, 13, 17, and 20) alloys. The alloys were prepared via arc melting and treated at 950 °C/1 h, and then quenched in water. The microstructures were analyzed by optical microscopy, transmission electron microscopy, and X-ray diffraction. Mechanical properties were based on Vickers microhardness tests and Young’s modulus measurements. Microstructural characterization showed that α″ and ω stability is a function of Nb content for the Ti–12Mo base alloy. Nb addition resulted in the suppression of the α″ phase and decrease in the ω phase volume fraction. Although the ω phase decreased with higher Nb contents, ω particles with ellipsoidal morphology were still observed in the Ti–12Mo–20Nb alloy. The α″ phase suppression by Nb addition caused a marked increase in the Young’s modulus, which decreased back to lower values with higher Nb concentrations. On other hand, the decrease in the ω phase continuously reduced alloy hardness. The study of the effect of chemical composition in controlling the volume fraction of these phases is an important step for the development of β-Ti alloys with functional properties.

Resumo: This work focuses the effect of secondary austenite (γ2) on corrosion resistance of welded joints. The welded joints were obtained by pulsed gas metal arc welding (GMAW-P) with three different heat inputs. Each joint and their respective sub-regions through thickness were characterised by optical microscopy and scanning electron microscopy. The results were correlated with double loop electrochemical potentiodynamic reactivation (DL-EPR) and sulphide stress corrosion tests. The results suggest a good agreement between the DL-EPR and the four point bending tests. It was also verified that the simple presence of γ2 does not necessarily gives rise to loss of corrosion resistance.

Resumo: Fracture mechanics concepts applied to tests in aggressive environments are a challenge for integrity analysis. Specifically about hydrogen, the concentration of this element in defects or in trapping sites can cause unexpected failure. The present paper presents results showing the influence of hydrogen in the reduction of fracture toughness and a discussion about how to deal with it in high strength alloys. The results show that the hydrogen reduces the plasticity and consequently the applications of CTOD concepts are questionable for the studied materials.

Resumo: The influence of heat treatments on microstructure and magnetic domains in duplex stainless steel S31803 is studied using an innovative structural characterization protocol. Electron backscatter diffraction (EBSD) maps as well as magnetic force microscopy (MFM) images acquired on the same region of the sample, before and after heat treatment, are compared. The influence of heat treatments on the phase volumetric fractions is studied, and several structural modifications after heat treatment are highlighted. Three different mechanisms for the decomposition of ferrite into sigma phase and secondary austenite are observed during annealing at 800 °C. MFM analysis reveals that a variety of magnetic domain patterns can exist in one ferrite grain.

Resumo: Eddy current transducer with sensing coils placed orthogonally and connected in differential mode was introduced to evaluate fatigue cracks in clad pipeline circumferential welds. A dedicated embedded electronic hardware was developed to drive the transducer and measure the electrical complex impedance of the coils, and was specifically designed for operation under autonomous in-line inspection tool. In the laboratory experiments, an automated inspection was performed with the goal to evaluate transducer’s detectability, and different scanning speed was tested to reproduce in service situation. The results have confirmed that the introduced eddy current transducer is a potential solution for fatigue crack detection in clad circumferential weld root, while the hardware developed presented a reasonable SNR reaching the data rate required to be incorporated in an autonomous in-line inspection tool.

Resumo: An X-ray transmission microtomography (CT) system combined with an X-ray fluorescence microtomography (XRFCT) system was implemented in the Brazilian Synchrotron Light Laboratory (LNLS), Campinas, Brazil. The main of this work is to determine the elemental distribution map in reference samples and breast tissue samples in order to verify the concentration of some elements correlated with characteristics and pathology of each tissue observed by the transmission CT. The experiments were performed at the X-Ray Fluorescence beamline (D09B-XRF) of the Brazilian Synchrotron Light Laboratory, Campinas, Brazil. A quasi-monochromatic beam produced by a multilayer monochromator was used as an incident beam. The sample was placed on a high precision goniometer and translation stages that allow rotating as well as translating it perpendicularly to the beam. The fluorescence photons were collected with an energy dispersive HPGe detector placed at 90deg to the incident beam, while transmitted photons were detected with a fast Na(Tl) scintillation counter placed behind the sample on the beam direction. The CT images were reconstructed using a filtered-back projection algorithm and the XRFCT were reconstructed using a filtered-back projection algorithm with absorption corrections.

Resumo: Species of the genus Brachycephalus, have a snout-vent length of less than 18 mm and are believed to have evolved through miniaturization. Brachycephalus ephippium, is particularly interesting; because its entire skull is hyperossified, and the presacral vertebrae and transverse processes are covered by a dorsal shield. We demonstrate in this paper that, at the macroscopic level, a completely hyperossified skull and dorsal shield occur only in B. ephippium, but not in B. ferruginus, B. izechsohni, B. pernix, B. pombali, B. brunneus, B. didactylus, and B. hermogenesi. An intermediate condition, in which the skull is hyperossified but a dorsal shield is absent, occurs in B. vertebralis, B. nodoterga, B. pitanga, and B. alipioi. The microscopic structure of hyperossification was examined in skulls of B. ephippium and B. pitanga, revealing a complex organization involving the presence of Sharpey fibers, which in humans are characteristic of periodontal connections.

Resumo: The hydrogen evolution reaction (HER) in H2S and H2S/CO2 solutions at different pressures was studied using platinum and stainless steel as working electrodes, with polarization curves and electrohydrodynamic impedance. When Pt was the working electrode, the polarization curves in H2S solutions without CO2 presentedonly one current plateau, while two plateaus were seen when a mixture of H2S/CO2 was used. However, when steel was the working electrode, two plateaus always existed even in the presence of H2S without CO2. HER was interpreted by another source of H2 coming from the H2S reaction coupled to the classical direct reduction of H+.

Resumo: The super duplex stainless steels have a microstructure composed by two phases, ferrite (α) and austenite (γ). This dual microstructure improves simultaneously the mechanical and corrosion resistance properties. However, the welding of these steels is often a critical operation. The present work evaluated the fracture toughness through critical tip open displacement (CTOD) tests of welded joints, with two different heat input, 1.1 kJ mm−1 and 2.0 kJ mm−1. The steel used was a super duplex stainless steel (UNS S32750) in presence of hydrogen. The CTOD tests (according BS 7448-1 and BS 7448-2 standards) were performed in air and under different times of hydrogenation. The procedure of hydrogenation has been performed using cathodic potential of −1400 mVSCE by 96 and 360 h. The microstructural analysis allowed to determine relevant aspects (α/γ balance, inter austenitic spacing and γ morphology) and to compare with CTOD results. The results showed strong evidence that the reductions of CTOD values is related to differences in the γ2 morphologies. Another important result was the high statistic dispersion in the measures of austenitic spacing, according DNV RP F112-08, which implies in low reliability of using this standard in presence of high anisotropy. The paper also aims to discuss and evaluate which is the best approach to hydrogenated duplex stainless steels: linear elastic fracture mechanics or elasto plastic fracture mechanics.

Resumo: This paper addresses the hydrogen evolution reaction (HER) occurring on platinum in an aqueous solution containing dissolved CO2 at several pressures. A new setup that uses a low inertia rotating disk electrode (RDE) adapted in an autoclave is proposed. This setup allows obtaining polarizations curves and electro-hydrodynamic (EHD) impedance, the latter for the first time in pressured conditions. New equations to adjust the Levich plots are proposed and briefly discussed.

Resumo: The resistance of dissimilar joints to hydrogen was assessed using fracture toughness in an aggressive environment and slow strain rate tests. Six weld joint conditions were evaluated. To determine the distribution of microconstituents and elements along the interfaces, techniques such as optical and scanning electron microscopy, tomography, and nano hardness were employed. The results demonstrated that the susceptibility to hydrogen embrittlement is directly linked to the fraction of discontinuous regions present along the dissimilar interface. Additionally, a critical evaluation of the methodology concerning the positioning of stress concentration at the dissimilar interface was carried out, and alternative approaches were presented.

Resumo: A new meta-heuristics is introduced here: the Multi-Particle Collision Algorithm (M-PCA). The M-PCA is based on the implementation of a function optimization algorithm driven for a collision process of multiple particles. A parallel version for the M-PCA is also described. The complexity for PCA, M-PCA, and a parallel implementation for the MPCA is developed. The efficiency for optimization for PCA and M-PCA is evaluated for some test functions. The performance of the parallel implementation of the M-PCA is also presented. The results with M-PCA produced better optimized solutions for all test functions analyzed.

Resumo: A mathematical model for electrohydrodymanic impedance was developed in which hydrodynamic and convective diffusion equations were coupled by a relationship between viscosity and concentration. This procedure allows better understanding the physical problem separating the mass transport and the hydrodynamic effects and the model fit to previously reported experimental results revealed a larger viscosity gradient than previously inferred. These results are consistent with the hypothesized formation of a colloidal suspension of ferrous sulfate particles.

Resumo: The new extreme faces strain gauges (XFS) technique, when compared to the direct current potential drop (DCPD) and back face strain gauge (BFS) methods, has shown superior accuracy and reliability in studying corrosion fatigue in high pressure. The XFS method serves a dual purpose by accurately measuring the crack length and acting as a mechanical load transducer. The results indicate that all three techniques can predict the final crack length effectively. However, BFS is unsuitable for high-pressure environments, and the current DCPD method can affect the crack propagation rate. The developed XFS methodology shows excellent performance in accurately evaluating corrosion fatigue studies.

Resumo: Superduplex stainless steel is a widely used material in many industrial areas, due to its significant properties in terms of mechanical and corrosion resistance. In order to guarantee the quality of these steels, the ferrite evaluation is an important analysis since many properties depend on the control of the ferrite content. During equipment manufacturing or field inspections, the most conventional way to evaluate the ferrite content is through ferritoscope measurements, due to its portability and easy interpretation. However, it has been observed that the calibration pattern used for ferritoscope calibration can lead to inaccurate ferrite quantification in superduplex inspection. In order to analyze this influence, different characterization techniques were performed in superduplex samples, such as optical microscopy, X-ray diffraction, and vibrating sample magnetometer, to compare with the measurements obtained by a ferritoscope. It was concluded that for high ferrite values, with the calibration made from the calibration pattern provided by the ferritoscope manufacturers, the ferrite values measured showed significant deviations from the real values. The current work presents a solution for using the ferritoscope for a more accurate quantification of the ferrite content in superduplex stainless steels. © 2018 Brazilian Metallurgical, Materials and Mining Association.

Resumo: This paper presents a failure analysis of a CFRP mast of a racing sailboat that collapsed on duty and an evaluation of NDT techniques, for failure assessment in composite materials. Visual inspection, pulsed thermography, radiography, and computed tomography tests were performed to obtain information about the locations, types, and orientations of the damage. Based on these results, four samples were taken and analyzed in an SEM, revealing information about the propagation directions of the defects and the predominance of mode II fracture. The weak interface between the composite layers, manufacturing defects, and the stress concentration effect due to the abrupt geometry transition, possibly caused the failure. The severe damage made it difficult to reach a clear conclusion about the cause of the failure and its origin. However, the inspection and characterization techniques applied made it possible to identify defects and potential causes that led to or contributed to the failure.

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Resumo: This paper is dedicated to the establishment of experimental conditions for practical use of Double Loop Electrochemical Potentiodynamic Reactivation method (DL-EPR) to characterize the degree of sensitization in AISI 304 austenitic stainless steel based in the standard ISO 12732. The steel undergoes heat treatments to solubilize the commercial material and later controlling its sensitization degree. Microstructure of the samples with quantification of the sensitization was obtained according to ASTM E1245. The standards ASTM A262 and ASTM G48 were used, respectively, to rank the sensitization and the susceptibility to pitting corrosion of the different samples. Solutions of sulfuric acid 0.5 mol.dm−3 with three contents of KSCN (0.001, 0.01, 0.05 mol.dm−3) and three different potential scan rates (0.56, 1.67 and 4.2 mV.s−1) were used for DL-EPR measurements. Results illustrate the high dependence of Ir/Ia on KSCN concentration and scan rate, even respecting the standard limits. Therefore, table presented by ISO 12732 addressing Ir/Ia to sensitization degree can be misleading as it is not linked with specific experimental conditions. On the other hand, DL-EPR can be direct related to sensitization when reference materials are used. For that, heat treated steel must be used to obtain DL-EPR curves considering electrolyte composition and potential scan rate. These results are the base to establish a reference curve of Ir/Ia versus the sensitization degree. This curve can be used later to detect sensitization of the same kind of steel in-service with Ir/Ia values measured in-situ. The diagnosis of susceptibility to localized corrosion obtained by various standard procedures is critically evaluated.

Resumo: The present work estimated the accuracy of non-destructive tests in quantifying the delaminated area in CFRP samples submitted to a 4-point end notched flexure test, to evaluate the relevance of measuring the delamination area to calculate fracture toughness in mode II, instead of of the traditional method which evaluates the delamination length visually through the sample lateral faces. In this way, IR thermography, eddy current, ultrasonic microscopy, and X-ray computed microtomography (as reference) tests were employed. A methodological sequence based on image processing algorithms was performed to calculate the values of the delaminated areas for all NDT techniques. The first two techniques did not provide a clear separation between the defective and intact zones and are strongly influenced by edge effects. The result is different for the two last tests, which demonstrated a satisfactory definition of the delamination limit region. The ultrasonic microscopy test revealed results similar to microtomography, proving to be a promising alternative for this type of measurement. In addition, the importance of using more accurate methods in calculating the crack length is emphasized, as the traditional visual measurement can be highly susceptible to errors and does not allow evaluating potential tunneling effects or an uneven delamination front.

Resumo: This paper presents the evaluation of hydrogen degradation in AISI 4340 steel based on the multispectral analysis of magnetic Barkhausen noise. Previous studies using acoustic and magnetic response of the Barkhausen effect have shown a large change in the course of the phenomenon as a result of the progression of hydrogen destruction of steel, and the applied time-frequency analysis has been limited to aggregated data in a few frequency bands. Thus, due to the complex nature of changes in the Barkhausen noise course, this study uses the analysis of the multi-domain representation of the measured signals, enabling a broad characterization of various aspect of obtained signal distributions by multiple feature assessment.

Resumo: Unloading compliance technique in fracture toughness tests according to ASTM E1820 standard is used to obtain the resistance curve (R-curve) of metallic materials in air tests. Even in this situation, there are aspects inherent to work hardening around the crack-tip that could affect the unloading compliance technique and that are not well discussed. Another important aspect is the application of this methodology in conditions involving corrosive environments. Indeed, the presence of hydrogen around the crack-tip can promote significant changes in the strain and stress around the process zone, leading to the phenomenon called subcritical crack growth. This phenomenon can affect the compliance increasing the divergence between the crack sizes obtained by the unloading compliance technique and the correct crack sizes measured after the test. The aim of this paper is to analyse the influence of subcritical crack growth and to present a methodology to correct crack sizes and the influence of work hardening during fracture.

Resumo: Flow accelerated corrosion (FAC) is a steel degradation that occurs in heat recovery steam generators in the power industry. The mechanism of this corrosion comprises an electrochemical dissolution of the semi-protective magnetite layer (Fe3O4) that is formed within the pipes employed in the boilers. The FAC is influenced by different factors such as fluid velocity, pH and dissolved oxygen concentration. In this context, Rotating Cage tests were used to evaluate the influence of pH and dissolved oxygen content on FAC of A210, P11 and P22 steels. General corrosion was lower for P11 and P22 steels, an effect consistent with the presence of chromium in their compositions. General corrosion was most critical at pH 8.5. The corrosion intensity decreased for the three steels when the dissolved oxygen concentration increased, at 2 m/s. This behavior is coherent considering the most effective precipitation of Fe2O3 inside the pores of the Fe3O4 layer in a more oxidizing environment. For 3 m/s, the corrosion intensity increased for both materials when oxygen increased, showing the shear stress effect. These behaviors were more significant at pH 8.5. About pitting corrosion, the analyzes show localized attack in the majority of coupons, however with very low number of pits.

Resumo: HP steels are commonly used in steam reforming tubes, which are exposed to harsh operational conditions causing microstructural changes. These microstructural changes cause variations in the magnetic properties, which can be measured by different techniques. This work aims at the measurement of the magnetic and electric variations in HP-Nb modified alloys with different chemical composition using scanning probe microscopy (SPM) techniques. The results show that, despite the microstructural change due to variation of chemical composition, samples with aging state I exhibit a magnetic response at the carbides boundary, while for advanced aging states, the magnetic response is not evidenced.

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Resumo: Synchrotron X-ray imaging systems with fluorescence techniques were developed for biomedical research at the Brazilian Synchrotron Laboratory. Two different X-ray fluorescence systems were implemented to analyze human prostate samples with and without disorders.

Resumo: An X-ray transmission microtomography (CT) system combined with an X-ray fluorescence microtomography (XRFμCT) system was implemented in the Brazilian Synchrotron Light Laboratory (LNLS), in order to determine the elemental distribution in prostate samples aiming at establishing a correlation between the concentration of some elements and the characteristics and pathology of the tissues. The CT images were reconstructed using a filtered-back projection algorithm and the XRFμCT images were reconstructed using a filtered-back projection algorithm with absorption corrections.

Resumo: Prostate cancer (PCa) currently represents the second most prevalent malignant neoplasia in men, representing 21% of all cancer cases. Benign Prostate Hyperplasia (BPH) is an illness prevailing in men above the age of 50, close to 90% after the age of 80. The prostate presents a high zinc concentration, about 10-fold higher than any other body tissue. In this work, samples of human prostate tissues with cancer, BPH and normal tissue were analyzed utilizing total reflection X-ray fluorescence spectroscopy using synchrotron radiation technique (SR-TXRF) to investigate the differences in the elemental concentrations in these tissues. SR-TXRF analyses were performed at the X-ray fluorescence beamline at Brazilian National Synchrotron Light Laboratory (LNLS), in Campinas, São Paulo. It was possible to determine the concentrations of the following elements: P, S, K, Ca, Fe, Cu, Zn and Rb. By using Mann–Whitney U test it was observed that almost all elements presented concentrations with significant differences (α=0.05) between the groups studied.

Resumo: The kinetics of zinc electrodeposition from acid sulphate solution on a platinum electrode was investigated by means of stationary polarization curves, interfacial pH measurement and electrochemical impedance spectroscopy. The effect of pH, namely pH 2, 3 and 4, was analyzed. A significant dependence of Zn electrodeposition with solution pH was verified. The results obtained cannot be predicted by the available models for Zn electrodeposition. A reaction model is then proposed based on the predominant steps as a function of the potential and the electrode surface nature.

Resumo: Electrochemical and surface analyses were carried out to study the leaching of chalcopyrite in acid media, aiming to increase copper extraction from low-grade chalcopyrite ores. Unpublished results include the use of electrochemical impedance spectroscopy (EIS) to characterize the dissolution resistance of chalcopyrite surfaces in 0.1 mol·L− 1 of hydrochloric, nitric or sulfuric acids. Potentiodynamic polarization, atomic absorption spectrometry and EIS analysis showed that hydrochloric acid solutions are more efficient leaching agents than nitric and sulfuric acids. The impedance results suggested that the chalcopyrite dissolution is a diffusion-controlled process in hydrochloric and sulfuric acids. The use of Raman spectroscopy and scanning electron microscopy with energy dispersive spectrometers (SEM/EDS) allowed the partial identification of lead and bismuth sulfides as impurities. Two products were identified on the surface of chalcopyrite after anodic polarization, i.e., sulfur in the sulfuric acid only and covellite in all three acids.

Resumo: The Nickel-based superalloy 718 is a precipitation-hardened material, especially by the ordered and coherent phases γ” (Ni3Nb) and γ″ (Ni3 (Al, Ti)). In addition to these phases, precipitation of carbides and δ-phase is possible. This material has high strength, creep, and corrosion resistance at temperatures up to 650 °C. However, despite the alloy’s outstanding performance under harsh environments, research effort has been put into optimizing its properties and increasing the operation temperature. Manipulation of microstructural parameters such as grain boundary character distribution (GBCD), microtexture, second phase fraction, etc. is frequently betaken in order ot achieve better properties. In this context, this work aimed to assess the influence of Thermomechanical Processing on the recrystallization texture of the material and its influence on the alloy’s mechanical behavior. The material was submitted to four iterative processing routes, composed of deformation-heat treatment cycles. The alloy’s microtexture data were obtained through the Electron Backscattered Diffraction technique. Data processing was performed using the MTEX toolbox, where Orientation Density Functions were obtained for microtexture analysis. It was observed that the deformation imposed during thermomechanical processing significantly affects the recrystallization texture of the material so that smaller deformations induce the formation of typical recrystallization texture components; on the other hand, high degrees of deformation lead to a retained deformation texture after annealing. Mechanical properties were evaluated by depicting the influence of different strengthening mechanisms and δ-phase fraction on yield strength and ductility, respectively. It was observed that the main strengthening parameters for the alloy were grain boundaries and intrinsic resistance (Pierls-Nabarro and solid solution), meanwhile ductility was greatly influenced by δ-phase and ∑3n boundaries fractions.

Resumo: With the development of non-destructive inspection techniques, more and more challenging situations have arisen and the correct choice of operating parameters can be decisive for a good detection sensitivity. Based on that, an algorithm was developed to obtain the best combination of an eddy current sensor operation parameters. The results obtained demonstrate the improvement in the cracks detection in welded parts after optimization.

Resumo: The paper describes a new transducer dedicated for evaluation of a duplex stainless steel (DSS). Different phases which exist in DSS have influence on mechanical as well as on electrical properties. Therefore, an eddy current transducer was utilized. In order to achieve high sensitivity, a differential type of the transducer was selected. The performance of the transducer was verified by utilizing the samples which had a different amount of sigma phase.

Resumo: Super duplex stainless steel (SDSS) is a two-phase material where the microstructure consists of grains of ferrite (δ) and austenite (γ). SDSS exhibit an attractive combination of properties, such as: strength, toughness and stress corrosion cracking resistance. Nevertheless, SDSS attain these properties after a controlled solution heat treatment, leading to a similar volumetric fraction of δ and γ. Any further heat treatment, welding operation for example, can change the balance of the original phases, or may also lead to precipitation of a deleterious phase, such as sigma (σ). For these situations, the material corrosion resistance is severely impaired. In the present study, several SDSS samples with low σ phase content and non-balanced microstructure were intentionally obtained by thermally treating SDSS specimens. Electromagnetic techniques, conventional Eddy Current Testing (ECT) and Saturated Low Frequency Eddy Current (SLOFEC), were employed to characterize the SDSS samples. The results showed that ECT and SLOFEC are reliable techniques to evaluate σ phase presence in SDSS and can provide an estimation of the δ content.

Resumo: Rigid pipelines installed in offshore structures for oil and gas production are built from pipe sections connected by circumferential welds. Such welds are generally points of stress concentration and therefore the regions that most demand periodic inspection. The weld geometry and the inspection speed required for in service inspection are the main challenges associated to the inspection procedure. In the present work an eddy current transducer with sensing coils placed orthogonally and connected in differential mode was introduced to evaluate fatigue cracks in weld root. A dedicated embedded electronic hardware was developed to drive the transducer and measure the electrical complex impedance of the coils and was specifically designed for operation under autonomous in-line inspection tool in a speed range between 0.5 – 1.0 m/s. The achieved results have confirmed that the introduced eddy current transducer is a potential solution for fatigue crack detection in irregular surfaces like weld root, while the hardware developed presented a reasonable SNR and achieved the data rate required to be incorporated in an autonomous in-line inspection tool.

Resumo: Orthogonal eddy current sensors operating in differential mode was applied to evaluate fatigue cracks in clad pipelines circumferential welds. A dedicated electronic hardware was developed to drive the sensors and measure the electrical impedance. In the preliminary experiments, an automated inspection was performed with the goal to evaluate sensors detectability and different scanning speed was tested to reproduce in service situation. The results have shown that the presented eddy current transducer is a potential solution for a fatigue crack detection on a clad circumferential weld bead.

Resumo: HP austenitic stainless steel undergoes microstructural aging due to prolonged exposure to oxidizing and corrosive atmospheres in steam reforming furnaces. The derived aging states are classified by its service temperature and microstructural markers and monitoring it is important to residual life assessment. In this regard it was used a portable Eddy Current inspection system with the aid of machine learning classification tools, characterizing aging states in HP steel in real-time. The classification profile of a 12-meter tube was acquired, validated through Field Metallurgical Replication. The developed Eddy Current inspection system successfully differentiates three regions, revealing a progression of aging states.

Resumo: Austenitic stainless steels are alloys with desirable features especially in corrosive environments. However, some processes, such as cold-work, can change their original properties owing to the formation of α′-martensite during a strain-induced process. Many techniques have been employed to detect and quantify this metallurgical phase and the non-destructive methods are particularly interesting for quality control in industrial plants. In this work, the use of impedance phase angles from the eddy current testing is proposed to quantify the martensite volume fraction. Methods such as optical microscopy, X-ray diffraction, and vibrating sample magnetometry were also employed to characterize the samples microstructure. Upon magnetic measurements, it was found that the phase angle and martensite volume fraction are related by an exponential fit.

Resumo: The aim of this work is to make a survey of typical flaws presented by modern anticorrosive coatings commonly employed for inside protection of petrochemicals storage tanks and discuss what can be expected from nondestructive inspection with conventional eddy current technique. In this sense, advantages and limitations of the method are discussed taking into account the characteristics of the coatings. Controlled defects were machined in carbon steel substrates in order to simulate localized corrosion. The detectability of the eddy current technique was evaluated for as-applied insulating coatings (with different thicknesses) in presence and absence of iron oxide inside the simulated corrosion defects. Comparing the results obtained with the original C-Scan maps and after the image processing, the machined defects were successfully detected. In this comparison, it was observed a significant improvement for the false defects elimination using image processing.

Resumo: This paper is focused on eddy current measurements of C/SiC samples in different status of the manufacturing process. The measurements are compared with results of X-Ray, Scanning Acoustic Microscope (SAM) and optical images and discussed.

Resumo: The importance of temperature variations on coatings aging is well known. The aim of this paper is to evidence how aging kinetic, monitored by EIS, can be complemented by dynamic mechanical analyses to access susceptibility of high performance corrosion protective composite coatings, designed for harsh conditions, when subjected to temperature variations, proposing methodology to aid in the selection criteria. Five coatings provided by recognized brands were submitted to corrosion tests with immersion and temperature cycling or shocking. The range of testing temperatures included the so-called humid Tg obtained by Arrhenius-type plot of low frequency impedance modulus. Different aging kinetics were evidenced by EIS for the coatings. Pull-off adhesion measurements complemented by SEM indicated loss of cohesion with cracks and voids nucleation at filler-matrix interfaces as one important feature of the coatings with more accelerated thermal aging kinetics. The irreversibility of impedance on Arrhenius-type plot, follows the thermal stress, but does not predict performance of the coatings. On the other hand, associating EIS with mechanical dynamic analyses allows understanding susceptibility to thermal aging, by considering the coatings viscoelastic properties measured within the range of testing temperatures. The input given by DMA testifies to the importance of having this technique included in coatings assessment protocols whenever temperature variations are in context. With this, one can not only better understand the behavior of the coatings, but also get clues to develop products with even better performance.

Resumo: The formation of three-dimensional cell microspheres such as spheroids has attracted attention as a useful culture technique. In this study, we investigated the distribution (mapping) of Fe, Cu and Zn in cellular spheroid derived human prostate tumor cells. The measurements were performed in standard geometry of 45∘ incidence, exciting with a white beam collimated with the help of a 20 μm diameter optical capillary in the XRF beam line at the Synchrotron Light National Laboratory (Campinas, Brazil). The results showed that all the elements analyzed presented non-uniform distribution. The spheroids analyzed showed different elemental distribution of Fe and Cu. Zinc concentrations were higher in the central regions of the spheroids analyzed

Resumo: This discussion presents an analysis of the recent paper by Kahyarian, Brown and Nesic published in this Journal Kahyarian et al. (2017). Indeed, the paper claims an anodic participation of CO2 in the iron dissolution mechanism, not detected by our work also published in this same journal Almeida et al. (2017). The anodic role was, however, only limited to the analysis of Tafel slopes behaviour. This is what was typically done in the early works of iron dissolution in acid media during the 1960′s, so that a discussion about this methodology based on the progress of the electrochemistry that has been developed since the 1980′s is absolutely necessary.

Resumo: This paper presents a discussion of the particularities and challenges involved in the elaboration of reaction mechanisms. The use of steady state techniques to establish reaction models is critically analysed. Indeed, this paper shows that the same Tafel slope may be associated with different mechanisms; therefore, the Tafel slope cannot be used by itself to determine a specific mechanism with reasonable certainty. Furthermore, a critical analysis of electrochemical methods frequently used to determine corrosion rate, such as the Tafel Slope and LPR, shows the necessity of knowing the mechanisms of reactions beforehand to avoid mistakes in corrosion rate predictions. Reaction mechanisms must be established using both steady state and transient techniques. Finally, in cases where the kinetics are controlled by mass transport, electrohydrodynamic impedance emerges as a very useful tool, whose use is exemplified here by copper electrodissolution in sulphate medium.

Resumo: The Use of composite materials made technological advances possible in biomedical and industrial areas. Polymeric matrices reinforced by glass fiber are the most common among the composite materials used for pipe manufacturing. However, they may present intrinsic issues due to important factors, such as nonuniformity and nonconformities related to reinforcement and matrix. Visual inspections can identify the characteristic fiber distortion discontinuities, surface bubbles, and dry areas of impregnation. To detect porosity, cracking, or delamination, other methods are required. This paper presents the technique of digital radiography for the inspection of composite materials. An amorphous silicon (a-Si) type flat panel detector, a constant potential X-ray source, and a software-controlled rotation table were used. Radiographs of two laminated joints of 4 in. (101.6 mm) glass fiber reinforced polymer (GFRP) pipes were performed. As a result, delamination, debonding, cracking, and porosity discontinuities were detected, which could not be detected visually.

Resumo: Although carburization is not a typical occurrence in steam reforming furnaces, this localized damage can occur and its detection is an important issue. A magnetic sensor based in the magnetic flux density variation has been proposed for the carburization detection in samples coming from steam reformer tubes. A three-dimensional model, by finite-element method (FEM), supported the optimization and development of a magnetic sensor for the detection of carburized samples. The experimental results indicated that the developed sensor, with high sensitivity, allowed to detect regions with moderate carburization damages.

Resumo: This article presents experimental viscosity and density data for binary systems containing ethanol and one of the following 1-alkanols as the second component: butan-1-ol, pentan-1-ol, heptan-1-ol, octan-1-ol, nonan-1-ol, and decan-1-ol. These properties were measured at 0.1 MPa and at five different temperatures, ranging from 283.15 K to 313.15 K. The viscosity data have also been correlated by a model which combines Eyring’s theory of viscous flow with a thermodynamic framework (Ind. Eng. Chem. Res. 2000, 39, 849). The model binary interaction parameters, for each of the binary systems, are also reported. The agreement between calculated and experimental data was rather good. The overall mean relative standard deviations did not exceed 0.01. The experimental viscosity deviations, obtained by the difference between the viscosity of the mixture and the mole fraction average of the pure component viscosities, were adjusted by means of Redlich–Kister polynomials. For all the systems studied negative values of viscosity deviations were obtained, for all temperatures, and over the whole mole fraction range.

Resumo: In this work are described the crystal structures of two alkaline earth salts as well the vibrational spectra of three alkaline earth salts of 3,5-bis-(dicyanomethylene)cyclopentane-1,2,4-trionate (known as croconate violet – CV2−). The compounds obtained are a mixed salt of potassium and magnesium [MgK2(CV)2], beyond of calcium and barium salts (CaCV and BaCV, respectively). The structures of MgK2(CV)2 and BaCV have been confirmed by single crystal X-ray diffraction and spectroscopic analysis. These compounds crystallize in monoclinic P21/n space group, showing four and five water molecules for MgK2(CV)2 and BaCV, respectively. The dianionic units [MgK2(CV)2(H2O)4] adopt a slight distorted octahedral geometry in which the metallic center is coordinated by six oxygen atoms (four from CV2− and two from water molecules). These units are connected through intermolecular hydrogen bonding giving rise to a supramolecular array in a two-dimensional arrangement (2D). The potassium ion shows monodentate coordination, whereas the magnesium ion presents a chelate coordination in the MgK2(CV)2 salt and for the BaCV, the coordination geometry of metal site is monodentate and chelate coordination; it is straightforward to mention that the barium compound is the only pure divalent salt obtained until now in the literature. In the vibrational spectra, the most important vibrational markers for croconate violet ion are the ν(Ctriple bondN) and ν(Cdouble bondO) modes, which present different behavior due to the modification of chemical. In general way, the bands assigned to ν(Ctriple bondN) and ν(Cdouble bondO) in MgK2(CV)2, CaCV and BaCV present small wavenumber shifts, which can be associated to the different interionic interactions between anion and cations.

Resumo: This paper uses numerical analysis and experimental data to validate the use of strain gauges for load and crack propagation measurements in corrosion fatigue. It was shown that the measurement of crack length and load by strain gauges can be done following the requirements of ASTM E647-15. The results open the possibility for using strain gauges directly positioned on the samples, replacing both the classical load cells to measure load and direct current potential drop to determine fatigue crack growth rate, as neither are easily usable for high-pressure corrosion fatigue tests.

Resumo: The corrosion resistance of chromium-plated steel sheets produced on an industrial scale was investigated. Two parameters of the production process were considered: pickling and chemical treatment. The specimens were produced at the industrial plant considering two different pickling conditions and two different chemical treatments: non-electrolytic and electrolytic pickling and non-electrolytic and electrolytic passivation respectively. Accelerated corrosion tests in the humid chamber, microscopy analyses, analyses of roughness and content of trivalent chromium in the passivation film and analyses of the content of metallic chromium in the coating by coulometry technique were performed. The results showed a low corrosion resistance of the materials produced with the non-electrolytic passivation, regardless of the pickling condition. The highest degree of protection of the base steel was achieved for the specimen produced by using the electrolytic route for both pickling and chemical treatment steps. This condition produced a mass of trivalent chromium in the passivation film greater than 8.0 mg∙m-2, which provided an effective performance of the chromium-plated steel sheet.

Resumo: The anticorrosive performance of medium-long (54–59%) alkyd paints modified with linseed and soy oils was compared by accelerated tests (Prohesion Cycle) and natural exposition in marine and industrial atmospheres. Differences on the protection mechanism of anticorrosive pigments due to substitution of linseed oil by soy oil were investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Complementary tests such as water vapor and ions permeability in freestanding films were also performed. Results suggested that the type of oil influenced the barrier properties of the paint pigmented with zinc phosphate. The same tendency was verified by resistance values obtained from impedance diagrams. Polarization curves suggest that the action of the pigments in the alkyd paintings is practically the same for both oils. The substitution of linseed oil by soy oil did not impair the anticorrosive performance of alkyd paints and from the economic point of view this substitution could be very interesting.

Resumo: For calibration of eddy current testing, artificial defects are commonly used by virtue of its simple production and ease control of geometric parameters. However, such defects are significantly different in terms of geometric aspects from real ones, even with a precise control of the manufacturing process. To ensure reliable calibration results, it is mandatory to establish a relationship between the signals from artificial (machined) and real defects. This work exposes a detailed study correlating eddy current signals from electrical discharge machine notch (EDM notch) and fatigue cracks. To perform the tests an absolute pencil probe was used. Although there is a significant difference between the signals of EDM notch and fatigue cracks, the results show that it is possible to use artificial defects to represent fatigue cracks reliably if a proper correction is implemented.

Resumo: In the present paper, three different coatings (epoxy, alkyd, polyurethane paints) were characterized by electrochemical impedance measurements, permeability tests, free-standing film impedance and local impedance measurements. The increase in resistance with immersion time of alkyd paint was linked to the nature of the polymeric network and not to phenomena occurring at the metal/paint interface. For polyurethane paint, local impedance was not able to detect defects in the paint, which was attributed to the fact that the defects are smaller than those observed in alkyd paint and also that they are less active and homogeneously distributed through the coating. Although electrochemical impedance methods (global and local) are excellent tools to monitor the behaviour of organic coatings, these techniques alone are not sufficient to screen different paints.

Resumo: The present work compares graphene oxides produced by the Marcano's method and the subsequent reduction process using a microwave system with different power and time sets. The thermal profiles of the reduction processes were analyzed, emphasizing the heat capacity from the 600 W test of 3.44 kJ/K. The X-ray diffraction showed a reduction in the interlayer space and the number of layers in all powers. The infrared and UV-Vis spectroscopy results showed a clear decrease in the bands corresponding to the oxygenated group and partial restoration of aromatic bonds. The Raman spectroscopy showed that the 1000 W power set originated a higher defective structure. The observed results allow the conclusion that the 600 W power promotes a little better result between the analyzed power sets.

Resumo: This work presents the characterization of the external oxide scale of a centrifugally cast HP steel tube, modified with Nb and Ti, after 90,000 h of operation in a steam reforming furnace, showing different aging states as a function of the column height and exposure temperature. The objective was to relate the oxide microstructural morphology to its magnetic response for three different microstructural aging states. The morphological and compositional characterization was performed by high resolution scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. The magnetic response of the external surface was analyzed by magnetic force microscopy and scanning magnetic susceptometer. The results showed the formation of a multilayer oxide scale with different compositions along its thickness. In addition, a microstructural modification was identified in the scale-matrix interface, due to the depletion of chromium. It was also observed that the magnetic response is dependable both on the oxide scale thickness and the chromium carbides depleted zone. Magnetic force microscopy was able to identify the origin of the magnetic response resulted from the steel tube surface.

Resumo: HP austenitic stainless steels are extensively used in the oil and gas industry as radiant tubes in reformer and pyrolysis furnaces. These steels exhibit high resistance to oxidation, thermal stability, and creep resistance at elevated temperatures. Their microstructure changes as a function of temperature, leading to different aging states. In addition, creep voids can be formed due to furnace operating conditions such as time and stress. Therefore, the characterization of the microstructural conditions is necessary for service life assessment. This study aims at characterizing two modified HP steel samples with different aging states and volumetric fraction of creep voids via scanning electron microscopy and ultrasonic testing. Fast Fourier transforms were applied to the second backwall echo of the acquired ultrasonic signal. Spectral analysis established a correlation between the microstructural conditions and the signal response. According to the methodology developed, the ultrasonic parameters and spectral analysis results were sensitive to microstructural changes caused by aging and the presence of creep voids.

Resumo: This paper is focused on eddy current measurements of C/SiC samples in different status of the manufacturing process. The measurements are compared with results of X-Ray, Scanning Acoustic Microscope (SAM) and optical images and discussed.

Resumo: O comportamento de ligas NiFe é objeto de intensa investigação devido ao grande número de aplicações desses materiais no meio industrial. A eletrodeposição é um dos processos mais utilizados para produção dessas ligas devido ao seu baixo custo e sua capacidade de recobrir geometrias complexas. Variáveis do processo, como pH, densidade de corrente e composição do banho, podem afetar a cinética de deposição da liga bem como a morfologia e a estrutura dos depósitos obtidos. O objetivo do presente trabalho é estudar o efeito do pH sobre a cinética de deposição, composição e morfologia dos filmes. Os resultados das curvas de polarização e análise química mostram duas regiões: a primeira refletindo a redução de H+. Com aumento da polarização a corrente passa a variar fortemente com o potencial e a redução metálica ocorre com boa eficiência. A morfologia dos filmes varia com o pH da solução. Em pH 5, os depósitos são homogêneos e compactos. Para menores valores de pH (pH 1), são observadas trincas ao longo da superfície.

Resumo: The osmotic compressibility factor of several polymer solutions was correlated with the polymer concentration and temperature through different cubic equations of state, with particular focus on the McMillan–Mayer solution theory. The equations of state employed were those of van der Waals, Redlich–Kwong, Peng–Robinson, and Soave—Redlich–Kwong. All of these equations present two parameters that take into account the attractive and repulsive interactions between the solute molecules in a given solvent, with these parameters being dependent on the nature of the system (solute and solvent) and on the temperature. As the attractive and repulsive interactions are well defined in the parameters of the cubic equations of state, the theta temperature for each polymer system studied may be calculated by a simple and efficient procedure. For the purposes of comparison, the virial equation truncated at the third term was also included in this study. It was confirmed that the attractive parameter has a linear dependence on the temperature, while the repulsive parameter varies according to a quadratic profile. Accordingly, the model to be minimized presents five adjustable parameters that depend only on the nature of the polymer system. The agreement between the experimental and calculated values is within the experimental error.

Resumo: The main of this work is to determine the elemental distribution in breast and prostate tissue samples in order to verify the concentration of some elements correlated with characteristics and pathology of each tissue observed by the X-ray transmission microtomography (μCT). The experiments were performed at the X-ray fluorescence beamline of the Brazilian Synchrotron Light Laboratory. The μCT images were reconstructed using a filtered-back-projection algorithm and the XRF microtomographies were reconstructed using a filtered-back-projection algorithm with absorption corrections.

Resumo: This paper presents the corrosion test results of 9% Ni steels (ASTM A522 type 1 and ASTM A333 grade 8) in presence of aqueous solutions containing H2S and CO2. A forged bar and a seamless pipe, manufactured to be used in high-pressure CO2 lines, were tested by NACE TM0177, TM0284, and ISO 7539-2. Localized corrosion and cracks were observed in the sulfide stress cracking (SSC) tests, in both base materials, and welded joint. These types of attack were associated to specific metallurgical features of the products (forged bar and seamless pipe), indicating that a better evaluation of the corrosion resistance of these materials is necessary. No hydrogen induced cracking damage was detected after the standard testing time, but microcracks were identified, reducing the impact energy levels. The welded joint presented high susceptibility to SSC cracking.

Resumo: High quality tubular products are essential to the oil and gas industry. Quality control during their production focuses on the non-destructive detection of surface defects. The structured light technique is a candidate for the challenge to detect, monitor and evaluate such defects in real-time. In the present study the automatic processing of structured light measurements is performed and validated. The algorithm for the automatic analysis of inspection data has an advantage over current data evaluation methods based on individual assessments of operators.

Resumo: The elastohydrodynamic (EHD) lubrication straight line contact conjunction is studied to evaluate the mixed lubrication heat generation experimentally over bordering operating conditions in a disc-on-disc machine. An experimental investigation is carried out using an accessory device that collects and measures the outlet lubricant temperature. The experimental results show the typical transition from mixed to elastohydrodynamic lubrication, tracking the difference of outlet lubricant temperature and the total average full-film EHD temperature. A new variable coupling flash temperature was introduced as an in situ approach to demonstrate the lubricant capacity of removing heat from asperity interaction in mixed lubrication contacts. It was possible to estimate the metal–metal contact area in mixed lubrication by coupling flash temperature as a direct correlation to the true flash temperature in relation to correspondence to final surface roughness characterizations.

Resumo: This paper addresses the electrochemical parameters proposed in ISO 12732 standard that are used to quantify undesirable phases in a superduplex stainless steel. The relationship among these electrochemical parameters (listed as the maximum current and overall charges ratio during the activation and reactivation polarization curves) and the quantity of undesirable phases were evaluated. It was shown that ferrite is always preferentially corroded in that steel. For aged conditions, the undesirable phases were satisfactorily detected by Double Loop Electrochemical Potentiokinetic Reactivation. A new experimental protocol developed made possible the characterization of the attack occurring at each polarization range.

Resumo: The cavitation phenomenon in polymers, commonly known as whitening, has been quite studied in the last two decades due to its relevance to the plastic deformation process and the overall behavior of the material. Its occurrence has been proposed to be either on equatorial or at polar region of the spherulite during deformation. The detection techniques usually employed are small angle X-ray scattering (SAXS) or light scattering, and neither one is suitable for field inspection. The present study focused on nondestructive methodologies to detect the cavity phenomenon in two grades of poly(vinylidene fluoride), comparing simple visual inspection (VI), optical densitometry (OD) and ultrasound velocity (US). The results showed that the last two techniques were able to identify the existence of voids very earlier along the deformation path, about 2%–5% strain, where visual whitening was not even detected. The OD and US showed to be highly effective in distinguishing the effect of the processing conditions on the occurrence of cavitation, via simple and fast methods. The use of ultrasound technique for cavity detection becomes a very promising approach for the production inspection of the pressure sheath of raisers, polymer pipes and other products, as well as for evaluating the integrity of the component that may be affected by occurrence of cavities.

Resumo: During the reactor operation, aluminum tank and the core components can experience radiation damage, resulting in limitation of its life span. Effects of radiation on the aluminum alloys are not yet fully understood, especially when material is obtained from upward directional solidification under transient heat-flow condition. For this paper, an experimental research has been conducted to investigate the radiation effects on the as-cast aluminum 1050, with focus on the microstructure, microhardness and porosity for different position along casting. Firstly, thermal parameters were determined during solidification experiment and then correlated with cellular spacings, microhardness and porosity content. The experimental results show that thermal parameters such as solidification speed, thermal gradient and cooling rate exerts an influence on the microstructure, microhardness and porosity. Experimental laws for microstructure, microhardness and porosity have been determined, indicating that the increase in thermal parameters has induced a refinement effect on the microstructure, increase in microhardness and a decrease in the porosity content. Further, measurable effects of the gamma radiation on the microstructure, microhardness and porosity formation along the ingot of aluminum 1050, were experimentally determined. It stands out among results that gamma radiation has favored an increase in cellular spacings, microhardness and porosity in ingot, obtained from a vertical upward directional solidification. However, even after the gamma radiation exposure, microstructure, microhardness and porosity found along the casting are dependent of the solidification thermal conditions.

Resumo: Guanine was investigated as a potential green corrosion inhibitor to API 5L X65 carbon steel in HCl 0.1 mol.dm-3 solution, at pH = 2.0, under hydrodynamic conditions using electrochemical, weight loss and Raman spectroscopy experiments. Cyclic voltammetry and potentiodynamic polarization curves suggested that Guanine does not change the metal/solution interface appreciably and weight loss tests conrmed the low inhibition eciency (IE) of Guanine in protecting the X65 steel in this corrosive medium. An IE = 22% was determined after 48 h of exposure, a value lower than that reported in the literature on the mild steel/Guanine/HCl system. Raman spectroscopy was employed to gain insight on the nature of the steel/Guanine interaction and the results pointed out to a weak physisorption of the molecule, thus explaining the very low IE values obtained.

Resumo: This article presents the development of an active thermography algorithm capable of detecting defects in materials, based on the techniques of Thermographic Signal Reconstruction (TSR), Thermal Contrast (TC) and the physical principles of heat transfer. The results obtained from this algorithm are compared to the TSR technique and the raw thermogram obtained by stepped thermography inspection. Experimentally, a short thermal pulse is used and the surface temperature of the sample is monitored over time with an infrared camera. Due to the volume of data, the first step is data compression. Newton's law of cooling was used to store the normalized temperature data pixel-by-pixel over time and a compression ratio of 99% was obtained. The main contributions of the developed algorithm are: only four parameters for data compression and the concept of change in the direction of the heat flow to delimit the edges of the defects, where the borders are identified with a remarkable accuracy. Some well known image processing technique are also integrated to improve the thermal analysis: edge detection/interface between the sample and the image background; consolidation in a single image by aggregating the indicators referring to the concept of cooling/heating time constant, maximum thermal amplitude and contrast. INDEX TERMS Active thermography, thermal analysis, infrared imaging, data compression, change detection algorithms, image processing.

Resumo: A methodology for quantifying the contamination after abrasive blasting by Aluminum Oxide and Martensitic Carbon Steel particles in Super Duplex and Carbon Steel substrates has been developed. The method consisted of performing x-ray diffraction in the blasted steel substrates and calculating the particle contamination using Rietveld Quantitative Method. In this way, it is possible to evaluate the substrate volume in which the abrasive particles have been trapped (taking into account the surface roughness) rather than solely performing visual examination, as indicated by standards documents. Equations describing the intensity model of the diffracted peaks as well as those describing the quantitative measurements are presented. Correction functions are also employed to compensate the effect of the surface roughness generated on the metallic substrates after blasting. Alumina and martensitic steel abrasives contaminations were detected and quantified in both steel substrates. Results showed that Super Duplex Steel substrates revealed a higher degree of contamination when compared to the Carbon Steel substrates, both for alumina abrasives as for martensitic abrasives. Also, the abrasive that generated the lower degree of contamination was the Martensitic Carbon Steel, for both substrates.

Resumo: Raman experiments of aluminum chloride and formamide (FA) solutions in different compositions and temperatures were carried out. Spectral changes provoked by the increase of the salt concentration were observed in different regions. The νCO and νCN modes of FA upon complexation were upshifted and suggest that the single bondCONHsingle bond hybrid (II) is stabilized by Al(III). Bands at 547 and 295 cm−1, which are assigned to the νAlO and νAlN vibrations, respectively, evidence coordination through both O and N atoms of FA. The quantitative analysis performed at the carbonyl stretching region found 5 FA molecules around this cation, resulting in the formation of the [Al(FA)5]Cl3 complex. Its stability is maintained by whole studied concentration range and up to around 100 °C. At higher temperatures, distortions in the FA shell begin occurring and a new component at 356 cm−1 is then observed and assigned to the [AlCl4]− complex.

Resumo: The formamide (FA)/pyridine (py)/pyridazine (prd) system was investigated by FT-Raman spectroscopy and the results in situ show that FA is preferentially bound to py, as experimentally pointed out by the proton affinity (PA) values of these azabenzenes. Temperature-dependent further investigations for the FA/prd mixture clearly show that the 2:1 FA:prd complex is more stable than the 1:1 FA:py adduct, even though its formation is influenced by the extremely negative entropy of the system, which becomes the spontaneously unfavorable global process. Linear relationships of the complex formation enthalpies (ΔH°) with band shifts (Δν) and dipole moments (μ) of these azabenzenes are observed and are in excellent agreement with our recent studies.

Resumo: 

Resumo: The electrochemical mechanism of Ni electrodeposition in an acid sulfate medium with pH ranging from 1 to 6 is evaluated. For pH ≤ 3, a reaction model already available in the literature accounts satisfactorily for the experimental results shown in Part I of the present paper. However, this model cannot explain the results obtained in the pH interval of 4-6. A complementary model is then proposed, considering the formation of two species: (i) [Ni (OH)]ads+, the relaxation of which is associated with a capacitive loop at medium frequencies, and (ii) [Ni (OH)]ads, the relaxation of which gives rise to an inductive loop at low frequencies. The validation of this model has been accomplished by the comparison with the experimental polarization curves and impedance measurements. A good agreement is found between the simulated and experimental results. By using the previous model proposed by Epelboin [J. Electroanal. Chem., 119, 61 (1981)] for pH ≤ 3 together with the present complementary model, Ni electrodeposition can now be explained in the whole pH range of 1-6.

Resumo: For fatigue studies, load cells are generally used to measure the cyclic loading applied to the specimen. However, the literature reports that an internal force arises when fatigue tests are performed inside pressurized vessels, acting directly on the vessel shaft. Another component, the friction force, arises due to the sealing system. These two forces impose substantial differences between the values measured by external load cells and the true loading applied on the specimen. Faced with this problem, this study aims to analyze the influence of friction in pressurized testing of corrosion-fatigue, the sealing system of which has been specially designed with reduced stick-slip effect to avoid nonlinearities in the cyclic load. A new methodology based on a strain gauges system installed on the CT specimen was developed and tested, solving the problems of cyclic load and crack length measurements for corrosion-fatigue tests under high pressure. The innovation of this system is that the specimen itself simultaneously acts as a crack length transducer and a load cell. Such a system was properly designed to be used under high pressures and is resistant in aggressive environments. Therefore, it is possible to perform corrosion fatigue tests, obtaining Fatigue Crack Growth Rates (FCGR) without all the measurement problems caused when a load cell is used. In addition, the resulting errors obtained when using a classical load cell in the tests can also be measured by the present experimental setup. In this paper errors were verified in corrosion-fatigue tests using a conventional load cell. These errors could be greater than 700 percent, not meeting the requirements of ASTM E4 and E647 standards. Consequently, the crack length measurements do not agree with the values obtained by an optical microscope, even when tunneling does not occur.

Resumo: An X-ray Transmission Microtomography (CT) system combined with an X-ray Fluorescence Microtomography (XRFμCT) system was implemented in the Brazilian Synchrotron Light Laboratory (LNLS), Campinas, Brazil. The main objective of this work is to determine the elemental distribution in biological samples (breast, prostate and lung samples) in order to verify the concentration of some elements correlated with characteristics and pathology of each tissue observed by the transmission CT. The experiments were performed at the X-Ray Fluorescence beamline (D09B-XRF) of the Brazilian Synchrotron Light Laboratory, Campinas, Brazil. A quasi-monochromatic beam produced by a multilayer monochromator was used as an incident beam. The sample was placed on a high precision goniometer and translation stages that allow its rotation as well as translation perpendicular to the beam. The fluorescence photons were collected with an energy dispersive HPGe detector placed at 90° to the incident beam, while transmitted photons were detected with a fast Na(Tl) scintillation counter placed behind the sample on the beam direction. The CT images were reconstructed using a filtered back-projection algorithm and the XRFμCT were reconstructed using a filtered back-projection algorithm with absorption corrections. The 3D images were reconstructed using the 3D-DOCTOR software.

Resumo: Splits are delaminations that may appear perpendicular to the crack plane during fracture toughness tests of certain materials, such as hot-rolled metal alloys. X-ray computed tomography (CT) was used to conduct a 3D analysis of the geometrical and morphological characteristics of the splits in SE(B) specimens machined from a DH36 steel. Tomograms and 3D reconstructions of the CT results were compared with high-resolution images obtained through optical microscopy (OM) and scanning electron microscopy (SEM). Quantitative and qualitative comparisons revealed a good agreement between the results, validating the split characterization by CT. It was discussed whether characterizing the splits just by the routinary fracture surface observation conducted in fracture mechanics specimens can hide important phenomena such as plane changes, branching, and interactions between delaminations. On the other hand, CT enables an accurate and comprehensive characterization of the morphological and geometrical attributes of splits. Contrasts between the analysis and characteristics of deformed and undeformed splits were made. Finally, the limitations and challenges of the 3D split characterization by CT were also discussed, exploring experimental and image processing issues. These findings emphasize that a more thorough understanding of the internal structure of splits can be achieved by applying CT analysis, contrasting with traditional fracture surface examination. This study highlights the relevance of CT in revealing hidden complexities within the internal structure of specimens with splits.

Resumo: The super duplex steel has been used in equipment for oil primary processing. Despite being assigned to this type of steel excellent anticorrosive properties, inadequate working conditions may impair its performance. In general, when this happens, metallic or organic coatings are applied aiming at prolonging the equipment lifetime. However, there is no information about the behavior of coated super duplex. This paper compares the performance of commercial organic coatings applied to carbon steel and super duplex, when subjected to harsh conditions present in the primary processing of oil, namely: high salinity, high temperature, presence of H2S and CO2. The adopted experimental approach allows discussion about: (i) organic coatings state-of-art for this industrial field; (ii) influence of super duplex on the coatings performance and (iii) development of methodology to aid on the organic coatings selection for such aggressive conditions. The experimental consisted of immersion testing at 150 °C and 180 °C in autoclave during one year, with performances monitored by electrochemical impedance, visual inspection and adhesion measurements. At the end of this test all coatings had some kind of deterioration, pointing to the need of research and development in this area. There were cases where the super duplex adhesion losses were more significant than with carbon steel, suggesting that special attention in super duplex surface treatment is important. The glass transition temperatures (Tg) of the coatings were determined by dynamic mechanical analysis. Permeability to water vapor and impedances were measured with free-films of the coatings at temperatures above and below Tg. These last results confirm the importance of the thermal behavior characterization of the coatings, particularly for conditions involving exposure to temperatures above Tg. Marked differences on Arrhenius-type plots of free-films impedance modulus at low frequency range were associated with performance and appears as a tool that can assist the selection of coatings for high temperature service.

Resumo: Guanine inhibition of copper corrosion in 0.1 M HCl was characterized by electrochemical and weight loss experiments under hydrodynamic conditions as well as by Surface-enhanced Raman spectroscopy (SERS). Cyclic voltammetry and polarization measurements revealed that Guanine adsorption modifies copper surface, thus inhibiting its corrosion. Weight loss and electrochemical impedance experiments showed that Guanine has an inhibition efficiency (ξ) of ∼87 % and that its protection is maintained up to 333 K. SERS measurements revealed that neutral Guanine adsorbs on copper at a wide potential range, forming a Cu(I)Guanine complex at greater immersion times.

Resumo: The objective of this work is to gather historical aspects about the use of EIS for evaluation of corrosion protective organic coatings performance, emphasizing experimental care, contributions and limitations for wider technological application. Contributions are rescued from authors who made important work in development and evaluation of organic coatings with the support of electrochemical techniques. The knowledge of these fellows in organic coatings paved the way for the use of EIS in this field; particularly, some contributions of J.E.O. Mayne are reverenced. This paper does not provide a complete review of the subject, but rather outline keypoints, that were selected according to their relevance in the technological applications to which impedance measurements could contribute, as: early detection of underfilm corrosion, indirect measurement of delaminated areas, prediction of coatings service life by water uptake and modeling with analog electric devices as a tool to obtain the parameters needed for the mentioned applications. Fundamental aspects of EIS in this field have extensive literature which is referenced. The massive current use of EIS justifies this retrospective, revisiting some basics as a source for new users, sharing critical comments and reinforcing the importance of some experimental care.

Resumo: Effects of lamellar reconstruction methods in the release of molybdate ions encapsulated in Layered Double Hydroxides (LDH) are evaluated. The methodology consisted of two stages: i) treatment of LDHs and interlayer substitution with molybdate; ii) characterization of morphology and kinetics of molybdate release in chloride solution and deionized water. Commercial hydrotalcite (HT) was calcined and then reconstructed in water (HTCCa), terephthalic acid (HTCTe), glycerol (HTCGl) and in molybdate solution (HTCMo). XRD showed that lamellar reconstruction succeeded only with HTCCa, HTCTe and HTCGl. Afterwards, substitution of interlamellar anions by molybdate was done. Molybdate release over time, monitored by ion chromatography, was higher in chloride solution suggesting ion exchange. Increasing temperature to 85 °C doubled the molybdate released by HTCTe-Mo, accelerating the kinetic process compared with room temperature. The kinetics release was different for each LDH doped with molybdate. Gradual liberation of molybdate characterizes HTCTe-Mo while HTCGl-Mo promotes quick release. Therefore by the choice of reconstruction routes it is possible to modulate the liberation of molybdate by LDH.

Resumo: Commercial bulk hydrogen is mainly produced in petrochemical steam reforming furnaces inside centrifugally cast Nb-modified HP austenitic stainless steels tubes, which operate at temperatures above 900°C. In-service aging causes well known microstructural modifications such as the transformation of primary niobium carbides, NbC, into the G-phase (Ni16Nb6Si7). Unexpected operational problems, such as reduced feedstock flow may, in a few minutes, cause severe overheating. These short-time temperature surges, can lead tubes to premature failure often through the formation of large longitudinal cracks. Little is known about the integrity of the tubes that undergo a temperature surge without cracking. Thus, understanding the microstructural changes brought upon by these events becomes extremely important when assessing the reuse of these tubes. In the present work, by means of optical microscopy, scanning electron microscopy microscopy and transmission electron microscopy with energy dispersive X-ray spectroscopy, two Nb and NbTi-modified HP steels tubes, which cracked due to high temperature surges, were analyzed. Results show that insitu dissolution of the G-phase in the thermally affected regions causes this phase to be replaced by fine NbC or (NbTi)C precipitates. These microstructural transformations suffered by the tubes during the short-time overheating and cooling cycles are thus presented and discussed in terms of their practical consequences.