Synthèse et fonctionnalisation de phyllosilicates de types talc : applications à des revêtements sol-gel pour la protection contre la corrosion

L'utilisation des revêtements sol-gel pour la protection contre la corrosion des métaux est une alternative aux traitements aux chromates, proscrits du fait de leur forte toxicité. Ces travaux ont porté sur l'incorporation de charges inorganiques fonctionnalisées par des inhibiteurs de corrosion organiques dans des revêtements élaborés par voie sol-gel. Les charges inorganiques choisies sont des phyllosilicates de type talc. La caractérisation de ces matériaux a montré qu'ils possèdent la structure lamellaire du talc naturel mais, contrairement à celui-ci, leur structure et leur grande surface spécifique permet de les fonctionnaliser facilement par greffage covalent d'inhibiteurs de corrosion. La petite taille des particules (environ 300 nm) et leur caractère hydrophile sont aussi des paramètres importants car ils favorisent la dispersion des phyllosilicates de type talc dans les revêtements. L'incorporation des matériaux greffés et non-greffés dans les revêtements déposés sur l'acier au carbone XC35 a permis de renforcer les propriétés barrière et diminuer la corrosion du métal. En revanche, il a été impossible de conclure quant au rôle des inhibiteurs de corrosion greffés du fait de la faible adhésion du revêtement sur le substrat métallique.Sol-gel coatings for corrosion protection of metals are a good alternative to replace toxic chromate treatments. The present work was focused on the incorporation of inorganic fillers functionalized with organic corrosion inhibitors in a sol-gel coating. Talc-like phyllosilicates were selected as inorganic fillers. Talc lamellar structure was evidenced but, in contrast with natural talc, the large specific surface allows talc-like phyllosilicates to be easily functionalized by covalent grafting of corrosion inhibitors. Small size (about 300 nm) and hydrophilicity of the particles are also important parameters because they improve the talc-like phyllosilicates dispersion in sol-gel coatings. Grafted and non-grafted materials incorporation in coatings deposited on a XC35 carbon steel permitted to reinforce barrier properties and to decrease metal corrosion. On the other hand, it was impossible to conclude about grafted corrosion inhibitors efficiency due to the low adhesion of the coating on the metal substrate

Improvement of barrier properties of a hybrid sol-gel coating by incorporation of synthetic talc-like phyllosilicates for corrosion protection of a carbon steel

Sol–gel coatings for corrosion protection of metals are a good alternative to toxic chromate treatments. The present work focussed on the incorporation of inorganic fillers in a sol–gel coating to improve the barrier properties of the film. Talc-like phyllosilicates obtained by hydrothermal synthesis at 160°C, 260°C and 350°C, called T160, T260 and T350 respectively, were selected as inorganic fillers. The synthetic materials showed talc lamellar structure but, in contrast with natural talc, their smaller size (about 300 nm) and their hydrophilic character allowed easier dispersion of the particles in the sol–gel matrix. Electrochemical impedance measurements performed on the sol–gel coatings deposited on XC35 carbon steel showed that the incorporation of T260 and T350 at a concentration of 20 g L− 1 strongly enhanced the barrier properties of the coating by comparison with the filler-free system. As a consequence, the corrosion protection of the metal substrate was improved

Functionalization of synthetic talc-like phyllosilicates by alkoxyorganosilane grafting

A range of talc-like phyllosilicates were prepared via a hydrothermal synthesis performed at five different temperatures from 160 to 350 °C. The organization of the lattice and the degree of crystallinity of the new materials were evaluated by different techniques such as XRD, FTIR, solid-state 29Si NMR, TEM, FEG-SEM and TG-DTA. When synthesized at low temperature the material presents high degree of hydration, low crystallinity and flawed structure. This was attributed to stevensite-talc interstratified product present in the samples. The stevensite/talc ratio and the hydration decrease in the talc-like phyllosilicate samples when the hydrothermal synthesis temperature increases and so the crystallinity becomes higher. A thermal treatment at 500 °C allowed a significant flaw reduction in talc-like phyllosilicate structure; the synthesized sample at 350 °C and heat treated presents a structure close to that of talc. The different talc-like phyllosilicates were grafted covalently by two organoalkoxysilane reagents, N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole (IM2H) and 2-hydroxy-4-(3-triethoxysilylpropoxy)-diphenylketone (HTDK). The grafted amounts of the hybrids, determined by elemental analysis and confirmed by thermogravimetric data, are dependent on the hydrothermal synthesis temperature and organoalkoxysilanes; they become smaller when the synthesis temperature increases and when HTDK is used. FTIR and solid-state 13C CP MAS NMR were applied to characterize the grafted organic groups. So, in this work it is shown that by choosing the hydrothermal synthesis temperature or by performing an additional annealing it is possible to adjust the amount of defects in the structure of talc-like phyllosilicates which seems to be strongly correlated to the grafting performance

Synthèse et fonctionnalisation de phyllosilicates de type talc (applications à des revêtements sol-gel pour la protection contre la corrosion)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF