Papers by Author: Thierry Chartier

Abstract: The transient stage is critical due to the stress induced by the chemical and thermal strain. In order to predict this strain, the oxygen activity field through the membrane needs to be known. Usually, the membrane is divided into three zones: the bulk where diffusion takes place and the two surfaces where exchanges between atmosphere and membrane take place. Oxygen bulk diffusion is well described by the Wagner theory. A consensus has not yet emerged regarding the surface exchange models proposed in the literature. Moreover, these models describe the permanent state, and cannot be extended to the transient stage. A new macroscopic surface exchange model which allows computing transient stage is proposed. This model assumed that the oxygen flux is governed by the association/dissociation of adsorbed oxygen and by the high energetic cost of oxygen reduction/oxidation. Then, the balance of transient specie only present on the surface is introduced to account for these two phenomena. The oxygen activity fields predicted by the proposed model are in agreement with the measures of chemical potential drop between the membrane and the atmosphere in permanent state. Transient stage measured during isothermal expansion test is partially reproduced.

Abstract: The purpose of this study was to develop bioceramics with a well-defined porous structure in order to control drug loading and release over time. Porous structures were obtained through colloidal processing, using polymethyl methacrylate (PMMA) microspheres as templates (core) and hydroxyapatite (HA) nanoparticles as inorganic building blocks (shell). Dispersed HA suspensions were prepared and their electrokinetic properties were studied to determine a dispersant giving a high positive zeta potential (opposite to the negative zeta potential of PMMA). Upon mixture of well-dispersed HA and PMMA suspensions of opposite charge, core-shell structures were formed via heterocoagulation. After consolidation, polymers were removed by calcination, resulting in a porous structure of controlled size and distribution.

Abstract: During the last decade, the use of metal matrix composites (MMCs) materials such as Al/SiC or CuW for microelectronic devices have made powder modules more reliable. Today, due to the continuous increasing complexity, miniaturization and high density of components in modern devices, high power microelectronic industries are looking for new adaptive thin films with high thermal conductivity, low coefficient thermal expansion, and good machinability. This paper presents an original and new elaboration method (tape casting and hot rolling) which has been optimized in order to elaborate copper/silicon carbide thin film composite materials. The first part presents the optimization of the tape casting parameters used (powder mixing; optimization of the nature and concentration of organic additives; tape casting, debinding and pre-sintering conditions). In the second part, the main characteristics of thin film obtained are discussed, such as thermomechanical properties of the composite Cu/SiC thin films.