Sur la décomposition par ordinateur et l'interprétation des domaines d'absorption « moyennes fréquences » de plusieurs zéolithes synthétiques A, obtenues par échanges de cations

Les spectres d'absorption diélectrique de nouvelles zéolithes de structure A, obtenues par échanges de cations, sont relevés. Ils montrent tous des domaines « moyennes fréquences » distribués. Les auteurs développent une méthode d'analyse permettant de décomposer rapidement les domaines distribués en domaines élémentaires non distribués lorsqu'ils existent. Pour cela, ils utilisent les propriétés des dérivées des diagrammes linéaires ε' = G(ε"/f) et ε' = H(ε"f). Ils indiquent les processus numériques mis au point et donnent le domaine de validité de la méthode utilisée, testée à partir d'exemples connus. Les auteurs montrent ensuite que les domaines expérimentaux relevés avec les zéolithes A sont tous décomposables en un petit nombre de domaines élémentaires non distribués. Ils attribuent chaque domaine élémentaire à une population de cations existant dans les cavités des zéolithes. A l'aide d'un modèle théorique, ils calculent les temps de relaxation et les moments des ensembles cation-site anionique de la structure, assimilés à des dipôles. Ils discutent des résultats obtenus

Corrosion behaviour of galvanized steel and electroplating steel in aqueous solution: AC impedance study and XPS

International audienceThe efficiency of a new triazole deriv., namely, 2-{(2-hydroxyethyl)[(4-methyl-1H-1,2,3-benzotriazol-1-yl)methyl]amino}ethanol (TTA) has been studied for corrosion inhibition of galvanized steel and electroplating steel in aq. soln. Corrosion inhibition was studied using electrochem. impedance spectroscopy (EIS). These studies have shown that TTA was a very good inhibitor. Data obtained from EIS show a frequency distribution and therefore a modeling element with frequency dispersion behavior, a const. phase element (CPE) has been used. The corrosion behavior of galvanized steel and electroplating steel in aq. soln. was also investigated in the presence of 4-methyl-1H-benzotriazole (TTA unsubstituted) by EIS. These studies have shown that the ability of the mol. to adsorb on the steel surface was dependent on the group in triazole ring substituent. XPS surface anal. with TTA shows that it chemisorbed on surface of galvanized steel and electroplating steel

Ru-Pyrochlores: Compositional Tuning for Electrochemical Stability as Cathode Materials for IT-SOFCs

International audienceUsing XRD, impedance spectroscopy, and XPS, it was shown that both Bi2Ru2O7 and Pb2Ru2O6.5, generally announced as attractive electrode materials for IT-SOFCs, chemically react with CGO. In addition, a never-mentioned time-instability under electrochemical measurements with YZS as electrolyte mediates the polarization tests. For Pb2Ru2O6.5, long time experiments (stabilization time > 900 h, previously to complementary electrochemical tests), yields strong increasing of the resistance polarization. Concerning Bi2Ru2O7, a partial transformation into Bi3Ru3O11 is observed after impedance measurements. The investigation of the Bi2−xMxRu2O7−δ (M = Sr, Pb) solid solutions was performed with the aim to improve the catalytic/electric properties. For low x values, it shows a time and chemical stabilization of the electrode/electrolyte cells, able to preserve high electrode performances of these materials. For higher substitution, the chemical/electrochemical instability reappears. According to our polarization measurements versus oxygen pressure and temperature in the so-called “stabilized” samples, the electrode performance appears limited by the diffusion of adsorbed oxygen on the triple point boundary. It is fully compatible with the metallic behavior checked in all the series

Physico-chemical and biological evaluation of excimer laser irradiated polyethylene terephthalate (pet) surfaces.

The aim of this work was to investigate the consequences of excimer laser irradn. on the physico-chem. and biol. properties of polyethylene terephthalate (PET) films, currently used for medical devices. Three PET films from different origins were studied in the present work, chosen with respect to their chem. and phys. properties, which are of high importance for ulterior medical application as vascular prostheses. Multiple assays were carried out to characterize the phys. and chem. effects of the laser irradn.: surface morphol. tests (light microscopy, Dektak profilometer and confocal laser scanning microscopy) showed the strong transformation of the surface with the laser treatment. Contact angle measurements revealed a significant increase of the surface energy for each PET depending on the applied fluency. Finally XPS characterization of the surface demonstrated the appearance of new chem. species favorable for cell attachment. This aspect had to be strongly considered regarding to the multiple biol. effects of laser irradiated surfaces on living cells. Different cell culture expts. were carried out with L132 human epithelial cells after 6-days culture: proliferation and vitality rate, cell adhesion and cell morphol. Results clearly revealed that laser treatment improved cell proliferation (up to 140% with respect to controls), vitality (10% higher than controls), morphol. and adhesion kinetics (more than 16% of control). A significant correlation (R2=0.906) was also established on one PET between the fluencies of laser treatment and the cellular response. These results emphasized high importance of the choice of the PET material for a medical application: only one of the three considered PET films showed really improved cellular response

Flexible variable-specific-impulse electric propulsion systems for planetary missions

Variable-specific-impulse electric propulsion systems can provide important advantages and cost reductions to any scale of planetary mission. The first part of this paper describes their potential benefits, with special emphasis on mission analysis aspects. The second part identifies the physical limitations of traditional electric propulsion technologies and presents some preliminary development results achieved within the frame of ongoing European activitie

Flexible variable-specific-impulse electric propulsion systems for planetary missions

Variable-specific-impulse electric propulsion systems can provide important advantages and cost reductions to any scale of planetary mission. The first part of this paper describes their potential benefits, with special emphasis on mission analysis aspects. The second part identifies the physical limitations of traditional electric propulsion technologies and presents some preliminary development results achieved within the frame of ongoing European activities

Flexible variable-specific-impulse electric propulsion systems for planetary missions

Variable-specific-impulse electric propulsion systems can provide important advantages and cost reductions to any scale of planetary mission. The first part of this paper describes their potential benefits, with special emphasis on mission analysis aspects. The second part identifies the physical limitations of traditional electric propulsion technologies and presents some preliminary development results achieved within the frame of ongoing European activities