Development of new processes to protect zinc against corrosion, suitable for on-site use

Protection against corrosion of metals is well known as an important issue in numerous fields. In all cases, the improvement of durability of these metals has to be connected to the development of environmentally friendly processes. Sol–gel protective coatings have shown excellent chemical stability and enhanced corrosion resistance for zinc substrates. Further, the sol–gel method, used as technique of surface protection, showed the potential for the replacement of toxic pre-treatments. This paper highlights the recent developments and applications of silane based sol–gel coatings on zinc substrates. Then, the challenges for industrial transfer of the developed process are also discussed because this process presents a disadvantage for on-site use, which is the too time-consuming thermal treatment. So, the goal of this study was to determine the convenient experimental conditions to reduce the duration of heat treatment of the hybrid sol–gel layer, compatible with the severe industrial requirements, without reducing the protection against corrosion. To reach this objective, a correlation between the results of chemical analyses and the protection against corrosion efficiency was established

Développement de nouveaux revêtements anti-corrosion sur alliages de zinc par des voies sol-gel en milieu aqueux ou faiblement solvanté

Ces travaux de thèse ont eu pour objectif la mise au point de revêtements anti-corrosion obtenus par voie sol-gel sur alliage de zinc et issus de solutions majoritairement aqueuse. Cette étude a donc porté sur la recherche de performances anti-corrosion demandées par la société Umicore, mais aussi, sur la compréhension des phénomènes mis en jeu. Plusieurs pistes, mises en évidence lors de nos recherches bibliographiques, ont été étudiées. Ces voies ont été adaptées à nos conditions d'élaboration, et optimisée pour augmenter l'efficacité des couches formées. Les performances des revêtements ont ensuite été caractérisées par un test industriel de corrosion accélérée, et plus finement par des analyses électrochimiques. Ces évaluations ont permis de mettre en avant une voie particulièrement intéressante. Par la suite, nous nous sommes focalisés sur cette voie : la formulation de la solution et les conditions de mise en forme et de séchage ont été étudiées en détail par RMN et IRTF. Ainsi, il a été montré que l'augmentation de la concentration en précurseur d'aluminium permettait de favoriser la réticulation des revêtements. De plus, le taux de réticulation peut être augmenté par effet thermique en ajustant le temps et la température du séchage des films. Ces phénomènes ont un effet direct sur la perméabilité du film et ses performances anti-corrosion. Cette étude a apporté une solution faiblement solvantée permettant une protection efficace du zinc, mais aussi a mis en évidence des corrélations importantes entre la structure chimique du réseau et les propriétés anti-corrosion et mécaniques des revêtements.The main objective of this study was to elaborate protective coatings on zinc by an aqueous sol-gel route. It was expected to reach sufficient anticorrosive efficiency with this kind of layer and to improve our knowledge of the involved phenomena. Based on Scientific literature, several routes have been investigated. These routes were adapted to our shaping constraints and optimized in order to increase coatings efficiency. Anticorrosive performances were then evaluated by an industrial accelerated corrosion test and by electrochemical techniques. By this way, one promising route has been underlined. Afterward, we focused on this efficient route: the formulation of the solution and the conditions of shaping and drying were studied by NMR and FTIR. It was shown that the increase of the aluminium precursor concentration improved the coating reticulation. Furthermore, the study highlighted that reticulation rate can be increased by thermal effect by adjusting the duration and the temperature of the drying step. These phenomena have a direct effect on the permeability of the layers and its anticorrosive performances. This study brought a weakly solvated solution, allowing an effective protection of the zinc, but also highlighted important correlations between the chemical structure of the network and the anticorrosive and the mechanical properties

Sol-Gel Routes to Replace Chromate Based Treatments for Protection Against Zinc Corrosion

Regarding the environmental consciousness and requirements relative to industrial processes, researchers and end users have to move to more green surface treatments. That is why, the use of toxic compounds such as chromates must be strictly prohibited. So, in order to replace this element preserving an efficient protection against corrosion of metals, a new route using sol-gel process clearly appears as a promising alternative method. In this paper, we investigated three different sol-gel systems in various media (alcohol and/or water) and compared their efficiency in terms of protection against corrosion and environmentally friendliness. Thus, industrial normalized corrosion test and electrochemical analyses such as polarisation curves and EIS measurements were carried out in order to both evaluate and discuss coatings behaviour in corrosive environment

Développement de nouveaux revêtements anti-corrosion sur alliages de zinc par des voies sol-gel en milieu aqueux ou faiblement solvanté

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Invasive Fallopia × bohemica interspecific hybrids display different patterns in secondary metabolites.

International audiencePlant secondary metabolites are important traits that can benefit an invasive plant in its new environment. In the case of rapid evolution in the invaded area, the chemical weapons of introduced plants may diversify, and novel combinations or extreme concentrations of these secondary metabolites may be expressed. The invasive Fallopia species complex (F. japonica, F. sachalinensis, and the F. × bohemica interspecific hybrids) is a good model to assess how chemical traits can vary during post-introduction evolution. We analyzed and compared the composition of secondary metabolite extracts in F. × bohemica hybrids and in the parental species grown in the introduced area. HPLC-DAD profiles were obtained for each Fallopia species, and the main peaks of the HPLC chromatograms represent phenolic compounds. Analyses based on secondary metabolite profiles showed that F. × bohemica hybrids are closer to F. japonica. The F. × bohemica hybrids expressed the compound families described in F. japonica and F. sachalinensis, with quantitative variations between them. Hybrid chemical cocktails showed a diversification of chemical weapons. Furthermore, transgressive segregation was observed. Three dianthrones were identified for the first time in a Fallopia species and were more highly expressed in F. japonica and F. × bohemica hybrids. These results suggest an evolution in the chemical traits of Fallopia taxa in invaded areas such that certain genotypes may well have acquired new chemical cocktails resulting from post-introduction hybridizations

Autophagy induction by the pathogen receptor CD46.

International audienceAutophagy is a highly regulated self-degradative mechanism required at a basal level for intracellular clearance and recycling of cytoplasmic contents. Upon intracellular pathogen invasion, autophagy can be induced as an innate immune mechanism to control infection. Nevertheless, pathogens have developed strategies to avoid or hijack autophagy for their own benefit. The molecular pathways inducing autophagy in response to infection remain poorly documented. We report here that the engagement of CD46, a ubiquitous human surface receptor able to bind several different pathogens, is sufficient to induce autophagy. CD46-Cyt-1, one of the two C-terminal splice variants of CD46, is linked to the autophagosome formation complex VPS34/Beclin1 via its interaction with the scaffold protein GOPC. Measles virus and group A Streptococcus, two CD46-binding pathogens, induce autophagy through a CD46-Cyt-1/GOPC pathway. Thus, upon microorganism recognition, a cell surface pathogen receptor can directly trigger autophagy, a critical step to control infection