Influence of the 316 L stainless steel interface on the stability and barrier properties of plasma fluorocarbon films

Coatings are known to be one of the more suited strategies to tailor the interface between medical devices and the surrounding cells and tissues once implanted. The development of coatings and the optimization of their adhesion and stability are of major importance. In this work, the influence of plasma etching of the substrate on a plasma fluorocarbon ultrathin coating has been investigated with the aim of improving the stability and the corrosion properties of coated medical devices. The 316 L stainless steel interface was subjected to two different etching sequences prior to the plasma deposition. These plasma etchings, with H(2) and C(2)F(6) as gas precursors, modified the chemical composition and the thickness of the oxide layer and influenced the subsequent polymerization. The coating properties were evaluated using flat substrates submitted to deformation, aging into aqueous medium and corrosion tests. X-ray photoelectron spectroscopy (XPS), time of flight-secondary ion mass spectrometry (ToF-SIMS), ellipsometry, and atomic force microscopy (AFM) were performed to determine the effects of the deformation and the aging on the chemistry and morphology of the coated samples. Analyses showed that plasma etchings were essential to promote reproducible polymerization and film growth. However, the oxide layer thinning due to the etching lowered the corrosion resistance of the substrate and affected the stability of the interface. Still, the deformed samples did not exhibited adhesion and cohesion failure before and after the aging.     

Cation and anion disorder in HgBa2Can−1CunO2n+2+δ

Cu and C substitution for Hg in Hg-based cuprate superconductors is discussed. The large Hg Debye-Waller factor usually obtained from refinements based on diffraction data should be interpreted as an indication of carbon substitution for the Hg cations. This assumption is corroborated by HREM, powder x-ray anomalous dispersion, and powder neutron diffraction investigations.     

Experimental analysis of damage creation and permanent indentation on highly oriented plates

This paper presents an experimental investigation concerning low-velocity impact and quasi-static indentation tests on highly oriented laminates used in aeronautical and aerospace applications. The damage observed in such laminates is very particular. Post mortem analysis were carried out which helped to define an impact damage scenario. Microscopic observations led to explain the mechanism of permanent indentation formation which is a fundamental point of damage tolerance justification. Equivalence between static and dynamic is also discussed.     

Poisoning of platinum surfaces by hexamethyldisiloxane (HMDS): application to catalytic methane sensors

The evolution of the catalytic activity of platinum ribbons towards methane oxidation has been studied as a function of the exposure to hexamethyldisiloxane (HMDS) at various temperatures. Below 950 K, and at moderate exposure, HMDS acts as an inhibitor, the surface is progressively covered by patches of silica and the number of active sites decreases as the exposure to HMDS is increased. Above 950 K, the interaction of platinum with HMDS produces irreversibly the formation of a silica overlayer, the mechanism of the catalytic oxidation of methane is deeply modified. The consequences on the resistance of catalytic methane sensors are analysed as a function of the working conditions.     

Evolution of crystallographic texture during equal channel angular extrusion of copper: The role of material variables

The evolution of crystallographic texture during equal channel angular extrusion (ECAE) using route A has been investigated experimentally as well as by simulations for three types of materials: pure, commercially pure, and impure (cast) copper. The ECAE texture of copper can be compared with simple shear textures. However, there are deviations in terms of location of the respective components. These differences can be nearly reproduced using a recent flow line approach for ECAE deformation (L.S. Tóth, R. Arruffat-Massion, L. Germain, S.C. Baik, and S. Suwas: Acta Mater., 2004, vol. 52, pp. 1885–98) with the help of the viscoplastic self-consistent polycrystal model. The main texture components common to all three materials are A_1E and B_E/B_E; the latter ones are significantly stronger in the cast material. The effect of further deformation on texture modification depends on material variables, such as purity, initial microstructure, and texture.     

Structural, microstructural and transport properties study of lanthanum lithium titanium perovskite thin films grown by Pulsed Laser Deposition

Lanthanum lithium titanate thin films were grown by Pulsed Laser Deposition. La_0.57Li_0.29TiO₃ dense films with smooth surfaces were obtained after optimization of the growth parameters. Such films deposited at 700 °C under 15 Pa are nano-crystalline with domains corresponding to the cubic and tetragonal modifications of this phase. In relation to the measured conductivities/activation energy and to previous works, we clearly underlined that the films of practical interest, prepared at relatively low temperature, are predominantly formed from the tetragonal ordered phase.     

Study of interlayer spacing collapse during polymer/clay nanocomposite melt intercalation

The influence of the chemical structure of alkylammonium organo-modifying montmorillonite clays on the ability to form nanocomposites by melt blending, depending on the processing temperature and the organoclay thermal treatment, has been investigated. On one side chlorinated polyethylene/Cloisite 30B (nano)composite has been prepared by melt intercalation at 175 degrees C and its wide angle X-ray diffraction pattern revealed that the peak characteristic of the interlayer spacing of the organoclay was shifted to lower d-spacing, indicating a collapse of the organoclay structure. On the other side, (nano)composites based on ethylene-vinyl acetate copolymer/Cloisite 30B have been prepared by melt intercalation at 140 degrees C. At this temperature, exfoliation was observed with the as-received organoclay while the same organo-modified clay, simply dried at 180 degrees C for 2 hours, induced again the formation of a composite with a collapsed structure. The effect of the Cloisite 30B thermal treatment on the morphology and mechanical properties of ethylene-vinyl acetate-based (nano)composites was investigated using wide angle X-ray diffraction and tensile tests. In order to shed some light on the origin of this clay interlayer collapse, organoclay modified with various ammonium cations bearing long alkyl chains with different amounts of unsaturations were studied using wide angle X-ray diffraction and X-ray photoelectron spectroscopy before and after thermal treatment at 180 degrees C for 2 hours. Isothermal thermogravimetric analysis of all organoclays was also investigated. The layers collapse effect is discussed depending upon the level of unsatured hydrocarbon present in the organic surfactant.     

Fast-grown CdS quantum dots: Single-source precursor approach vs microwave route

A cross-disciplinary protocol of characterization by joint techniques enables one to closely compare chemical and physical properties of CdS quantum dots (QDs) grown by single source precursor methodology (SSPM) or by microwave synthetic route (MWSR). The results are discussed in relation with the synthesis protocols. The QD average sizes, reproducible as a function of the temperatures involved in the growth processes, range complementarily in 2.8–4.5 nm and 4.5–5.2 nm for SSPM and MWSR, respectively. Hexagonal and cubic structures after X-ray diffraction on SSPM and MWSR grown CdS QDs, respectively, are tentatively correlated to a better crystalline quality of the latter with respect to the further ones, suggested by (i) a remarkable stability of the MWSR grown QDs after exposure to air during several days and (ii) no evidence of their fragmentation during mass spectrometry (MS) analyses, after a fair agreement between size dispersities obtained by transmission electron microscopy (TEM) and MS, in contrast with the discrepancy found for the SSPM grown QDs. Correlatively, a better optical quality is suggested for the MWSR grown QDs by the resolution of n > 1 excitonic transitions in their absorption spectra. The QD average sizes obtained by TEM and deduced from MS are in overall agreement. This agreement is improved for the MWSR grown QDs, taking into account a prolate shape of the QDs also observed in the TEM images. For both series of samples, the excitonic responses vs the average sizes are consistent with the commonly admitted empirical energy-size correspondence. A low energy PL band is observed in the case of the SSPM grown QDs. Its decrease in intensity with QD size increase suggests a surface origin tentatively attributed to S vacancies. In the case of the MWSR grown QDs, the absence of this PL is tentatively correlated to an absence of S vacancies and therefore to the stable behavior observed when the QDs are exposed to air.