Étude des propriétés mécaniques des géomateriaux argileux associant la décoction de Parkia Biglobosa (néré)

Researches for non-energy intensive construction products, that are durable and cheaper is today of global concern because of the limited resources (energy, financial, etc.). To address this issue, the present work presents the combination of the decoction of pods of Parkia Biglobosa (néré) that is rich in tannins compounds including gallic acid, epicatechin gallate and epigallocatechin, with a clay-sand mixture. The clay used is referenced KORO and contains montmorillonite, illite, quartz, albite, orthoclase, kaolinite and goethite. The study of the mechanical properties of geomaterials formulated from the mixture shows that they have values of mechanical resistance higher and that their behavior becomes viscoplastic. This is due to the formation of chemical complexes from carboxylic groups of tannins macromolecules with the iron oxy-hydroxide in the interlayer spacing of clay minerals. This process is enhanced by the sorption of tannins on the surface of clay minerals.     

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 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.     

Une propriété inconnue du réactif de Mayer

Zusammenfassung Auf Grund eines Vergleiches von Alkaloidreagenzien wird eine bisher unbekannte Eigenschaft des Mayerschen Reagens dargelegt. Die Alkaloide lassen sich damit nach vier Kategorien unterscheiden. Die qualitative und quantitative Anwendung wird beschrieben. Abgesehen von seiner Verwendung als allgemeines Alkaloidreagens ist diese Selektivität des Mayerschen Reagens bisher noch unausgenützt.

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Summary This paper reveals an unknown property of the Mayer reagent, drawn from a comparison of various alkaloid reagents. The Mayer reagent divided the alkaloids into four categories. This property permitted refined qualitative and quantitative applications in this study. As a general alkaloid reagent, Mayer's reagent thus combines with this generality a selectivity that has not been utilized heretofore.

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Résumé Cette publication expose une propriété inconnue du réactif deMayer, déduite d'une comparaison entre réactifs des alcaloides.A l'expérience, elle répartit les alcaloïdes en quatre catégories. Cette propriété permet des applications qualitatives et quantitatives esquissées dans ce travail.Réactif général des alcaloïdes, le réactif deMayer combine ainsi à cette généralité une sélectivité restée inexploitée à ce jour.

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Dédié à Monsieur le professeurA. A. Benedetti-Pichler à l'occasion do son 70ème anniversaire.     

Étude critique des réactions des cations : Nickel

The authors have tried out the spot tests suggested for the cation nickel between 1937 and 1947. After a critical examination they recommend following the details of the second Report as drawn up by WENGER AND DUCKERT, in particular the use of the dioxime of 1:2-cyclohexanedione, known commercially under the name nioxime.     

Étude critique des réactions des cations : Cobalt

The authors have critically examined the reactions proposed for cobalt between 1937 and 1947. Their findings are in agreement with the conclusions, of the second Report (wenger and duckert). However, the reaction with potassium cyanate can be replaced by the closely similar test, using sodium thosulpliate, a more accessible reagent, there is no interference; from copper, iron and nickel.     

Étude critique des réactions des cations : Uranium

A critical examination has been made of all drop reactions proposed for uranium during the period 1937–1917. In view of the preparation of the fourth Report, it is proposed to retain only the micro-chemical reaction given by an alkaline thiocyanate and sparteine, even in presence of a large excess of iron.     

Étude critique des réactions des cations : Rhénium

For the reactions proposed for rhenium, the author is in agreement with the conclusions of the “Second Report” (wenger AND duckErt) with one exception, the microchemical test with pyridine seems preferable to that using acridine.     

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 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 de la phényl-2 oxine et de ses chélates: Préparation et propriétés des phényl-2 oxinates

The authors have studied the potentiometric curves obtained during the neutralization, in dilute alcoholic media, of acid solutions containing 2-phenyl-8-quinolinol and metallic cations, with sodium hydroxide. By thermogravimetric analysis the number of water molecules and regions of stability for hydrates and anhydrous compounds were also established.Moreover these results were compared with those previously obtained for oxinates and methyl-2 oxinates.     

Étude des spectres vibrationnels des cyclotétraphosphates

The analysis of the infrared and Raman spectra of a number of cyclotetraphosphates shows that it is possible to characterize the cyclic anion P₄O⁴⁻₁₂. The number, positions and shapes of the infrared absorption bands observed in the symmetric stretching region provide an indication of the symmetry of the P₄O⁴⁻₁₂ ring in each compound.     

Électroactivité des halogénures

The intensity-potential curves pertaining to the oxidation of iodides, bromides and chlorides at a polished platinum electrode, undergo deformations when the following factors are varied: initial concentration of halogen, pH, addition of ions that complex or reduce the halogen formed. Analysis of these deformations has led us to assume that the electrochemical behaviour of the three halides can be represented by a reaction of the type: 2 x₃^--2e ? 3 x₂ and not of the type: 2 x^-- 2e ? x₂ As far as bromides and chlorides are concerned the coulometric study agrees with this hypothesis     

Effet de la polarité du solvant sur les propriétés des états électroniques excités du 1,1′-binaphtyle: étude par spectroscopie UV-visible

A UV-vis emission spectroscopy study of the flexible molecule, 1,1′-binaphtyl as a function of solvent polarity allows one to obtain information on the excited singlet states. We show the existence of a charge transfer (CT) character state. This CT is evidenced by the solvent polarity effect, the measurement of polarization ratio and finally by comparison of the ratio intensities of phosphorescence and fluorescence.     

Caractérisation des propriétés électriques des parois de pores d’une membrane

The characterisation of the surface electrical properties of membrane materials is critical for understanding and predicting the filtration performances of membranes. In this paper, four simple experimental methods – streaming potential, electro-osmosis, pore conductivity and membrane potential –, allowing the characterisation of the charge state of membrane pore walls are presented. The four experimental parameters provide information about the sign of the electrical net charge. Examples illustrating the influence of the pH, electrolyte concentration and nature on the four experimental parameters are given. The zeta potential can be then deduced from these measurements by means of a model.     

Étude du processus photochimique impliqué dans la réaction d'ouverture du cycle benzopyrannique des spiropyrannes photochromiques

The analysis of absorption and emission spectra of different hetero-cyclic spiropyrans leads us to question the previously accepted general assumption of intramolecular energy transfer from the heterocyclic part to the chromene part, and to consider the concept of spiroconjugation.The singlet and triplet excited states responsible for the photochemical opening of spiropyrans are of the ππ^* type with an intramolecular charge-transfer character. The participation of singlet or triplet states depends essentially on the nature of the heterocyclic moiety. In the indolinic series the photochemical reaction proceeds through the triplet state, whereas in the benzodithiolic series it occurs almost completely in the singlet state.     

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 de la réactivité des radicaux α-ester : influence des centres stéréogènes en position α’ et β’

The formation of 2-syn and 2-anti addition products, between a 1-E olefin and an acyclic radical is under kinetic control, although addition of n-Bu₃Sn^• to the 1-Z leads to 1-E olefin. Hydride capture is often independent of the nature of the radical, but the difference of behaviour between A^• and B^• radicals results from their stability, induced by the existing chiral centres present in the molecule. Capture of the intermediate radical in α of the ester by deuterium occurs with a diastereomeric excess, varying between 30 and 78%, depending on the nature of the centres situated in α’ and β’ positions.     

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.