Etude des nombres de transport ioniques dans les melanges cryolithe—alumine fondus selon le principe de la methode de hittorf—II. Resultats

The application of Hittorf's method to the study of ionic transference numbers in molten mixtures of cryolithe—alumina is now possible, thanks to the boron nitride cell described in Part I.

The results establish that sodium exclusively transports the current, at least in the neutral and basic baths (transference number nearly 1); in the acid baths, the transference number of sodium is slightly lower than 1, the fluorine taking part in the conduction.

Zusammenfassung

Die Anwendung der Hittorf'schen Methode zur Untersuchung der Ueberführungszahlen in geschmolzenen Kryolith-Tonerde-Mischungen ist heute, dank der früher beschriebenen Bornitridzelle, möglich. Die Resultate bestätigen, dass zumindest in neutralen und basischen Bädern praktisch der gesamte Strom nur vom Natrium transportiert wird (Ueberführungszahl ungefähr eins). In den sauren Bädern ist die Ueberführungszahl von Natrium etwas kleiner als eins, da heir auch das Fluor zur elektrischen Leitung beiträgt.     

Etude de l'oxydation des carbones en oxyde graphitique

The oxidation of several types of carbons leading to the formation of lamellar oxides was studied. The progression of formation of graphitic oxides was followed by use of X-ray diffraction, i.r. spectroscopy, electron microscopy and by a study of carbon dioxide evolution. Kinetic studies of the formation of carbon dioxide indicate the existence of two reaction stages during the oxidation. The fraction of carbon transformable into graphitic oxides is independent of the reaction temperature and carbon characteristic. The oxidation rate of graphitic oxide into carbon dioxide depends on the structural organization of the initial carbon.     

Etude potentiostatique et spectroscopique de l'aluminium recouvert par une couche d'oxyde: effet de differents anions

The effect of different anions on the formation and the breakdown of the passivating film on aluminium was studied by means of stationary and transient potentiostatic measurements associated with analysis of the surface region of the metal by photoelectron spectrometry (ESCA). The progressive penetration of chloride ions into the oxide layer, dependent on the electrode potential was pointed out. The perchlorate ion was shown to be reduced at the film-solution interface.     

Etude des interactions eau-liaison imide II. Conductivité électrique de la poly-L-proline II selon ses états d'hydratation

The Characterization Of Water – Poly-L-Proline Ii Interactions As A Function Of Water Content Led Us To Study The Electrical Behaviour Of This Polyimidoacide During Hydration. The Static Conductivity Would Be Due To Electronic Charge Carriers Till The Water Content Rises To 8% (G Of Water Per 100G Of Dry Product) I.E., One Water Molecule For Two Carbonyl Groups. Then An Ionic Conduction Mechanism Appears, Which Becomes The Main One Above 18% Of Sorbed Water (I.E., One Water Molecule Per Carbonyl Group). A Conduction Mode Is Proposed For These Different Steps In Hydration.     

Etude voltammetrique de l''electrosorption de la 2,2′-bipyridine et de ses complexes photoactifs de ruthenium et de rhodium sur des electrodes binaires platine—or

The adsorption of 2,2′-bipyridine and its photoactive complexes with Ru^II and Rh^III was studied on binary platinum—gold electrodes chosen as models of the bifunctional catalysts for water photo-decomposition. The adsorption isotherms show that the geometrical arrangement of the adsorbed species, and their interaction with the electrode surface depend on their structure and on the nature of the metallic substrate and the superficial composition of the catalyst. The interpretation of the role played by the relay molecules in the electrocatalytic photodecomposition of water allows a discussion of the preparation and the behaviour of Pt—Au binary catalysts used for the production of photolytic hydrogen.     

Etude de la reduction electrochimique d'alkyl-2 ethoxycarbonyl-2 cycloalcanones. Influence des conditions experimentales sur la stereochimie de la reduction

A few 2-alkyl-2-carbethoxy-cycloalkanones are selectively reduced with high yields into 2-alkyl-2- carbethoxy-cycloalkanols, electrochemically on mercury pool in hydroorganic medium. Carbon dioxide is bubbled with nitrogen through the solution to maintain the pH at about 9 to avoid side reactions.Cis and trans esters-alcohols were determinated by gas chromatography. The ratio is depending on several factors: the size of the cycle, the nature of the alkyl substituent, the nature of the cation of the supporting electrolyte, the nature of the cathode material and the temperature of the reaction. This last one is very important. At low temperature (?6°C) we have got preferentially the cis isomer and at high temperature (80°C) we have got almost exclusively the more thermodynamically stable trans isomer.To explain the mechanism we consider the presentation of the molecule on the electrode, the protonating effect of the medium and the thermodynamical equilibrium of the intermediate carbanion.     

Etude de la formation d'un complexe de surface graphite-eau relation avec la reaction d'oxydation

Using a gas flow apparatus under atmospheric pressure with infrared CO and CO₂ detection and an apparatus operating under low pressure with a mass spectrometer for analysis, we have found the following: The chemisorption of water becomes appreciable above 200°C. The water chemisorbed on graphite previously degassed at 1000°C forms a surface complex which on raising the temperature decomposes with simultaneous evolution of CO and H₂, thus showing that hydrogen enters into the composition of the complex. The programmed thermal decomposition of the complex shows two peaks. The first peak corresponds to the sites which disappear with the degassing of the CO and H₂; these sites are formed by the ‘labile’ carbon atoms created by the prior degassing. The second peak corresponds to the sites which are constantly renewed after degassing the CO molecules, and which are therefore formed by graphite atoms normally linked to the graphite lattice. The reaction rate of the oxidation of graphite by water shows two transient rates before attaining a stationary value. Correlations between the CO thermo-desorption and these reaction rates are found which indicate that the formation of a surface complex is a necessary step in graphite-H₂O reaction.     

Etude numérique et paramétrique de la combustion de particules d'aluminium

Several numerical models have been investigated to study the reactivity of aluminium particles coming from the combustion of solid propellants in spatial launchers. The Law model has been rapidly selected as it yields a continuous model from an aluminium drop to an oxide drop. The model also gives the residue size at the end of the combustion process. This could explain the scaling observed in the rocket engines. In order to study the coupling between the flow and the combustion, the combusion of aluminium drops has been widely analyzed with 0D computation. The main mechanisms of the combustion process have been identified.     

Etude des nombres de transport ioniques dans les mélanges cryolithe-alumine selon le principe de la methode de Hittorf—I. mise en oeuvre de la methode

We describe a boron nitride cell permitting the direct application of Hittorf's method for the study of ionic transference numbers in cryolite-alumina melts, as used in practice. The grade of purity of the material, more especially its electrical conductivity, is discussed. We show that in spite of its defects, it is utilizable for the purpose. Other phenomena to be dealt with, especially the evaporation of the baths, are pointed out.     

Etude de la validite de la loi de Fick pour le transfer de matiere dans un fluide viscoelastique

An experimental study has been realized in a viscoelastic fluid to know if the Fick's law can be applied. This study also permitted to give some precisions about the differencies observed between the mass transfer measurements and the theorie results from the Ostwald's law.     

Applications de la spectrométrie de rayons x à l'analyse de matériaux macromoléculaires. II. Etude de polyéthylènes chlorés en surface

The chlorine concentrations in the range up to about 500 μg.cm^-2 of surface chlorinated polyethylene films were determined by X-ray fluorescence spectrometry. By using appropriate standards, it is shown that the investigated samples can be regarded as thin films only when the energy of the «equivalent» primary X-radiation is high enough. Results allow to estimate (in the range up to about 4 μm) the chlorinated film thicknesses versus duration of the halogenation processes.     

Etude de la resistivité de corps pulvérulents à base de carbone en fonction de la compression

Electrical resistance measurements were performed on different varieties of carbon blacks (Sterling Fr, MT, S, Black Pearls 2) under compression up to 660 kgf/cm² to determine the real resistivity of the carbon material. The general shape of the curves log p= - s log P are in good agreement with those reported by Mrozowski. Two theories have been proposed to explain the mechanism of the current flow through the particles. Holm's Contacts and the Tunnel effect between particles. The results for thermal blacks seem to agree with the first interpretation while the behaviour of the Channel blacks rather follows the second.     

Etude de l'effet retardateur du zinc sur l'hydratation de la pate de ciment Portland

The retarding effect of zinc on the hydration of C₃S and C₃A, the two principal Portland cement components, has been investigated by X - ray diffraction. The results show that the C₃S retardation is more important than that of C₃A. This retardation is due to the precipitation of an amorphous layer of zinc hydroxide around the anhydrous grains. The effect of this coating depends on its permeability. The hydration reaction starts again through the transformation of the zinc hydroxide into the crystalline calcium zinc hydroxide Ca Zn₂ (OH)₆, 2H₂ O.     

Comportement electrochimique et reactivite du systeme Ag(II)/Ag(I)-bipyridine dans le carbonate de propylene—III. Etude du mecanisme et de la cinetique de la reaction d'oxydation catalytique de la bipyridine

The electrochemical behaviour of the Ag(II)/Ag(I)-bipyridine system has been investigated in solutions containing bipyridine in excess with respect to the Ag⁺-bipy: 1–2 stoichiometry. The nature of the coupled chemical reaction indicates a chemical catalysis of an electrochemical reaction. The rate constant of the reaction of destruction of the intermediate complex (k₂ = 1.8 × 10^?3s^?1) has been calculated from measurements performed during electrolysis of Ag^I(bipy)⁺₂-bipy solutions.