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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.

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.

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

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.