Bifunctional coatings: coupling an organic adhesion promoter with an anticorrosion inorganic layer

International audienceIn this work, a multifunctional non-toxic chromium free treatment is proposed. Hexavalent chromium, largely used for anticorrosion surface treatments of aluminum alloys in aeronautics, will soon be completely banned due to its high toxicity (European REACH regulation) and new solutions are required. Here, in a first step, a polymeric film was grafted at the aluminum surface by the surface induced reduction of a diazonium salt. In a second step, the grafted surface was submitted to an anodization treatment, forming a thick aluminum oxide layer protecting the underlying metal against corrosion. No change in the organic coating was detected after the second step of the process. This leads to a multilayer coating, which provides competitive results regarding both the adhesion of paint and corrosion protection

Modelling of the kinetics of pitting corrosion by metal dusting

Commercial 800HT alloy was exposed to 49.1%H2–12.8%CO–3.1%CO2–1.6CH4–33.4%H2O gas at 21bars and 570°C up to 5000h. Metal dusting attack by pitting was observed. The kinetics parameters were identified to be the incubation time, pit density and individual pit growth rate. These parameters were introduced in a nucleation-growth model to simulate the pitted surface area kinetics. This model was then extended to the volume considering several geometrical hypotheses. Considering only surface coalescence of the pits without their volume coalescence allowed to correctly reproduce the experimental mass loss kinetics. An even simpler conservative model was proposed for an easy lifetime modelling

Metal dusting corrosion of austenitic alloys at low and high pressure with the effects of Cr, Al, Nb and Cu

Commercial and model alloys were exposed at 570°C to metal dusting conditions at 1 and 21bar in CO-H2-H2O and CO-H2-CO2-CH4-H2O atmospheres, respectively, with similar ac and PO2. γ” precipitation beneath the surface of 625 superalloy was due to Nb diffusion toward the Cr-depleted zone formed during oxidation. 693 superalloy was more carburised than 690 superalloy. α-Al2O3 formation was believed to induce cracks through the oxide scale, resulting in the alloy carburisation. Cu addition to a FeNiCr model alloy lead to the formation of an almost continuous Cu layer at the oxide/metal interface, greatly improving the metal dusting resistance

CrVI^{VI}-Free anti-corrosion protection and adherence promotion through the grafting of organic underlayer with a diazonium salt

International audienceHexavalent chromium (Cr$^{VI}$) which is at the basis of most of the treatments used to prepare the metallic surfaces before painting in aeronautic, is classified as carcinogenic, mutagenic and reprotoxic (CMR). The time for using Cr$^{VI}$ will soon pass, and alternatives must now be found. For this purpose, PROTEC Industry, a major actor for technical surfaces treatment in aeronautics is associated with CEA, a public research agency recognized among others for its innovations in surface modification. The strategy that we selected is based on the grafting of an organic underlayer, the anchoring of the layer to the metal being ensured by a specific chemical function bared by the precursor, namely a diazonium. With the aim of adapting the process to the aeronautic branch, CEA and PROTEC have shared their knowledge, manpower, device and knowhow through the creation of a common laboratory supported by ANR and ANRT, in 2012

Synthèse et caractérisation de primaires d'adhésion de peinture pour l'aéronautique inspirée de la chimie des sels de diazonium

International audienceA l'heure actuelle, les traitements utilisés pour améliorer les propriétés anticorrosion des matériaux de l'aéronautique contiennent du chrome VI, un élément classifié cancérigène, mutagène et reprotoxique. Pour cette problématique, PROTEC Industrie s'est associé au LICSEN (CEA de Saclay) pour évaluer la potentialité d'une modification de surface par la chimie des sels de diazonium. La stratégie est basée sur le greffage d'une fine couche organique à base de sels de diazonium. Pour satisfaire les critères industriels et passer les tests normatifs, le revêtement réalisé doit assurer au revêtement une bonne résistance à la corrosion, spécifiquement au brouillard salin et aux tests de corrosion filiforme, ainsi qu'une bonne adhérence avec la couche de peinture. Développer un revêtement qui garantit de remplir simultanément ces trois critères est néanmoins délicat, c'est pourquoi, des méthodes de caractérisation physico-chimique sont mises en place pour s'affranchir des tests normatifs et raccourcir les cycles d'innovation basés sur une procédure mettant en jeux successivement des étapes de procédés et des étapes de caractérisation. Diverses approches sont testées, à la fois physico-chimiques (MEB, AFM, etc) et électrochimique-classique et locale-notamment via la microscopie électrochimique à balayage (SECM). Le lien entre les propriétés désirées et les résultats obtenus est alors établi par une procédure de calibration