Amélioration De L'aptitude Au Décochage Et Au Débourrage: Des Sables Liés Au selicate De Soude Et Durcis: Par Le Gaz Carbonique

Improvement In the aptitude to discharge and to unstop of sands binded with sodium silicate and hardened by carbon dioxide. Chemically hardened sands offer a large choice of moulding and coring processes by the use of organic and mineral compounds. The use of these binders requires a knowledge of associated risks, to obtain a reduced residual resistance (in order to facilitate the discharging and the unstopping of the parts) and for the success of the products.The aim of this study was to rationalise the utilisation conditions of sodium silicate moulded sands, with additives, hardened by carbon dioxide. This should minimize the eventual defects in the cast parts. Sand resistance is very important right after the casting; it makes more difficult the tasks of discharging and unstopping. The need to incorporate organic matter to the sands becomes a necessity. The role of the organic matter is to reduce the sand resistance. The use of silicate binder requires the identification of the mechanism of the mixture hardening by carbon dioxide. It also calls for a knowledge of the gel structure formation, and of the influence of certain parameters on the properties.The experimental part is concerned with a comparative study of the behaviour of these sands in the foundry.The factors influencing this behaviour are: grain size, carbon dioxide blowing-in time, binder rates, adjuvant ratios and mixing time, etc…A thermographie study was carried out in order to perform the experimental work in real conditions.The obtained results have led to the determination of the optimal values of the above-mentionned parameters. This allows to obtain the smallest residual resistance, hence to improve the discharging and unstopping processes.This approach is clearly exhaustive and shows all possible interactions of the adjuvants with sodium silicate and the considered sands.     

Comportement des solutions d'hydroxypropylcellulose en présence d'un sel inorganique

Few solvents for cellulose have been found; dimethylacetamide + lithium chloride is one of them. The main aim of this work is to understand the influence of LiCl on the increase of solubility of a mesomorphic polymer. We have performed phase diagram and texture studies on hydroxypropylcellulose in solution in dimethylacetamide (DMAC), acetic acid (AA) and water, with addition of LiCl. In the presence of LiCl, the critical concentrations for mesomorphic phase transition are increased with an aprotic solvent (DMAC) while no modification of behaviour of lyotropic solutions is found with a protonated solvent (AA), and the formation of gel becomes easier (water). In all cases, LiCl reduces the value of the pitch of the cholesteric solutions obtained.     

Déformation de la surface libre d'une couche mince d'un liquide isolant sous l'action de forces electrostatiques: mise en evidence d'une déformation cellulaire

Abstract

On analyse sommarirement deux types de déformation de la couche déposée sur une plaquete substrat: - indirecte sous l'influence de charges fixes présentes sous le substrat isolant; - directe en apportant des charges sur la surface libre du liquide, le substrat étant conducteur. On montre qu'il est possible d'obtenir dans ce dernier cas une déformation périodique dans les deux dimensions. On précise en particulier la déformation dite “cellulaire”, avec illustration expérimentale     

Sur Les Phénomènes D'oxydo-réduction En chimie Analytique

The theoretical bases of oxidation-reduction phenomena, from the point of view of analytical use, have been surveyed.The phenomena mainly considered have been: apparent potentials, dismutation, measured electrode-potentials, and allied to these the very important practical case of so-called irreversible systems.     

Comportement viscoélastique à l'état fondu du polypropène renforcé de fibres de verre

A study of the viscoelastic properties of molten polypropene reinforced with fibre glass allows us to propose the existence of an interphase in the vicinity of the fibres. This interphase may be due to less mobile entanglements bound to the fibres via the coupling agent.     

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.     

Ene Réaction et Réaction de Substitution sur Des Hétérocycles Catalysées par les Sels de Bi(III)

Carbonylated electrophiles react with furan, thiophene, or pyrrole derivatives in the presence of catalytic amounts of bismuth triflate or chloride, leading to either electrophilic substitution or ene reaction products.     

Des régularités très significatives dans les observations interférométriques de Dayton C. Miller 1925–1926

The analysis of the hodographs corresponding to the interferometric observations of Dayton C. Miller 1925–1926 demonstrates the existence of a very marked coherence underlying these observations, quite unexplainable by perverse effects (e.g. temperature).     

Détermination microchimique de l'indium

Résumé Parmi les réactions microchimiques actuellement connues bien peu se prêtent à une caractérisation facile, dans le cas où l'indium est en mélange avec des quantités notables d'autres métaux du même groupe; la méthode au chloro-indate de rubidium, avec quelques modifications, peut fournir d'utiles indications.La précipitation de l'indium à l'état métallique, non employée jusqu'à ce jour, permet une détection précise dans de bonnes conditions.On décrit les observations faites dans différents cas, notamment en présence de fer, d'étain, de cadmium, en utilisant comme métal précipitant le zinc, le magnésium et l'aluminium.

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Summary Among the microchemical reactions that are well known at present few give an easy characterization in the case where indium is present in mixture along with notable amounts of other metals of the same group. The method employing rubidium chloro—indate may furnish useful indications if it is somewhat modified.The precipitation of metallic indium, which has hitherto not been employed, gives a precise indication under favorable conditions.The observations made in the various cases are described, notably in the presence of iron, tin, cadmium, the precipitating metal being zinc, magnesium, or aluminium.

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Zusammenfassung Unter den bis jetzt bekannten mikrochemischen Reaktionen finden sich nur wenige, die sich für einen einfachen Nachweis des Indiums eignen, wenn sich dieses Element in Gesellschaft größerer Mengen anderer Metalle derselben Gruppe vorfindet. Bei gewissen Modifikationen kann sich der auf dem Rubidiumchlorindat beruhende Nachweis nützlich erweisen.Die Fällung des Indiums als Metall, die bis jetzt nicht verwendet wurde, gestattet einen genauen Nachweis unter günstigen Bedingungen. Es werden die für bestimmte Fälle, besonders für die Gegenwart von Eisen, Zinn und Cadmium unter Verwendung von Zink, Magnesium und Aluminium als Reduktionsmittel durchgeführten Beobachtungen mitgeteilt.

     

Comportement d'une couche limite thermique en écoulement cisaillé avec chauffage spatio-périodique à la paroi

The evolution in time of a thermal boundary layer generated at the interface shear flow/flat plate is studied by means of an integral method, when the plate is suddenly heated with a periodical flux density in space. From the deduced analytical steady state solution based on the use of a no-thickness plate hypothesis, it is shown that the thermal boundary layer is more influenced by spatial cooling phases than by heating phases.     

Dosage Simultane Des Traces D′eau Et C′oxygexe Dans Les Solvants Crganiqufs

Abstract

The method involves gas-liquid chromatographtc detenninatlons of samples picked up from the liquid phase of an organometalllc solution and from the gas phase above it; the first sample is hydrolyzed before analysis. Comparfng the results before and after introduction of a known amount of a solvent to be analyzed give simultaneous determination of owgen and water present in this solvent of contents less than one part per million.     

Comportement mécanique de l'acier inoxydable martensitique 17-4 PH en corrosion sous contrainte et à la fragilisation par l'hydrogéne environnemental

Age hardened martensitic stainless steels have high resistances to mechanical stress, to friction corrosion and to stress-corrosion cracking (after certain ageing heat treatments). These steels have also high mechanical toughness levels. The mechanical strength of these steels increases when performing specific heat treatments in order to promote the precipitation of hardening phases such as copper-rich ε and/or chromiumrich α′. However, it is well known that the susceptibility to stress-corrosion cracking and to hydrogen embrittlement increases when the mechanical strength of the martensitic steels is high.This paper is devoted to a study the mechanical behaviour of the 17-4 PH martensitic stainless steel with respect to stress-corrosion cracking and to embrittlement by environnemental hydrogen in different ageing conditions, i.e. ageing temperatures (200 to 650 °C) and ageing times (1 and 4 hours). The two behaviours were studied by carrying out low strain rate tensile tests (ε′ = 2.7×10⁻⁶ s⁻¹) in H₂SO₄ 1N. By using differential scanning microcalorimetry, we have identified the precipitation mechanisms of ε and α′ phases, and calculated their activation energies by applying KISSINGER'S relationship.The results obtained show that the susceptibility to stress-corrosion cracking and to hydrogen embrittlement is maximum at the optimum ageing temperature for which the strength level is maximum. The optimum ageing temperature increases when the ε phase, initially coherent, becomes non-coherent. The fracture mechanism changes from cleavage to intergranular mode, respectively. Finally, the fracture mechanism by stress-corrosion cracking is the same as that provoked by hydrogen embrittlement.     

Reactivite Des N 1 -Tosylamidrazones Vis-À-Vis du Chlorure de Thionyle et du Reactif de Lawesson: Obtention Des Thiatriazoles et Des Triazaphospholines

Thionyl chloride 2 and Lawesson Reagent (L.R.) 4 react with N 1 -tosylamidrazones 1 to give respectively 1-oxyde-1,2,3,5-thiatriazole 3 and triazaphospholines 5 derivatives. The structure of products 3 and 5 is confirmed by IR and NMR spectroscopy.