Sur de nouveaux verres oxyfluores a base d'antimoine

A new family of oxyfluoride glasses is obtained by quenching mixtures of Sb₂O₃ with various fluorides (Li, Na, K, Ba, Cd, Pb, Mn, Zn). Thermal, mechanical, magnetic and optical properties have been studied. A structural model is proposed on the basis of Raman scattering spectra.     

Etude de verres de se et Se-Te (6% at. Te) Par analyse thermique differentielle

Glasses of Se and Se-Te (6 at. % Te) have been investigated by semi-micro DTA (samples of a few mg). Crystallization, influence of quenching and annealing at various temperatures aroundT _g are clearly and conveniently observed on this semi-micro scale.     

Etude par spectroscopie de photoelectrons (XPS) de la surface de profiles a base de PVC

Variations of the surface composition (over a thickness of 50 Å) of stabilized and rigid PVC for outdoor applications and of pure moulded PVC resin have been investigated by photoelectron spectroscopy (ESCA or XPS) after extrusion, outdoor and accelerated ageing and photooxidation. Extrusion is accompanied by a pronounced migration of lead thermal stabilizers and of calcium stearate, used as an external lubricant, towards the outer surface. This treatment however, induces neither significant oxidation nor formation of a great quantity of ionic chloride. Natural and accelerated weathering were compared and were characterized by a large decrease in the lead surface concentration. The surface of this material is unaffected when exposed to air in a closed vessel and protected from external radiations. Finally, surface photooxidation by u.v. exposure has been evaluated and compared for the stabilized material and for the pure resin. This treatment involves formation of carbonyl and carboxylic groups. ESCA spectroscopy, a speedy and non-destructive surface analytical method, is well suited for study migration of stabilizers and lubricants.     

Etude de la stabilisation du polychlorure de vinyle avec des molecules modeles—IV. Composes epoxydes

Chloro-4-hexene-2 (C4H2), a model compound for the study of polyvinylchloride stabilization, reacts with epoxy compounds in dichloroethane but not in tetrahydrofuran. In the latter case, the reaction is catalysed by zinc chloride but this compound is also a catalyst for the polymerization of the epoxy function. The zinc chloride is then modified so that the kinetic laws for etherification and dehydrochlorination of C4H2 are more complex than when the catalyst is CdCl₂, as previously studied by Anderson and McKenzie. With zinc and calcium stearate, one also observes esterification of C4H2, the three reactions being competitive. The synergistic effect of epoxy in the presence of stearate is induced chiefly by modification of ZnCl₂ through the initiation reaction for the polymerization. Therification, as well as esterification, may be reversed by HCl which regenerates C4H2; this fact explains the catastrophic character of degradation after the stabilizer has been consumed. The results of the study on model compounds can be applied to the degradation of PVC upon mastication in a Brabender plastograph.     

Etude dilatometrique de l'anisotropie d'une tole a base d'aluminium obtenue par solidification rapide

Dilatometric study of the anisotropy of an aluminium alloy sheet obtained by rapid solidification. An Al-1.99%Mn-0.80%Mg-0.60%Cr-0.40%Zr-0.13%Fe-0.05%Ti alloy produced by the twin roller melt spinning technique was characterized in terms of thermal stability at low temperature in the range 80–300K. Differences in thermal expansion coefficients in the three directions were evidenced, and revealed the presence of an anisotropy. The differences are mainly due to the nature of the intermetallic phases present in the aluminium matrix. It is important to note the low thermal expansion coefficient obtained along the direction normal to the rolling plane, as compared to those of aluminium alloys prepared by conventional methods.     

Determination de la capacite calorifique de quelques verres oxyazotes

Six oxygenated and oxynitrided glasses in the Ca-Si-Al-O-N system were prepared from pure lime, silica, alumina and aluminium nitride. Their enthalpies were measured by drop enthalpimetry with a Calvet calorimeter in a 100–1000° temperature range including glass transitionsT _g. Their heat capacityC _p in glassy and liquid states were deduced by derivation. TheC _p variations atT _g were calculated. The glass transition temperature were checked by differential calorimetric analysis.     

Etude de la stabilisation du polychlorure de vinyle avec des composes modeles—III. Action des stearates de zinc et de calcium

Esterification of chloro-4-hexene-2 with zinc stearate in tetrahydrofuran at 60° is a moderate reaction, strongly catalysed by zinc chloride. That catalyst is necessary in the case of calcium stearate. The synergistic effect between the two reactants cannot be explained first by the exchange reaction between zinc chloride and calcium stearate; that reaction is reversible and limited. A better explanation is based on the formation of complexes between both stearates, or both chlorides, or eventually between zinc chloride and calcium stearate. The catalytic activity of zinc chloride in these complexes is decreased or even inhibited. There is no true synergistic effect between aliphatic phosphites and zinc stearate at 60° in THF. There is only catalysis of allylic chlorine substitution by a phosphonate group by the zinc chloride produced in the reaction. In dichloroethane at 60°, each of the two stearates has a stabilizing effect, although by different mechanisms, zinc stearate being more active; the zinc chloride which is formed is a catalyst, in the presence of hydrochloric acid, for hexadiene oligomerization. Transposition of the previous results to the polymer has been carried out by using a Brabender plastograph. A direct correlation has been obtained concerning the efficiency of mixtures of the two stearates versus the dehydrochlorination and the crosslinking reactions.     

Etude Raman de l'oxy-pentasulfure de gallium et de trilanthane GaLa3OS5

The polarized Raman spectra of La₃GaOs₅ in single crystal form have been investigated in the 50–700 cm⁻¹ frequency. An interpretation of the observed bands is given.     

Etude de la stabilisation du polychlorure de vinyle avec des molecules modeles—V. Stabilisation par l'α-phenyl-indole

α-Phenyl-indole is a secondary stabilizer of PVC; it reacts with labile allylic chlorine atoms by one or more substitutions, first on the hydrogen atom of the trisubstituted double bond in the heterocycle, and then on the aromatic rings. The reaction is catalysed by ZnCl₂ which is complexed with α-phenyl-indole. The substituted products are insensitive to HCl so that the stabilization is definite. α-Phenyl-indole may give synergistic effects with other stabilizers, but the condition is that they must be present in amounts enough to neutralize all the HCl produced.     

Etude de la stabilisation du polychlorure de vinyle avec des molecules modeles—I: Degradation thermique du chloro-4-hexene-2

This paper describes an extensive kinetic study of thermal dehydrochlorination for 4-chloro-2-hexene (model of an allylic unstable structure in polyvinylchloride) in solution in dichloroethane. di-ethyl-2-hexyl phthalate and other solvents. The reaction, which is reversible, has an ionic mechanism. It is catalysed by a charge transfer complex between hexadiene and hydrochloric acid. It is inhibited by complexing agents for hydrochloric acid, such as tetrahydrofuran. The addition of hydrochloric acid to conjugated dienes has been shown to occur also in the case of β-carotene.     

Etude theorique de la cycloaddition dipolaire 1–3

A theoretical study of the 1,3-dipolar cycloaddition reaction of: diazomethane with ethylene has been carried out by the LCAO-SCF-MO method. The potential energy hypersurface for the reaction and the electronic structure of the transition state have been investigated.     

Etude structurale de l'heptafluorouranate de nitrosyle

A structural study of NOUF₇ complex is presented. An interpretation of X-ray and neutron diffraction data has been drawn from comparison with those obtained for NOUF₆ complex. An NMR study on fluorine has shown different atomic motions in the complex fluoride.     

Analyse de couches minces de verres chalcogenures par diffusion elastique de protons et mesure de gammas prompts

Résumé Une méthode d'étude de la composition stoéchiométrique de couches minces (10 à 500 μg/cm²) de verres chalcogénures est développée. L'étude des réactions nucléaire; induites par bombardement de protons de basse énergie (<4 MeV) sur les éléments constitutifs Ge, As, Te et S, conduit à choisir la diffusion élastique et la détection de gammas prompts pour le dosage simulatené. La précision et la sensibilité de la méthode sont discutées à partir des résultats obtenus. L'utilisation de la résonance fine sur le soufre (p, p'γ) est appliquée à l'étude de l'homogénéité des cibles.     

Etude Structurale de Cations-Radicaux

Mass analysed ion kinetic energy spectrometry has been used to study the structure of radical cations from 26 precursor molecules. Metastable ion characteristics, viz. kinetic energy releases, abundance ratios, and isotope distribution in labelled compounds, show that all the metastable ions are isomerized into a common structure or similar mixture of structures before fragmentation. Collision induced dissociations and collisional ionization to doubly charged ions have been used to study stable ions whose lifetimes are greater than the time-of-flight from the source to the collector, and the results are interpreted on the basis of the occurrence of mixtures of initial and isomerized species.     

Etude en serie as-triazine—XIV : Etude de la synthese et de la tautomerie de phenyl-3 et phenyl-6 triazinones-5

Methylated derivatives of 3-phenyl and 6-phenyl 5-triazinones have been prepared; spectral characteristics for identification are given. Infrared, ultraviolet and NMR spectra indicate the predominance in solutions of the paraquinonoid structure for 3-phenyl and 6-phenyl 5-triazinones, but in solid state, infrared spectra show the predominance of the 5-hydroxy triazinone tautomeric structure.     

Etude de la fragmentation de semi-carbazones terpeniques

Terpene semicarbazones have been investigated using high resolution mass spectrometry. We have studied correlations between rings and functional semicarbazone degradations. The mass spectra are more complicated than the mass spectra of oximes, methyloximes and hydrazones. Cleavages are explained by known mechanisms. An interpretation of almost all the peaks is offered. The fragmentation of the semicarbazone skeleton is less marked than in the oximes. Fragmentation processes induced by the functional group are numerous. Ions obtained are concerned in secondary cleavages. Thus it is not surprising that the predominant feature is localisation of charge upon the imino nitrogen atom. Other centres may, however, be responsible for the appearance of several peaks.     

Etude de proprietes physico-chimiques de l'hydrure d'aluminium

Journal of Thermal Analysis and Calorimetry - L'hydrure d'aluminium exempt de solvant a pu Être préparé avec une bonne pureté, et sa stabilité thermique a...     

Drug-induced stabilisation of a mismatched C-T base pair in a DNA hairpin

We have shown that a key feature of drug binding, namely specific G-C base pair recognition at a 5'-TG step, can induce a number of novel structural features when an extrahelical base is inserted in close proximity to the drug binding site; we have clearly demonstrated the formation of a stabilised C-T mismatched base pair at a non-terminal site.     

Etude dielectrique de melanges polypropene-polybutene

As part of a study of poly-α-olefins dealing particularly with the mechanisms responsible for ß-relaxations, the dielectric behaviour of polypropene, polybutene and their blends has been examined over a wide temperature range at various frequencies.