Effect of cerium concentration on corrosion resistance and polymerization of hybrid sol–gel coating on martensitic stainless steel

Stainless steels are increasingly used in the aeronautics field for the manufacture of structural parts. One of them, the X13VD martensitic stainless steel (X12CrNiMoV12-3), known for its good mechanical properties, has a poor corrosion resistance in confined or severe environments. In the past years, Cr(VI) based pre-treatments have been currently used for corrosion protection of different metals, however, they are toxic and due to environmental regulations, they will be definitely banned in a near future. Alternatives to replace Cr(VI) show advantages and drawbacks considering key properties such as: corrosion resistance, adhesion of coatings, fatigue resistance, durability and reliability. However, some of their possible alternatives show high potential. In this paper, a process was developed to improve the corrosion resistance of the martensitic stainless steel. Organic–inorganic hybrid coatings with different cerium concentrations were deposited onto stainless steel by sol–gel process. Corrosion resistance of the coatings was evaluated by electrochemical impedance measurements and it has been proved that cerium concentration of 0.01 M into hybrid coating was an optimal content. Adhesion tests were also carried out by "nanoscratchtest" to characterize the coatings mechanical properties as a function of cerium concentration but results do not clearly show the influence of cerium for the coating adhesion toward the substrate. To try to correlate with the electrochemical properties, liquid 29Si NMR spectroscopy was then performed to investigate hydrolysis and condensation reactions of sol–gel process, and by this method, it was demonstrated that for higher cerium concentration (>0.01 M) there is a modification of the chemical structure of the sol–gel network

The construction of a reliable potential for GeO2 from first-principles

The construction of a reliable potential for GeO2, from first-principles, is described. The obtained potential, which includes dipole polarization effects, is able to reproduce all the studied properties (structural, dynamical and vibrational) to a high degree of precision with a single set of parameters. In particular, the infrared spectrum was obtained with the expression proposed for the dielectric function of polarizable ionic solutions by Weis et al. [J.M. Caillol, D. Levesque and J.J. Weis, J. Chem. Phys. 91, 5544 (1989)]. The agreement with the experimental spectrum is very good, with three main bands that are associated to tetrahedral modes of the GeO2 network. Finally, we give a comparison with a simpler pair-additive potential.Comment: 9 pages, 8 figure

The preparation of double-walled carbon nanotube/Cu composites by spark plasma sintering, and their hardness and friction properties

Double-walled carbon nanotube (DWCNT)/copper composite powders were prepared by a rapid route involving freeze-drying without oxidative acidic treatment or ball-milling. The DWCNTs are not damaged and are homogeneously dispersed in the matrix. Dense specimens were prepared by spark plasma sintering. The Vickers microhardness is doubled, the wear against a steel or an alumina ball seems very low and the average friction coefficient is decreased by a factor of about 4 compared to pure copper. The best results are obtained for a carbon loading (5 vol%) significantly lower than those reported when using multi-walled carbon nanotubes (10–20 vol%). Maximum Hertzian contact pressure data could indicate that the surface DWCNTs and bundles of them are deformed and broken, possibly resulting in the formation of a graphitized lubricating tribofilm in the contac

Microscale friction reduction by normal force modulation in MEMS.

Friction in MEMS-scale devices is troublesome because it can result in lateral stiction of two sliding surfaces. We have investigated the effect of modulation of the normal force on the friction between two sliding MEMS surfaces, using a fully MEMS-based tribometer. We have found that the friction is reduced significantly when the modulation is large enough. A simple model is presented that describes the friction reduction as a function of modulation frequency as well. Using this technique, lateral stiction-related seizure of microscopic sliding components can be mitigated

Savignac-de-Miremont – La Ferrassie

Lien Atlas (MCC) :http://atlas.patrimoines.culture.fr/atlas/trunk/index.php?ap_theme=DOM_2.01.02&ap_bbox=-0.923;44.949;0.973;44.982 La première année de l’opération triannuelle 2012-2014 consacrée à la partie ouest du site de la Ferrassie a apporté des données nouvelles et importantes pour la compréhension du site. Les stratigraphies des trois secteurs de fouille ont été unifiées, puis cette synthèse comparée aux observations faites par D. Peyrony (tableau ci-dessous). Industries Selon D. Pe..

A transferable ab-initio based force field for aqueous ions

We present a new polarizable force field for aqueous ions (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+ and Cl-) derived from condensed phase ab-initio calculations. We use Maximally Localized Wannier Functions together with a generalized force and dipole-matching procedure to determine the whole set of parameters. Experimental data is then used only for validation purposes and a good agreement is obtained for structural, dynamic and thermodynamic properties. The same procedure applied to crystalline phases allows to parametrize the interaction between cations and the chloride anion. Finally, we illustrate the good transferability of the force field to other thermodynamic conditions by investigating concentrated solutions.Comment: 31 pages, 8 figure

Le Causse de Gramat

Lien Atlas (MCC) :http://atlas.patrimoines.culture.fr/atlas/trunk/index.php?ap_theme=DOM_2.01.02&ap_bbox=1.656;44.713;1.769;44.816 Durant l’année 2013, nous avons travaillé sur les trois volets du projet autorisé, soit sur la vallée de l’Alzou, la vallée du ruisseau de Théminettes et la recherche de remplissage archéologique dans plusieurs cavités de la Braunhie. Dans la vallée de l’Alzou, la visite de plusieurs cavités a permis de constater que la plupart d’entre elles renfermaient encore de..

Improvement of the tribological behavior of PTFE-anodic film composites prepared on 1050 aluminum substrate

A model anodic film was prepared to incorporate PolyTetraFluoroEthylene (PTFE) nanoparticles into the porous structure of the film. Firstly, the influence of the anodization parameters on the morphology (thickness and pore diameter) was studied, using notably FEG scanning electronic microscopy. Then, using an improved sedimentation technique, the nanoparticles were successfully inserted into the porous structure and onto its surface. EDX and Raman spectroscopy attested the presence of PTFE particles down to the bottom of the pores. Secondly, the study demonstrated the benefit of incorporating the PTFE particles. Tribological tests were also carried out and the lubricating properties of the composite analyzed. Friction coefficient curves showed a 75 fold improvement of the total lifetime of the anodic film with a reduced friction coefficient

New sol-gel formulations to increase the barrier effect of a protective coating against the corrosion of steels

Films were deposited onto AISI 430 stainless steel substrates by dip-coating technique. The aim is to reach the AISI 304L stainless steel anti-corrosion properties by a coated AISI 430 stainless steel system. Sol formulation is done from the starting precursors tetraethylorthosilicate (TEOS) and 3(trimethoxysilyl) propyl methacrylate (MAP). After the hydrolysis of these precursors, sol-gel reactions occur before the addition (or not) of a controlled quantity of cerium nitrate. The addition of the PEG (polyethylene glycol), used as plasticizer has been studied in this paper and both physical and chemical properties of the synthesized hybrid films were studied by varying PEG ratios. Based on SEM observations and mass gain measurements, the thickness of the films has been adjustable. Another parameter plays a key role: the drying step of the whole system. It has been investigated and optimized in this paper to lead to coatings with a high barrier effect. The efficiency of the anti-corrosion protection of hybrid-coated stainless steel was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) after immersion of the material in a 3.5% NaCl solution. Double-layered systems were successfully developed and a good compromise between PEG content and drying conditions has been found. Potentiodynamic polarization curves showed that the hybrid coating prepared using a TEOS/MAP/PEG yielded the best anti-corrosion performances. It acts as an efficient barrier similar to AISI 304 stainless steel used as reference, increasing the total impedance and significantly reducing the current densities