Étude thermodynamique du système compatible polyfluorure de vinylidène-polyméthacrylate d'éthyle par chromatographie gaz-liquide

The thermodynamics of interaction between poly(ethyl methacrylate) and poly(vinylidene fluoride) have been studied by gas-liquid chromatography on their homogeneous blends (40 < PVDF < 80% by weight) in the liquid state (t > 140°C) using a variety of probes covering a wide range of polarity and of affinity for the polymers. The average and most representative interaction parameter χ₂₃′ (Flory-Huggins) is estimated as −0.32 ± 0.09, showing only slight sensitivity to temperature between 160 and 200°C and composition of the blend. The purely interactional χ₂₃ parameter (Prigogine-Flory-Patterson) is strongly negative (χ₂₃ = −6.5 J/cm³) as a result of dipolar and hydrogen bond interactions between the polymers.     

Polymérisation et post-polymérisation de l'acrylate de méthyle en milieu précipitant

The radiation initiated polymerization of methyl acrylate was investigated under precipitating conditions in n-hexane In 10 and 25% monomer solutions, the conversion curves are auto-accelerated and post-polymerization is observed in the dark. The initial rate of this post-polymerization steadily increases with the degree of conversion reached during irradiation, suggesting that trapped growing chains are responsible for the effect. The post-polymerization was followed at 23, 40 and 60°. From the results, it is concluded that chain termination is negligible under such conditions. The addition of methanol to the monomer solutions results in decreased rates and in a reduction of the extent of auto-acceleration. No influence of any “matrix effect” could be detected in these systems.     

Étude du mécanisme de polymérisation de l'acide silicique par potentiométre

Ionization and solubility of silicic acid with variation of pH and concentration of silicic acid are studied by potentiometric measurements. Two characteristic points appear on titration plots: the first point occurs at pH = 3 with formation of the ionized silicic acid; the second at pH = 7 is interpreted as revealing monomeric species. Diverse species of ionized silicic acid are in sols between pH = 3 and 7; the sols contain the smallest species of polymer for pH < 6 and show an optimum of polymerization for pH ≥ 6.     

Étude de l'ordre local par mesure enthalpique différentielle et par exafs en transmission dans les matériaux du système GeTeSb

Study of local order by differential scanning calorimetry and by EXAFS in the GeTeSb system. The local structures of vitreous GeTeSb of near-eutectic and peritectic compositions were studied by using Extended X-ray Absorption Fine Structure performed at the Ge-K edge. Our results show that the Ge atoms are fourfold coordinated by only Te atoms at a distance of 2.60 Å with a Debye-Waller factor of 0.045 Å. We have also shown that the coordination number N decreases when decreasing the tellurium percentage in the samples. The results obtained by EXAFS were interpreted by using differential scanning calorimetry (D.S.C.).     

Nouvelle méthode de lavage et d'isolement du sulfate de baryum dans le microdosage du soufre par gravimétrie

Résumé L'auteur décrit une méthode de lavage et d'isolement du précipité de sulfate de baryum en vue du microdosage du soufre par gravimétrie.Le précipité, transvasé dans un tube de quartz taré, y est lavé et séparé des eaux de lavage par centrifugation et siphonnage automatique. Le précipité est ensuite désséché puis le tube est porté au rouge. On pèse après refroidissement.L'auteur a vérifié que les tubes de quartz employés conservaient rigoureusement leur masse malgré un chauffage au rouge prolongé.

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Summary A new technique is described for use in the determination of sulphur in organic substances; it enables the barium sulphate precipitate to be weighed without the employment of either aPregl filter-tube or a microNeubauer crucible.After the organic substance has been decomposed by the customary methods using either a microCarius' tube or aPregl tube, the contents of the tube are transferred to a Jena glass test-tube, and evaporated on the waterbath. If aPregl tube has been used for the attack on the substance, the barium sulphate is to be precipitated before the evaporation is carried out. The precipitate is then stirred up with 1% hydrochloric acid, and transferred to a previously weighed quartz test-tube by rinsing with ethyl alcohol and 1% hydrochloric acid alternately. After centrifuging, the supernatant liquid is withdrawn by means of suction, the precipitate again stirred up with 1% hydrochloric acid, and the supernatant liquid removed as before after centrifuging. These operations are repeated twice more. The test-tube containing the precipitate is then dried, heated to redness for a short time, cooled in a desiccator, and weighed. A simple device is given which affords a ready and effective means of ensuring that no fine particles of the precipitate have been carried away during the removal of the supernatant liquid.

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Zusammenfassung Es wird eine neue Technik beschrieben, die es gestattet, bei der Schwefelbestimmung in organischen Substanzen den Bariumsulfatniederschlag ohne Verwendung einesPreglschen Filterröhrchens oder eines Mikro-Neubauer-Tiegels zu wägen.Nach dem in bekannter Weise vorgenommenen Aufschluß der organischen Substanz in derCarius-Mikrobombe oder imPregl-Rohr wird der Inhalt der Bombe, bzw. desPregl-Rohres in einer Proberöhre aus Jenaer Glas auf dem Wasserbad eingedampft. Bei Ausführung des Aufschlusses imPregl-Rohr wird vor dem Eindampfen noch der Bariumsulfat-Niederschlag ausgefällt. Der Niederschlag wird hierauf unter Benützung einer Schnepfenfeder mit 1%iger Salzsäure aufgewirbelt und unter abwechselndem Nachspülen mit Äthylalkohol und 1%iger Salzsäure in eine gewogene Proberöhre aus Quarz übergeführt. Nach dem Zentrifugieren saugt man die überstehende Flüssigkeit ab, bringt den Niederschlag abermals mit 1%iger Salzsäure in Suspension, zentrifugiert und saugt neuerlich die überstehende Flüssigkeit ab. Dies wird noch zweimal wiederholt. Die Proberöhre mit dem Niederschlag wird sodann getrocknet, kurze Zeit zur Rotglut erhitzt und nach dem Abkühlen im Exsiccator gewogen. Eine einfache Apparatur ermöglicht eine leichte und wirksame Kontrolle darüber, ob beim Absaugen der Flüssigkeit keine Niederschlagsteilchen mitgerissen worden sind.

     

Isolement de fractions antigéniques membranaires de Toxoplasma gondii par l'intermédiaire de microsphères de méthacrylate

The authors describe a method for isolation of Toxoplasma gondii antigenic membrane components. Technical work is described into four points:

• 1.1) specific labelling of membrane proteins was realised by DD¹²⁵ISA;
• 2.2) methacrylate microspheres were bound to unbroken toxoplasma membranes by the mean of an indirect technic with antibody molecules (double sandwich); these microspheres were used to modify the membrane density;
• 3.3) toxoplasmas bound to microspheres were broken by sonication;
• 4.4) microspheres fixed to membrane components were isolated by isopycnic ultracentrifugation on continuous sucrose gradient.

     

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.     

Approche du phénomène de galop par un modèle d'effort retardé et validation expérimentale

We consider the case of elongated cylinders submitted to a cross-flow. We propose a time delayed force model for the galloping oscillations for which the linear study allows to calculate the critical velocity with quasi-steady coefficients. The phase delay between force and position is based on the Strouhal number of the cylinder measured in static conditions. The experimental validation is presented on square and rectangular sections cylinders.     

Synthièse de nouveaux systèmes hétérocycliques renfermant le benzothiazole,le 1,3,4-thiadiazole et le furane

The 2-(4-methylphenyl)acyl-l,3-benzothiazole 3b reacts with the N-bromosuccinimide to give the dimerised compound 4. This product leads to the furane 5 by refluxing in triethylphosphite. The 2-phenylacyl1,3-benzothiazole 3a leads to 1,3,4-thiadiazoles 9 and 10 by sulfurisation and condensation with nitrilimines 7 and 8.     

La séparation et le dosage du tungstène et du molybdène au moyen du chlorure de calcium

A rapid and simple method is described for the separation and the determination of molybdenum and tungsten. Both metals are extracted as their soluble salts, sodium molybdate and sodium tungstate, by means of an alkaline fusion (Na₂CO₃ + Na₂O₂), after which they are separated by precipitation with calcium chloride as reagent. The precipitates of calcium molybdate and calcium tungstate are filtered, washed and then decomposed by concentrated hydrochloric acid. Calcium molybdate passes completely into the filtrate while calcium tungstate leaves a precipitate of tungstic acid. By calcining this precipitate, tungstic trioxide is obtained and weighed. The tungsten content is calculated therefrom.The filtrate from tungstic acid serves for reprecipitation of calcium molybdate on making the solution alkaline and by boiling. Calcium molybdate is filtered by means of a porcelain crucible filter and then calcined. When the weight of the calcined precipitate is constant, the molybdenum content is obtained by multiplying the weight of the precipitate by the conversion factor. Results are satisfactory, separation and determination of both metals not taking more than a day's work.     

Etude du système Li0,5Ga2,5O4CuGa2O4 par spectrométrie IR et diffraction de neutrons

The phase diagram of the system (1 − s) Li_0·5Ga_2·5O₄−s CuGa₂O₄ has been established by quenching, DTA, X-ray diffraction at high temperature and IR spectrometry. The change from the disordered (space group P4₃32) to the ordered cubic form (space group Fd3m) is made by means of an extensive biphase (0·25 ⩽ s ⩽ 0·52). The thermal stability of copper and mixed gallates has been studied by thermogravimetric analyses. The spectrum of Cu²⁺ in spinels (0·8–2·5 μ, s ⩾ 0·54) discloses copper on A and B sites. The cation distribution is deduced from neutron diffraction.     

Un modèle du spectre des ondes de surface générées par le vent

A model of wind-generated surface waves is discussed. The energy equilibrum between excitation effects, nonlinearity, and dissipation are governed by a self-regulating process. The numerical results are compared with experimental data. © 1999 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS     

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.