Synthèse de l’analcime et caractérisation par DRX, MEB et MET

Des investigations préliminaires ont permis de mettre au point une voie assez originale de synthèse de l’analcime. Cette zéolithe est obtenue par cristallisation hydrothermale d’un gel d’aluminosi1icate sous pression et agitation permanente. Le produit se caractérise par un rapport Si/Al variant de 3,42 à 3,85 et un taux de cristallisation supérieur à 90 %. La phase cubique est prépondérante et présente un paramètre de maille de 13,7 Å. Dans de telles conditions opératoires, la pression semble jouer un rôle déterminant en réduisant le temps et la température de cristallisation

Elaboration and characterization of solid materials of types zeolite NaA and faujasite NaY exchanged by zinc metallic ions Zn2+

AbstractThe present work deals with the elaborated of NaA and faujasite NaY solid materials according to a hydrothermal crystallization of amorphous gels composed of solutions of silicon, aluminum and sodium. The process elaboration has been achieved in autoclaves made of steel lined in Teflon under different operating conditions of temperature of heating, time of contact and stirring. After crystallization, the samples were characterized by different techniques such as X ray diffraction, scanning electronic microscopy, infrared spectroscopy, thermal analysis, and chemical analysis. Pure solid materials NaA and NaY zeolites were obtained and were impregnated by (Zn2+) ions by ion exchange process. The effects of various parameters such as initial metal concentration, pH, solid-liquid ratio (R) and temperature on the exchange percentage are studied. The equilibrium isotherms of zinc ions sorption are also evaluated using Langmuir and Freundlich models. Thermodynamic parameters, i.e. enthalpy of adsorption ΔHads∘, entropy change ΔSads∘ and Gibbs free energy ΔGads∘ for the sorption of zinc ions on NaA and NaY zeolites were examined

Effect of Isothermal Hold on the Microstructural Evolution of the Stainless Steel 304L/Zircaloy-4 Interface

International audienceThe transition from solid-state bonding of the stainless steel 304L/Zircaloy-4 diffusion couple to a partial liquid-phase bonding is important for the bonding process at temperatures ranging from 950 to 1050 degrees C. In this study, the temperature at which a melting process occurs at the interface after 45 min of isothermal holdings is determined experimentally. This melting process leads to a drastic change in the thickness of the reaction products zone (RPZ) as well as on its microstructure. Diffusion couples were characterized by SEM-EDS, and quantitative chemical analyses of different phases are performed by EPMA. The RPZ consists of three layers: the (alpha-Fe-Cr) phase layer and two layers consisting of Zr(Fe, Cr)(2) (epsilon), Zr-2(Fe, Ni) and (alpha-Zr) phases. The thickness of these layers strongly depends on the holding temperature. The analysis allowed the description of the physicochemical phenomena occurring during isothermal holding as well as during cooling. The solidification paths are determined at 1000, 1020 and 1050 degrees C. Hardness tests are performed on the bonded samples in order to qualify the mechanical properties of different phases of the RPZ. This study leads to a better understanding of the complex phenomena intervening in the joining process which is very useful for applications in industrial scale