Chromate-free smart release corrosion inhibitive pigments containing cations

A smart release chrome-free inhibiting system is utilised in an organic coating system to inhibit cathodic disbondment of hot dip galvanised steel. The non-toxic smart release cation system is relatively cheap, easy to process and highly effective. An in-situ scanning Kelvin probe is used to assess the protection offered by the cation containing pigments in a poly-vinyl-butyral model coating. The inhibition of cathodic delamination under the SKP testing conditions exceeds that of hexavalent chromate by the inhibitor system containing magnesium(II) ions

Crystallography of Stress corrosion cracking of austenitic stainless steel by scanning electron microscope and electron backscatter diffraction

In this study, Stress Corrosion Cracking (SCC) produced for 304L austenitic stainless steel in different concentrations of chloride containing sulfuric acid solutions was analyzed using both Scanning Electron Microscope (SEM), and Electron Backscatter Diffraction (EBSD). X-Ray Diffraction (XRD) was used to analyze the residual-applied stresses before and after cracking. Crack observation using SEM revealed clear traces of successive slipping planes and consequent dissolutions on the facets of the obtained cracks. Moreover, ruptured grains were analyzed for their orientation using EBSD technique. Analysis disclosed two preferential rupture planes; {110}, {111} with percentage of 48% and 37% respectively. After cracking, XRD stress profile analysis showed a gradual stress relaxation through sample’s depth from the applied stress in the bulk of the material to the inherent residual stress attributed to fabrication processes in the zone where the cracks are present

Effect of stress on passivation kinetics and passivation modelling of 304L stainless steel in acidic medium

Stress Corrosion Cracking (SCC) is a typical failure of engineering materials applied in corrosive environments. In light water reactors for example, this results in loss of electrical capacity and related costs of repair and replacement. Film Rupture-dissolution Model explains interganular SCC as a phenomenon resulting from repetitive activation/passivation cycles (Fig.1). Activation takes place mechanically by slip-induced film breakdown which causes excessive material dissolution until it repassivates again. In this study, potentiodynamic cycling experiments serve effectively to perform in-Lab electrochemical simulation of this process. Conventional electrochemical techniques and Inductively Coupled Plasma – Optical Emission Spectroscopy are used to in-situ measure the corrosion transients and dissolution rates. A model was developed proving that stainless steel repassivates according to the High Field Ion Conduction Model in acidic solutions. Having this, quantification of the instantaneous passive film thickness and corrosion susceptibility of the passive film constructed over the surface has been successfully achieved (Fig.2). Quantified results showed that for stressed materials, the time to repassivation is longer, and the constructed passive film, though thicker, is more susceptible to corrosion than passive films developed over non-stressed materials

Soldats et travailleurs portugais en France (1916-1918)

Jusqu’à la Première Guerre mondiale, on ne comptait qu’un millier de Portugais en France, des rentiers aisés, des artistes puis, à la fin du xixe siècle, de petits groupes d’exilés républicains réfugiés et quelques dizaines d’ouvriers venus après avoir travaillé avec des entreprises françaises au Portugal. La Première Guerre mondiale a marqué un tournant radical en amorçant l’immigration portugaise en France. Jusque-là, les Portugais émigraient massivement vers le Brésil et, beaucoup moins, v..

Les incertitudes et les contradictions d’une « bonne intégration »

L’article analyse les difficultés d’adaptation entre les immigrants portugais et les catholiques français, durant la quinzaine d’années d’essor exceptionnel de l’immigration portugaise en France (1960-1974). Il n’a pas été facile de dépasser les malentendus et les contradictions entre deux mondes alors très éloignés. D’une part des migrants, très majoritairement catholiques, venus de villages où une profonde religiosité populaire était étroitement encadrée par un clergé conservateur et d’autre part le monde urbain des catholiques français engagés dans l’élan de Vatican II. Jusqu’à la chute de la dictature, le 25 avril 1974, les rapprochements, qui ne purent pas compter sur la Mission portugaise en France, furent le résultat des efforts conjugués de petits groupes de prêtres, religieuses et fidèles, français et portugais, épaulés par les responsables de la Pastorale des migrants. L’avènement de la démocratie, les changements dans l’Église au Portugal et l’insertion progressive des Portugais dans la société française, ont modifié la situation, sans toutefois résorber tous les contentieux ni effacer les spécificités religieuses et culturelles des immigrants catholiques portugais en France.This contribution describes the problems and adjustments between the Portuguese, Catholics migrants and French Catholics, all along the years of exceptional development of Portuguese immigration in France (1960-1974) It was difficult to overcome misunderstanding and contradictions between these two Catholics cultures. On one side Portugueses Catholics, small farmers migrants, coming from villages where an important popular religiosity was strictly supervised by a conservative catholic clergy. On the other side, the French Catholics, mainly urban, approving with Vatican II concile. Until the end of the Portuguese dictature, the 25th of April 1974, the connection between this two religious cultures came only from little groups of French and Portuguese priests, nuns and believers. The settlement of democracy and the changes into the Portuguese church and parallely the progressive insertion of Portugueses into French society, have changed the situation. However all the problems are not reduced because Portuguese Catholics migrant’s religious and cultural specificities remains

L’accueil en France des réfugiés après le 11 septembre 1973

La réussite notable de l’accueil des réfugiés chiliens en France repose sur un contexte particulier : la solidarité du monde associatif vis-à-vis des opposants à la junte s’est doublée de la bienveillance des autorités françaises. Le système d’accueil performant a concerné tout autant les réfugiés chiliens que les opposants latino-américains qui avaient trouvé refuge dans le Chili d’Allende. Information, hébergement, orientation professionnelle…, tout a été mis en œuvre pour que ces exilés puissent reconstruire leur vie en France

In situ monitoring of corrosion mechanisms and phosphate inhibitor surface deposition during corrosion of zinc–magnesium–aluminium (ZMA) alloys using novel time-lapse microscopy

In-situ time-lapse optical microscopy was used to examine the microstructural corrosion mechanisms in three zinc-magnesium-aluminium (ZMA) alloy coated steels immersed in 1% NaCl pH 7. Preferential corrosion of MgZn2 lamellae within the eutectic phases was observed in all the ZMA alloys followed by subsequent dissolution of Zn rich phases. The total extent and rate of corrosion, measured using time-lapse image analysis and scanning vibrating electrode technique (SVET) estimated mass loss, decreased as Mg and Al alloying additions were increased up to a level of 3 wt% Mg and 3.7 wt% Al. This was probably due to the increased presence of MgO and Al2O3 at the alloy surface retarding the kinetics of cathodic oxygen reduction. The addition of 1 x 10-2 mol/dm3 Na3PO4 to 1% NaCl pH 7 had a dramatic influence on the corrosion mechanism for a ZMA with passivation of anodic sites through phosphate precipitation observed using time-lapse. Intriguing rapid precipitation of filamentous phosphate was also observed and it is postulated that these filaments nucleate and grow due to super saturation effects. Polarisation experiments showed that the addition of 1 x 10-2 mol/dm3 Na3PO4 to the 1% NaCl electrolyte promoted an anodic shift of 50mV in open circuit potential for the ZMA alloy with a reduction in anodic current of 2.5 orders of magnitude suggesting that it was acting primarily as an anodic inhibitor supporting the inferences from the time-lapse investigations. These phosphate additions resulted in a 98% reduction in estimated mass loss as measured by SVET demonstrating the effectiveness of phosphate inhibitors for this alloy system

Cathodic driven coating delamination suppressed by inhibition of cation migration along Zn|polymer interface in atmospheric CO2

International audienceThe degradation of the Zn|polymer interface is inhibited by CO 2 gas in a humid environment. The inhibition mechanism varies greatly for different polymer matrices and depends on the affinity of the polymer to CO 2. Coatings based on polymers with high affinity to CO 2 such as polyacrylamide show high delamination rates due to the fast uptake of water. In this case, the cation transport that causes the initial pull down of potential for initiating the oxygen reduction reaction occurs via the polymer. Here CO 2 decreases water uptake due to competitive absorption into the polymer matrix, inhibiting the delamination rate. CO 2 can quickly reach the interface of polymers with functional groups with a low affinity to water and CO 2 , such as polyvinyl butyral and polyvinyl alcohol. In this case, the inhibition of the delamination rate is achieved by a strong decrease in cation migration rate at the Zn| polymer interface accompanied by the formation of mixed hydrozincite/absorbed CO 2 layers on the ZnO surface underneath the polymers. Further experiments showed that the presence of CO 2 accelerates anion migration, suggesting an influence of CO 2 on the surface charge at the Zn|coating interface, thus affecting ion migration. Inhibition of cation migration has never been reported before and should be taken into account into the mechanism of cathodic-driven delamination on Zn under atmospheric conditions

In situ surface film evolution during Mg aqueous corrosion in presence of selected carboxylates

Mechanisms of inhibition of Mg aqueous corrosion in presence of chloride by sodium salicylate (Sal), 2,5-pyridinedicarboxylate (PDC) and fumarate (Fum) were studied by in situ Raman spectroscopy, ATR-FTIR, GD-OES and hydrogen collection. In situ detected surface films were composed by Mg(OH)2 nano-crystals and included inhibitors. All carboxylates significantly modified Mg(OH)2 growth kinetics as well as pevented chloride incorporation in the film. Vibrational spectra of the surface films demonstrated specific interactions between the carboxylates and the surface: adsorption of Sal and Fum on the oxide/hydroxide, precipitation of coordination polymer by PDC, dissolution of iron inclusions via formation of iron-Sal soluble complexes.publishe