Corrosion behavior and microstructural characterization of friction stir welded API X70 steel

Friction stir welding (FSW) is an excellent alternative process used in pipelines circumferential welds due to fusion welded joint low corrosion resistance. This study describes the corrosion resistance as a function of the microstructural features resulting from an API X70 FSW welded joint. The microstructural features were examined by optical microscopy, scanning electron microscopy, and x-ray diffraction. The corrosion analysis was conducted employing potentiodynamic polarization tests using an electrochemical microcell, which allowed to test small circular areas delimited by a 2 mm in diameter O-ring gasket. The base metal and heat-affected zone were the most susceptible regions to corrosion due to their banded microstructures. The re-stirred-zone and stir zone were the most resistant regions to corrosion which was associated to grain refinement. The corrosion rate presented by the base metal and the heat-affected zone was approximately six times higher than the region of least susceptibility to corrosion, in this case, the re-stirred-zone.Peer ReviewedPostprint (author's final draft

Cerium conversion coating and sol-gel coating for corrosion protection of the WE43 Mg alloy

In this work, the electrochemical behavior and morphological characterization of a system consisting of a cerium conversion layer, a hybrid sol-gel coating, and the two coatings applied sequentially (duplex) have been evaluated for the corrosion protection of WE43 Mg alloy. The different characterization techniques showed that the surface coverage by the hybrid coating was improved by the previous application of the conversion coating. The fitting of the impedance diagrams with electrical equivalent circuits allowed to propose a physical model for the coating, evidencing its interaction with the porous Mg oxide/hydroxide layer. Self-healing properties of the duplex coating were also disclosed.This study was funded in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. The authors would like to thank the SMM/EESC-USP for the use of the laboratory facilities and EMBRAER for providing the material. O.M. Prada Ramirez is thankful to CAPES Proc. 88887.388129/2019-00. Haroldo C. Pinto is a CNPq fellow. HG de Melo is thankful to Fundação de Amparo à Pesquisa do Estado de São Paulo - Brazil (FAPESP) Proc. 2018/01096-5 and Proc. 2013/13235-6.Postprint (author's final draft

Comparison of the Corrosion Resistance of Several Conversion Treatment for Galvanized Steel in NaCl Solution

Chromate conversion treatments have been widely used due to their excellent corrosion resistance properties, however their use is increasingly restricted because of the highly toxic cromatic acid solutions required, with consequent effluent disposal and ecological problems. The elimination of these toxic chemicals is considered a priority within European Union.Centro de Investigación y Desarrollo en Tecnología de Pintura

Local electrochemical investigation of copper patina

The patination of copper is known for its complexity and heterogeneous formation. For a deeper investigation, a locally resolved surface analysis was considered. An exact determination of the accessed area and a potentiostatic control in a three-electrode configuration was reached with the use of the electrochemical microcell technique, which enables local electrochemical measurement such as local electrochemical impedance spectroscopy and cyclic voltammetry. Such a technique provides a unique way for performing the investigation of heterogeneities on electrode surfaces. The local electrochemical measurements on the artificially patinated surface have allowed distinguishing areas of different reactivity even when the analysis of the surface revealed a homogenous chemical composition of patina. Local measurements with the electrochemical microcell showed the presence of small defects on the patina layer that can be modelled by considering a hemispherical diffusion process at small active areas surrounded by larger less reactive domains.CAPESSpanish Education Ministr

Etude de la corrosion localisée de l'alliage d'aluminium 7475 T621 par spectroscopie d'impédance électrochimique globale et locale en milieu sulfate de sodium

PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Etude de la corrosion du cuivre en milieu sulfate et chlorure au moyen de la microélectrode à cavité et de la microcellule électrochimique

PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Electrochemical impedance spectroscopy investigation of the electrochemical behaviour of copper coated with artificial patina layers and submitted to wet and dry cycles

International audienceDue to rain events historical monuments exposed to the atmosphere are frequently submitted to wet and dry cycles. During drying periods wetness is maintained in some confined regions and the corrosion product layer, generally denominated patinas, builds up and gets thicker. The aim of this study is to use electrochemical impedance spectroscopy (EIS) to investigate the electrochemical behaviour of pure copper coated with two artificial patina layers and submitted either to continuous or to intermittent immersion tests, this latter aiming to simulate wet and dry cycles. The experiments were performed in 0.1 mol dm(-3) NaCl solution and in artificial rainwater containing the most significant pollutants of the city of Sao Paulo. The results of the continuous immersion tests in the NaCl solution have shown that the coated samples behave like a porous electrode with finite pore length. On the other hand, in the intermittent tests a porous electrode response with semi-infinite pore length can be developed. The results were interpreted based on the model of de Levie and a critical comparison with previous interpretations reported in the literature for similar systems is presented

Electrochemical study of modified non-functional bis-silane layers on Al alloy 2024-T3

In the last few years great efforts have been made in order to find and to develop environmentally friendly substitutes for Cr6+ pre-treatments applied on aluminium alloys used in the aircraft industry. Among the potential substitutes, silane layers have attracted considerable interest from researchers and from the industry. The present work investigates the anti-corrosion behaviour of (bis-1, 2-(triethoxysilyl) ethane (BTSE)) silane layers modified with Ce ions and/or silica nanoparticles applied on Al alloy 2024-T3 substrates. The corrosion behaviour was investigated in 0.1 M NaCl solution via d.c. polarization and electrochemical impedance spectroscopy (EIS). Contact angle measurements and XPS were used to assess information on the chemistry of the silane pre-treated surfaces. The results have shown that the introduction of additives improves the corrosion protection properties of the silane layer. (c) 2008 Elsevier Ltd. All rights reserved

Taurodontism In Patients With Nonsyndromic Cleft Lip And Palate In A Brazilian Population: A Case Control Evaluation With Panoramic Radiographs

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Objectives. The purpose of this study was to evaluate the prevalence of taurodontism in patients with nonsyndromic cleft lip and palate (NSCLP) within a Brazilian population. Study Design. The study was designed as an epidemiologic case-control single-center study. Three hundred eighty-eight patients were included: 88 had NSCLP, and 300 comprised the control group. The first and second permanent mandibular molars were included in this study. By using panoramic radiographs, taurodontism was categorized as mesotaurodontism, hypotaurodontism, and hypertaurodontism. Results. Seventy patients (23.3%) from the control group and 36 patients (40.9%) from the case group presented taurodontism (P < .001). In the control group, 108 (9%) teeth showed taurodontism, whereas in the case group with cleft lip and palate (CLP), 64 (18.2%) teeth showed dental anomalies (P < .001). In both groups, most taurodontic teeth presented hypotaurodontism, followed by mesotaurodontism, while hypertaurodontism was found in only two teeth. The probability of taurodontism in patients with cleft lip (CL) was 2.36 (P = .010) times higher compared with those with CLP, whereas the occurrence of taurodontism in patients with cleft palate (CP) was 3.15 (P = .002) times greater than in patients with CLP. Conclusions. The results from this study indicate a close relationship between taurodontism and NSCLP and the possibility of different cleft subphenotypes.1206744750Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)State University of Montes ClarosConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Electrochemical study of modified cerium-silane bi-layer on Al alloy 2024-T3

In this paper, the performance of bis-1, 2-(triethoxysilyl) ethane (BTSE) as a pre-treatment to protect the AA 2024-T3 against corrosion has been investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and the scanning vibrating electrode technique (SVET). The microstructural and morphological characterizations were carried out via scanning electron microscopy and atomic force microscopy and the chemical composition evaluated using contact angle measurements and X-ray photoelectron spectroscopy (XPS). The electrochemical results showed that the additives improved the anticorrosion properties of the coating. The chemical characterization indicated that additives contribute to an increased degree of surface coverage, as well as to a more complete reticulation. The SVET results evidenced the self-healing abilities of Ce ions. (C) 2009 Elsevier Ltd. All rights reserved.FAPESPCNP