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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.

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.

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.