Electrochemical behavior of cobalt oxide coatings on cold-rolled steel in alkaline sodium sulfate

The electrochemical behavior of a coating of cobalt oxide on cold-rolled steel in alkaline sodium sulfate was Studied using the electrochemical techniques of open-circuit potential measurements and electrochemical impedance spectroscopy. The coating was prepared at different annealing temperatures ranging from 350 to 750 degreesC and characterized by SEM, EDX and XRD. Below 550 degreesC the composition of the coating was basically of Co3O4. At 750 degreesC CoO was formed and big cracks appeared on the film exposing an inner layer of iron oxides. Analysis of the EIS data is very difficult because of the complexity of the interface structure. It can be inferred that the charge transfer resistance of the coatings prepared at 350 and 450 C were higher than those for the coatings prepared at temperatures above 550 degreesC. (C) 2002 Published by Elsevier B.V. Ltd.

Changes on iron electrode surface during hydrogen permeation in borate buffer solution

Hydrogen interaction with oxide films grown on iron electrodes at open circuit potential (E-oc) and in the passive region (+0.30 V-ECS) was studied by chronopotentiometry, chronoamperometry and electrochemical impedance spectroscopy techniques. The results were obtained in deaerated 0.3 mol L-1 H3BO3 + 0.075 mol L-1 Na2B4O7 (BB, pH 8.4) solution before, during and after hydrogen permeation. The iron oxide film modification was also investigated by means of in situ X-ray absorption near-edge spectroscopy (XANES) and scanning electrochemical microscopy (SECM) before and during hydrogen permeation. The main conclusion was that the passive film is reduced during the hydrogen diffusion. The hydrogen permeation stabilizes the iron surface at a potential close to the thermodynamic water stability line where hydrogen evolution can occur. The stationary condition required for the determination of the permeation parameters cannot be easily attained on iron surface during hydrogen permeation. Moreover, additional attention must be paid when obtaining the transport parameters using the classical permeation cell. (c) 2007 Elsevier Ltd. All rights reserved.

CATHODIC BEHAVIOUR of ANODIZED TITANIUM IN SIMULATED PHYSIOLOGICAL CONDITIONS

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrochemical Behavior of Cu-9% Al-5% Ni-2% Mn Alloy in Chloride Media

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Corrosion behaviour of thermal sprayed nitinol coatings

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Evaluation of 316L Stainless Steel Corrosion Resistance in Solution Simulating the Acid Hydrolysis of Biomass

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudio de la pasivacion de la aleacion Co-Cr-Mo en suero fisiologico

Results are presented on the mechanism of passivation of Co-Cr-Mo biological implant alloys in physiological serum using open circuit potentiometry, potentiodynamic curves, and electrochemical impedance spectroscopy. The potential dependence of impedance data and the analysis of the parameters obtained indicate a progressive diminution of the initial layer thickness and the simultaneous formation of a second higher resistive layer. In more severe conditions than the existent in human body, the metallographic examination of the alloy surface shows localized corrosion in interdendritric regions. Elemental analysis of the surface reveals the presence of higher chromium content in these regions. The presence of chlorine was not detected, which suggested that during preferential attack, soluble species are also formed.

Microstructural characteristics and electrochemical behavior of Co3O4 sintered electrodes

Co3O4 can be used as electrocatalyst for oxygen evolution reaction. The macro and microstructure of the oxide, obtained by compacting and sintering lithium-doped Co3O4 powder in atmosphere of dry air and in conditions of controlled temperature and time was analyzed by metallographic techniques. The porous material was characterized by XRD, SEM and EDS combined techniques. For working temperatures up to 1200°C, the pellet was consituted of particles with varying sizes over a wide range of particle size and, at higher temperatures CoO is formed and polymorphic transformation was observed. The materials were also characterized electrochemically in alkaline media by open circuit potential and potentiodynamic I/E measurements. The results were compared to those previously prepared by others by thermal deposition.

Comparison between different conditions of the chemical polymerization of polyaniline on top of PET films

Composites produced during the in situ chemical polymerization of aniline on top of a poly(ethylene terephthalate) (PET) film, in different conditions, were studied by open-circuit potential (Voc), ultraviolet-visible, and infrared spectroscopy, electrical conductivity measurements, scanning electron microscopy, and atomic force microscopy. The polymerization monitoring by Voc showed a maximum associated with the intermediate pernigraniline oxidation state and a final formation of polyaniline (PANI) in the doped emeraldine salt (ES) form. Furthermore, high electrical conductivity values were obtained for the PANI-ES coating prepared under selected conditions. A globular formation was observed for the doped PANI-ES coating with globules of sizes of the same order and same shape of the PET, demonstrating the influence of the substrate on the coating morphology.

Influence of thermal treatments in the corrosion behaviour of HVOF Cr 3C2-NiCr coatings

Thermal spray coatings as Cr3C2-NiCr obtained by high velocity oxy-fuel spraying (HVOF) are mainly applied due to their behaviour against aggressive erosive-abrasive and corrosive atmospheres and their thermal stability at high temperatures [1]. In order to increase the corrosion protection that it offers to the substrate trying to close the interconnected pores, it is possible to apply a thermal treatment with the gun during the spraying of the coating. This treatment could be applied in different ways. One of these ways consists of spraying only a few layers of coating followed by thermal treatment and finally the spray of the rest of layers. This thermal treatment on spraying is studied related to the corrosion properties of the system. The study comprises the electrochemical characterisation of the system by open circuit potential (OC), polarisation resistance (Rp), cyclic voltammetry (CV) and impedance spectroscopy measurements (EIS). Optical and scanning electron microscopy characterisation (OM and SEM) of the top and cross-section of the system has been used in order to justify the electrochemical results.

Um estudo sobre a corrosão aquosa de ligas de alumínio 7xxx submetidas a diferentes tratamentos térmicos

This job aim has been to study the aqueous corrosion of the 7xxx heattreatable aluminium alloys, used in the aeronautical industry. The 7010, 7050 and 7475 alloys, have been supplied in the T7 condition and submitted to the annealed and aging thermal treatments of in order to study their behaviours front to corrosion in 5% NaCl pH 6,0, air-saturated and deaerated solutions. The electrochemical study has been accomplished through potential measures in open circuit, potentiodynamic polarisation curves and electrochemical impedance spectroscopy (EIS). The aged alloy resulted to be the most resistant to corrosion and annealed the less resistant ones. In spite of it they have different chemical compositions, in each mean, the alloy with the same thermal treatment has behaved in a similar way. In aerated solution, the process is controlled by oxygen diffusion and in oxygen absence for dissolution through a film. Hardness and mass loss measures, after corrosion test, have supported this research.

Efeito do nitrato e nitrito na corrosão das ligas de alumínio 2024 e 7050 em soluções de NaCl

The 2024-T3 and 7050-T7 aluminium alloys electrochemical behavior has been studied in NaCl 5% neutral solutions and 0,1M concentration containing NO 3 - or NO 2 -. The current job supports corrosion research on aluminium alloys used in aeronautic industry. Open circuit potential, polarisation curves and electrochemical impedance spectroscopy techniques have been used. In chloride solutions, alloys corrosion takes place through a pitting mechanism. Added anions to aerated solutions do not possess inhibition effect. In deaerated solutions, nitrite has diminished anodic dissolution rate, probably by incorporating this anion in the oxide and/or hydroxide film.

Synthesis and characterization of poly-o-toluidine: Kinetic and structural aspects

Poly(o-methylaniline) (poly-o-toluidine, PTOL) was synthesized by chemical oxidation of o-toluidine with ammonium peroxydisulfate in an aqueous 1.0 mol L -1 HCl solution. The progress of polymerization was followed by measuring the open-circuit potential (OCP) of a Pt electrode immersed in the reaction medium with the polymerization time. The chemical synthesis of PTOL was carried out at different monomer:oxidant (M:O) molar ratios (4:1, 2:1, 1.5:1, 1:1, and 0.66:1), and the products obtained were characterized by infrared spectroscopy, gel permeation chromatography, and X-ray diffraction. The molecular weight and percentage of crystallinity of PTOL are higher for samples synthesized in an excess of the monomer, i.e. at higher M:O ratios. However, the yield of PTOL prepared at higher M:O ratios is considerably low, in particular at a 4:1 M:O ratio, which is the M:O ratio most commonly used in the literature to synthesize polyaniline and its derivatives.

Screen-printed carbon electrode modified with poly-L-histidine applied to voltammetric determination of chromium (VI)

The present work reports the use of a screen-printed carbon electrode (SPCE) modified by poly-L-histidine film to determine chromium (VI). Stable films can be formed by direct addition of PH solution 1 % (w/v) on the electrode surface, followed by heating at 80°C during 5 min. Calibration curves can be constructed for Cr(VI) from 1.0 × 10-5 mol L-1 to 7.0 × 10-5 mol L-1 Cr (VI) in acetate buffer pH 4 using a preconcentration step of 60s at open circuit potential. A relative standard deviation of 3.2% was for five determination of 4.0 × 10 -5 mol L-1 Cr (VI). The method was successful applied to determination of Cr(VI) in wastewater samples from a leather dyeing industry. copyright The Electrochemical Society.

Influence of cerium (IV) ions on the inorganic and organic phase for preparation of a siloxane-PMMA based film on tin plate substrate

Tinplate is one of the most widely used food canning materials, however, there are significant problems related to the use of tinplate cans, such as alterations in sensory features affecting food quality and corrosion phenomena of the canning material. To avoid corrosion problems different methods have been used for the passivation of tinplate such protective lacquers or different kinds of corrosion inhibitors (chromate and dichromate). However, chromates and dichromates are extremely harmful to the environment and can cause carcinogenic tumors to humans. An option, protective coatings obtained by the sol-gel process, act as a physical barrier, which isolates the surface of metal protecting from the corrosive agents. The aim of this work is to study the influence of addition of cerium (IV) ions in the inorganic and organic part of sol-gel processing in the formation of hybrid coatings based on siloxane-PMMA on tin plate. The coatings were obtained by dip-coating technique and evaluated by open circuit and impedance measurements, linear polarization and polarization curves obtained in 3.5% NaCl solution. The results have clearly shown the improvement on the protective properties of the Ce 4+ modified film when added into the organic phase, which can be due to the formation of a more uniform and densely reticulated siloxane-PMMA film. © 2009 by NACE International.