Analyse par observation directe de reactions nucleaires de l'oxygene et du carbone au voisinage de la surface d'echantillons de bore

Ion-beam surface analysis of light elements such as oxygen and carbon in light matrices (boron in our case) is mainly subject to matrix interferences. Using a telescope detection system we show that (d, p) reaction for carbon and proton backscattering for oxygen are able to lead to concentration profiles on the first microns of bulk boron samples. Data processing is described and analytical results are shown, making evidence of the purification obtained using electronic bombardment furnace. Comparing with other phhsical methods of analysis, limitation and improvements of this procedure are discussed.      

Le monofluorophosphate de manganese: Une nouvelle classe d'inhibiteurs de corrosion

Manganese monofluorophosphate : a new classe of corrosion inhibitors. The preparation of manganese monofluorophosphate by the process of Lange was investigated. To characterize the resulting compound, analytical techniques including infra-red spectroscopy (IR), Thermogravimetric Analysis (TGA) and Differential Thermal analysis (DTA) were used. The use of manganese monofluorophosphate as a corrosion inhibitor in NaCl 3% medium during summer was investigated by electrochemical techniques such as polarization curves and open-circuit potential measurements. However, the determination of the chemical nature of the film required the use of surface analysis techniques such as scanning electron microscope (MEB) and photo electron spectroscopy (ESCA).     

Analyse destructive de traces de rubidium dans des echantillons mineralogiques par radioactivation au moyen de neutrons de 14 MeV

Increasing interest is devoted in geochemistry to the determination of minor elements in rocks and minerals with the best analytical precision. The use of different methods is quite useful to point out and overcome the systematic and specific interferences of the geological matrix. 14 MeV neutron activation analysis can be used for such a purpose as an additional check method. A successful attempt has been made in the determination of rubidium in different geochemical standards. A sensitivity of 100 ppm can be reached with a 5% precision without any interference problem.     

Spectres de vibration de l'acide cyclopropane dicarboxylique-1.1 et de ses sels de potassium en solution aqueuse

Raman and infrared spectra of the cyclopropane-1.1 dicarboxylic acid and its potassium salts in aqueous solution were recorded from 100 to 4000 cm⁻¹. An assignment of the observed lines as fundamentals is proposed. The analysis of the polarization of the Raman lines indicated that the salts belong to the C₂ group. The intramolecular hydrogen bonds which exist in the acid, persist in aqueous solution in both the acid and the acid salt.     

Etude de la decomposition thermique de fluorapatites carbonatees

Using a precipitation method, variably carbonated samples of fluorapatite-like francolite were prepared from solutions containing diammonium phosphate, ammonium fluoride and ammonium carbonate. Thermal analysis, gas chromatography and IR spectroscopy were performed. The results show that cyanate ions (CNO^?) appear between 400 and 500 °C, probably as a result of the thermal evolution of ammonium ions. Above 500°C, nitrogen gas was detected with CO₂. N₂ arises presumably from cyanate ion decomposition. Decarbonation of these apatites occurs in three steps, the first of these is attributed to carbamate ions.     

Étude d'une méthode de résolution matricielle en vue de la détermination du pourcentage de fixation de modèles chimiques sur le polychloroformiate de vinyle

Poly(vinyl chloroformate) obtained by free radical polymerization has been used as a polymer support for biological active compounds. Some preliminary experiments with model molecules (phenol and amine) have permitted to determine the percentage of fixation by mathematical resolution. This paper describes the study of a method by matrix resolution in using the results of analysis of modified polymers. This work can be used in all cases of modified polymers when there are identified secondary reactions.     

Modelisation de la reaction chimique de durcissement d'un systeme epoxy

Chemical, as well as spectroscopical methods, were used to try to describe, as quantitatively as possible, the different kinds of chemical bonds constituting the network of a cured epoxy matrix, the tgmda/ DDS system. The chemical approach consisted, on the one hand, in synthesizing model compounds; on the other hand, model reactions from diepoxy and amino compounds were followed by chemical, chromatographical and spectroscopical analysis, in order to correlate structure of the products with reactivity of the starting molecules. Spectroscopical method, which was found most useful for this resin system, is solid state ¹³C CP/MAS NMR spectroscopy. As the spectra were not directly interpretable, because consisting largely of broad, bad-resolved peaks, the aliphatic carbon region was decomposed into elementary lines. Structural assignments of the latter were made by using the solution state ¹³C NMR data of model compounds. On account of the anticipated mechanisms, 85 % of the aliphatic carbons could be identified and quantified.     

Determination par calorimetrie de dissolution des enthalpies de formation de quelques silicates,aluminates et alumino-silicates de calcium

The enthalpies of formation of 13 calcium silicates, aluminates, alumino-silicates and ferro-alumino-silicates were measured by dissolution calorimetry with the help of a high-temperature Calvet calorimeter. Dissolution experiments were performed in a lead metaborate (2PbO?B₂O₃) baths at 1173 K. The synthesis of the samples was realized by melting together pure silica, alumina, ferric oxide and calcium carbonate in appropriate ratios. The samples obtained in this way were examined by X-ray diffraction and scanning electronic microscopy. The free lime content was also determined by chemical analysis. The enthalpy of formation of silicates and aluminates obeys two different linear relations with respect to the ratio Ca/X (X=Al or/and Si) except for Ca₁₂Al₁₄O₃₃ which does not exist in its pure form but has to be stabilized by anions as OH^? or Cl^?. The data corresponding to the two aluminosilicates are located between these lines. The enthalpy of formation of tricalcium silicate (Ca₃SiO₅ i.e. C₃S according to the Bogue terminology) from dicalcium silicate and lime could be calculated as ?6kJ·mol^?1. This reaction is the most important one in the industrial process of clinkerization.     

Contrôle de la pureté d'échantillons de niobium et de tantale par spectrométrie gamma directe après irradiation au moyen de protons de 10 MeV

Non-destructive analysis of samples of niobium and tantalum has been achieved by activation with 10-MeV protons and γ-ray spectrometry. Niobium and molybdenum have been detected and determined in tantalum, as well as molybdenum and tungsten in niobium. Upper limits of concentration have been established for over thirty other undetected elements; most of these limits are below the p.p.m. level, and some reach the p.p.b. level.     

Etudepar rpe des radicaux formes lors de la decomposition thermique sous vide de sulfites et de thiosulfates: III. Composes de Magnesium et de Potassium

Paramagnetic species formed during the vacuum thermal decomposition of Mg- and K-sulfites and -thiosulfates are identified by EPR.

During the thermal decomposition of the magnesium compounds, SO⁻₂ is observed as a radical stabilized at the surface of the solid residue.

In the case of K₂SO₃, another SO⁻₂ radical species is observed; this SO⁻₂ is formed inside the crystalline lattice of K₂SO₃ as a result of dislocations during the thermal treatment. If K₂SO₃ results from the “in suit” decomposition of K₂S₂O₃ 1/3H₂O, we observe moreover that the decomposition of the thiosulfate is accompanied with the intermediary formation of SO⁻₂ and S⁻??? radicals. The combined thermal analysis techniques of thermogravimetry and EPR show that K₂Mg(S₂O₃)₂. 6H₂O decompose in the same manner as an equimolar mixture of K₂S₂O₃·1/3H₂O and MgS₂O₃·6H₂O.     

Cinetique de degradation thermique de polycondensats reticules

Statistical methods are applied to the theoretical study of the kinetics of the thermal degradation of crosslinked polycondensates. The parameters required by the theory are the crosslinking degree, the molecular weight of monomers, and the number of free chain ends of the polymer sample. There is a good agreement between theoretical results and experimental data obtained by isothermal thermogravimetric analysis of specially synthesized s-triazinic polycondensates.     

Etude de la repartition de l'uranium dans les roches par la methode des traces de fission. Application a l'echantillonage en vue du dosage de l'uranium

The distribution of uranium in two different rock species: basalt from the Fangataufa atoll (located in Polynesia) and granit from the Hoggar mountains (located in Sahara) was studied by the fission track method. The two distributions observed appear quite different: uranium is uniformly distributed in the vitrous part of the basalt while in granit it is located on the intergranular joints. Applying the sampling model proposed by A. D. WILSON to the observed distributions of uranium, the weight of the analytical sample corresponding to a required sampling error can be estimated. Results show that representative sample weights of the bulk powdered material, as usually obtained by milling, are about some tenths of milligrams for basalt and more than the grams for granit (for uranium analysis). So, in trace element analysis, the sampling error could be more important than the analytical one. This fact could explain the relatively poor accuracy of trace determinations in rock samples (including the reference samples).      

Mise en evidence de points de transition dans des grains de polyterephtalate d'ethylene par retention de vapeurs

Chromatographic elution analysis was used to study the retention of vapours, in particular methanol, on granular polyethyleneterephthalate. Three transition phenomena of the polymer were revealed between 60 and 250°. Differential thermal analysis allowed further precision in the obtained results. These phenomena were related to structure modification in the polymer.     

Croissance et caracterisation de monocristaux de fluorure de neodyme obtenus par la methode des flux

Single crystals of neodynium fluoride NdF₃ have been grown by a flux technique using a melted mixture of neodynium chloride and potassium chloride. They have been characterized by chemical analysis X-ray diffraction and optical studies. The electrical transport properties are reported and discussed.     

Etude des spectres d'absorption infrarouge de l'hydroxyde de strontium et de ses hydrates

Résumé L'étude des spectres d'absorption infrarouge de Sr(OH)₂ et de ses hydrates, jointe à l'analyse par A. T. D. et thermogravimétrie a mis en évidence la formation d'une deuxième forme de monohydrate et les diverses liaisons d'inégale force de l'eau dans ces composés: eau d'insertion, eau de cristallisation.

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Summary A study of the infrared absorption spectra of Sr(OH)₂ and its hydrates, combined with the analysis by differential thermal analysis and thermogravimetry has indicated the formation of a second form of the monohydrate and the various bonds of unequal strength of the water in these compounds: water of intercalation, water of crystallization.

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Zusammenfassung Das Studium der IR-Absorptionsspektren des Strontiumhydroxids und seiner Hydrate ergab im Zusammenhang mit der thermischen Differentialanalyse und Thermogravimetrie den Nachweis der Bildung einer zweiten Form des Monohydrats und des Vorhandenseins von Wasserbindungen unterschiedlicher Stärke in diesen Verbindungen, und zwar von nichtstöchio-metrischem und von Kristallwasser.

     

Influence des conditions experimentales du depot de SiC par RCVD sur l'infiltration de substrats de carbone poreux

The infiltration by SiC of porous substrates of carbon or graphite powders by reaction between the substrate and an SiCl₄-H₂ gaseous mixture has been studied by the reactive chemical vapor deposition (RCVD) method as a function of temperature gaseous mixture composition and total flow rate. β-SiC has been characterised using ESCA spectroscopy, X-ray diffraction and chemical analysis with MASE spectroscopy. The silicon carbide is present throughout the sample. The growth rate of the SiC layer is very slow and the activation energy of the process is evaluated at 168 kJ mol⁻¹. High temperatures (1430 °C) and flow rates (950 cm³ min⁻¹) promote the deposition on the surface of the sample and the correct orientation of the crystals. The presence of whiskers has also been detected in the pores of the substrates.     

Degradation thermique des copolymeres methacrylate de methyle-chlorure de vinylidene

The thermal degradation, under inert atmosphere, of a set of methyl-methacrylate-vinylidene chloride copolymers prepared by free radical copolymerization with constant composition conditions, is studied by thermogravimetry coupled with titration of HCl evolved and with gas chromatographic analysis of volatile products (monomers, methyl chloride). Only the formation of methyl methacrylate can be related to the sequence distribution.     

Evolution des rejets saumatres des stations de dessalement de l'eau de mer au cours de leur evaporation isotherme

Desalination of sea-water was investigated. Effluent of desalination plant was evaporated in isotherm and isobar condition. Density, electric conductivity measurements and chemical analysis were carried out during the process. The results characterising the crystalline phase provide the fields and limits of the precipitation and separation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthese assistee par ordinateur de la phosphacarnegine-I Etablissement du plan de synthese avec l'aide de pascop

Using a retrosynthetic analysis of the target structure1, the chemist-PASCOP team has developed a synthetic plan for this new phosphine.     

Spectres de vibration et champs de force de valence de quelques composes π benzoate de methyle Cr(CO)3-nLn: II. Benzoate de methyle chrome tricarbonyle

A valence force field of methyl benzoate tricarbonylchromium is determined from the force field of methyl benzoate and that of hexacarbonylchromium. The results show the perturbation made both to the aromatic ring and to the carbonyl bonds by the chromiumring bond. This work is the first complete analysis of the vibrational spectra of methyl benzoate tricarbonylchromium.