Étude de l’élimination du Cr(VI) par l’oxyde mixte obtenu par calcination de l’hydroxyde double lamellaire MgAl

A magnesium aluminium hydrotalcite-like compound (HT) containing carbonate anions in the interlayer space and with a final Mg/Al ratio of 2 was synthesized by the co-precipitation method. The obtained material was characterized by powder X-ray diffraction (XRD), Fourier-Transform–Infrared spectroscopy (FT–IR), thermal analysis (ATG/ATD), and surface area measurements (BET). The interaction of the clay with Cr(VI) has been studied by ultraviolet–visible (UV–vis) spectroscopy. The calcined hydrotalcite (HT-C) showed the highest capacity of removal of chromium ions, and their sorption capacities for Cr(VI) are 4.85 mmol/g. The effect of various parameters on the preparation conditions for the removal of chromium, such as the contact time, the amount of sorbent, the initial concentration of Cr(VI), and the pH values of aqueous solution were also investigated to identify their influence on Cr(VI) sorption. The characterization of the calcined hydrotalcite (HT-C) after interaction with Cr(VI) ions by FT–IR spectroscopy showed that Cr(VI) was adsorbed and intercalated by the solid.     

Étude des structures électroniques de In2O3 pur et dopé avec l’étain

The electronic structures of the sesquioxide In₂O₃ and Sn-doped In₂O₃ are examined both self-consistently within the ab initio local density functional theory and using the non self-consistent extended Hückel method. A direct band gap and a wide dispersion of the bottom of the conduction band are obtained in the non-doped case. In the doped case, a narrow, half-filled band assigned to Sn is found at the bottom of the conduction band, in agreement with the metallic and transparent characteristics observed experimentally.     

Sorption de biomolécules par membrane échangeuse d’ions : étude expérimentale et modélisation

Microporous membranes are an alternative to conventional packed columns chromatography. They offer the main advantage compared to bulk material to reduce diffusion phenomena, reduce residence time and pressures drops, and thus, facilitate rapid purification of large quantities of molecules. A wide range of chromatographic membranes involving different molecules retention mechanism (ion exchange, affinity, etc…) is now commercialized. Despite their success, the influence of the geometry of the membrane chromatography devices remains relatively unexplored from a theoretical point of view.This study on the sorption of bovine serum albumin (BSA) on a chromatographic ion exchange membrane (type Sartobind Q from Sartorius Stedim Biotech-Goettingen, Germany), aims to experimentally evaluate the influence of operating conditions (fluid flowrate, initial concentrations) on the breakthrough curves. Two types of geometries (plane module or spiral module) were used and helped to highlight the influence of the type of flow (axial or radial) on separation. The experimental study was conducted on an Akta Prime chromatography system (General Electrics, France). In order to understand the observed phenomena, to predict the performance of different modules and to develop a tool for improving the design of membrane chromatography capsule, a mathematical model was developed in CFD (Computational Fluid Dynamics) and successfully simulated.     

Étude par spectrographie infrarouge de la structure de l'acide iodique,de l'acide anhydroiodique et des polyiodates alcalins

Résumé L'étude par spectrographie infrarouge entre 2 et 33 des divers produits de déshydratation de l'acide iodique et des nombreux iodates «acides» et «pyroiodates» qu'il donne avec les iodates alcalins montre l'existence de ponts I-O-I analogues à ceux qui existent dans l'anhydride iodique I₂O₅. Ces liaisons se caractérisent dans la région explorée par deux groupes de bandes fortes à 400–460 cm^–1 et à 515–646 cm^–1, c'est-à-dire en dehors des régions d'absorption caractéristiques des groupements IO₂ ou IO₃.

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Summary The infrared spectrographic study between 2 and 33, of various products of dehydration of iodic acid and numerous acid iodates and pyroiodates which it yields with alkaline iodates reveals the existence of I-O-I bridges analogous to those in I₂O₅. In the regions explored, these links are characterized by two groups of strong bands at 400–460 cm^–1 and at 515–646 cm^–1, i. e. beyond the absorption regions characteristic of the IO₂ or IO₃ groups.

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Zusammenfassung Die IR-spektrographische Untersuchung verschiedener durch Wasserabspaltung aus Jodsäure hergestellter Produkte, zahlreicher saurer Salze und mit Alkalijodaten gebildeter Pyrojodate zwischen 2 und 33 zeigt das Vorhandensein von J-O-J-Brücken, wie sie analog im Jodsäureanhydrid J₂O₅ vorliegen. Charakteristisch für diese Bindung sind im untersuchten Bereich zwei starke Bandengruppen bei 400 bis 460 cm^–1 und bei 515 bis 646 cm^–1, das heißt jenseits des Bereiches der charakteristischen Absorption der Atomgruppen JO2 oder JO3.

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En l'honneur du ProfesseurF. Feigl, pour son 70^e anniversaire.     

Étude numérique de la stabilité des écoulements de convection naturelle dans des espaces annulaires horizontaux de faible épaisseur

The mechanisms driving the multiplicity of multicellular natural convective flows found at the top of narrow horizontal air-filled concentric annuli (the inner cylinder temperature exceeding the outer) are considered. For radius ratio less than R = 1.20, the base flow undergoes an imperfect bifurcation. The two stable branches are characterised.     

Étude du dosage du phosphore et de l'arsenic dans les aciers par colorimétrie

Phosphomolybdic and arsenomolybdic acids are formed and reduced to their blue reduction products at normal temperature in the presence of certain metallic ions: bismuth, zirconium, titanium. Of these ions, the last two catalyse the reduction of molybdic acid under acid conditions favourable to the reduction of phospho- and arsenomolybdic acids. Bismuth does not bring about this last reaction. It was chosen because of its analytical applications, which are related to the estimation of phosphorus and arsenic in steels. The working methods proposed are given in an appendix.     

Influence de la non stoechiométrie sur les modes de vibration,les amplitudes vibrationnelles,et les intensités infra-rouge dans les alumines β

The normal coordinate analysis of nonstoichiometric β-alumina containing cations such as Na⁺, K⁺, Tl⁺, or Ag⁺ with different nonstoichiometric models (Frenkel defect associated with various cation distribution in the conducting plane) is reported. Mean square amplitudes and infrared intensities have been estimated on the basis of normal mode calculations for sodium β-alumina (stoichiometric and nonstoichiometric). The results obtained are in good agreement with experimental data. The spectral modifications that have been observed can be explained by splitting of degenerate levels and modification of selection rules due to the loss of local symmetry induced by the Frenkel defect. The good agreement between the in-plane (a, b) vibrational calculated frequencies of interstitial oxygen (O_i) and Raman or neutron scattering data shows that the compensating oxygen is tightly bounded to the spinel blocks. The difference between the calculated and crystallographic mean square amplitudes can be explained in terms of the static deviation of the bridging oxygen (O(5)) of 0.1 Å (at 300 K) from its ideal site.     

Dosage colorimétrique de l'antimoine dans les zincs,aluminiums et étains et dans leurs alliages

The colorimetric method using methyl violet is applied to the determination of antimony in zinc, aluminium, tin, and in their alloys.Applying the method to the determination of small quantities of antimony, the following domains of strengths are covered : Zinc alloys : Sb < 0.015 % Aluminium alloys : Sb < 0.030 % Tin : Sb < 0.15 %The amounts of metal used in the determination can be decreased in order to raise the maximum of these strengths, and conversely the latter can be lowered, with the correlative increase in the sensitivity of the determination, increasing conveniently the importance of the aliquot parts withdrawn in the course of the analysis.     

Caractérisation par émission acoustique de l’adhérence et de l’endommagement d’un revêtement : cas d’un revêtement WC–Co sur acier

This note presents a characterization method of the ‘adhesion’ of a coating by acoustic emission technique. In situ acoustic emission measurements which were investigated in terms of amplitude, absolute energy, position of the event, etc. were performed on WC–Co coated specimens prepared by HVOF (high velocity oxy fuel) during four-point bending tests. The microscopic observations of the specimens show two types of cracks: transversal cracks (regularly spaced on the coating surface) and interfacial cracks. Acoustic emission results show two different types of acoustic events in terms of absolute energy and amplitude, which are representative of two cracking mechanisms.     

Étude de l'ordre local par mesure enthalpique différentielle et par exafs en transmission dans les matériaux du système GeTeSb

Study of local order by differential scanning calorimetry and by EXAFS in the GeTeSb system. The local structures of vitreous GeTeSb of near-eutectic and peritectic compositions were studied by using Extended X-ray Absorption Fine Structure performed at the Ge-K edge. Our results show that the Ge atoms are fourfold coordinated by only Te atoms at a distance of 2.60 Å with a Debye-Waller factor of 0.045 Å. We have also shown that the coordination number N decreases when decreasing the tellurium percentage in the samples. The results obtained by EXAFS were interpreted by using differential scanning calorimetry (D.S.C.).     

Comparaison par une étude en spectroscopie UV des effets de complexation par liaison hydrogène et de N-éthylation sur les spectres d'absorption du carbazole

A study of the spectral shifts of the electronic transitions of the carbazole molecule induced by a solvent “cage” effect, by H-bonding and by N-ethylation is reported. These various perturbations produce different effects on the first two bands in the UV absorption spectrum of carbazole and lead to phenomena which are manifest in solvents of different proton availabilities.     

De Réaumur à la Première Guerre Mondiale : les étapes de la maîtrise de l’acier,l’essor des aciers spéciaux

After a brief survey of the history of steel-making we shall concentrate on the period extending from Réaumur's work on that topic (1722) until World War one. Those two centuries saw the transition from empirical steel production processes to industrial steel manufacturing. We shall see how problems linked to the quenching and cementation of steel caused both scientists and steel manufacturers to develop efficient research leading to the establishment of an authentic metal science around 1900. These scientific discoveries then contributed to the prodigious development of special steel. Originally produced empirically to fulfill military requirements, these new types of material were to answer the needs of emerging industries, such as electrical engineering, as well as car manufacturing.     

Transformations de N-acylaziridines catalysées par des supports à base de silice et d’alumine : une élucidation mécanistique

The silica gel, neutral alumina and acid activated clays transform the N-acyl-2,2-dimethylaziridines 1 into a mixture of N-methallylamides 2, oxazolines 3 and amidoalcohols 4. The reaction of N-benzoyl-2,2-dimethylaziridine with benzylcyanid anion leads to a mixture of amidopyrroline 5 and iminopyrrolidine 6. The product 5 was converted into its tautomer 6 by chromatogaphy on silica gel. Ionic mechanisms were then proposed to explain the formation of products 2–6 resulting from the regioselective ring opening on the more substituted C2 carbon side.     

Application Des Réseaux de Neurones Avec la Régularisation Bayésienne pour la Modélisation de la Synthèse de l’hydroxyapatite Élaborée à Partir du Carbonate de Calcium et de L’acide Phosphorique

We have used a new, robust model mapping technique—a Bayesian-regularized neural network—to develop a quantitative relationships model for the synthesis of the phosphocalcic hydroxyapatite by precipitation from a calcium carbonate solution and a phosphoric acid solution. This model was preformed by using a set of factors consisting on the pH of reactional medium, the Ca/P molar ratio of the reagents, reaction time, and the initial concentration of calcium. The results show that the method is robust and gives satisfied results. The Levenberg–Marquardt's algorithm implemented in the neural network Matlab's toolbox allowed a drastic improvement of the performance of the model. Very satisfactory results are then obtained by testing the validity by cross-validation technique.

We have also turned our interests to the explanatory capacities of our methodology to explore the relative contribution and/or the contribution profile of the input factors by using Garson weight portioning method.     

Polymérisation de monomères organiques dans les plasmas froids—4: Étude des structures de polyéthylènes et polytétrafluoroéthylènes,en particulier par résonance paramagnétique électronique

The ethylene and tetrafluoroethylene polymerization in a “cold plasma” leads to polymers with considerable deficiencies of hydrogen or fluorine atoms. With electronic spin resonance, the various kinds of radicals trapped in the macromolecular structure have been detected and in some cases identified and determined. The mechanisms could be partly explained in thermodynamic terms. Irradiation of the corresponding commercial polymers gives some information about degradation processes in the plasma.     

Étude de la réactivité des radicaux α-ester : influence des centres stéréogènes en position α’ et β’

The formation of 2-syn and 2-anti addition products, between a 1-E olefin and an acyclic radical is under kinetic control, although addition of n-Bu₃Sn^• to the 1-Z leads to 1-E olefin. Hydride capture is often independent of the nature of the radical, but the difference of behaviour between A^• and B^• radicals results from their stability, induced by the existing chiral centres present in the molecule. Capture of the intermediate radical in α of the ester by deuterium occurs with a diastereomeric excess, varying between 30 and 78%, depending on the nature of the centres situated in α’ and β’ positions.     

Étude théorique des polarisabilités électroniques et de la polarisation spontanée du composé KD2PO4 (DKDP) dans la phase ferroélectrique

The electronic polarizabilities and the spontaneous polarization of KD₂PO₄ (DKDP) compound are discussed quantitatively from a microscopic model taking into account of the dipole-dipole interactions due to the local fields acting on the constituent ions. The electronic polarizabilities of the K, PO₄ and oxygen ions are determined so as to satisfy the experimental data of the refractive indices. The effective charges of the different ions are calculated by taking into account of the experimental value of the spontaneous polarization. The result of the calculations point out the important role of the deuterium-bonds.