30 research outputs found
Quantification of Hydrogen Flux from Atmospheric Corrosion of Steel Using the Scanning Kelvin Probe Technique
No full textThe atmospheric corrosion of high-strength steels can lead to hydrogen absorption directly linked to hydrogen embrittlement or delayed fracture phenomena. A scanning Kelvin probe (SKP) and electrochemical permeation technique (EPT) were applied to correlate the potential of an oxidized surface with the flux of hydrogen across a thin steel membrane. The side of the membrane opposite the corroding or electrochemically charged area was analyzed. The potential drop in the oxide was calibrated in terms of surface hydrogen activity, and SKP can be applied in situ for the mapping of hydrogen distribution in the corroding metal. A very low flux of hydrogen can be characterized and quantified by SKP, which is typically observed under atmospheric corrosion conditions. Therefore, hydrogen localization that drives steel durability under atmospheric corrosion conditions can be evaluated
Scanning Kelvin Probe for Detection in Steel of Locations Enriched by Hydrogen and Prone to Cracking
No full textHydrogen, due to corrosion processes, can degrade high strength steels (HSS) through embrittlement and stress corrosion cracking mechanisms. Scanning Kelvin probe (SKP) mapping of surface potential was applied, to visualize the locations with an increased subsurface concentration of hydrogen in mild steel and martensitic HSS. This work can help to determine the reasons behind hydrogen localization in a steel microstructure, leading to embrittlement and hydrogen-assisted cracking. Cathodic charging was used to insert hydrogen, which decreased the steel potential. Hydrogen effusion in air passivates steel, increasing the potential of HSS and mild steel. The passivation of steels was monitored depending on different conditions of cathodic pre-charging and the amount of absorbed hydrogen. The SKP could determine the area of diffusible hydrogen and the area of cracks. In addition, low potential locations linked to the hydrogen trapped in the deformed HSS microstructure were also determined, which delayed the steel passivation. Mild steel showed a uniform potential distribution related to interstitial hydrogen, without potential extremes attributed to locally accumulated hydrogen. Thus, SKP sensing can detect locations containing increased concentrations of hydrogen and sensitive to steel cracking
Corrosion behavior of additively manufactured AISI 316L stainless steel under atmospheric conditions
No full textInternational audienc
Alternativas nutricionales para la cunicultura
No full textEn el actual documento de investigación bibliográfica se presenta el tema de nutrición en la cunicultura, partiendo de un análisis del panorama internacional en materia de alimentación en la producción Cunícola, aterrizándolo al contexto nacional, descripción hecha en el primer capítulo para luego entrar en materia donde se podrá encontrar un segundo capítulo que muestra las diferentes alternativas que se conocen para la alimentación del conejo, así como los requerimientos nutricionales de la especie, con los que se pretende presentar un material de consulta producto de la recopilación y análisis de datos, donde se utilizando como método de investigación la investigación documental y el uso de herramientas de investigación como la consulta de páginas web, artículos de investigación, documentos y libros, donde como resultado final se organizó secuencialmente la información que el autor considera es la más relevante para la construcción de la monografía alternativas nutricionales para la cunicultura.In the current bibliographic research document, the issue of nutrition in cuniculture is presented, based on an analysis of the international panorama in the field of food in cunicula production, landing it in the national context, a description made in the first chapter and then entering into the subject where a second chapter can be found that shows the different alternatives that are known for rabbit feeding, as well as the nutritional requirements of the species, with which it is intended to present a consultation material product of data collection and analysis, where using documentary research as the research method and the use of research tools such as consulting web pages, research articles, documents and books, where as a final result the information that the author considers is the most relevant for the construction was sequentially organized of the alternate monograph nutritional tives for cuniculture
Effect of mechanical pre-loadings on corrosion resistance of chromium-electroplated steel rods in marine environment
No full textInternational audienceProviding high hardness, low friction coefficient, as well as, relatively good corrosion resistance, chromium-plated coatings (similar to 20 mu m) are widely used for steel cylinder rods in marine environment. However, the standardized corrosion test method (ISO 9227, NSS) used to evaluate efficiency of this type of coatings does not take into account in-service mechanical loadings on cylinder rods. Nevertheless, the uniform initial network of microcracks in chromium coating is changing under mechanical loadings. Propagation of these microcracks explains premature corrosion of the steel substrate. The aim of the study was to evaluate relationship between mechanical loadings, propagation of microcracks network and corrosion resistance of chromium coatings. After monotonic pre-loading tests, it was demonstrated by microscopic observations that the microcracks propagation started at stress levels higher than the substrate yield stress (520 MPa). The microcracks become effective, i.e. they have instantly undergone through the whole coating thickness to reach the steel substrate. The density of effective microcracks increases with the total macroscopic level, i.e. the intercrack distance goes from 60 +/- 5 mu m at 1% of total strain to approximately 27 +/- 2 mu m at 10%. Electrochemical measurements have shown that the higher the plastic strain level applied during mechanical loading, the more the corrosion potential of the sample decreased until reaching the steel substrate value of approximately -0.65 V/SCE after 2 h of immersion. The polarization curves have also highligthed an increase in the corrosion current density with the strain level. Therefore, electrochemical measurements could be used to realize quick and comprehensive assesment of the effect of monotonic preloadings on corrosion properties of the chromium coating
Rhamnolipids as an eco-friendly corrosion inhibitor of rebars in simulated concrete pore solution: evaluation of conditioning and addition methods
No full textInternational audienceThe objective of this study was to evaluate the use of rhamnolipids (RLs) extracted from Pseudomonas aeruginosa as a possible eco-friendly inhibitor for the corrosion protection of rebars in concrete. Two application methods were tested: application of RLs as a coating on the steel (conditioning method) and addition of the RLs directly to the aggressive environment (addition method). Both methods were evaluated for their ability to protect steel in simulated concrete pore solution containing 0.5M NaCl. The results highlight a delay in the initiation of local corrosion followed by a rapid propagation rate of corrosion for conditioning method. This evolution is in relation with the heterogeneity of the formed RLs layers. The addition method provides a different film formation and better protection against corrosion. Using a 1gL concentration, the inhibition effect was observed at least for 24h of immersion
Effect of Cathodic Polarisation Switch-Off on the Passivity and Stability to Crevice Corrosion of AISI 304L Stainless Steel
No full textThe effects of cathodic polarisation switch-off on the passivation of AISI 304L stainless steel in air and its crevice corrosion susceptibility in 3.5 wt.% NaCl aqueous electrolyte were investigated. Scanning Kelvin probe (SKP) data showed that the oxide film is significantly destabilised and the rate of steel passivation in air is slowed down. Thermal desorption analysis (TDA) highlighted that hydrogen absorption is proportional to the applied cathodic current density. A special crevice corrosion set-up was designed to realise simultaneous reproducible monitoring of potential and galvanic current to study the impact of prior cathodic polarisation on crevice corrosion onset
Kinetics of corrosion reactions on press hardened steel in atmospheric conditions under thin electrolyte films
No full textSteels with high mechanical performance are prone to hydrogen embrittlement and environmental assisted cracking. Under atmospheric corrosion conditions, the source of hydrogen can be the steel corrosion process itself or galvanic coupling with a metallic coating. Electrochemical behaviour of Press Hardened Steel (PHS) under electrolyte films of different thicknesses using local electrochemical techniques was studied on a fundamental level. Scanning Vibrated Electrode Technique (SVET) was applied to study the evolution and localization of the corrosion process during PHS immersion in NaCl electrolyte. Kelvin Probe (KP) was used as a reference electrode to obtain cathodic and anodic polarization curves on PHS surfaces which were covered by thin electrolyte films (60 to 500 µm) of 0.1 M NaOH and 0.6 M NaCl. For both electrolytes, a strong increase in the oxygen reduction rate due to the decreasing of electrolyte thickness has been clearly demonstrated. Data are correlated well with a theoretical plot determined by Nernst-Fick equation. The influence of the rust layers on the kinetics of corrosion reactions under thin electrolyte films was investigated using KP. © 2023</p
Quantification of subsurface hydrogen in corroding mild steel using Scanning Kelvin Probe calibrated by electrochemical permeation technique
No full textScanning Kelvin probe (SKP) can be applied for mapping of subsurface hydrogen in steels. The good spatial resolution is combined with poor quantification. Controversy, the electrochemical permeation technique (EPT) is extremely sensitive to hydrogen flux but has low spatial resolution. Thus, a local hydrogen quantification method using SKP measurements calibrated by EPT was developed. The fixed amount of hydrogen flux in mild steel membrane was obtained by cathodic polarization and was detected using the two methods. A semi-logarithmic relationship between SKP potential drop and the hydrogen sub-surface concentration underneath of the corroding surface was established. SKP quantification was applied for mapping the subsurface hydrogen in steel corroding under various atmospheric corrosion conditions. </p
Effet d'une sollicitation mécanique sur la tenue à la corrosion de tiges en acier chromées
No full textColloque avec actes et comité de lecture. Internationale.International audienceLes tiges de vérin en acier utilisées en environnement marin sont revêtues d'une fine couche de chrome (∼20 µm) afin de les protéger contre la corrosion. Cependant, les dépôts de chrome présentent en surface un réseau uniforme de microfissures qui peut évoluer sous chargement mécanique, la propagation de ces microfissures est à l'origine de la corrosion prématurée du substrat d'acier. Cette étude porte sur l'effet d'un chargement en traction monotone sur l'évolution du réseau de microfissures et sur la tenue à la corrosion des revêtements chromés. Il a été mis en évidence par des observations au microscope optique que les microfissures se propageaient pour des niveaux de contraintes supérieurs à la limite d'élasticité du substrat, celles-ci deviennent instantanément traversante sur toute l'épaisseur du revêtement. Le nombre de fissures propagées augmente avec le niveau de déformation du revêtement, la distance moyenne inter-fissures passe de 80 µm pour 1% de déformation totale à 45 µm pour 10%. Les courbes de polarisation réalisées sur des échantillons ayant subi différents niveaux de déformation ont montré la dégradation de la tenue des éprouvettes. Le potentiel de corrosion passe de-200 mV/ECS (potentiel de corrosion du revêtement non déformé) à-650 mV/ECS (potentiel de corrosion du substrat en acier) après 5 ou 10 % de déformation totale. Ces résultats montrent que le revêtement de chrome devient complètement inefficace lorsqu'il est déformé à au moins 5%. Abstract : Steel rods used for hydraulic cylinders in marine environment are protected against corrosion by a thin coating of chromium electroplated (∼20 µm). However, a uniform network of microcracks in chromium coating is evolving under mechanical loadings. The propagation of these microcracks is in the origin of the premature corrosion of the steel substrate. The aim of the study was to evaluate the effect of a tensile monotonic loading on the evolution of the microcracks network and the corrosion resistance of chromium coatings. After monotonic tests, it was demonstrated by microscopic observations that the microcracks propagation began only for stress levels higher than the yield stress of the substrat (520 MPa). Some of microcracks become effective ones, ie. they have passed instantly through the whole thickness of the coating and reached the steel substrate. The density of microcracks increases with the level of total strain, the inter-crack distance go from 80 µm at 1% of total strain to 45 µm at 10%. Electrochemical measurements have shown that the higher the level of plastic strain applied during the mechanical loading, the more the corrosion potential of the sample decreases until reaching that of 1 23 ème Congrès Français de Mécanique Lille, 28 au 1 er Septembre 2017 the steel substrate of approximately-0.65 V/ECS after 2 hours of immersion. The polarization curves also evidenced an increase in the corrosion current density with the strain level. Moreover, we note the absence of the characteristic passive region of the reference samples that have not undergone any loading
