Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures

[EN] This paper studies the general corrosion behaviour of the micro-plasma arc welded AISI 316L stainless steel in phosphoric acid at different temperatures (25-60°C) and at a Reynolds number of 1456. Galvanic corrosion has been studied using zero-resistance ammeter (ZRA) measurements and polarization curves (by the mixed potential theory). Results show that the microstructure of the stainless steel is modified due to the micro-plasma arc welding procedure. Coupled current density values obtained from polarization curves increase with temperature. ZRA tests present the highest iG values at 60°C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluates the importance of the galvanic phenomenon. Both techniques present the most positive potentials at the highest temperature. This study reveals that micro-plasma arc welded AISI 316L stainless steels are appropriated working in the studied H3PO4 media from a corrosion point of view for all the temperatures analysedThe authors would like to express their gratitude to the Spanish MAEC (PCI Mediterráneo C/8196/07, C/018046/08, D/023608/09) and to Asuncion Jaime for her translation assistance.Sánchez Tovar, R.; Montañés Sanjuan, MT.; García Antón, J.; Guenbour, A.; Ben Bachir, A. (2011). Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures. Corrosion Science. 53(4):1237-1246. https://doi.org/10.1016/j.corsci.2010.12.017S1237124653

Passivation behaviour of Alloy 31 (UNS N08031) in polluted phosphoric acid at different temperatures

The influence of temperature (20–80 °C) and chloride concentration (0.06–0.42 wt.% KCl) on the electrochemical behaviour of the UNS N08031 was studied in 40 wt.% polluted phosphoric acid solution. Passivation behaviour was investigated by using potentiostatic tests at different potentials. From the linear regions of the log i vs. log t transients, the parameter n was obtained. The results showed that the applied potential hardly affects on the passivation rate n. However, n values decreased when temperature increased. The values of n demonstrated that the passive film formed on Alloy 31 was compact and highly protective.The authors express their gratitude to the MAEC of Spain (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09 and D/030177/10), to Programa de Apoyo a la Investigacion y Desarrollo de la UPV (PAID-06-09) and to the Generalitat Valenciana (GV/2011/093) for the financial support and to Dr. Asuncion Jaime for her translation assistance.Escrivá Cerdán, C.; Blasco Tamarit, ME.; García García, DM.; García Antón, J.; Guenbour, A. (2012). Passivation behaviour of Alloy 31 (UNS N08031) in polluted phosphoric acid at different temperatures. Corrosion Science. 56:114-122. https://doi.org/10.1016/j.corsci.2011.11.014S1141225

Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions

tThe influence of temperature and the effect of aggressive anions on the electrochemical behaviour of UNSN08031 stainless steel in a contaminated phosphoric acid solution were evaluated. Stabilisation of thepassive film was studied by potentiodynamic polarisation curves, potentiostatic tests, electrochemicalimpedance spectroscopy (EIS) measurements, Mott Schottky analysis and X-ray photoelectron spec-troscopy (XPS). The stability of the passive film was found to decrease as temperature increases. The filmformed on the stainless steel surface was a n-type semiconductor and the XPS spectrum revealed thepresence of fluoride ions.Authors express their gratitude to the Ministry of Education of Spain (MHE2011-00202) for its financial support during the stay at University of Manchester, to MAEC of Spain (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09 and D/030177/10) and to the Generalitat Valenciana (GV/2011/093) for the financial support. The authors would also like to acknowledge the support of the School of Materials at the University of Manchester for providing analytical and technical support for the study.Escrivá Cerdán, C.; Blasco Tamarit, ME.; García García, DM.; García Antón, J.; Akid, R.; Walton, J. (2013). Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions. Electrochimica Acta. 111:552-561. https://doi.org/10.1016/j.electacta.2013.08.040S55256111

La corrosion localisée des aciers en milieu NaHCO3/NaCl et son inhibition par les ions HPO42 et NO2 (rôle des composés à base de Fe(II))

The aim of this work is to understand the pitting mechanisms of S235 carbon steel in aerated aqueous NaHCO3/NaCl solutions and to study the effect of two inhibitors (HPO42- and NO2-) on pitting of steel in the same media. Electrochemical measurements coupled to spectroscopic analysis were used to characterize pitting corrosion. The activity of a given pit has been studied by scanning Vibrating Electrode Technique (SVET). The micro Raman spectroscopy is used to identify and to follow, in situ, the evolution of the corrosion products formed in the pits. In parallel, a chemical study of synthesis and oxidation of the products likely to form in the pit has been done in experimental conditions similar to those found in the pits. The characterization, in situ, of the products of corrosion formed in the pits showed that the first corrosion product formed is an iron carbonate FeCO3 named siderite. The oxidizing action of the dissolved oxygen present in solution, transforms siderite into carbonated green rust, that is then oxidized into goethite. These results seem to show that a meaningful relation exists between the nature of the corrosion products and the process of development of the pits. Indeed, the formation of siderite and green rust signs a fast development of the pit, whereas the formation of ferric compounds is associated to a slowing of the development of the pit and an acceleration of their repassivation. The same methodology has been used for the study of the effect of two corrosion inhibitors (HPO42- and NO2-) on the process of pitting of the studied steel. The inhibition by the HPO42- ions is explained by a reduction of the proportion of siderite formed to the profit of an iron phosphate (vivianite), product known to be rather protective. For elevated concentrations of HPO42-, the exclusive formation of the vivianite gives a better protection against pitting. For the NO2- ion, the inhibiting effect seems to come from the formation of Fe(III) complexes [Fe(H2O)6]3+. Indeed, the characterization of the corrosion products formed in the pits in presence of the nitrite ions gave the complex [Fe(H2O)6]3+ with a weak proportion of siderite. NO2- ions oxidize quickly the dissolved Fe(II), giving a Fe(III) complex probably precursors of the Fe(III) spinel oxides of the passive film.LA ROCHELLE-BU (173002101) / SudocSudocFranceF

Raman spectroscopic studies of the corrosion of model iron electrodes in sodium chloride solution

We have explored the un-enhanced Raman spectra of both single and twin electrodes in 3.5% NaCl solution (at ambient temperatures) over a range of applied potentials (between 20 and 200 mV) and times (between 0 and 5 h). Under these conditions, we observed the initial formation of 'green rust' (hydroxychlorides and/or hydroxycarbonates), followed by the formation of magnetite (Fe3O4) and then a mixture of the alpha- and gamma-FeOOH (goethite and lepidocrocite, respectively). These data are consistent with a model for corrosion during which the initially formed magnetite is either covered, or replaced, by layers of the FeOOH oxidation products. Fitting of the data as a function of time and potential shows that, although the product range is independent of potential, the relative kinetics of formation of magnetite and its subsequent conversion to the gamma-FeOOH were potential and time dependent. Analysis by mapping of the dry corroded surface showed a variety of species, including green rust, some Fe(OH)(3), as well as the gamma-FeOOH, and possibly some beta-FeOOH. But no surface magnetite was found, indicating that this material had been either covered up or converted to FeOOH. We noted several complications during this work, including the interference of resonance effects (on the Raman intensities) and the heterogeneity of the corrosion process (and hence distribution of species on the corroded surface). However, we believe that the use of un-enhanced Raman methods has led to conclusions more likely to be relevant to 'real' corrosion processes. Copyright (c) 2007 John Wiley & Sons, Ltd

Controlled electrodeposition of iron oxide/nickel oxide@Ni for the investigation of the effects of stoichiometry and particle size on energy storage and water splitting applications

Controlled synthesis of nickel/iron multimetal oxides with different stoichiometry and particle sizes was carried out by varying the pH of the reaction medium. Electrodeposited samples grown at different pH values showed a wide range of electrochemical properties such as dissimilar current response and potential window due to the formation of different stoichiometry and surface morphologies. Smaller particle size and higher content of NiO are advantageous due to the creation of a facile diffusion path. Moreover, electrical conductivity as well as series resistance increased for the samples with smaller particle size due to the quantum size effect. The quantum size effect was confirmed from the blue shift of the UV-vis absorbance spectrum. The facile diffusion path lowered the charge transfer resistance and accelerated the reaction rate for water splitting. Furthermore, the quantum size effect shifted the flat-band potential and increased the overpotential in the water splitting reaction. Multimetal oxides exhibited a small overpotential of ∼−0.27 V (corresponding to the current response of 10 mA cm−2) and a small Tafel slope of ∼63 mV dec−1. Finally, an asymmetric supercapacitor (ASC) cell was fabricated with electrodeposited samples, which showed a large potential window of ∼1.6 V along with a high energy and power density of ∼91 W h kg−1 and 7200 W kg−1, respectively. Furthermore, the ASC exhibited very low relaxation time constant (∼1.3 ms) and long stability of ∼83% after 10 000 CD cycles, ensuring the effectiveness of electrodeposited multimetal oxides for energy storage as well as water splitting applications