Application des superalliages aux disques de frein ferroviaires

Le transport ferroviaire connaît une évolution rapide et les exigences sont accrues en termes de sécurité, de fiabilité, de confort et de réduction des coûts de maintenance. Cette évolution passe par un système de freinage à performances améliorées nécessitant des approches adaptées et l'utilisation de matériaux aptes à résister aux conditions de vitesse de glissement, de puissance à dissiper et de température instantanée atteinte. Les exigences fonctionnelles du frein sont multiples et souvent contradictoires et le choix des matériaux constitutifs est complexe. L'étude concerne la caractérisation et l'optimisation de disques de frein revêtus de superalliages associés à une garniture céramique développée au LAMIH. Des méthodes de caractérisation dynamiques (tribologie de freinage) et quasi-statiques (fiabilité des interfaces substrat/revêtement) en similitude avec une configuration réelle (freinage TGV) reposant sur des modélisations analytiques et numériques ont été développées.An increasing development of the Railway transportation lead to important requirements in term of the security, the reliability, the passagers comfort and the reduction of maintenance costs. Better performances of braking device are so involved with specific design approaches and friction materials suited to sliding velocity conditions, dissipative power and maximal transient temperature. Functional requirements of braking device are often contradictory and frictional materials selection is difficult. The study is relative to the characterisation and the optimisation of the braking discs coated with superalloy and LAMIH's specific ceramic pad. Dynamic characterisation (braking tribology) and quasi-static (reliability of coating/substrat bonding) methods are use with a similarity factor towards train braking device (TGV braking) ; to that effect, numerical and analytical models have been developped.VALENCIENNES-BU Sciences Lettres (596062101) / SudocSudocFranceF

Transition Metal Complexes Coordinated by Water Soluble Phosphane Ligands: How Cyclodextrins Can Alter the Coordination Sphere?

The behaviour of platinum(II) and palladium(0) complexes coordinated by various hydrosoluble monodentate phosphane ligands has been investigated by 31P{1H} NMR spectroscopy in the presence of randomly methylated β-cyclodextrin (RAME-β-CD). This molecular receptor can have no impact on the organometallic complexes, induce the formation of phosphane low-coordinated complexes or form coordination second sphere species. These three behaviours are under thermodynamic control and are governed not only by the affinity of RAME-β-CD for the phosphane but also by the phosphane stereoelectronic properties. When observed, the low-coordinated complexes may be formed either via a preliminary decoordination of the phosphane followed by a complexation of the free ligand by the CD or via the generation of organometallic species complexed by CD which then lead to expulsion of ligands to decrease their internal steric hindrance

Amphiphilic photo-isomerisable phosphanes for aqueous organometallic catalysis

International audienc

Chemically Modified Cyclodextrins: An Attractive Class of Supramolecular Hosts for the Development of Aqueous Biphasic Catalytic Processes

During these last years, cyclodextrins have contributed greatly to the development of catalytic processes in water. These cyclic oligosaccharides composed of 6(α), 7(β) or 8(γ) glucopyranose units improve the mass transfer in aqueous-organic two-phase systems and are useful compounds to design new catalysts. Thus, chemically modified cyclodextrins can be used to: (i) increase significantly the rate and selectivity of reactions catalyzed by water-soluble organometallic complexes, (ii) design new water-soluble ligands for aqueous organometallic catalysis, (iii) stabilize catalytically active noble metal nanoparticles in water and (iv) favour the dispersion and activation of the palladium on charcoal in water

«Fatty acid modified cyclodextrins as mass transfert promoters for aqueous rhodium catalyzed hydroformylation»

National audienc

Hydrohydroxymethylation of Ethyl Ricinoleate and Castor Oil

International audienceThe direct functionalization of the carbon–carbon double bonds of castor oil and its derivatives is of major interest to access biosourced building blocks. In particular, polyol derivatives can be produced in this way and find application in the field of bio-based polyesters and polyurethanes. In this study, we described the synthesis of polyhydroxylated derivatives via a hydrohydroxymethylation reaction consisting of two consecutive Rh-catalyzed reactions: a hydroformylation reaction followed by a hydrogenation reaction of formyl groups. A catalytic system based on Rh(acac)(CO)2 and a trialkylamine proved to be active both in hydroformylation of carbon–carbon double bonds and reduction of the resulting aldehydes into primary alcohols. By optimizing the reaction conditions, yields in alcohols of 74 and 80% were reached for castor oil and ethyl ricinoleate, respectivel

Complexation of Monosulfonated Triphenylphosphine with Chemically Modified β-Cyclodextrins: Effect of Substituents on the Stability of Inclusion Complexes

International audienceno abstrac

Phosphane-Based Cyclodextrins as Mass Transfer Agents and Ligands for Aqueous Organometallic Catalysis

The replacement of hazardous solvents and the utilization of catalytic processes are two key points of the green chemistry movement, so aqueous organometallic catalytic processes are of great interest in this context. Nevertheless, these processes require not only the use of water-soluble ligands such as phosphanes to solubilise the transition metals in water, but also the use of mass transfer agents to increase the solubility of organic substrates in water. In this context, phosphanes based on a cyclodextrin skeleton are an interesting alternative since these compounds can simultaneously act as mass transfer agents and as coordinating species towards transition metals. For twenty years, various cyclodextrin-functionalized phosphanes have been described in the literature. Nevertheless, while their coordinating properties towards transition metals and their catalytic properties were fully detailed, their mass transfer agent properties were much less discussed. As these mass transfer agent properties are directly linked to the availability of the cyclodextrin cavity, the aim of this review is to demonstrate that the nature of the reaction solvent and the nature of the linker between cyclodextrin and phosphorous moieties can deeply influence the recognition properties. In addition, the impact on the catalytic activity will be also discussed

Rhodium-Catalyzed Aqueous Biphasic Olefin Hydroformylation Promoted by Amphiphilic Cyclodextrins

International audienc

Chemically Modified Cyclodextrins: An Attractive Class of Supramolecular Hosts for the Development of Aqueous Biphasic Catalytic Processes

During these last years, cyclodextrins have contributed greatly to the development of catalytic processes in water. These cyclic oligosaccharides composed of 6(α), 7(β) or 8(γ) glucopyranose units improve the mass transfer in aqueous-organic two-phase systems and are useful compounds to design new catalysts. Thus, chemically modified cyclodextrins can be used to: (i) increase significantly the rate and selectivity of reactions catalyzed by water-soluble organometallic complexes, (ii) design new water-soluble ligands for aqueous organometallic catalysis, (iii) stabilize catalytically active noble metal nanoparticles in water and (iv) favour the dispersion and activation of the palladium on charcoal in water.cyclodextrin; aqueous organometallic catalysis; nanoparticles; palladium on charcoal