Étude théorique de la dynamique du réseau de PbTiO3 dans la phase quadratique

The lattice dynamics of lead titanate PbTiO₃ is discussed quantitatively using a shell model taking into account the electronic polarizabilities of the constituent ions, and including Coulomb and short-range interactions. Our calculations highlight the important role played by the anisotropic polarizability of oxygen and show good agreement between calculated and experimental dispersion curves.     

Étude de la rétention des sels monovalents et bivalents par nanofiltration

Study of the retention of monovalent and bivalent salts by nanofiltration. The objective of this work was to study the influence of applied pressure, solution concentration and conversion rate on the salts retention by nanofiltration. Our study showed that the bivalent ions SO₄^2– are better retained than the monovalent ions F^–, Cl^– and I^– by nanofiltration. We also observed that the small ions F^– and Mg²⁺ are better retained than the big ions Cl^–, Ca²⁺, and I^– by effect of solvation. In spite of the bigger size of ion Ba²⁺ compared to Ca²⁺, Ba²⁺ is better retained than Ca²⁺; this is due to the effect of pressure. We also noticed that the increase of the (NH₄)₂SO₄ concentration and of the conversion rate leads to a decrease in the retention of SO₄^2–. To cite this article: A. Abouzaid et al., C. R. Chimie 6 (2003).     

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 paramétrique de la thermogravitation en milieu poreux

This note reports on a numerical study of the thermogravitational diffusion existing in a porous medium saturated with a binary mixture and subjected to a horizontal thermal gradient. It deals with a study of the influence of the dimensionless characteristic parameters on the species separation, using a two-dimensional numerical code based on a spectral method. The existence of a maximum separation ratio corresponding to an optimal Rayleigh number, associated to an optimal permeability, is shown. The results are also compared with analytical and experimental results coming from previous works.     

Étude analytique de la propagation d'ondes en conduites déformables

In this paper, an analytical resolution of a periodic signal propagation equation is presented. At a given site of the conduit, the proposed solution allows one to isolate the part linked to the signal emitted at the extremity of the conduit and the part that would exist in its absence. The investigation of the evolution of this signal located at the extremity allows us to determine the length of the tube (in the particular case of a solitary wave) using the analysis of reflections at a given site.     

Étude de la résonance du mode géostrophique dans un tore

We show that when (ΩR/c₀) ≪ 1, and (a/R) ≪ 1, the air motion in a torus is governed by the problem of inertial oscillations in this torus excited by a perturbation on its surface, which moves with constant angular velocity Ω and gets recurrently at the same place with period 2π/Ω. This excitation makes one of the inertial oscillation modes enter in resonance, the geostrophic mode, which increases proportionally to time when t → ∞.     

Étude par chromatographie en phase gazeuse de nouveaux composés cristaux liquides nématiques à chaîne latérale

The analytic performances of three stationary phases ‘liquid crystal’ to side chain have been presented. Mesogenic compounds studied in this work are:– 3-CH₃: 2-(3-methylbenzyloxy)-3-n-hexyloxy-4-(4-chlorobenzoyloxy)-4’-(4-methyl benzoyloxy)-azobenzene;– 4-CH₃: 2-(4-methylbenzyloxy)-3-n-hexyloxy-4-(4-chlorobenzoyloxy)-4’-(4-methyl benzoyloxy)-azobenzene;– 3-Cl : 2-(3-chlorobenzyloxy)-3-n-hexyloxy-4-(4-chlorobenzoyloxy)-4’-(4-methyl benzoyloxy)-azobenzene.The originality of these three compounds is essentially due to the presence of a substituted benzyloxy group, more voluminous, which is close to the n-hexyloxy flexible chain. Retention properties of these new liquid crystals have been characterised by the capillary column treated and impregnated according to the dynamic method. The position, ortho or para, of the methyl group on benzyloxy does not interfere significantly on the retention mechanism. In the case of the replacement of the methyl group by a halogen atom (chlorine), we noticed a radical change of the retention properties.     

Étude de la phényl-2 oxine et de ses chélates: Constantes de dissociation de la phényl-2 oxine

The authors determined, by spcctrophotometric and potentiometric methods, the ionization constants of 2-phenyl-8-quinolinol in hydroalcoholic solutions.     

Étude par la fluorescence aux rayons-X du changement de coordinence de l'aluminium dans les silico-alumines armorphes

Sans résumé     

Étude de la photolyse de sels de sulfonium,photoamorceurs cationiques

Arylonium salts allowed the development of cationic photopolymerization. A number of reports about the photolysis of triarylsulfonium salts can now be found in the literature. These works deal with salt photofragmentation kinetics, the visualization of the photolysis process by real time pH mesurements and with the acid photoliberation kinetics by potentiometric titrations.     

Étude par spectrographie infrarouge de la structure de l'acide iodique,de l'acide anhydroiodique et des polyiodates alcalins

Résumé L'étude par spectrographie infrarouge entre 2 et 33 des divers produits de déshydratation de l'acide iodique et des nombreux iodates «acides» et «pyroiodates» qu'il donne avec les iodates alcalins montre l'existence de ponts I-O-I analogues à ceux qui existent dans l'anhydride iodique I₂O₅. Ces liaisons se caractérisent dans la région explorée par deux groupes de bandes fortes à 400–460 cm^–1 et à 515–646 cm^–1, c'est-à-dire en dehors des régions d'absorption caractéristiques des groupements IO₂ ou IO₃.

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Summary The infrared spectrographic study between 2 and 33, of various products of dehydration of iodic acid and numerous acid iodates and pyroiodates which it yields with alkaline iodates reveals the existence of I-O-I bridges analogous to those in I₂O₅. In the regions explored, these links are characterized by two groups of strong bands at 400–460 cm^–1 and at 515–646 cm^–1, i. e. beyond the absorption regions characteristic of the IO₂ or IO₃ groups.

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Zusammenfassung Die IR-spektrographische Untersuchung verschiedener durch Wasserabspaltung aus Jodsäure hergestellter Produkte, zahlreicher saurer Salze und mit Alkalijodaten gebildeter Pyrojodate zwischen 2 und 33 zeigt das Vorhandensein von J-O-J-Brücken, wie sie analog im Jodsäureanhydrid J₂O₅ vorliegen. Charakteristisch für diese Bindung sind im untersuchten Bereich zwei starke Bandengruppen bei 400 bis 460 cm^–1 und bei 515 bis 646 cm^–1, das heißt jenseits des Bereiches der charakteristischen Absorption der Atomgruppen JO2 oder JO3.

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En l'honneur du ProfesseurF. Feigl, pour son 70^e anniversaire.     

Étude physique et numérique de la circulation cérébrale en pathologie carotidienne

A realistic and versatile physical model was built to simulate blood flow through the circle of Willis. Experimental data were then compared to those provided by numerical simulations. When the network is symmetrical and free of stenosis, the results of a linear model closely fit the experimental data. In presence of severe obstructive lesions of internal carotid arteries, the pressure drops induced by sudden changes of section or direction at the level of the communicating arteries must be taken into account. Introducing empirical flow-pressure drop relationships in the theoretical model, leads to an excellent agreement between experimental and simulated data. © 1999 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS     

Étude ultrasonore de mélanges de polymères

Ultrasonic experiments have been performed on polyethylene/polystyrene blends of various compositions. Attenuation and velocity measurements were performed on samples made either by injection moulding or by compression. Attenuation varies through the same sample and variations are greater for compressed plates than for moulded plates. Velocities are of the same order of magnitude for both types of samples.     

Étude de la phényl-2 oxine et de ses chélates: Préparation et propr1étés de la phényl-2 oxine

The authors prepared phenyloxin by three different methods. They obtained a product whose melting point was 59° C and then another form melting at 72° C. Ultraviolet absorption spectra were determined in cyclohexan and in alcohol-watermixtures; from these determiaations, the solubilities of phenyloxin in water and in alcohol-water mixtures of different concentrations were obtained. If ultraviolet absorption spectra are plotted for different pH values (from 1.1 to 13.7) several isobestic points are noted.     

Étude de la distribution des ions sur colonnes échangeuses

Résumé L'auteur étudie la distribution de divers ions seuls ou mélangés sur une résine cationique, par voie semimicro-analytique.

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Summary A column constructed from eight sacks filled with ion exchangers was used to study the distribution of metal ions of various valency from pure solutions or mixtures. If the chlorides of the metals are used in all cases, sodium and ammonium are retained in the first two sacks; magnesium and zinc in all sacks, especially in the first and sixth; iron and aluminium in all, particularly the first and sixth; nickel and cadmium in the first two, particularly the first; thorium in the first sack. These findings, which are independent of the atomic weight and valency, are possibly related to the formation of solvates and their various stabilities.

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Zusammenfassung Mit Hilfe einer Säule, die aus acht mit einem Ionenaustauscher gefüllten Säckchen bestand, wurde die Verteilung von Metallionen verschiedener Wertigkeit aus reinen Lösungen oder Gemischen untersucht. Verwendet man stets Chloride der betreffenden Metalle, so werden Natrium und Ammonium in den beiden ersten Säckchen, Magnesium und Zink in allen Säckchen, insbesondere im ersten und sechsten, Nickel und Cadmium in den beiden ersten, insbesondere im ersten, Eisen und Aluminium in allen, insbesondere im ersten und sechsten, Thorium im ersten Säckchen zurückgehalten. Diese von Atomgewicht und Wertigkeit unabhängigen Ergebnisse stehen möglicherweise mit der Bildung von Solvaten und deren verschiedener Stabilität im Zusammenhang.

     

Étude et dosage polarographique de la di-dnp-histidine dosage de l'histidine

The di-DNP-histidine has been prepared, and studied polarographically.A standardization curve has been composed by means of which it is possible to estimate 1 γ of di-DNP-histidine in 1 ml.A method of estimating the histidine lias been established. It is allowed to react with an excess of DNFB. The excess is removed by extracting twice with ether. One can then determine polarographically the excess of DNFB, 01 the di-DNP-histidine formed, By this method up to 10 γ histidine can be determined.The error lies between 0.5 and 10% according to quantity.     

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 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.