Papers by Author: Philippe Marcus

Abstract: An XPS investigation was carried out on the surface film formed by exposure to high-purity water, on mechanically polished Mg and the two Mg-Al intermetallic compounds: Al3Mg2 and Mg17Al12. The result for mechanically polished pure Mg indicates that a film of MgO covered by a Mg(OH)2 layer, formed by the reaction of MgO with water vapour in the air. On immersion in distilled water, this film was hydrated to a duplex film with an inner MgO layer next to the Mg metal and an external porous layer of hydroxide. For both intermetallics, there was preferential dissolution of magnesium from the mechanically ground surface and also during aqueous immersion. After immersion, there was a 10 nm thick, stable film on the surface; the film composition on Al3Mg2 was whilst that on Mg17Al12 was .

Abstract: The present project is focused on the plasma-deposition of thin films (~150 nm) containing silver nanoparticles embedded in a polymeric matrix, to prevent microbial adhesion to stainless steel. The process originality relies on a dual strategy associating silver target sputtering and plasma polymerization in argon-hexamethyldisiloxane (HMDSO) plasma, using an asymmetrical RF discharge (13.56 MHz). The physico-chemical properties of the obtained films were investigated by transmission FTIR and XPS. To determine the anti-adhesive efficiency, detachment experiments were performed in a shear stress flow chamber with silver-containing and silver-free deposits. The maximal detachment efficiency was achieved with the polymeric matrix alone. Silver antimicrobial effect is assumed to be related to Ag+ ion progressive release from the embedded particles into the surrounding medium. This release was confirmed by ICP-MS measurements. Furthermore, film biocide activity was observed for silver-containing film.

Abstract: Thermal barrier systems, used for turbine blades, are made of a nickel-based superalloy, a nickel aluminide bond coat layer and a ceramic thermal barrier. The aim of the present work is to study the initial stages of oxidation of the AM1/NiAl(Zr) system. It is currently of prime importance to characterize the initial thin oxide layer that covers the bond coat prior to the topcoat deposition. Indeed, the adhesion of the thermal barrier layer and the lifetime of the system are partly influenced by the substrate pre-heating oxidizing treatment. In order to determine the contribution of zirconium during this intermediate temperature range oxidation, the AM1/NiAl(Zr) system was heat treated at 950°C, in two vacuum conditions, that were close to the industrial ones. The compositions of the extreme surface of the nickel aluminide and of the thermally grown oxide were investigated by Xray photoelectron spectroscopy. In particular, these experiments allowed us to detect zirconium at the surface of the system and to determine its oxidation state.