Un modèle de prédiction de l'érosion des matériaux ductiles par la cavitation

Cavitation erosion is a complex phenomenon involving the interaction of hydrodynamical, mechanical, metallurgical and chemical factors. A mathematical model is proposed to predict the erosion rate as a function of cavitation conditions and material properties.     

Synthèse assistée par plasma d'un revêtement de h-bn: composition et vieillissement

A thin film containing h-BN was deposited on a silicon substrate from the reaction between a flowing nitrogen plasma and B₂H₆. The influence of various durations of pre-treatment and post-treatment by the nitrogen plasma on the chemical composition of the coating and on its ageing in open air was studied by FTIR and XPS.     

De Réaumur à la Première Guerre Mondiale : les étapes de la maîtrise de l’acier,l’essor des aciers spéciaux

After a brief survey of the history of steel-making we shall concentrate on the period extending from Réaumur's work on that topic (1722) until World War one. Those two centuries saw the transition from empirical steel production processes to industrial steel manufacturing. We shall see how problems linked to the quenching and cementation of steel caused both scientists and steel manufacturers to develop efficient research leading to the establishment of an authentic metal science around 1900. These scientific discoveries then contributed to the prodigious development of special steel. Originally produced empirically to fulfill military requirements, these new types of material were to answer the needs of emerging industries, such as electrical engineering, as well as car manufacturing.     

Synthèse électrochimique d'esters arylacétique et arylpropionique via des complexes du nickel

Aryl acetic and aryl propionic esters are obtained by an electrochemical process. The σ-arylnickel complex ArNiXL₂ (L  PPh₃) obtained in the presence of an aromatic halide with THF/HMPT or THF/NMP as solvent reacts with σ halide aliphatic esters to give the corresponding aryl-substituted esters.     

Principes pour la préparation de poudres fines par la technique verrière—application a l'hexaferrite de baryum

The “glass synthesis method,” performed in three steps, is widely applicable for the preparation of microcrystalline powders. A glass is first made by fusion of a mixture of a glass-former material F, a modifier M, and a metallic oxide O. Annealing then precipitates microcrystals of MO in a FM glass matrix. The microcrystals are recuperated in the last step by dissolving the matrix. The preparation of hexagonal platelets of BaFe₁₂O₁₉ from the glass B₂O₃ (F)BaO (M)Fe₂O₃ (O) is given as an example. The annealing temperature was found to be the critical parameter to control the grain size of the powder.     

Séparation de traces de manganèse par électrolyse sur cathode de mercure renouvelée

The authors describe conditions of electrolysis which permit a quantitative deposit of traces of manganese to be obtained from sulphate and perchlorate solutions. Theoretical considerations based on the application of polarisation curves lead to a quantitative explanation of some of the experimental results, especially those concerned with the effect of different factors on the kinetics of deposition.     

Synthèse racémique et énantiosélective d’énol-lactones et leur évaluation comme inhibiteurs de la protéase du VIH-1

Racemic and enantioselective synthesis of enol-lactone and their biological activity as potent HIV-1 protease inhibitors. A series of enol-lactones was prepared and evaluated for its activity against HIV-1 protease. The preparation of (R,S)-5,6-dihydro-4-hydroxy-6-phenyl-2H-pyran-2-one (3) is the key intermediate for the synthesis. The synthesized enol-lactones (5 and 8–11) were kinetically evaluated against a HIV-1 protease substrate and were found to exhibit moderate inhibitory activity. The enantioselective synthesis of enol-lactone is achieved to give the two enantiomers. To cite this article: S. Ibrahimi et al., C. R. Chimie 8 (2005).     

Effet de la température,de la pression et de la composition sur l'intensité diffusée par un mélange de deux polymères

Phase diagrams of polymer blends and solutions are usually studied by measuring the scattered intensity (by light or neutrons) as a function of composition, temperature and pressure. If one expands Flory's χ parameter as a function of the composition, one sees that in order to have deviations from Flory's laws, thermodynamic quantities such as volume, heat capacity or compressibility should vary with respect to composition by a power law of degree larger than two. In some cases, the direct measurement of these quantities could lead to a more precise and rapid determination of the miscibility conditions.     

Sur l'électrophorèse d'un ensemble de particules portant la même densité uniforme de charges

We consider the electrophoresis of solid particles embedded in a possibly non-uniform electric field E_t8. For particles admitting the same uniform zeta potential, the rigidbody motion of each particle is obtained without calculating the total electric field E within the electrolyte.     

Activation mécanique d'oxydes de fer et de vanadium en vue d'une synthèse de ferrite de vanadium nanométrique similaire au composé issu de la chimie douce

Co-milling of iron and vanadium oxides allows us to obtain an intimate oxide mixture at a nanoscale, similar to a coprecipitate elaborated by soft chemistry. Reduction of such a mixture in the same temperature and oxygen partial pressure conditions (500 °C and 10⁵ Pa) as the Pa) as the soft chemistry products leads to a nanometric vanadium ferrite with only a spinel phase. Homogeneity of grain size and chemical composition is reached if the initial oxides have similar grain sizes.     

Synthèse et étude d'une prodrogue de dipyridamole: application de la stratégie ADEPT à la résistance multiple (MDR) en chimiothérapie anticancéreuse

A glucuronyl-spacer-dipyridamole prodrug has been synthesized from dipyridamole, a reversal agent of MDR. Combined use of this compound with a glucuronyl-spacer-doxorubicin prodrug (HMR 1826), restored in vitro the sensibility of a resistant cancerous strain. This prodrug was therefore selected for in vivo tests according to ADEPT strategy on MDR resistance expressing tumours.     

Application Des Réseaux de Neurones Avec la Régularisation Bayésienne pour la Modélisation de la Synthèse de l’hydroxyapatite Élaborée à Partir du Carbonate de Calcium et de L’acide Phosphorique

We have used a new, robust model mapping technique—a Bayesian-regularized neural network—to develop a quantitative relationships model for the synthesis of the phosphocalcic hydroxyapatite by precipitation from a calcium carbonate solution and a phosphoric acid solution. This model was preformed by using a set of factors consisting on the pH of reactional medium, the Ca/P molar ratio of the reagents, reaction time, and the initial concentration of calcium. The results show that the method is robust and gives satisfied results. The Levenberg–Marquardt's algorithm implemented in the neural network Matlab's toolbox allowed a drastic improvement of the performance of the model. Very satisfactory results are then obtained by testing the validity by cross-validation technique.

We have also turned our interests to the explanatory capacities of our methodology to explore the relative contribution and/or the contribution profile of the input factors by using Garson weight portioning method.     

Structure électronique des éthers vinylique et divinylique: Introduction de la déformation des orbitales σ

Résumé La théorie L.C.A.O. améliorée est appliquée à l'étude des éthers vinylique et divinylique. La grande différence d'électronégativité entre les orbitales atomiques entrant dans la liaison entre l'oxygène et le carbone nous a conduits à introduire la déformation réciproque de ces orbitales. Les énergies calculées pour la première transition N V, 6,5 et 6,3 eV, sont en excellent accord avec l'expérience.

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The improved L.C.A.O. theory is applied to the vinyl and divinyl ethers. The large differences of electronegativity between the atomic orbitals which enter the-bond between oxygen and carbon led us to the introduction of the mutual deformation of these orbitals. The calculated energies for the first N V transition, 6,5 and 6,3 eV are in excellent agreement with experiment.

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Zusammenfassung Die verbesserte L.C.A.O.-Theorie wird auf Vinyl- und Divinyläther angewandt. Die große Elektronegativitätsdifferenz zwischen den an der-Bindung zwischen Sauerstoff und Kohlenstoff beteiligten Atomzuständen hat uns veranlaßt, die gegenseitige Deformation dieser Zustände einzuführen. Die für die erste N V-Elektronenbande berechneten Energien, 6,5 und 6,3 eV, stimmen ausgezeichnet mit der Erfahrung überein.

     

Nouvelle méthode de synthèse d’acides et d’esters arylboroniques par électroréduction de dérivés aromatiques halogénés en présence d’agents boratants

Novel synthesis of arylboronic acids and esters by electroreduction of aromatic halides in the presence of borating agents. A novel strategy for the one-step synthesis of arylboronic acids and esters by an electrochemical coupling reaction is described. It is based on the reductive coupling between the aromatic halides and a borating agent (trialkyl borate or pinacolborane). The reactions are carried out in DMF or THF with the use of sacrificial magnesium or aluminium anodes in a single-compartment cell. Arylboronic acids and esters are obtained with moderate-to-good isolated yields. To cite this article: C. Laza, E. Duñach, C. R. Chimie 6 (2003).     

Synthèse régiosélective par voie organométallique de pyridines, 4-picolines et 3,5-lutidines substituées en 2 par un groupe insaturé et/ou fonctionnel

A regioselective one-pot synthesis of 2-substituted pyridine derivatives from N-alkoxycarboxylpyridinium salts and α-unsaturated organozinc compounds is described. Similarly, functional alkynyl organomagnesium compounds lead to 2-alkynyl-ω-functional pyridines, from which (E)-2-alkenyl or 2-alkyl-ω-functio pyridines can be obtained by partial or complete reduction.     

Synthèse de composés macrocycliques comportant deux fragments coordinants séparés et différents,de type bipyrldyl-2,2' et diphényl-2,9 phénanthroline-1,10.

Macrocyclic compounds containing a 2,9-diphenyl -1,10-phenanthroline subunit and a peripheral 2,2'-bipyridine chelate have been synthesized. In compound 4, the links between both coordinating fragments are flexible enough to allow complete folding of the molecule during complexation whereas in 5, the complexing moieties are rigidly held apart and cannot bind to the same metallic center.