Une généralisation de la théorie de brönsted en chimie analytique

The proposal is made that all reactions be considered as corresponding to the exchange of particles (particules).1. Exchange of electrons between an oxidising agent and a reducing agent. This is the classical conception of oxidation-reduction reactions.2. Exchange of ions (or of polar molecules) between an “acceptor” of the ion and a “donor” of the same ion. In the case of exchange of protons the reaction is one between acids and bases, according to Brönsted.The majority of reactions concern the exchange of different ions. It is proposed to apply to these reactions, and that for each type of particle exchanged, the type of reasoning which Brönsted has used for the exchange of protons.The analogy thus created between the different types of reactions leads to a considerable simplification. It allows identical reasoning and the use of similar formulations for all reactions.Further, the distinction between reactions in terms of the nature of the particle exchanged permits recognition of the respective influence of the factors which are available for controlling the reactions.It is suggested that the use of this conception is advantageous in teaching analytical chemistry.     

La théorie exacte de la flexion des plaques

A new approach is introduced for the analysis and computation of homogeneous, isotropic elastic plates subjected to any bending loads. This approach is based upon a partitioning, which is independent of thickness, of the 3D reference solution into both a part with large variation length and localized effects, whose generalized stress-displacement values are zero. The part with large variation length can easily be computed from data as well as from generalized quantities that represent ‘averages’ in the thickness. These generalized quantities coincide with those obtained from the 3D reference solution; they constitute the solution to an ‘exact’ theory of plate bending.     

Amélioration de la tenue à la corrosion atmosphérique de matériaux utilisés en connectique (nickel doré). Traitements de surface par implantations d'ions

Improvement of the atmospheric corrosion resistance of materials used in connectics. Surface treatments by ion implantation. Tests of corrosion of a material, constituted of brass covered with an electrochemical nickel coating (thickness ≈ 5 μm) and with a gold coating (thickness ≈ 0.4 μm or ≈ 1 μm), used in electrical contact applications, have been carried out in humid synthetic air with low contents of NO₂ (0.2 vpm), SO₂ (0.2 vpm) and Cl₂ (0.01 vpm). The results obtained show that the corrosion products are well localised on the surface. The aggregates formed are principally constituted of basic nitrate, sulphate and chloride of nickel and zinc. These studies showed that the corrosion of the material is due to the presence of porosities in the gold and nickel layers. X-ray analysis (SEM/EDS) revealed the presence of carbon in these porosities, probably related to the presence of organic compounds in the electrolytic coating baths. During the galvanic corrosion of nickel and zinc, the carbon is rejected to the periphery of the aggregates. The amount of carbon was determined by Van De Graaff analysis, by (d,p) nuclear reaction. Some treatments of the material by ion implantation (titanium or titanium and nitrogen or helium) have been realised in order to suppress the porosities of the gold layer. These treatments lead to a remarkable improvement of the corrosion resistance of the material. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASatmospheric corrosion / nickel / brass / gold coating / ion implantation     

Dépassement de la limite de réflexion de la lumière des cristaux liquides cholestériques : de Plusiotis resplendens aux gels à inversion d'hélicité

Beyond the reflectance limit of cholesteric liquid crystals: from Plusiotis resplendens to helicity-inversion gels. Due to its helical structure, a cholesteric liquid crystal (CLC) selectively reflects the light when its wavelength matches the helical pitch. The reflectance is limited to 50% of ambient, unpolarized light, because circularly polarized light of the same handedness as the helix is reflected. We report the elaboration procedure and the properties of a CLC gel for which the reflectance limit is exceeded in the infrared region. Photopolymerizable mesogens are introduced in the volume of a CLC exhibiting a thermally induced helicity inversion, and the blend is then cured with ultraviolet light when the helix is right-handed. The reflectance exceeds 50% when measured at the temperature assigned at a cholesteric helix with practically the same pitch, but a left-handed sense before reaction. From scanning electron microscopy investigations, it is shown that the organization of the mesophase is transferred onto the structure of the network. The gel structure is discussed as consisting of a polymer network with a helical structure containing two populations of LC molecules. Each of them was characterized by a band of circularly polarized light, which is selectively reflected. Novel opportunities to modulate the reflection over the whole light flux range are offered. Potential applications are related to the light and heat management for LC smart windows or reflective polarizer-free displays with a larger scale of reflectivity levels.     

Etude theorique de la dynamique du réseau de batio3 en phase quadratique

The lattice dynamics of barium titanate BaTiO₃ is discussed quantitatively in the framework of a shell model taking into account the electronic polarizabilities of the constituent ions and including Coulomb and short-range interactions. The results of calculations point out the important role of the anisotropic oxygen polarizability. There is a good agreement between calculated and experimental dispersion curves.     

Application de la dynamique des solutions concentrées de polymères à la résonance acoustique de réticulation

One can characterize the large-scale displacements of a macromolecule by the time required for the chain to renew completely its conformation. These displacements are displayed by changing the topological orientation of the condensation reactions. This effect is produced by putting the medium through a sound wave or an alternating electric field that is in resonance with the Brownian motion of the macromolecule. The physical contact between the chains is enhanced and the intermolecular reactions are more frequent than the intramolecular reactions. The application of a sound wave or an electric field of a characteristic frequency on the elastomers during chemical crosslinking produces a noticeable change in the crosslinking density.     

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.     

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 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     

Le satellite Hipparcos. Une moisson de résultats astrophysiques

The European Space Agency (ESA) satellite Hipparcos was the first satellite to accurately measure angular displacements on the sky. The mission and its results (positions, trigonometric parallaxes and proper motions of unprecedented accuracy and multi-epoch photometry for about 118 000 stars and 50 solar system objects) have been presented in a previous paper. The mission results were published in June 1997, and the papers using this fantastic amount of new and accurate data are already very numerous in the main journals of the domain. They deal with a great variety of subjects: reference systems, stellar physics and evolution, galactic kinematics, dynamics and evolution, distance and age scale in the Universe. A selection of the most striking applications is presented here.     

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.     

De l'analyse de la résistance interne par perçage à la détermination du profil de dureté des aciers traités en surface

The thrust measured during a drilling test is related to the hardness of the material tested. When the test is performed on a superficially heat-treated specimen, the results do not exactly correspond to the hardness profile obtained by the Vickers micro hardness technique. The difference is due to the integration of heterogeneous resistance along the cutting edge of the conic drill. By discretising the drilled thickness, we have developed an algorithm yielding the hardness of each elemental thickness. Results are very close to those obtained by Vickers hardness profile measurements.     

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.     

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.     

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.     

Une nouvelle stratégie de calcul micro/macro en mécanique des structures

A new micro-macro computational strategy is proposed for the analysis of structures which are described up to the “micro” level, such as composite structures. It is intended to replace standard homogenization techniques coupled with a local reanalysis, at least for several domains of interest. This paper describes the basis of the new approach.     

Les réactifs de l'analyse minérale moderne dans la chimie de l'azote organique

Résumé L'auteur introduit les réactifs de l'analyse minérale moderne dans la chimie de l'azote organique par substitution des cations organiques aux cations minéraux. L'exemple proposé applique un réactif de Cu á l'isolement de l'éphédrine; la limite de sensibilité de cet isolement á froid passe ainsi de 5000g á 20g/ml sans que les pertes dépassent 2%.Seconde originalité de ce travail: l'emploi, pour le contrôle de cet isolement, d'une réaction d'addition á intensité compensée: dans le milieu oú apparaît le composé d'additionA (B) n, n augmente systématiquement par diminution de [A].

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Summary The reagents employed in modern inorganic analysis have been now introduced into the chemistry of organic nitrogen compounds by substitution of organic cations for the inorganic cations. For example a reagent for copper is applied for the isolation of ephedrine. The sensitivity limit of this isolation in the cold exceeds 5000g at a concentration of 20g/ml and the loss does not exceed 2%.

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Zusammenfassung Reagenzien der modernen anorganischen Analyse lassen sich für organische Stickstoffbasen heranziehen, die als Kationen an die Stelle anorganischer Kationen treten. So eignet sich zum Beispiel ein Reagens für Kupfer zur Abscheidung von Ephedrin; die Nachweisempfindlichkeit wird so in der Kälte von 5000 auf 20g/ml verbessert, ohne daß der Verlust 2% übersteigt. Eine weitere Eigentümlichkeit dieses Nachweisverfahrens ist darin zu sehen, daß mit zunehmender Bildung des AdditionsproduktesA(B) n der Wertn durch Minderung der Konzentration vonA erhöht wird.