Elaboration par voie sol-gel et caracterisation de materiaux ceramiques PbTiO3 dopes au lanthane

Preparation and characterization of sol-gel derived La-doped PbTiO₃ ceramics. La-doped lead titanate bulk powders of perovskite type were prepared by a sol gel process. An excess of lead (5%) was added in order to compensate the Pb losses during the annealing process. The effect of temperature on the evolution of the powders was studied using Fourier Transform Infrared (FTIR) spectroscopy, Thermal Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA) and X-Ray Diffraction (XRD). The effect of La-doping concentration on the crystal structure was also investigated. The La-doped lead titanate bulk powders (PLT) annealed at 600°C for 2h crystallize in a perovskite phase with cubic structure.     

Elaboration de capteurs de gaz a partir de ceramiques conductrices ioniques de type NaSICON

The elaboration of Na⁺ super-ionic conductor (NaSICON) ceramics is studied in this work. These solid electrolytes can be used as sensor for detection of polluted gases in air. Two sorts of ceramics with different chemical compositions are synthesised by soft chemistry route: a zirconium-based NaSICON and a hafnium-based NaSICON. DTA-TG and temperature depending X-ray diffractometry were used to follow the thermal decomposition of the precursor phases. The electrical properties of these ceramic sodium ionic conductors are investigated by complex impedance spectroscopy (CIS). The substitution of the zirconium by the hafnium increases the ceramic conductivity and decreases the activation energy E ^a (from 0.29 to 0.12 eV). This revised version was published online in August 2006 with corrections to the Cover Date.     

Chromatographie par complexe de transfert de charge. Application à l'analyse d'hydroliquéfiats du charbon par HPLC

Résumé L'analyse de coupes lourdes (huile de distillation sous vide et huile issue du séparateur à chaud) provenant de l'hydroliquéfaction catalytique du charbon a été réalisée par mise en ouvre de différentes techniques chromatographiques. L'identification des principales structures résulte de l'application de la chromatographie par couplage de transfert de charge en mode HPLC et des spectroscopies UV et de masse.

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Donotor-acceptor complex chromatography —Application to analysis of coal liquefaction products by HPLC

Summary A Vacuum gas oil and the corresponding residue of a coal liquefaction product were investigated by means of HPLC and MS. Nearly a complete identification was performed by chromatographic, UV-spectroscopic methods and MS.

     

Identification de polymeres par analyse thermique differentielle

Nineteen different polymers having no melting endotherm (foam urea-formol, PVC, vinyl polyacetate, vinyl polybutyral, polymethacrylates, polystyrene and its copolymers) are studied by DTA. The identification is realized due to endothermic decomposition peak and exothermic peaks, according to the general method which has been described previously.

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Zusammenfassung Mittels DTA wurden neunzehn verschiedene Polymere ohne endothermen Peak beim Schmelzen untersucht (Schaum Carbamid-Formol, PVC, Vinylpolyacetat, Vinylpolybutyral, Polymethacrylate, Polystyrol und seine Kopolymere). Die Identifizierung erfolgte in Übereinstimmung mit der unlängst beschriebenen allgemeinen Methode anhand der endothermen Zersetzung speaks und der exothermen Peaks.

     

Formation inattendue de digermane optiquement actif au cours de la reaction de substitution des germanes par le chlorure de benzyl-magnesium active par les complexes du nickel

An optically active digermine is obtained in the reaction of PhCH₂ MgCl (activated by a Ni^II complex) with α-NpPhMeGeH. This observation indiates the formation of a GeMgX reagent ant its activation by Ni^II, allowing cleavage of the Gebond with retention of configuration.     

Monoacetamidation de quelques hydrocarbures polycycliques par voie electrochimique

Anodic oxidation in acetonitrile of five polycyclic hydrocarbons gives products in ratios related to the relative stabilities of intermediate carbocations. If “non-classical” ions form they arise apparently from “classical” transition states.     

Etude par analyse thermique de quelques vegetaux mediterraneens

Thermal analysis can be used for the study of the behaviour of plants during heating, and most particularly in the risk prevention of forest fire.Simultaneous thermal analysis (DTA-TG) of some mediterranean vegetals (needles of Pinus halepensis, leaves of Quercus coccifera; leaves of Rosmarinus officinalis; prickles, flowers and branchs of Ulex parviflorus; leaves and branchs of Acacia dealbata; leaves of Cistus albidus) shows the presence of several exothermic peaks. The first one, about 300°C, is responsible for a brutal ignition of the evolved gas. We compare the different samples by using the DTA and DTG peak temperatures and the weight loss by volatilization at 300°C.

     

Determination of tetracyclines in surface water and milk by the magnesium hydroxide coprecipitation method

A simple coprecipitation method was developed for the determination of tetracyclines (TCs) in surface water and milk by high-performance liquid chromatography with diode-array detection (HPLC–DAD). Magnesium ion was added into the surface water or the acetonitrile (MeCN) extract of milk. After alkalinization, magnesium hydroxide precipitates which had been formed can be separated from the matrix solution easily by centrifuging and then a dissolution step was performed by adding a small amount of acid. The final solution could be introduced directly into HPLC system for the determination of the analytes. Under optimal conditions, recoveries for the analysis of spiked surface water samples ranged from 83.6% to 95.1% with relative standard deviation of 2.0–5.5%. For milk samples, relative recoveries were 95.9–104.6% with relative standard deviation of 3.4–6.7%. The enrichment factors ranged from 41.5 to 48.1 for 10 mL water samples, and from 3.6 to 4.4 for 1 mL MeCN extracts of milk. Limits of detection ranged from 0.13 to 0.51 ng/mL, and from 3.0 to 8.5 ng/g for four TCs in surface water and milk samples, respectively.     

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.     

Caracterisation par analyse thermique de la lignine,de la cellulose et de quelques uns de ses derives etherifies

Cellulose and its derivatives (methyl cellulose, sodium carboxymethyl cellulose, hydroxymethyl cellulose and hydroxypropyl cellulose) used as excipients in pharmaceutical industry can be characterised by simultaneous thermoanalytical (DTA and TG) methods, based on the temperatures of exothermic peaks. Lignine cellulose can be identified by taking into account the difference in temperature between the first exothermic DTA peak and the corresponding DTG peak.

     

Etude de L'oxydation de Polyethylenes Par Analyse Thermique Identification des produits de dégradation par infra-rouge

The oxidation of pure and recycled polyethylene samples was studied by thermal analysis (DTA-TG-DSC): presence of two exothermic peaks and mass loss. The thermo-oxidation products, containing C-O and C=O links, were identified by IR spectrometry and GC-MS spectrometry. The oxidation is easier from low to high density polyethylene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dosage de traces de zirconium dans les materiaux a la base d'aluminium par spectrographie

Sans résumé

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Determination of Traces of Zirconium in Aluminium Based Material Bestimmung von Zirkoniumspuren in Al-haltigen Materialien

     

Parametres cinetiques de systemes epoxy/acide par analyse calorimetrique differentielle (DSC)

We have studied the curing of epoxy resin diglycidylether of bisphenol A (DGEBA), by two different hardeners poly(styrene-co-acrylic acid) (SAAx) at different acid percent and poly(acrylic acid). We follow the kinetics by non-isothermal and isothermal. In non-isothermal mode the heating rates were between 2.5 and 20°C min^-1 in the temperature range of 25-250°C. The reaction was supposed to follow the n ^th order. In isothermal mode, four temperatures for each system were done. In this case the reaction was autocatalysed. The interpretation of the exotherms allowed to determine the kinetic parameters of the studied systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Etude Comparative de Cinq Vegetaux Mediterraneens par Analyses Thermique et Chimique

The comparative thermal and chemical study was done on five mediterranean plants: Acacia dealbata, Quercus coccifera, Rosmarinus officinalis, Thymus vulgaris, Ulex parviflorus. Results were independent of the drying way of samples (110°C, 60°C or lyophilisation). The correlation between the maximum decomposition rate at about 300°C and the content of cellulose was confirmed. The samples cut on the same foot of Ulex parviflorus, in spring, produced, for the thorns and sprigs, a minimum in cellulose content, and a maximum in lignine content. The results were inverse in winter. This revised version was published online in July 2006 with corrections to the Cover Date.     

Etude ATD-ATG du polyethylene ignifuge par l’hydroxyde de magnesium

Fire resistance of polyethylene is realized by magnesium hydroxide which is distinguished from halogenated fire-proofing agents by its lower cost and its non toxicity. Magnesium hydroxide decomposed by an endothermic reaction with liberation of water, contributing to fire proofing. The sample used (Kisuma 5A-N^*) is constituted from a powder (0.6–0.8 micrometre) its surface is treated by plastic material in order to ameliorate its compatibility. We studied the thermal decomposition by DTA and TG, of mixtures constituted by polyethylene and magnesium hydroxide. A sudden decomposition began at 385°C for pure polyethylene and decomposition took place at 429°C for the mixture polyethylene-Kisuma (50–50). Incorporation of magnesium hydroxide in polyethylene increases fire resistance.     

Transfert de chaleur par conduction et rayonnement dans les materiaux semi-transparents

We show here an adaptation of the classical Flash Method permitting the measure of the thermal conductivity of semi-transparent porous materials. A flash lamp send a heat pulse on the upper face of a cylindrical sample and lower face temperature is analysed. The semi-transparent material is sandwiched between two copper slices. The sample used scatters thermal radiation, and absorbs it very little. It is therefore possible to account for two parts of heat transfer through the material: a pure conductive phenomenon and a radiative one. In most insulating materials radiative transfer represents about 1/3 of the total heat flux at the ambiant temperature. The problem is solved with electrical analogy, quadripoles technique and Laplace transform. The modelization brings out two physical character parameters of the material and a coefficient qualifying the thermal exchange between the sample and the environment during the experiment.     

L'electrode a Pate de Carbone Modifiee Son Utilisation en Voltammetrie par Redissolution Anodique a Impulsions Differentielles en Presence d'Un Film de Mercure

Abstract

The various problems which are associated with the use of carbon paste electrode as thin mercury film electrode (TKFE) for anodic stripping voltammetry (ASV) can be overcame in a very easy and rapid way. The procedure consists to coat the carbon paste surface by spraying a graphite based conductive solution. For example, the dispersion of colloidal graphite in a mixture of methyl polymethacrylate with butyl acetate (as solvent) gives interesting results. Such a surface is easily renewable and the electrode does not require any pretreatment procedure like cleaning or polarization cycles…, after coating. The technique offers the advantage to limit the risk of sample contamination and memory effects. After pulverisation, a hard, uniform and compact layer is formed after evaporation of the solvent excess.

The resulting electrode, electrochemically coated with mercury, exhibits a good stability as shown for the differential pulse anodic stripping voltammetry (DPASV) for cadmium ions. Replicate measurements were carried out in two different buffers at pH 8.5 and 5.0. Compared to the originally carbon paste electrode, a marked improvement of the reproducibility of the peak currents is observed. Calibration curves obtained by using the method of standard additions show a good linear relationship between cadmium ions concentration and peak current (down to 4×10^?10 M.L^?1).

After a deposition time of 10 minutes, the detection limit for cadmium is 1×10^?10 M.L^?l in both media).     

Etude comparative par analyses thermique et chimique de quelques vegetaux mediterraneens

Thermal analysis can be used for the behaviour of plants during heating and most particularly in the risk prevention of forest fire. Cellulose, holocellulose and lignin are the most important compounds determinated by analytical procedures in six mediterranean vegetals: Acacia dealbata, Pinus halepinsis, Quercus coccifera, Rosmarinus officinalis, Thymus vulgaris, Ulex parviflorus. TG-DTA is applied to the powders obtained after drying (110°C), pounding and sifting. The rate of pyrolysis about 300°C allows a semi-quantitative estimate of the cellulose present in the vegetal and its flammability.

Nous tenons à remercier, pour leur collaboration technique, mesdames J. Campocasso, A. Crestin et M. F. Vergnes.     

Analyse de la pyrolyse menagee du bois par un couplage TG-DSC-IRTF

This paper deals whith thermal degradation of wood at low pyrolysis temperature. Chemical modifications are investigated in order to explain the new properties of treated wood.