Claude Favotto

Synthèse par chimie douce et caractérisation d'oxynitrate de hafnium HfO(NO3)2, xH2O

Abstract Synthesis by soft chemistry and characterization of hafnyle (IV) nitrate hydrate HfO(NO3)2, xH2O. This paper deals with the synthesis and characterization of hafnyle (IV) nitrate hydrate from HfCl4. The elaboration method is a soft chemistry one which allows to obtain a pure product. The nitrate was characterized by FTIR spectra, X ray diffraction and thermal analysis data (TDA-TGA). The degree of hydration was determined to be 2.

Local order in liquid phases of Al-Ga-Zn alloys

Abstract In this paper, neutron scattering experiments at different temperatures allow us to study local order in the different liquid phases which can exist in Al–Ga–Zn alloys. The ternary phase diagram of these phases has been established from calorimetry and X-ray diffraction results. This study showed that the liquid structure factors in these samples agreed with the presence of a local icosahedral order in the liquid state, when the sample is totally molten. For lower temperatures, the local order owns an analogous liquid cluster structure to that of the solid phase(s) in equilibrium with the liquid. The knowledge of structural data of liquid and the liquid local order variations with temperature has confirmed previous results obtained by calorimetry and X-ray diffraction.

Élaboration par chimie douce de compositions nasicon déficitaires en zirconium

Abstract This paper deals with the preparation of a family of ionic conductor ceramics known as NaSICON (Na Super Ionic CONductor) and with their characterization. For this family constituted of silicon, sodium, phosphorus and zirconium, an original process is proposed to obtain pure ceramics. Precursors are sodium nitrate, zirconyl nitrate, ammonium phosphate, tetraethoxysilan (TEOS), nitric acid and ethanol. New compositions unknown in literature (Na 3.2 Zr 1.9 Si 1.5 P 1.5 O 12 et Na 2.8 Zr 1.8 Si 1.1 P 1.9 O 12 ) were studied. The thermal decomposition of the precursors was performed with a slow heating rate. It was studied by ATD-ATG and X-ray diffraction.The thermal decomposition leads to the oxide at 750 °C, which was characterized by X-ray diffraction.

Thermodynamique des melanges binaires LiPO3-Pb(PO3)2: Diagramme de phases et étude thermodynamique du liquide

Study of solid-liquid phase diagram of LiPO3-Pb(PO3)2 binary system, in certain calcination conditions, shows the existence of several metastable phasis. When heated at a temperature of 723 K the binary mixtures lead uncompletely to a defined compound Pb2Li(PO3). On heating these ternary solid mixtures, three eutectic reactions have been observed: LiPO3+Pb(PO3)2→Liquid at a temperature of 793 K(1) LiPO3+Pb2Li(PO3)5→Liquid at a temperature of 843 K (2) Pb2Li(PO3)5+Pb(PO3)2→Liquid at a temperature of 891 K (3) The metastable liquid phase appears in the system at temperature of 793 K. DTA experiments performed on the binary LiPO3-Pb(PO3)2 mixtures, show a superposition of two diagrams. The first one is metastable and the second represents the stable equilibrium phase diagram. Measurements of liquid enthalpy of binary LiPO3-Pb(PO3)2 system at temperature of 979.65 K were reported. The corresponding values were very small and so the binary system can be considered as athermal. Assuming an ideal behaviour, the liquidus curves in the metastable diagram were calculated and the eutectic reaction (LiPO3-Pb(PO3)2→Liquid) was confirmed at 793 K.

Elaboration de capteurs de gaz à partir de céramiques 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 Ea (from 0.29 to 0.12 eV).

Oxygen exchange study in phase transformations of superconducting bismuth cuprates (Pb2212 and Pb2223)

The oxygen exchange between the condensed phase(s) and the gas phase was studied as a function of temperature for superconducting phases of the system (Bi,Pb)-Sr-Ca-Cu-O.An oxygen probe apparatus allowed confirmation that the variation in oxygen composition in the Pb2212 and Pb2223 superconducting phases is a reversible phenomenon on heating and cooling. It was demonstrated that the mass loss of both phases, for the 905 and 980°C isotherms, was due to the oxygen composition variation and to PbO loss (this latter phenomenon begin irreversible).

Élaboration et carac′erisation de céramiques de type PHT substituées au tantale Pb1−x/2□x/2(HfyTi1−y)1−xTaxO3 (PTHT)

Abstract Preparation and characterization of tantalum-substituted PHT ceramics Pb 1−x/2 □ x/2 (Hf y Ti 1−y ) 1−x Ta x O 3 (PTHT) . This paper deals with the preparation of five oxalic precursors containing lead, hafnium, titanium and tantalum with Pb 1−x/2 ) [(NH 4 ) 2(1−x)(1−y)+3x H 2y(1−x) ] (2x/(2+x)) [(Hf y Ti (1−y) ) 1−x Ta x O(C 2 O 4 ) (x+2) ], dH 2 O general formula [for each precursor y = 0.52 but x takes different values (0.01 ; 0.025 ; 0.05 ; 0.075 ; 0.1)]. The pyrolysis of the complex was performed with a slow heating rate. The thermolysis led to the oxides which were characterized from the microstructural point of view (XRD) and grain size distribution. After the sintering, the electrical properties of the ceramic were studied using Complex Impedance Spectroscopy.