Dépôt de revêtements peu rugueux de diamant sur un alliage de titane

Deposition of smooth diamond coatings on titanium alloy. A new process has been perfected to deposit smooth diamond coatings, at 600 °C, on titanium alloys. Scanning electron microscopy, X-ray diffraction, visible and UV Raman spectroscopy show that these coatings are smooth and mainly composed of crystalline diamond with a fine-grained morphology. The results are compared here to those obtained with classical rough polycrystalline coatings. Optical emission spectroscopy reveals important differences between the plasma species produced for the deposition of these smooth coatings and the plasma species produced for the deposition of both polycrystalline diamond and nanocrystalline films. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASdiamond / coating / titanium alloy / plasma / roughness / Raman spectroscopy / emission spectroscopy     

Caractérisation de revêtements PVD dans le Système V-C-N-O et comparaison avec les propriétés de revêtements similaires obtenus par OMCVD

Vanadium nitride, carbide, carbonitride and oxycarbide coatings were produced on steel substrates, by reactive magnetron sputtering from a vanadium target or by chemical vapor deposition using vanadocene as an organometallic precursor. The composition and crystallographic structure of coatings were determined by different techniques. The mechanical characteristics of the coatings are highly dependent on both their composition and the deposition technique.     

Analyses de matériaux provenant de la décomposition du benzène liquide au cours de l’interaction avec un faisceau laser pulsé

Materials have been obtained by decomposition of liquid benzene, owing to the acoustic shock wave induced by the stimulated Brillouin and Raman scatterings excited by a pulsed laser beam 〚1〛. First, amorphous carbon containing particles of graphite and chaoite have been characterized by X-ray diffraction; second, after distillation of the treated benzene and heating under vacuum, a solid residue with a yellowish colour is obtained and characterized by means of X-ray diffraction, mass spectrometry, and infrared, visible and ultraviolet spectroscopies. In this last material, there are several constituents: in a main part, monohydrogenated benzene cycles, along with compounds of naphtalene type, and, in a small part, polycyclic aromatic hydrocarbons.     

Prétraitements de nitruration compatibles avec les procédés MOCVD et PACVD: Influence sur l'adhérence de revêtements céramiques sur ACIER

The influence of nitriding pretreatments of steel substrates on the adhesion of representative ceramic coatings has been investigated. Vapor phase nitriding using the mixture NH₃/H₂/He has been applied before the growth by MOCVD of vanadium nitrides, carbonitrides and oxides. Similarly, microwave plasma nitriding using the mixture N₂/Ar was applied prior to the deposition by PACVD of silicon carbide based films. The nitriding pretreatment enhances the adhesion of plasma SiC(H) and MOCVD V(C,N) and V₂O₃ coatings but is not favorable to a better adhesion of MOCVD VN-type films. The different mechanical behaviors of these coatings are discussed in terms of compatibility between the combined processes.     

Le calcul du déplacement chimique,un outil de validation des structures d’acides nucléiques

The large majority of analytical NMR methods in chemistry or biochemistry are based on the quality of the chemical shift dispersion. The purpose of this work is to show that theoretical chemical shift back calculation starting from structures can be used to select molecular modeling structures in order to differentiate several conformational possibilities. Here we report the result of the chemical shift calculation carried out on two original structures corresponding to two DNA ‘kissing complexes’. The 46 nucleotides sequence corresponds to the RNA deoxyribose analogous implied in the HIV-1_Lai dimerization process. It is interesting to note that, even in cases we are very far from the classical helical structure (loop–loop interaction, AA base pairing, base stacking, misappariement...), the theoretical chemical shift is in very good agreement with the experimental chemical shift (±0.25 ppm). The satisfactory results obtained enable us to conclude that the comparison of the proton chemical shifts is an invaluable tool making it possible to select or to validate oligonucleotides structures.     

Étude de l’activité prébiotique potentielle de l’acide borique

Boric acid has always been neglected in prebiotic chemistry, because it is not a major component of biological macromolecules. We argue here for a potential catalytic role of boric acid in peptides and nucleic acid synthesis. Today boron is an important component of seawater (0.4 mM). Its concentration at prebiotic times was probably higher. In water, boron mainly appears in the form of boric acid or its derivatives (esters and anhydrides).     

Réaction d’isomérisation de l’acide urocanique et de ses dérivés: stabilité comparée des isomères Z et E

Thermal and photochemical isomérisation of urocanic acid and its derivatives (O- and/or N-alkylated) have been studied. The data show the wavelength and the molar extinction coefficient-dependent photochemistry of E urocanic acid and its derivatives. Thermal isomérisation of these compounds is difficult and undergoes a “one-way” Z → E reaction. Thus, E isomers are thermodynamically more stable than the Z ones. Under basic conditions, derivatives having an unsubstitued imidazole ring (NH function free) exist in their anionic forms, which lowers the energy barrier without changing the isomérisation pathway.     

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).     

Oxydation à haute température d’un nouvel alliage de titane α+β

A new α+β titanium alloy Ti-Mo_4.84-Ta_4.34 alloy named TMT has been oxidised under an atmospheric pressure of oxygen above the α ↔ β transformation temperature. The oxidation resistance increases strongly as compared to pure titanium (almost 50 %), which is mainly due to both alloying elements. The oxygen dissolution involves the α phase precipitation from the β phase, which becomes enriched with Ta and Mo. The diffusion takes place along α precipitates, whose orientations may depart from the normal to the surface. Diffusion is also discussed with regards to phase stability and our results are compared to literature data.     

Caractérisation mécanique par flexion,nano- et macro-indentation de revêtements de SiC par PACVD micro-onde sur acier

Various SiC coatings were deposited on a steel substrate in a micro-wave plasma activated CVD device, then tested by a depth-sensing indentation instrument for measurement of their hardness and of their Young's modulus. Tests by three-point bending and by Vickers and Rockwell C indentation yielded consistent results about their rupture and adherence properties. The mechanical origin of the damage patterns induced by indentation is discussed on the basis of a numerical simulation of the testing.     

Précurseurs métallorganiques pour le dépôt chimique à partir dune phase gazeuse de revêtements dans le système Ti-V-C-N

The various kinds of metallorganic precursors which can be used for the chemical vapor deposition of ceramic materials in the Ti-V-C-N system are reviewed. Selection criteria, and the use of one or several precursors for a selected ceramic coating are discussed. Several examples are presented to illustrate the benefits and problems resulting from such a process.     

Algorithme de dénombrement des graphes chiraux et achiraux d’un cycloalcane monocyclique hétérosubstitué de formule brute CnHm1Xm2Ym3

A general pattern inventory is given for the enumeration of chiral and achiral graphs of any monocyclic cycloalkane with a multiple heterosubstitution of binary type X and Y and an empirical formula C_nH_m1X_m2Y_m3, where m₁ + m₂ + m₃ = 2 n.     

Modélisation d'un revêtement précontraint à collage par points

We determine the homogenized density of energy associated with a viscoelastic sandwich beam, non-uniformly stuck. We are then able to obtain the global dynamic behaviour of a ‘real’ viscoelastic beam with fewer degrees of freedom.     

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.     

Influence d’alcools aliphatiques sur l’adsorption d’acides aminés sur charbon actif

Adsorption of aqueous solution of two amino acids – phenylalanine (Phe) and tyrosine (Tyr) – on powdered activated carbon (PAC) has been studied in the presence of linear or branched alcohols. Methanol has no influence on the adsorption. For the other alcohols, the adsorption decreases when the alcohol chain gets longer, from ethanol to 1-propanol, up to 85 %. Alcohol branching reduces this phenomenon. Adsorption kinetics have been tested according two models, allowing good representation of results and determination of kinetic constants.     

Influence de l’énergie interne sur la réactivité de l’ion Fe(CO)2+ avec le diméthyléther, étudiée dans un spectromètre de masse FT–ICR

The influence of the internal energy on the reactivity of iron carbonyl cations with dimethylether CH₃OCH₃ (DME) has been studied using a triple cell Fourier Transform Ion Cyclotron Resonance mass spectrometer. The experimental set-up as well as the data analysis are briefly presented before being detailed on the example of the reactivity of Fe(CO)₂⁺. The strong energy dependence upon the reactivity of the ion is shown: when working with thermalised ions, the only channels observed are the two successive substitutions of a CO ligand by one DME molecule, whereas other channels are opened up for excited ions (the cleavage of the C–O bond may be homolytic or due to a rearrangement). A reaction mechanism of the C–O bond activation is then proposed.     

Méthodes de concentration préalable dans la détermination spectrochimique d'éléments à l'état de trace

Résumé La concentration préalable est très intéressante en vue des déterminations analytiques des traces d'éléments qui, en très petite concentration, se trouvent dans les sols de culture, les engrais chimiques, et commes des impuretés, ou des petites quantités des éléments, dans des alliages ou d'autres divers matériaux. Pour cette sorte de microdosage, nous avons spécialement choisi les méthodes spectrochimiques, comme celles les plus convenables pour la détermination simultanée de plusieurs éléments dans les échantillons étudiés. Avec cette concentration préalable des traces d'éléments on obtient dans des méthodes spectrochimiques, l'élimination la plus grande possible des éléments principales qui peuvent troubler ou bien déguiser les lignes appropriées pour le dosage des traces d'éléments. Des divers techniques utilisées pour la concentration préalable nous avons poursuivi spécialement celles qui basent sur l'emploi des réactifs chimiques appropriés, aussi bien qu'à cause de leur spécificité de la précipitation, aussi bien qu'à cause des procès de coprécipitation ou trainage qu'elles provoquent. Parmi les méthodes qui employent des réactifs organiques on a étudié, entre autres, la détermination spectrographique quantitative de petites quantités de bismuth comprises dans des alliages ternaires en base de plomb. On a employé le cupferron comme un réactif sélectif qui précipite le bismuth en présence de plomb et de cadmium, après avoir étudié la zone optime deph (0,5–1,5) dans laquelle ceci est possible. On a aussi étudié la détermination spectrochimique des traces de baryum à l'égard des diverses problèmes, en concentrant préalablement le baryum moyennant un procès de trainage ou coprécipitation provoqué par le ion sulfate en présence de plomb, qui s'ajoute excessivement, et que nous employons comme étalon interne spectral. Cette méthode a été employée pour le dosage de baryum dans certains procès d'adsorption, étudiés dans nos laboratoires.

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Summary The preliminary concentration is of great interest with regard to analytical determinations of traces of elements which occur at very low concentrations in agricultural soils, chemical fertilizers, and as impurities, or of minute quantities of elements in alloys or other divers materials. For this kind of microdetermination, we have especially chosen spectrochemical methods as being the most convenient for the simultaneous determination of several elements in the samples studied. With this preliminary concentration of traces of elements, there is obtained in the spectrochemical methods, the greatest possible elimination of the principal elements which may interfere with or entirely disguise the appropriate lines to be followed for determining the traces of elements. Among the various techniques employed for the preliminary concentration, we have followed especially those which are based on the use of appropriate chemical reagents, both because of there specific precipitating action, or because of the process of coprecipitation or entrainment which they provoke. Among the methods, which utilize organic reagents, there have been studied, for instance, the spectrographic quantitative determination of small quantities of bismuth contained in ternary alloys containing principally lead. Cupferron has been used as a selective reagent, which precipitates bismuth in the presence of lead and cadmium, after establishing the optimalph zone (0,5–1,5) in which this separation is possible. A study has also been made of the spectrochemical determination of barium by means of an entrainment of coprecipitation process brought about by sulfate ion in the presence of lead, added in excess, and which we have used as an internal spectral standard. This method has been used for the determination of barium in certain adsorption processes studied on our laboratories.

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Zusammenfassung Die vorhergehende Anreicherung hat für die analytische Bestimmung von Spurenelementen in Ackerböden und im Kunstdünger oder von geringsten Beimengungen und Verunreinigungen in Legierungen oder sonstigem Material große Bedeutung. Wir verwenden für solche Mikrobestimmungen vor allem spektralanalytische Methoden, da sie sich für die gleichzeitige Bestimmung mehrerer Elemente in einer Probe am besten eignen. Mit einer solchen der Spektralanalyse vorangehenden Anreicherung erzielt man die größtmögliche Entfernung der Hauptbestandteile, die die zur spektralanalytischen Bestimmung der Spuren geeigneten Linien stören oder sogar überdecken können. Von den verschiedenen zur Anreicherung geeigneten Verfahren verwenden wir vor allem die mit Hilfe von chemischen Reagenzien, sei es daß sich diese zufolge ihrer Spezifität hierzu besonders eignen, sei es weil sie bei der Niederschlagsbildung die gesuchten Elemente mit ausfällen oder mitschleppen. Unter Zuhilfenahme organischer Reagenzien studierten wir unter anderem die spektralanalytische Bestimmung kleiner Mengen Wismuth, wie sie sich in Legierungen auf Bleibasis finden. Wir verwendeten hierfür als selektives Reagens Cupferron, welches Wismuth in Gegenwart von Blei und Cadmium ausfällt. Als geeignetstesph-Bereich hierfür wurde 0,5 bis 1,5 bestimmt. Weiters untersuchten wir die spektralanalytische Bestimmung von Bariumspuren mit Rücksicht auf gewisse Problemstellungen, indem wir das Barium vorher mit Sulfationen gleichzeitig mit Blei ausfällten, welches im Überschuß zugefügt und von uns als Vergleichssubstanz verwendet wurde. Diese Methode wurde zur Bariumbestimmung bei gewissen Adsorptionsversuchen verwendet, die in unserem Laboratorium durchgeführt werden.

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Avec 4 figures.     

Étude de l’élimination du Cr(VI) par l’oxyde mixte obtenu par calcination de l’hydroxyde double lamellaire MgAl

A magnesium aluminium hydrotalcite-like compound (HT) containing carbonate anions in the interlayer space and with a final Mg/Al ratio of 2 was synthesized by the co-precipitation method. The obtained material was characterized by powder X-ray diffraction (XRD), Fourier-Transform–Infrared spectroscopy (FT–IR), thermal analysis (ATG/ATD), and surface area measurements (BET). The interaction of the clay with Cr(VI) has been studied by ultraviolet–visible (UV–vis) spectroscopy. The calcined hydrotalcite (HT-C) showed the highest capacity of removal of chromium ions, and their sorption capacities for Cr(VI) are 4.85 mmol/g. The effect of various parameters on the preparation conditions for the removal of chromium, such as the contact time, the amount of sorbent, the initial concentration of Cr(VI), and the pH values of aqueous solution were also investigated to identify their influence on Cr(VI) sorption. The characterization of the calcined hydrotalcite (HT-C) after interaction with Cr(VI) ions by FT–IR spectroscopy showed that Cr(VI) was adsorbed and intercalated by the solid.     

Détermination de la composition énantiomérique dˈesters dˈacides aminés par spectroscopie de RMN à lˈaide dˈune chiroporphyrine de cobalt(III) comme agent chiral de déplacement chimique

We wish to propose a novel chiral shift reagent for the determination of enantiomer composition of amino acid derivatives. This reagent, chlorocobalt(III) tetramethylchiroporphyrin CoCl(TMCP), effects quantitative in situ derivatization of amino compounds in the NMR tube, without any detectable kinetic resolution. The influences of the chiral cavity and of the porphyrin ring current on the signals of the coordinated amino acid methyl ester L* can be seen in the high-field region of the ¹H NMR spectrum of the bis-adduct [Co(L*)₂(TMCP)]⁺Cl^–. The signatures of the (R) and (S) ligands are well resolved at 200 MHz, and their relative intensities can be readily determined by peak integration. To cite this article: M. Claeys-Bruno et al., C. R. Chimie 5 (2002) 21–25