Etude par resonance paramagnetique electronique de noirs de carbone traites par l'azodiisobutyronitrile en absence d'oxygene

Various carbon blacks were treated in absence of oxygen with azobisisobutyronitrile (AIBN). Samples of non-graphitized carbon blacks (Spheron 6, P33, Sterling FT) and graphitized carbon blacks (Graphon, P33 (HTT)) were studied by ESR before and after the AIBN treatment. The line width, g-factor, and the contributions of localized and conduction carrier spins were determined. The results obtained lead the authors to conclude that in the process of fixation of the products of the thermolysis of the AIBN no radicals are involved.     

Application de la thermoluminescence a l'etude de l'hydratation du silicate bicalcique

Hydraulic properties differences between β and γ dicalcium silicate varieties are well known. In this work, a water vapour chemisorption on the surface of both solid phases is shown by thermoluminescence and by quadrupole mass spectrometry.The similar behaviour of β and γ dicalcium silicate varieties in those experiments means that the fundamental difference between their hydraulic reactivities is not due to this hydration step.     

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 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.     

Etude du mecanisme de l'inhibition du zinc en milieu HCl n par les sels de phosphonium

The different steps of mechanism for zinc corrosion inhibition in a 1N HCl solution with phosphonium salts Ph_{4 ? y} P⁺nBu_y, X^? (0 ? y ? 4) are clarified according to the nature of the substituting groups.The secondary type of inhibition, involving the reduction products of these salts, ie phosphine does not appear when y is greater than 1. In this case, the electrostatic adsorption and chemisorption are the predominant steps.     

Influence de la temperature de recuit sur la cinetique de l'hydratation du silicate tricalcique

The tricalcium silicate annealing effect at a temperature range from 800 to 1600°C on its hydration kinetic has been studied by microcalorimetry.Only samples refired at 1000 and 1200°C show high free lime contents produced by thermal decomposition and different thermoluminescence curves; their hydration rates are also the slowest.It seems to be that not only partial thermal decomposition but also structure defects characteristics could influence the hydration rate of tricalcium silicate.Avrami's nucleation equation has been applied with success to the rising step of the calorimetric peak for every sample.     

L'electrolyse de l'alumine dans la cryolithe fondue. Etude du mecanisme de decharge cathodique a l'aide de l'electrode a disque tournant

The use of a rotating disk platinum electrode, on which aluminium has been previously deposited, has allowed us to determine the mechanism of the cathodic reaction during the electrolysis of cryolite—alumina melts. This mechanism requires three stages within the Nernst's diffusion layer. The first of these is the dissociation of the ion AlF^3?₆, at δ′ from the electrode, forming the ions Al³⁺ and F^?. The second one is the discharge of ions Al³⁺ diffusing towards the cathode and the third one, at δ″ from the electrode, is the reaction of the ions F^? with the ions AlF^?₄ to give again the ions AlF^3?₆. The ions Na⁺, which transport most of the current serve to maintain electro-neutrality.     

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.     

Chimisorption de l'hydrogene par les composes d'insertion graphite-potassium

At low temperature, graphite-potassium intercalation compounds of stage higher than one behave as molecular sieves as regards hydrogen [1,2]. At ambient and higher temperature, however, these compounds including the first stage one, chemically fix hydrogen by a completely different process. This reaction, which has been the object of previous papers [3,4], has been further studied so as to remove some of the previous uncertainties and imprecisions.The brown compound KC₈ after fixing hydrogen becomes blue, and saturates for an $\text{H}\text{K}$ ratio of $\text{2}\text{3}$. The reaction is reversible but does present noticeable hysteresis. Radiocrystallographic examination of the hydrogenated product shows that it involves a pure ternary phase of formula $\text{KC}{}_8\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$. The indexing of the 00l reflections indicates a second stage compound: each intercalated layer is composed of two metallic planes in the presence of hydrogen (Fig. 1). This stage change can be interpreted by the pleating of the graphite layers [5]. Neutrocrystallographic studies confirm the preceding results and allow (Table 2) to conclude that the hydrogen forms a layer between the two potassium planes (Fig. 2). The belonging to the second stage of the phase $\text{KC}{}_8\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ is further confirmed by the fact that the free graphite spacings are susceptible of fixing new alkaline metal layers (K, Rb or Cs) to form new compounds referred to as “bi-insertion compounds” [6].Attempts at hydrogen physisorption on the product during the course of chemical hydrogenation (Fig. 3), and the radiocrystallographic and kinetic measurements, clarify the finer points of the reaction. The hydrogen starts to be chemisorbed into the lattice of the compound KC₈ without any stage change (0A), then there appears progressively a second stage phase, unsaturated with hydrogen (AB). Saturation is only attained when the first stage phase has disappeared (BC).Low temperature hydrogen physisorption tests have been carried out on the second stage compound KC₂₄ during chemical hydrogenation. Figure 4 shows a linear decrease in the physisorption capacity, when the hydrogenation ratio increases. By extrapolation it is seen that this capacity should become zero for a chemisorption ratio $\text{H}\text{K}$ in the neighbourhood of $\text{2}\text{3}$.The results suggest the following hydrogenation model. Under the action of the gas, the intercalated metal forms double, hydrogenated layers, identical to those in the ternary $\text{KC}{}_8\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$. There also appear three types of graphitic spacings: free intervals, those occupied by lacunar single layers and those occupied by hydrogenated double layers. These spacings are distributed in such a manner that there appears a binary phase KC_12n coexisting with a ternary phase $\text{KC}{}_{\mathrm{4N}}\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ of equal or neighbouring stages n and N. Stoichiometry imposes a relationship between n and N. Figure 5 represents the variation of N as a function of n for various values of the hydrogenation ratio. At saturation the system would once again become single phase: a ternary, $\text{KC}{}_{24}\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ of sixth stage.In Table 3 are given the strongest 00l reflections and the corresponding interplanar distances, characteristic of the compound KC_12n and $\text{KC}{}_{\mathrm{4N}}\text{H}\text{2}\text{3}$. The experimental data taken from the X-ray diagrams, obtained for three KC₂₄H_y, compounds are compared to the values predicted by our model in Table 4. It is seen that the positions of the observed peaks are in good agreement with the 00l reflections of the model, confirming the interpretation we propose.In conclusion, hydrogenation of the potassium layers of KC₈ or of KC₂₄ always leads to the formation of dense and hydrogenated metallic double layers of formula $\text{KH}\text{2}\text{3}$. This process thus creates ternaries of higher stage than the starting binary.     

Etude des structures de dissolution anodique de l'or en milieu acide

Under potentiostatic regulation the Au electrode immersed in 1 M KCl 0.025 M H₂SO₄ exhibits a sudden transition between activity and passivity. Using an appropriate regulating device, the polarization curve is continuous, Z-shaped, and shows the multiplicity of the steady states. Anodic dissolution takes place only at the inner disc when the electrode is polarized in the overhang of the polarization curve. In this paper we show that the importance of the ohmic drop in the emergence of the particular structures of dissolution and of the multiplicity of the steady states.     

Etude electrochimique de l'iode et du brome en presence de cryptands

In presence of cryptands ([2.2.2], [2.2.1] and [2.1.1]) halogens X₂(bromide and iodine) give rise to the formation of an halonium ion complex in chloroformic solution. Preliminary voltammetric studies of halide and halogen alone allow to measure the stability constant of the trimeric X₃^? species in this solvent. By calculation it is then possible to determine the constant ratio: [cryptand —I⁺] [I₂]^?1 [cryptand]^?1 for iodine only, which is supposed to be a ratio fo the kinetic constants of formation and decomplexation of the halonium complexe.     

Etude theorique de mecanismes de regeneration du deuxieme ordre en voltammetrie en couche mince ou en surface—application a l'etude de la regeneration catalytique de l'iode par les iodates

A theoretical study of current-potential curves in thin layer or in surface potential sweep voltammetry is presented for second order regeneration mechanisms. The theory is applied to the study of the catalytic reduction of iodate by thin layer potential sweep voltammetry. A trace of iodine is added to the iodate solution and the electroreduction of iodine to iodide initiates the catalytic reduction of iodate. The rate constant of the reaction of iodate with iodide which is determined is in good accord with values given in the literature.     

Influence du mode d'excitation sur la thermoluminescence du silicate tricalcique

Thermoluminescence is very convenient to study excited centers in solids and specially structural defects (crystallographical and chemical). However, it is necessary to use several reproducible excitation processes. In this work, some excitation processes of tricalcium silicate: plasma, γ and U.V. rays are studied. A new thermoluminescence apparatus which allows use of small quantities of samples (20 mgr) is described.     

Etude de la reduction de l'oxygene sur les phtalocyanines monomeres et polymeres—I. principes fondamentaux,choix de l'ion central

The catalytic activity of compounds of the phthalocyanine type can be predicted by means of present theories of catalysis. Study of the activity of iron, cobalt, nickel and copper phthalocyanines shows that the Fe(II) compounds are the most active, the order being PcFe > PcCo > PcNi > PcCu. Molecular orbital theory can be used to relate the order of activity to the filling of the d-levels. The electrocatalysis of oxygen reduction has been experimentally examined.     

Etude electrochimique de l'oxydation simultanee de la galene (PbS) et de l'ethylxanthate—condition de formation du xanthate de plomb en surface de la galene

The electrochemical oxidation of galena (PbS) has been investigated in the pH range 9–10, by controlled potential electrolysis using a special bed electrode. In the absence of xanthate, the oxidation of PbS leads to the formation of elemental sulphur, thiosulphate and lead species (Pb(OH)₂). Simultaneous oxidation of galena and xanthate has also been studied and the products characterized by their uv-visible spectrum. The oxidation produces lead xanthate and dixanthogen. It has been established that lead xanthate comes from an ion exchange reaction between excess xanthate in solution and lead species resulting from the lead sulphide oxidation.     

Cinetique de formation d'une couche de passivation - II. Etude theorique de l'oxydation intensiostatique d'un alliage binaire

In an earlier paper we have presented a theoretical scheme accounting for the electrochemical behavior of metals under constant anodic current and with formation of compact oxide film. The kinetics of growth of this resulting oxide film, which insulates the metal from the electrolyte, was supposed to be governed both by the electron exchange reaction and by the diffusion of point defects (vacancy, interstitial) across the oxide film. In this paper, this theoretical scheme is used to describe the electrochemical behavior of binary alloys under similar conditions and with possible formation of a composite oxide. The variation of interfacial concentration of defects versus time is derived and we have drawn the chronopotentiometric curves corresponding to different types of point defects in the oxide and to different concentrations of the elements in the alloy.     

Etude de la reduction de l'oxygene sur les phtalocyanines monomeres et polymeres—III. Phtalocyanines monomeres de fer en couche mince sur l'or

Two kinds of iron phthalocyanine electrodes are prepared by vacuum deposition on gold substrates. The show remarkable differences of activity concerning O₂ reduction, and are investigated by X-ray, optical spectroscopy and X-ray photoelectron spectroscopy (ESCA) techniques. As predicted in a previous paper [3], the iron ion in the active form, is presenting a high spin d⁵ configuration.