Relation entre la morphologie des précurseurs et la microstructure de la céramique WO3 frittée

Relationship between the morphology of precursors and the microstructure of sintered WO₃ ceramics. The aim of this study is to perfect an elaboration process of ceramic WO₃, to control the main parameters, to understand the nature and the role of the precursors and to establish a relationship between the morphology of the powder and the microstructure of the final ceramic. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASpowder / granulometric / microstructure / precursors / sintering / ceramics     

Microdosage colorimétrique de la cystéïne et de la cystine

Thiofluorescein is bleached in alkaline medium by light but reforms its colour on reaction with —SH groups. This can be used for the colorimetric determination of cystine and cysteine in the micromolar range.     

Analyse de la réduction passive de la traînée laminaire

A theoretical multi-layer model is used to describe the influence of wall perturbations on the boundary layer flow. The originality and interest of the method lies in the use of non-regular second-order asymptotic expansions arising from the presence of two longitudinal length scales. From the lower deck canonical problem, the influence of wall perturbations on laminar drag reduction is inferred.     

Simulation numérique déterministe de la turbulence

We first present techniques of large-eddy simulation (LES) in physical und Fourier spaces. We show how LES allows vortex control in mixing layers, and good prediction of velocity statistics in a turbulent channel. We study also in a developed boundary layer the dynamics of high- and low-speed streaks at the wall, and the associated pressure fluctuations. Following this, we show in rotating shear flows a universal behaviour ol the mean velocity in regions whosw local Rossby number is sirictly inferior to — 1. Finally, we present for LES of compressible flows a formalism based on Favre averages.     

Sur la réaction colorimétrique de l'aluminium avec la quinalizarine

The reaction between aluminium and quinalizarin has been studied, and some modifications have been made to the analytical procedure usually followed.The absorption curve of the Al-quinalizarin compound and that of quinalizarin alone have been drawn. We applied the continuous variations method in order to determine the structure and composition of the reaction product. The spectrophotometric readings have shown that the constituents of the coloured compound are bound in a definite ratio. 2:3.     

Détermination de la dissipation caractéristique dans la propagation d'un front de recristallisation

We study the displacement of the boundary between the two grains of an ideal two-dimensional bicrystal having a hexagonal lattice within the plane. The boundary we deal with is a discontinuity straight line for the lattice orientation function that may move at a different velocity from the underlying matter; hence dissipation occurs, eventually equal to the rate of released energy. We estimate the characteristic dissipation in the propagation of the discontinuity.     

Phénomènes Transitoires et Influence de la Nature du Substrat dans la Déformation de la Surface Libre d'un Liquide Isolant Chargé

Abstract

On étudie l'établissement du régime final dans l'évolution électrohydrodynamique d'un liquide isolant soumis à un flux de charges dans le cas d'un substrat conducteur et dans le cas d'un substrat plus ou moins isolant; le cas d'un substrat ferroélectrique est envisagé plus particulièrement. Dans le cas d'un substrat isolant on étudie des mouvements latéraux du liquide. On montre que l'analyse de la déformation du liquide permet des études de substrats.

The establishment of the final behaviour is studied concerning the electrohydrodynamical evolution of an insulating liquid submitted to a flux of charges, for a conducting and for an insulating substrate of variable resistivity. In the case of an insulating substrate, lateral movements of the liquid are studied. One shows that analysis of the deformation of the liquid allows studies of substrates.     

Emploi de la thermogravimétrie et de la spectrophotométrie infrarouge pour suivre les réactions à l'état solide

Résumé L'auteur indique sur des exemples variés comment on peut combiner les indications de la thermobalance et du spectromètre infrarouge pour suivre les réactions à l'état solide, qu'il se dégage ou non un produit gazeux: action de la strontiane sur les pyrophosphates, polymérisation spontanée des métaborates, adsorption du permanganate par le sulfate de baryum, combinaison supposée SiO₂ + 12 MoO₃, action de l'iode sur la magnésie. Ensuite, il étudie plus longuement la synthèse des chromites et la mise en solution par l'oxylithe des oxydes métalliques; cette dernière réaction s'effectue suivant quatre mécanismes différents illustrés par des exemples concrets.

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Summary The writer shows by means of varied examples how the information furnished by the thermobalance may be combined with that derived from the infra red spectrometer in following solid state reactions, which may or may not produce gaseous products. Examples are: action of strontium oxide on the pyrophosphates, spontaneous polymerization of metaborates, adsorption of permanganate by barium sulfate, alleged compound SiO₂ + 12 MoO₃, action of iodine on magnesia. The investigation also included a lengthy study of the synthesis of chromites and the solution of metal oxides by sodium peroxide. The latter reaction, effected by four different mechanisms, is illustrated by concrete examples.

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Zusammenfassung An Hand verschiedener Beispiele wird gezeigt, wie man mit Hilfe der Thermowaage und des IR-Spektrophotometers Festkörperreaktionen mit oder ohne Gasentwicklung verfolgen kann. Als solche Beispiele werden angeführt: die Einwirkung von Strontiumoxyd auf Pyrophosphat, die Spontanpolymerisation von Metaboraten, die Absorption von Permanganat durch Bariunisulfat, die Bildung des Gemisches SiO₂ + 12 MoO₃ durch Erhitzen von Oxin-Silicomolybdat, Einwirkung von Jod auf Magnesiumoxydhydrat. Weiters wird die Synthese von Chromiten und die Auflösung von Metalloxyden mit Natriumperoxyd ausfuhrlich erörtert. Der letztgenannte Vorgang verläuft nach vier verschiedenen Reaktionsmechanismen, die an konkreten Beispielen erklärt werden.

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Conférence prononcée le 25 avril 1961, au Congrès de chimie analytique de Budapest.     

Dosage colorimétrique précis de la silice applications

A method is described for the colorimetric determination of silica as silicomolybdate. Conditions have been established for determining major amounts of silica with an accuracy of about 0.5%.The method has been applied to the analysis of compounds rich in silica and for the determination of silica in compounds containing fluorine.     

Un réactif spécifique du germanium: la phénylfluorone

Based on the action of methyl fluorone on Ge(IV) the use of this reagent for the detection of germanium is described. It is necessary to treat with 6N HCl to make this reaction specific.However, another derivative of fluorone, namely phenyl fluorone, is still better for identifying Ge(IV). By placing a drop of the solution under test, previously strongly acidified (3 N to 6N in HCl), on a phenyl fluorone reagent paper and adding 2 or 3 drops of 6 N HNO₃, a. sensitive and specific reaction for germanium is obtained.The only interfering ions are those of strong oxidising agents (Ce⁺⁴, Cr⁺⁶, Mn⁺⁷, etc.) which destroy the reagents and must be eliminated in the first place.Other ions and ions of the group of the sulphides soluble in alkalisulfides do not interfere, even in the proportion of 100 parts by weight, to 1 of Ge. The limit of dilution is about 10^-5.5.     

Applications analytiques de la phénothiazine

Spot tests carried out with the help of phenothiazine as reagent permit the detection of silver on a drop plate or on paper. D = 10^-5 or even 6.7.IO^-6 with a little less certainty. The reactions obtained are described in detail in the case of palladium, gold and platinum. Use of the reagent allows the detection of iron in presence of uranium (0.15γ iron in 0.053 ml in the presence of 107 times its weight of uranium). It also enables mercury to be detected in the presence of silver, even in the case of silver which is practically free from mercury. Finally, by the combined use of phenothiazine and diphcnylcarbazide it is possible to detect 0.54γ of silver in the presence of 100 times its weight of mercury.     

Mesure de la dispersion pour la solution éléments finis de l'équation de Helmholtz

The numerical solution of the Helmholtz equation suffers from a dispersion error. A general method to calculate a priori the dispersion error is formulated and applied to the methods suggested in the literature in order to minimize the dispersion.     

Simulation théorique de la torsion par liaison hydrogène de la 2,2-biquinoléine à l'état fondamental

Application of the semi-empirical AMI method gives significant evidence of the conformation of the isolated 2,2′-biquinoline (2,2′-BQ) in its ground state. The results obtained on the one hand by Fraga's method in which the molecule is simulated by the hydrogen bonding between a water molecule and the 2,2′-BQ, and on the other hand by CNDO calculations using Mataga's model, are in good agreement with the experimental results. They indicate that the spectral changes of 2,2′-BQ in its ground state in protonic media are caused by a trans-cis transformation resulting from a rotation around the single CC bond which links the two quinoline rings of the molecule     

Microdosages des composés caractéristiques de la fermentation butanediolique

Compounds characteristic of the butanediol fermentation are 2–3 butanediol, acetoin and diacetyl; tlie determination of each of these compounds is based on a determination of dimethylglyoxime by nickel (II) (as in the classical methods, which are time-consuming and not very sensitive). The method now deseribed uses the soluble red complex given by dimethylglyoxime with niekel (IV). By this means 4 colorimetric methods have been established which, respcetively, permit: 1. The determination in 5 minutes, to about 1 %, of 120 to 600 μg, of dimethylglyoxime in a 10 ml sample. 2. The determination in 30 minutes, to about 1 %, of 90 to 450 μg, of diacetylin a sample of 10, 50 or 100 ml. 3. The determination in 50 minutes, to about 1 %, of 90 to 450 μg, of acetoin in a sample of 10, 50 or 100 ml. 4. The determination in 70 minutes, to about 3 %, of 100–500 μg, of butanediol in a 10 ml sample. These methods, based on specific reactions of the substances being determined, (in contradistinction to the numerous methods recently proposed for the determination of butanediol) are applicable even when the substances are accompanied by 1000 times their weight of glucose, glycerol, etc.     

Application de la méthode de Melnikov pour l'étude du roulis non linéaire des navires dans la houle

For studying ship rolling within a global analysis more and more mathematical tools from chaos theory are available. For this purpose, however, drastic simplifications must be applied: (i) rolling is the single degree of freedom, (ii) motion is represented by an ordinary differential equation, and (iii) the study is achieved in the vicinity of vanishing stability. Here the Melnikov method is used in this application. The focus is on ships whose restoring moment is represented with an odd polynomial. Above the fifth degree, a harmonically excited system exhibits frequencies which cancel the fluctuating part of the Melnikov function. Hence the heteroclinic orbits still exist whatever the ‘smallness’ of the perturbation as soon as the system is undamped. The existence of such cancellation is otherwise confirmed from an analysis of the erosion of the attraction basin.     

De l'hydrogénation catalytique à la théorie chimique de la catalyse : Paul Sabatier,chimiste de génie,apôtre de la décentralisation

From catalytic hydrogenation to the chemical theory of the catalysis: Paul Sabatier, genius chemist, decentralization apostle. Paul Sabatier received the aggregation degree in the physical science in 1877 and received his doctorate in the physical science in 1880. In 1884, he was named to the chair of chemistry at Toulouse, when he was thirty, the minimum age for the position. Sabatier's initial researches were inorganic studies within the thermochemical tradition of Berthelot's laboratory. The Mond's preparation of nickel carbonyl instigated him to study gaseous molecules which might behave analogously to carbon monoxide: he succeeded in 1892 in fixing nitrogen peroxyde on copper, cobalt, nickel and iron. One year later he repeated the experience of Moissan and Moureu with unsaturated hydrocarbons and reduced nickel: he found that ethylene and acetylene were hydrogenated. With his student, J.-B. Senderens, he demonstrated the generality of his method to the hydrogenation of non-saturated and aromatic compounds, ketones, aldehydes, phenol, nitriles, nitrites, etc. In contrast of previous physical theories, Sabatier postulated that, in catalysis, a temporary, unstable intermediary between the catalyst and one of the reactants forms on the surface of the catalyst. He predicted the reversibility of the reaction: a catalyst of hydrogenation will be equally one of dehydrogenation. He was awarded the 1912 Nobel Prize in the same time with Victor Grignard. Paul Sabatier was a very reserved man. Elected Professor of chemistry at Toulouse in 1884, he was ever faithful to this town and turned down many offers of attractive positions in Paris. In 1913, he became the first scientist elected to one of six chairs newly created by the Academy for provincial members.     

Études sur la détection,la caractérisation et le dosage des aldéhydes: Méthodes d'oximation

Five methods for the estimation of aldehydes by oximation have been compared. In all the methods, a single or double branching in position α in the case of aliphatic aldehydes, and in positions 2 and 6 in the case of aromatic aldehydes, tends to lessen the accuracy (steric hindrance). Of the methods examined those of Bryant and Smith¹ and Smith and Mitchell³ are the most common.Three new oximes are described. For one of these, two modifications have been isolated, both of which are converted to acetate by the action of acetic anhydride and sodium carbonate. The question is discussed whether this is a case of the syn and anti forms of the oximo or of two polymorphic modifications.     

Une amélioration de la tomographie ultrasonore en réflexion

Via a simple algorithm given by the Born approximation one can reconstruct a tomographic image of the sound speed of an acoustically penetrable body, knowing its scattered sound field. This method is based on the hypothesis of weak contrast between the body and the external medium. Otherwise the image is a distorted version of the object. The distortion is characterised analytically. Thus we propose a modified algorithm that cancels the image defects so as to obtain a fast and reliable reconstruction method.     

Effet de la température,de la pression et de la composition sur l'intensité diffusée par un mélange de deux polymères

Phase diagrams of polymer blends and solutions are usually studied by measuring the scattered intensity (by light or neutrons) as a function of composition, temperature and pressure. If one expands Flory's χ parameter as a function of the composition, one sees that in order to have deviations from Flory's laws, thermodynamic quantities such as volume, heat capacity or compressibility should vary with respect to composition by a power law of degree larger than two. In some cases, the direct measurement of these quantities could lead to a more precise and rapid determination of the miscibility conditions.     

Statu quo sur la méthanation du dioxyde de carbone : une revue de la littérature

This review summarizes the statu quo and the perspectives of chemical methanation. CO₂ methanation, including catalyst deactivation, reactors, mechanisms, and thermodynamics are presented. This reaction serves as a test bed for our fundamental understanding of heterogeneous catalysis and is used in various industrial processes, including the removal of oxo-compounds (CO_x) in the feed gas for the ammonia synthesis, in connection with the gasification of coal, where it can be used to produce methane from synthesis gas, and in relation to Fischer–Tropsch's synthesis. Moreover, CO₂ methanation became of interest as a renewable energy storage system based on a “power-to-gas” conversion process by SNG (synthetic natural gas) production integrating water electrolysis and CO₂ methanation as a highly effective way to store the energy produced by renewables sources. The effectiveness and efficiency of the “power-to-gas” plants strongly depends on the CO₂-methanation process.