Étude physicochimique de nouveaux composés formés par incorporation directe d’hétéropolyacide dans une silice mésoporeuse organisée

Heteropolyacids (HPW) are known as active catalysts for various redox reactions. The direct incorporation of HPW species in a mesoporous organised silica molecular sieve during the synthesis was studied. The association of two type of surfactants is essential for the preparation of such solids. The silica-organised materials comprising heteropoly compounds thus obtained were thermally stable porous materials with mesopores and large surface areas.     

Fixation de lysine par sa fonction αNH2 sur chaîne oligométhacrylique

Lysine was fixed by its αNH₂ function to oligochloroformates. After fixation, carboxylic and NH₂ end-groups are released. H- and ¹³C-NMR and i.r. spectra of these compounds are given.     

Séparation des isoméres de l'hexachlorocyclohexane par chromatographie en phase gaz

Hexachlorocyclohexane isomers can be separated by a glass bead technique with polypropylene glycol Niax 1025 as the stationary phase. The principal isomers separated are the γ-hexachloro-cyclohexane (Lindane isomer), the α, β, ε, and δ isomers and γ-heptachlorocyclohexane. The life of the glass bead column is short — about 20 days in constant use. A longer column life can be obtained by pretreatment of the glass beads.     

Étude générale sur la nature des tungstates formés à haute température au cours de diverses réactions à l'état solide

Résumé L'étude de la décomposition du paratungstate de sodium par la chaleur met en évidence la formation de tétratungstate Na₂W₄O₁₃ et de bitungstate Na₂W₂O₇. Ce dernier tungstate, existant seulement à l'état solide, présente un spectre d'absorption caractéristique. On peut l'obtenir pur en faisant agir l'anhydride tungstique sur le tungstate de sodium Na₂WO₄.

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Summary The study of the thermal decomposition of sodium paratungstate reveals the formation of sodium tetratungstate Na₂W₄O₁₃ and the bitungstate Na₂W₂O₇. The latter tungstate exists only in the solid state and gives a characteristic absorption spectrum. It may be obtained pure by causing tungstic anhydride to react with sodium tungstate Na₂WO₄.

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Zusammenfassung Das Studium der thermischen Zersetzung von Natriumparawolframat erwies die Bildung von Tetrawolframat Na₂W₄O₁₃ und von Biwolframat Na₂W₂O₇. Letzteres besteht nur in festem Zustand und bietet ein charakteristisches Spektrum. Man erhält es in reinem Zustand durch Einwirkung von Wolframtrioxyd auf Natriumwolframat Na₂WO₄.

     

Étude des propriétés viscoélastiques de quelques polyfluorure de vinylidène fondus

The rheological behaviour of molten poly(vinylidene fluoride) was studied in steady flow and dynamic flow. An attempt was made to correlate the experimental results with extrudability.     

Étude de la compatibilité d'un système polyamide/phase caoutchoutique modifiée par l'anhydride maléique—I. Étude de la modification de la phase caoutchoutique par l'anhydride maléique

The study deals with the variation of physical properties of a blend (50/50 polyethylene/terpolymer ethylene-propylene-diene monomer) due to chemical modification by maleic anhydride. This compound is generally used as a rubbery domain in polyamide resins. The chemical modification induces cross-linking the amount of which is clearly revealed by the variation of the elastic modulus and the residual deformation of the samples. The crystallization ratio of the polyethylene, measured by differential scanning calorimetry, is also related to the chemical modification. This effect may be due to an increase in the miscibility of the two constituents of the blend.     

Application du modèle de chaînes de spins alternés sur le composé α Fe2PO5

In α Fe₂PO₅ the octahedrons containing the Fe²⁺ and Fe³⁺ ions share a common face. These octahedrons form zig-zag chains of alternating spin parallel to the b axis. Exchange interactions between Fe₂₊ and Fe³⁺ are ferromagnetic: this is confirmed by neutron diffraction. The alternating spin chain model, ignoring interactions between chains, was used. Our results show that αFe₂PO₅ exhibits ferromagnetic behavior.     

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.     

Dosages en analyse minérale par extraction à l'aide de cations colorés : Dosages par extraction a l'aide de colorants basiques d. dosage de traces de sulfate par le bleu de méthylène

A method is described for the determination of traces of sulphate. By means of an exchange resin the sulphate ions are exchanged with an equivalent amount of thiocyanate ions and these are determined by the extraction method using methylene blue as complexing agent.     

Contribution à l'étude Électrochimique de Dérivés de l'Acide Mercapto-2 Pyridinecarboxylique-5. II

Abstract

Electrochemical caracteristics of 2-mercaptopyridine-5-carboxylic acid and its methylic ester have been determined using recent polarographic techniques. Measurements have been carried out as a function of parameters such as frequency, others surimposed signals and as a function of concentration and pH. Results are compared to those obtained for selectively methylated on sulfur or nitrogen atoms derivatives. Interpretations of the data are given. The optimal conditions for a quantitative determination by D.C. and differential pulse polarography are fixed.     

Dosages en analyse minérale par extraction à l'aide de cations colorés : Dosages par extraction à l'aide de colorants basiques c. dosage de traces de phosphate par la safranine

An extraction method is described for the determination of traces of phosphate in the form of phosphomolybdate, in which safranine is used as complexing agent.     

Méthode indépendante des propriétés locales pour le calcul des indices de rétention en Chromatographie en phase gazeuse à température programmée

Retention indices of some phthalates, separated by temperature-programmed gas chromatography, computed using B-spline interpolations are more consistent with the scheme of this retention parameter. In applying this technique to a mixture of reference n-alkanes, which two successive members do not defer of more than four carbon atoms, it is possible to recover classical retention indices.     

Matériaux composites à base de graves et de liants polymères—V: Étude d'un nouveau liant à base de bitume et de polyéthylène ozonisé

Mixtures of bitumen with samples of polyethylene (10.5% by weight) having different melt indices have been studied. Pure and recovered samples of polyethylene were used and also ozonized samples. When ozonized polymers are used, there are increases in tenacity and softening point with decreases in penetrability and viscosity. Polymers have been examined by fluorescence microscopy, GPC and ¹H-NMR. It is concluded that reaction of the ozonized polymer with bitumen is responsible for the improvement in the materials.     

Spectres d'absorption détectés par effet photoacoustique en infrarouge par transformée de Fourier—applications à quelques médicaments

Photoacoustic detection in Fourier transform i.r. spectrometry has led to spectra obtained without sample preparation. This fact may be a very important advantage in biological applications, but these spectra are not directly in good agreement with transmission spectra. In the present work a simple mathematical correction treatment is presented which is in accord with the theory of the photoacoustic effect. This correction routine is applied to some drugs in view of a possible application to direct identification in pharmaceutical preparations.     

Contribution à l'étude cinétique du greffage du polyéthylène,en suspension dans l'eau,par l'acide acrylique

The radical grafting, in water suspension, of a polar monomer (acrylic acid) onto a non-polar polymer (low density polyethylene) was studied in the presence of t-butyl peroctoate. A preliminary study of the homopolymerization of acrylic acid was carried out under the experimental conditions used for the grafting and with: [A]₀ = 0.0025 and 0.0050 mol 1⁻¹ and [M]₀ = 0.125, 0.75 and 1.25 mol 1⁻¹. It is shown that the initial rate of polymerization is second order in monomer. The grafting experiments were carried out with [A]₀ = 0.0025 and [M]₀ 0.125, 0.75 and 1.25 mol 1⁻¹. For each experiment, the contents of grafted, homopolymerized and non-polymerized acrylic acid were determined separately. The initial rates of grafting and homopolymerization were determined as well as the orders in monomer. Several preliminary treatments of polyethylene led to a significant increase of the grafting efficiency.     

Dosages en analyse minérale par extraction à l'aide de cations colorés: Dosages par extraction a l'aide de colorants basiques b. dosage de traces d'étain par le violet cristallisé

An extraction method is described for the determination of traces of tin in which crystal violet is used as complexing agent.     

Étude théorique des polarisabilités électroniques et de la polarisation spontanée du composé KD2PO4 (DKDP) dans la phase ferroélectrique

The electronic polarizabilities and the spontaneous polarization of KD₂PO₄ (DKDP) compound are discussed quantitatively from a microscopic model taking into account of the dipole-dipole interactions due to the local fields acting on the constituent ions. The electronic polarizabilities of the K, PO₄ and oxygen ions are determined so as to satisfy the experimental data of the refractive indices. The effective charges of the different ions are calculated by taking into account of the experimental value of the spontaneous polarization. The result of the calculations point out the important role of the deuterium-bonds.     

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.).     

Étude par diffraction des rayons X,par résonance magnétique nucléaire 31P en phase solide et par spectrométrie infrarouge des hydroxyapatites mixtes cadmium–strontium

X-ray powder diffraction, solid-state ³¹P-MAS-NMR and IR spectroscopy of cadmium–strontium mixed hydroxyapatites. Strontium–cadmium hydroxyapatite solid solutions Cd_xSr_(10–x)(PO₄)₆(OH)₂ were prepared in aqueous medium. They were characterized by X-ray powder diffraction, ³¹P-MAS-NMR and IR spectroscopic analyses. The structural refinement, by X-ray powder pattern fitting (Rietveld method), indicates the limits of strontium–cadmium solid solutions (x≤4) and allows us to determine the cadmium repartition in the apatite cell. Through the progressive replacement of Sr²⁺ (r=1.32 Å) by the smaller cation Cd²⁺ (r=1.09 Å), all interatomic distances decrease according to the decrease of the cell parameters. However, contrary to what could be expected from the coordinance of the metallic sites S₁ (hexacoordination) and S₂ (heptacoordination) the small cadmium cation does not preferentially occupy the four sites S₁: it is almost statistically distributed over both sites, with a slight preference for S₂. The ³¹P- solid-state-NMR of the pure phases Sr₁₀(PO₄)₆(OH)₂ and Cd₁₀(PO₄)₆(OH)₂ reveals a moderate chemical shift anisotropy (≈20 ppm) corresponding to slight distortion of the phosphate tetrahedron. This observation holds also for the mixed species where the surrounding of the phosphate anion is expected to change significantly when substituting Cd for Sr. Through the progressive replacement of strontium by cadmium, the isotropic signal moves regularly to high frequency, according to the deshielding observed for Cd₁₀(PO₄)₆(OH)₂ (δ_iso=12.2 ppm) with respect to Sr₁₀(PO₄)₆(OH)₂ (δ_iso=2.9 ppm). Moreover the isotropic signal broadens considerably because of unresolved chemical shift distributions in the highly disordered material. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAShydroxyapatite / Rietveld refinement / ³¹P-MAS-NMR / cadmium / strontium / phosphate