Search results for "Pitting"
showing 10 items of 43 documents
Semiconductor electrochemistry approach to passivity and passivity breakdown of metals and metallic alloys
2004
AbstractA critical appraisal of the use of the theory of semiconductors in characterising passive films on metals and alloys is provided, with special emphasis on the use of Mott-Schottky theory for the location of characteristic energy levels of the passive film-electrolyte junction. Some inconsistencies between theory and experimental results in the case of thin passive films are discussed together with possible alternative ways for overcoming such problems. The role of semiconducting properties in determining the pitting behaviour of passive films on W in solutions containing halide is presented and discussed. The validity of a recently proposed correlation between the solid state proper…
Epicuticular wax content and morphology as related to ethylene and storage perfomance of 'Navelate' orange fruit
2010
8 pages, 6 figures, 1 table. -- Available online 15 September 2009.
A study of electrochemically-induced corrosion of low carbon steel in a medium modelling acid rain
1994
Complementary electrochemical, spectrophotometric and electron microsopic investigations were made in addition to the conversion electron Mossbauer spectroscopic (CEMS) measurements to learn more about the mechanism of corrosion of low carbon steel samples in aqueous sulfate and sulfite containing sulfate solutions (pH 3.5, 6.5 and 8.5). Passivation of iron in pure sulfate solution was studied in detail in earlier papers. In the present work, we used a solution containing both sulfate and sulfite anions to obtain more information about the effect of acid rain on low carbon steel samples. The compositions and thicknesses of the passive films formed due to the electrochemical treatments were …
Electrochemical and conversion electron mössbauer study of corrosion induced by acid rain
1993
Abstract The passivation of low carbon steel was studied in aqueous solution of 0.5M Na2SO4 +0.001M NaHSO3 (pH 3.5, 6.5 and 8.5) which can be considered as a model of acid rain. The used conversion electron Mossbauer spectroscopy (CEMS) with the complementary electrochemical investigations proved that the sulfite ions induce pitting corrosion at pH 3.5 and 6 5 while the measurements showed much weaker pitting at pH 8.5. The compositions and thicknesses of the passive films formed during the electrochemical treatments are determined from the CEM spectra. Only γ-FeOOH was found on the surface of the samples at pH 6.5 and 8.5. Nevertheless, at pH 3.5 the sextet belonging to Fe3C appears in the…
Chloride role in the surface of nickel electrode
1998
The chloride ion participation in the dissolution process on nickel electrodes in acid media as well as in the formation of the passive layer and in the pitting corrosion induction were studied. Composite electrodes containing nickel powder dispersed in a polymeric matrix show similar processes to those observed in polycrystalline nickel. Furthermore, phenformine hydrochloride inhibits the dissolution process due to the adsorption of the organic cation on the metal surface, although it does not protect the metal from pitting corrosion. Electrochemical impedance spectroscopy data allowed us to propose a physical model for the role of chloride ion in the dissolution and passivation processes …
Modeling and numerical simulation of the propagation of pitting corrosion of iron in chlorinated medium : contribution to the evaluation of the durab…
2012
This study deals with the understanding of the mechanisms of pitting corrosion susceptible to occur on carbon steel selected for high level nuclear waste containers. Transport/reaction models have been developed in order to simulate, by finite element method, the propagation of a pit on iron in chlorinated medium. For conservative models, pit is activated by imposing a potential on metal. Thanks to different parametric studies (geometry, environment…) simulations have permitted to classify, by severity order, the factors responsible of the increase or the inhibition of the localized corrosion rate. Otherwise, experiments on occluded (called « lead-in-pencil ») electrodes confirm that confin…
Renforcement de la résistance à la corrosion localisée de l’acier inoxydable 304L grâce au traitement de surface par laser impulsionnel
2013
L’acier inoxydable 304L est utilise dans de nombreux domaines. Cependant, il peut, dans certaines conditions, etre sensible a la corrosion par piquration. Dans cette etude, nous nous sommes interesses aux potentialites du traitement de fusion superficielle par laser nanopulse pour l’amelioration de la resistance a la corrosion de cet acier. Ce traitement consiste a focaliser un faisceau laser sur la surface du materiau, provoquant sa fusion quasi instantanee sur quelques microns, immediatement suivie d’un refroidissement ultra-rapide allant jusqu’a 1011 K/s. Les parametres laser impliquent des modifications des proprietes physico-chimiques. Nous avons notamment etudie l’influence du recouvr…
The use of local electrochemical probes and surface analysis methods to study the electrochemical behaviour and pitting corrosion of stainless steels
2007
Abstract In this paper, the electrochemical microcell technique is combined with ex situ (SIMS and XPS) and in situ (SVET) techniques to study the electrochemical behaviour and pitting corrosion of inclusion-contaning stainless steels. Dissolution of metallurgical heterogeneities, depassivation and pitting mechanisms are first discussed in 1 M NaClO4, pH 3, and 1 M NaCl, pH 3, by considering the chemical composition and morphology of inclusions. The influence of the chemical composition of passive films on the electrochemical reactions and the microgalvanic coupling processes occurring at the corrosion potential is also investigated on the same specimen microstructure.
The use of linear regression methods and Pearson’s correlation matrix to identify mechanical–physical–chemical parameters controlling the micro-elect…
2008
Abstract Machining introduces residual stresses at the specimen surface and modifies the microstructure and the texture in a small volume close to the surface. Such changes are important in controlling the corrosion behaviour of machined workpieces in the presence of an aggressive environment. In the present paper, the relationships between cutting parameters and the surface and subsurface characteristics of machined copper were first quantified experimentally using a complete plan of L 8 (2 3 ) and a linear regression method. The influence of surface characteristics on the local polarisation curves of machined surfaces was then investigated. The shear-type crystallographic orientation gene…
Recent advances in local probe techniques in corrosion research – Analysis of the role of stress on pitting sensitivity
2007
Local probe techniques have been largely applied to predict the spatial distribution of the electrochemical reactions and to quantify the corrosion rate. These local probe techniques are now being developed to capture the temporal information, in-situ and in real-time. Nevertheless only few works have been devoted to investigate with these local probes the role of stress on pitting sensitivity on passive materials. In this paper, a part of the most recent studies based on combination of local electrochemical measurements with finite element mapping of surface stress gradients are reported illustrating the role of inclusions under straining and the mechanical effect of surface preparation on…