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.     

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.     

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 par émission acoustique de l’adhérence et de l’endommagement d’un revêtement : cas d’un revêtement WC–Co sur acier

This note presents a characterization method of the ‘adhesion’ of a coating by acoustic emission technique. In situ acoustic emission measurements which were investigated in terms of amplitude, absolute energy, position of the event, etc. were performed on WC–Co coated specimens prepared by HVOF (high velocity oxy fuel) during four-point bending tests. The microscopic observations of the specimens show two types of cracks: transversal cracks (regularly spaced on the coating surface) and interfacial cracks. Acoustic emission results show two different types of acoustic events in terms of absolute energy and amplitude, which are representative of two cracking mechanisms.     

Les réactions solvothermales : implications en recherche de base et dans les procédés industriels

Solvothermal reactions have been developed both in solid state chemistry and in material science. In a first approach, seven main domains can be defined for the applications of such reactions: (i) the synthesis of new materials, (ii) the development of new processes, (iii) the preparation of microcrystallites, (iv) the thin film deposition, (v) the sintering and (vi) the crystal growth at moderate temperature compared to the conventional processes, (vii) the waste-retreatment. These different domains involving either the basic research or the industrial applications, in particular in the area of ceramics, are presented and their potential developments are analysed.     

Influence des traitements de revenu sur les caractéristiques mécaniques d'un acier rapide

Influence of treatments of tempering on the mechanical characteristics of a high-speed steel. The influence of tempering treatments on various mechanical characteristics (hardness, strength, resilience and toughness) was considered in this study. The investigated material was a strongly alloyed high-speed steel, Z 85 WCDV 06-05-04-02, in the order of decreasing contents of the elements tungsten, molybdenum, chromium and vanadium, which is used in manufacturing tools. This material is mainly subjected to wear and impacts. The experimental methods as well as an analysis of the chemical composition of the material are presented. Test specimens were of a normalized type. An analysis of the addition elements influence on the obtained results is discussed. The variation of mechanical characteristics in terms of applied thermal treatments is shown. These treatments reveal the influence of tempering. They allow to determine the best compromise between the obtained morphological structure on the one hand and the mechanical properties of this alloy on the other hand.     

Etude des réactions de l'acétylformazyle et de ses dérivés avec les ions minéraux

Résumé L'étude systématique de l'acétylformazyle et de ses dérivés pour l'analyse à la touche à fourni des réactions sensibles permettant la recherche du mercure avec la thiosemicarbazone, du cuivre et du palladium avec l'oxime.

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Summary The systematic study of acetylformazyl and its derivatives for spot test analysis has yielded sensitive reactions which permit the detection of mercury by means of the thiosemicarbazone, and of copper and palladium with the oxime.

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Zusammenfassung Die systematische Untersuchung von Acetylformazyl und seinen Derivaten für die Zwecke der Tüpfelanalyse führte zu empfindlichen Reaktionen zur Prüfung auf Quecksilber mit dem Thiosemicarbazon, auf Kupfer und Palladium mit dem Oxim.

     

Influence de la non stoechiométrie sur les modes de vibration,les amplitudes vibrationnelles,et les intensités infra-rouge dans les alumines β

The normal coordinate analysis of nonstoichiometric β-alumina containing cations such as Na⁺, K⁺, Tl⁺, or Ag⁺ with different nonstoichiometric models (Frenkel defect associated with various cation distribution in the conducting plane) is reported. Mean square amplitudes and infrared intensities have been estimated on the basis of normal mode calculations for sodium β-alumina (stoichiometric and nonstoichiometric). The results obtained are in good agreement with experimental data. The spectral modifications that have been observed can be explained by splitting of degenerate levels and modification of selection rules due to the loss of local symmetry induced by the Frenkel defect. The good agreement between the in-plane (a, b) vibrational calculated frequencies of interstitial oxygen (O_i) and Raman or neutron scattering data shows that the compensating oxygen is tightly bounded to the spinel blocks. The difference between the calculated and crystallographic mean square amplitudes can be explained in terms of the static deviation of the bridging oxygen (O(5)) of 0.1 Å (at 300 K) from its ideal site.     

Influence de l'oxygène sur les propriétés cristallographiques et électriques des materiaux de type tysonite

Influence of the substitution of oxygen for fluorine on the structural and electrical properties of Ce_1−xBi_xO_xF_3−2x solid solutions isostructural with ThOF₂ has been investigated. A structure of ThOF₂ has been proposed after use of a theoretical simulation method and comparison with that of LaF₃. Correlations between transport properties and structural data have been established.     

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.     

comportement en frottement sec de dépôts SiCx(H) (1,5

《Annales de Chimie Science des Materiaux》1998,23(5-6):879-890

Réactions des dérivés du phosphore trivalent avec les composés à halogéne positif—IV : Phosphite de triphényle avec les α-cyano α-halonitriles et α-cyano α-halo esters: Synthèse et propriétés de triphénoxyiminophosphoranes

α-Bromo-α,β-dicyano nitriles react with triphenylphosphite to give stable triphenoxyiminophosphoranes. α-Bromo-α,β-dicyano esters are converted, with triphenylphosphites, into the corresponding triphenoxyiminophosphoranes. These phosphoranes cyclise with acids to give substituted Δ²-pyrrolines.     

Étude des transferts de charge dans les dérivés carbonyle du cobalt et du fer avec les éléments de la colonne IV B

MM′ bonds in carbonyl derivatives of cobalt and iron have been compared to MM″ bonds; M is the transition metal, M′ a IVB element, and M″ a VB ligand atom. The two series having the same geometry configuration (CO)₄CoM′X₃ and (CO)₄FeM″X₃ (X = Cl, OMe, Ph or alkyl) have been particularly investigated.Infrared studies in the CO stretching vibrations region allows to determine the variation of charge transfer between M and M′ or M and M″ when M′ and M″ are varied, X remaining constant, and when X varies, M′ and M″ remaining constant.From dipole moment measurements it can be verified that a close relationship exist between the v(CO) frequencies of compounds of a same series and the charge transfer involving the bonds MM′ or MM″. This relationship confirms the spectroscopic results obtained and defines also the direction in which the transfer is taking place. Finally it allows to show that in metal carbonyls the central transition metal is not charge.A calculation of π overlap based on Slater's AO's allows to determine the trend of variation of the π component of the total charge transfer, when M′ or M″ varied.A representation of σ and π transfer in MM′ and MM″ bonds is proposed.     

Sur les zinciques issus des α-bromonitriles : I. Préparation,structure et réactivité avec les aldéhydes,les cétones et les alcoylidènes malonates d'éthyle

Organozinc compounds derived from α-bromonitriles are readily prepared in solution in tetrahydrofuran (THF) and exist in the C metallated form. They condense normally with aldehydes and saturated ketones. A number of new β-hydroxy-nitriles are described. The addition of conjugated unsaturated ketones results in the formation of β-hydroxynitriles or ketonitriles, depending on the nature of the initial bromonitrile. The stereochemistry of the reaction of benzaldehyde with zinc-α-bromonitrile is not influenced by the nature of the solvent. Condensation with diethyl-malonate alkylidenes lead to the expected 1,4-addition products.     

Deux modèles de plaque mince avec inclusions piézoélectriques et circuits électroniques distribués

This paper presents two models of thin elastic plates with periodically distributed piezoelectric inclusions and electronic circuits. This is a first example of a smart composite material, although the considered electronic is rather rudimentary.     

Préparation d’orthoesters originaux par addition d’acides carboxyliques sur des acétals cycliques de cétènes

Original orthoesters have been prepared by addition of carboxylic acids on the exocyclic double bond of 2- alkylidene -benzo[1,3]dioxin-4-ones. To cite this article: P. Babin et al., C. R. Chimie 6 (2003).     

Préparation et Étude Physico-chimique de Quelques Copolyamides Aromatiques Séquencés. II. Preuves de I'Existence de Séquencés dans les Copolycondensats

In order to prove a block structure, copolyamides synthetized by a two-stage low-temperature solution polycondensation process were extracted by suitable solvents. The fractions obtained were characterized by various physicochemical techniques. In particular, the presence of insoluble segments in the fractions containing soluble homopolyamide was revealed by means of thermogravimetry and infrared