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Different in situ coupled techniques were used to characterize the naphthenic corrosion of API 5L X70 steel at room temperature. In situ optical microscopy coupled with an electrochemical noise technique indicated a general corrosion process. In situ AFM images showed the early formation of the corrosion product with a thickness of 600 nm after 90 min of immersion. The main regions observed in the temporal evolution of FTIR spectra are evidence of the formation of an iron naphthenate film even at room temperature.

This work presents the development and characterization of a ring-shaped sensor built around a steel sample (AISI 1020) to determine the near-surface solution pH (NSSpH) during pitting corrosion. The pH sensor is constituted by a ring of IrOx, a material that is sensitive to pH changes, synthesized using the Pechini method on a glass tube with a gap of 1 mm between the pH sensor (ring) and the metal sample (disc). The evolution of the corrosion process was also followed using a temporal series of micrographs with an optical microscope. At the same time, the sensor followed the NSSpH during the passivation of the metal, during the breakdown of the passive film, and during the pit evolution in an aqueous basic solution containing HCO3− and Cl− species. When the pit potential was reached, the NSSpH was reduced by one pH unit.

In this paper, we present the optimization of porous anodic alumina membranes for ultrafiltration prepared by anodically oxidized aluminum foils. The membranes were characterized by field-emission scanning electron microscopy to measure the pore diameter and the membrane thicknesses. The liquid fluxes were estimated through gas permeability measurements using Darcy's and Forchheimerś equations. A 2(3) factorial design we used to optimize the membrane properties: pore diameter, membrane thickness, and liquid flux using as control variables the applied current density, solution composition and concentration. It was observed that the most import variables to control the pore diameter were current density and electrolyte composition. After the anodization both, metallic aluminum substrate and the barrier layer of alumina were removed using adequate solutions to obtain the free standing membrane. Then, Escherichia coli a common bacterial contamination of drinking water was removed using these PAA membranes with 100% of efficiency to obtain bacteria-free water.

In this work, the corrosion process of AISI 1020 in crude oil, to which different amounts of sea water (0.5 and 4.0% v/v), naphthenic acid (500 and 3000 ppm), and H 2 S (50 and 1000 ppm) were added, was investigated using electrochemical noise at open circuit potential. The different oil samples were prepared using a 2 3 factorial design involving the three species described above. To analyze the obtained data, wavelet transform and energy distribution plot were used. Using this technique it was possible to separate the contributions of two types of corrosion, generalized and localized, in oil samples with different compositions and to analyze the effect of those variables on the changes that occurred during 55 days of immersion in the experiment. The results showed an increase in pitting formation in those steel samples studied in oil containing H 2 S at 50 ppm and 4.0% sea water. The contribution of generalized corrosion on the metallic surface is higher in oil containing 3000 ppm naphthenic acid than in the other experimental conditions. The results were confirmed by morphological analysis of the corroded samples.

Multivariate linear regression aided by a successive projections algorithm (SPA-MLR) was applied in the evaluation of anodic stripping voltammetry data obtained in the simultaneous determination of metals under conditions where there were significant complications due to interference processes such as the formation of intermetallic compounds and overlapping peaks. Using simulated data, modeled from complex interactions experimentally observed in samples containing Cu and Zn, as well as Co and Zn, it was demonstrated that SPA-MLR selected variables that allow chemical interpretation. This feature was used to make inferences about the underlying electrochemical processes during the simultaneous determination of four metals (Cu, Pb, Cd, and Co) in a concentration range where all responses were complicated by interference processes (10-100 ng mL −1 ). Additionally, the analytical performances of MLR models for quantitative predictions were excellent despite the complexity of the system under study.

Pitting corrosion is difficult to detect, predict and design against. Modeling and simulation can help to increase the knowledge on this phenomenon as well as to make predictions on the initiation and progression of it. A cellular automaton based model describing pitting corrosion is developed based on the main mechanisms behind this phenomenon. Further, a sensitivity analysis is performed in order to get a better insight in the model, after which the information gained from this analysis is employed to estimate the model parameters by means of experimental time series for a metal electrode in contact with different chloride concentrations.

This work presents a method to study corrosion reactions in real time by the analysis of a temporal series of micrographs using in situ optical microscopy coupled to electrochemical techniques. The approach was applied to study the pitting corrosion of AISI 1040 steel during chronoamperometric measurements, in carbonate and chloride solutions. Using this coupled approach, it was possible to measure different pit parameters as well as to estimate the mean pit depth. The number of pits and the total pit area presented different behaviors as the chloride concentration increased and active and passive pits were detected.

Electrochemical noise coupled to in situ optical micrographs was used to study corrosion processes in AISI 1020 steel immersed in seawater. The noise data was analysed using wavelet transform. The results were represented in energy diagrams and showed that considerable changes occurred in the corrosion mechanism during the initial step of the experiment (until 7200 s). During this initial step, it was observed that the corrosion was predominantly localized by means of pitting formation and intergranular corrosion. After approximately 50,000 s (14 h) of immersion, general corrosion processes become dominant. The conclusions obtained from the analysis of the current noise signal using the wavelet transform were confirmed by optical micrograph which suggests that the coupling of electrochemical noise and optical microscopy techniques can be valuable in studying corrosion processes in this system. Another advantage of this procedure is the elucidation and separation of corrosion processes, such as, for example, pitting and intergranular ones, that are not commonly identified by other techniques.

This work presents a study of the initial instants in the pitting corrosion of AISI 1040 steel, analyzed by temporal series micrographs coupled to an open circuit potential (Eoc) and polarization curves. During the Eoc measurement, the pit induction time and the initial pit growth in MnS inclusions was detected in alkaline sulfide solution. The pit area behavior has two distinct rate of area changes in specific regions directly associated to current slope changes. Finally, it was possible to create a three-dimensional model of the pit depth evolution on the metal, using Faraday’s law and the bullet-shaped geometry.

This work presents the coupling of polarization curves and temporal series of in-situ micrographs during pit corrosion, thus allowing the current, the number of pits, and their area as a function of potential to be examined. Upon analyzing the data, it is possible to propose that the current slope changes are associated to the beginning of pit area growth without any change in their number. The pit potential is clearly correlated with the explosion in the number of pits. Finally, using the charge, the number of pits and their area, it was possible to estimate the mean pit depth and its growth law during the experiments. Keywords: Corrosive sulfide solution, In-situ optical microscopy, AISI 1040 steel, Pitting corrosion, Digital image processing

The main objective of this study was to evaluate the potential application of a lightweight concrete produced with lightweight coarse aggregate made of the water treatment sludge and sawdust (lightweight composite), by determining the thermal properties and possible environmental impact of future residue of this concrete. Two types of concrete were prepared: concrete produced with the lightweight composite dosed with cement/sand/composite/water in a mass ratio of 1:2.5:0.67:0.6 and conventional concrete dosed with cement/sand/crushed stone/water in a mass ratio of 1:4.8:5.8:0.8. The thermal properties were determined by the hot wire parallel technique. The possible environmental impact was measured using the procedures and guidelines of the Brazilian Association of Technical Standards – ABNT. The concrete produced with the lightweight composite presented a 23% lower thermal conductivity than the conventional concrete. The concrete produced with the lightweight composite presented a set of thermal properties suitable for the application of this concrete in non-structural sealing elements. The concentration of aluminum in the solubilized extract of the concrete produced with the lightweight composite was much lower than the concentration of aluminum in the water treatment sludge, confirming the possible reduction of environmental impact of this composite for use in concrete.

A new electrode, obtained by the dispersion of template carbon nanoparticles onto polyaniline, is presented in this paper. Template carbon was synthesized via the pyrolysis of the polyfurfuryl alcohol inside the nanometric pores of porous Vycor glass, and the electrodes were prepared by a polyaniline-template carbon mixture. Scanning electron microscopy showed that polyaniline-template carbon films presented a wholly modified morphology when compared to polyaniline and polyaniline-graphite films. Electrochemical characterization indicated that the interconversion reactions of polyaniline were strongly facilitated in the presence of the template carbon. The new electrode also exhibited excellent chemical and physical stabilities. Finally, anodic stripping voltammetry measurements revealed that the new electrode presented a noteworthy linear response to very low concentrations of Cu2+ and Pb2+ ions, under few minutes of pre-concentration. Keywords: Template carbon nanoparticles, Copper, Lead, Analytical applications

There are some electrocatalytic reactions in which the key parameter explaining their behavior is a local change in pH. Therefore, it is of utter importance to develop an electrode that could quantify this parameter in situ, but also be customizable to be used in different systems. The purpose of this work is to build a versatile rotating ring/disc electrode (RRDE) with IrOx deposited on a glass tube as a ring and any kind of material as disc. As the IrOx is sensitive to pH variation, the reactions promoted on the disc can trigger proportional pH shifts on the ring. In such assembly, the IrOx ring presents a fast response time even during the pH transients due to the small thickness of the ring (approximately 10 μm), which enables the detection of interfacial pH changes. The ring electrode was tested toward the interfacial pH shift observed during the electrolytic reduction of water on the disc and also characterized by acid-base titration to determine the response time. As the main conclusions, fast response and durable RRDE were obtained, and this assembly could be used to revisit many electrocatalytic reactions in order to test the importance of local pH on the process.

In this study, a combined pH microelectrode has been developed consisting of an indicator electrode made of IrO2 prepared using the polymeric precursor method and deposited in a platinum microwire. This electrode was mounted inside a stainless steel needle, the external surface of which was painted with conductive silver ink which is used as reference electrode. This device was compared with a conventional glass electrode, and the results presented linear behavior in the pH range from 2.0 to 12.5, in Na+ and K+ solutions, exceeding glass electrodes in the alkaline range. The sensitivity was 56.9±0.2 mV pH−1 and using ANOVA test we conclude that the electrode is not sensitive to the presence of alkaline cations such as Li+, Na+ or K+. Finally, the response time (t95) was 4.9 to 9.0 s depending on the solution pH. The combined pH microelectrode can be used several times and, after three years, continues to have a response similar to that of a freshly produced one. Keywords: Combined pH microelectrode, Iridium oxide, Polymeric precursor method

This paper presents a study of AISI 1040 steel corrosion in aqueous electrolyte of acetic acid buffer containing 3.1 and 31 × 10−3 mol dm−3 of Na2S in both the presence and absence of 3.5 wt.% NaCl. This investigation of steel corrosion was carried out using potential polarization, and open-circuit and in situ optical microscopy. The morphological analysis and classification of types of surface corrosion damage by digital image processing reveals grain boundary corrosion and shows a non-uniform sulfide film growth, which occurs preferentially over pearlitic grains through successive formation and dissolution of the film.

The pitting corrosion is one of the most dangerous forms of corrosion and its mechanism is not yet fully understood. The existence of stable pits when the pitting corrosion occurs in dissolved CO2 environments can be attributed to the precipitation of FeCO3 which occurs inside the pits and induces the acidification of the electrolyte in this region. Consequently, Cl- ions tend to accumulate at the interfacial pit boundary to counterbalance the H+ produced during the formation of siderite film and, as a consequence, pits grow on the metal surface. Therefore, it is expected that transient pH changes could be directly related to the processes of nucleation, growth, passivation and stabilization of pit. In this context, this work presents the development of a ring-shaped sensor built around a steel sample to determine the interfacial pH changes during the pitting corrosion. AISI 1020 steel is the constituent material of the disc in the center of the electrode surrounded by a ring of IrOx, a sensitive material to pH changes. The Pechini method was employed to generate the ring on a glass tube (gap between the ring and the disc) with thickness of 7 ± 2 μm. A disc area of 680 μm x 544 μm (steel sample) was observed in situ by temporal series of micrographs (TSM) with an optical microscope. At the same time, the sensor detected the interfacial pH changes during the initiation of pitting corrosion, its evolution and during the pit passivation. The study of pitting corrosion of carbon steel was performed in 0.1 mol dm-3 Na2HCO3 (pH 8.3) with Cl- ions during the open circuit potential (OCP), polarization curves (PC) and chronoamperometric (CA) measurements. Before the corrosion experiments, acid-base titration of NaOH 0.1 mol dm-3 by H3PO4 1.0 mol dm-3 were performed for characterization of pH sensor together with pH measurements on solution through a combined glass electrode. The behavior of sensor is very close to the pH determined with conventional pH electrode, e.i., it was observed the same profile for the first and second dissociations constants for H3PO4. Two regions that exhibit a linear response were observed for ring shaped sensor. The first one is the 2-3.5 pH range and the other is the 3.5-12.5 pH range. These two linear bands had slops of 52.1 mV pH-1 and 24.9 mV pH-1, respectively. The TSM obtained in the corrosion experiments was quantified using the ImageJ software to get the number of pits, during the passivity breakdown (nucleation of several pits over the metal surface), and to access the total pit area during the localized corrosion evolution. It was observed a slowly decrease and increase at pH in near surface solution during the passivation of steel sample. At passivity breakdown was observed approximately 6000 pits on the TSM and this value remained approximately constant after 740 s during the CA measurements performed up to 500.0 mV more positive than OCP. Besides, it was observed a slight decrease at pH during this process. Analyzing the total pit area changes during the breakdown of passive film, we noticed a shift when the number of pits becomes constant where two growth rates were calculated based on TSM. This behavior is due to nucleation of metastable and stable pits. This explains the reduction on this second growth rate after the number of pits gets constant. After the pitting potential the greatest variation on the sensor potential was observed. The pH in the solution near the electrode decreases one order of magnitude at the end of the anodic polarization due to anolyte released from pits. A surface mapping shows approximately 30 big pits on metal surface which could be related to this pH change.

According to NACE International, the global cost generated by corrosion is about US$ 2.5 trillion and up to 35% could be saved by using corrosion control practices[1]. However, the correct choice of the method to control the corrosion it is tied to the knowledge of how the process happens. In this aspect, the pitting corrosion on stainless surfaces is extremely worrying. This kind of corrosion is a localized form which cavities are produced in the materials, but it is more difficult to detect, predict and avoid or minimize. Here is proposed a new and cheap methodology to study the tridimensional format of the pitting corrosion using reconstruction of segmented images. The pitting were produced by polarization of stainless steel AISI 304 at 0.46 V (vs Ag/AgCl/KCl satured) into 0.1 mol L- 1 HCl during 10 minutes at 25 °C. Afterwards, the samples were cut, washed with pure water, dried and immersed into resin keeping the plane of surface in a perpendicular direction to the base of resin block. Next, the resin block was polished using sandpaper (mesh 2000) and alumina slurry (1 μm). Every 8 μm of scraping one optical microscopy image of the surface-bulk of the sample was taken. This procedure allowed a side view of the pitting detailing its shape and extension. Finally, the segmented images were reconstructed in a tridimensional one, which shows in detail the shape and extension of each pitting in the surface of stainless steel. Now, the distribution of pitting and its shape variation could be related to the other physical and chemical signals monitored during the pitting formation, as current intensity or chemical composition. This methodology, although destructive, is easily applicable and allows to evaluate in an inexpensive and reproducible way the pitting formation.