Variation de la composition de nanoparticules de 1-10 nm obtenues par séparation de phase dans un verre de silice

National audienceLes verres contenant des nanoparticules ont de nombreuses applications industrielles, notamment grâce à leurs excellentes propriétés thermo-mécaniques [1]. Ils présentent aussi un intérêt pour les propriétés optiques. En effet, l'encapsulation d'ions luminescents (ions de terre rare par exemple) dans des nanoparticules entraînent de nouvelles propriétés de luminescence qui n'existeraient pas dans le verre hôte (bande d'émission élargie, efficacité quantique augmentée, etc) [2]. La préparation de tels verres repose sur des mécanismes de nucléation, croissance et de démixtion dont les premières étapes sont encore assez mal connues. Mais l'avènement de nouvelles techniques de caractérisation à l'échelle nanométrique permet d'améliorer notre compréhension de ces phénomènes. Par exemple, une évolution structurelle des nanoparticules à travers des phases cristallines métastables [3] ou une transformation d'un nucléus amorphe vers une nanoparticule cristalline [4] ont été observées. Des changements de composition ont aussi été rapportés pour des particules de taille 1-10 nm dans des alliages [5] et dans des métaux [6]. Dans cette présentation, nous nous intéressons à la composition de nanoparticules amorphes obtenues par séparation de phase dans un verre de silice. De telles études ont été rendues possibles grâce au développement récent de l'APT (Atom Probe Tomography) pour l'analyse des verres [7]. Nous étudions une fibre optique à base de silice préparée par le procédé MCVD (Modified Chemical Vapor Deposition). Les nanoparticules sont obtenues en incorporant du magnésium qui déclenche une séparation de phase grâce aux traitements thermiques inhérents au procédé MCVD [8]. La composition des nanoparticules dans le verre de silice dopée avec Mg, P, Ge et Er est étudiée dans la gamme 1-10 nm. Nous montrons la partition de Mg, P et Er dans ces nanoparticules ainsi qu'une modification de la composition en fonction de la taille des particules

Fiber Optic Dielectric Nanoparticles Characterization by Atom Probe Microscopy

International audienceThe engineered processing of dielectric nanoparticles (DNPs) in optical fibers via luminescent ion-doping of silica-based glass aims at providing an enhanced spectroscopic behavior compared to pure silica. These DNPs should positively impact applications in high power fiber lasers, light sources with new wavelengths and telecommunications. The prevalence of large phase immiscibility domains in silicate systems containing divalent metal oxides (Mg for instance) promotes the formation of DNPs through phase separation since heat treatments take place during the MCVD process. Even after 60 years of glass-ceramics research, lack of experimental data concerning early nucleation stages imposes variations in composition and heat treatments as processing steps [1]. Although classical nucleation theory was the first model proposed to explain those phenomena, growth rate mismatches remain wide. According to this capillary assumption-based model, nuclei and bulk share similar structure-composition relationship. Recent articles disprove assumption of structure, pointing toward DNPs structural changes [2] and transition from amorphous nuclei to crystalline DNPs [3]. Compositional changes for small particle sizes (~1-10 nm) have been measured in alloys with Anomalous Small Angle X-Ray Scattering (ASAXS) [4] and in steels with Atom Probe Tomography (APT) [5]. Recent developments in APT has allowed the extension of such studies to glass-ceramics [6], and in the current work, we report experimental data disproving the second capillary assumption at the early stage of nucleation-growth process. The atomic distribution map of Mg DNPs in silica-based glass doped with Mg, P, Ge and Er is reported in Figure 1 after APT analysis. In addition, quantitative assessment of Mg, P and Er content levels in DNPs smaller than 10nm in diameter (Figure 2) could refine the theories behind nucleation and growth mechanisms

L’aventure entrepreneuriale Les Bouchons

International audienc

Variation of sub-10nm nanoparticle chemical composition in glass revealed by Atom Probe Tomography

International audienceThe study of amorphous Dielectric Nano-Particles (DNPs) smaller than 10 nm is a great challenge for the materials community. In conjunction with Transmission Electron Microscopy (TEM) and Electron-Probe Micro-Analysis (EPMA), we took advantage of a recent technology, Tri-Dimensional (3D) Atom Probe Tomography (APT) to investigate the variations of the chemical composition in sub-10-nm oxide nanoparticles, grown in silicate glass through heat treatments, at their early stages of nucleation. We provide here a comprehensive set of experimental data obtained from direct measurements of the concentration for P, Mg, Ge and Er within amorphous dielectric nanoparticles (DNP) of radii ranging from 1nm to 10nm. Most importantly, we report on the first observation of a plateau at the early stage of nucleation followed by an increase of the concentration of Mg and Pwith the size of the DNPs. We also demonstrate that the environment of erbium ions embedded in DNP changes with the size of the particles. These results have a profound impact on our understanding of amorphous phase separation mechanisms as well as spectroscopic properties of the luminescent ions and the design of (DNPs)-doped materials

quantification by epma of glass for nuclear application

International audienceThe confinement of high-level radioactive waste from spent nuclear fuel reprocessing is a key issue in the nuclear fuel cycle. In France, waste storage concept is based on four containment barriers including respectively glass matrix for radioactive waste immobilization, a primary stainless steel canister, a thick carbon steel overpack and finally a host rock. Numerous researches are carried out on nuclear glass to improve the properties of the confinement material. Depending on glass composition and process parameters crystals can appear in the matrix (Fig. 1). The characterization of these phases (range of micrometer size) and of the glass surrounding them is of great importance for a proper understanding of the glass properties and its long term performance. The composition of these phases can be characterized by means of electron microprobe (CAMECA SX 100) with a standard resolution electron beam. In order to improve the quantification of such small dimension inclusions, the use of FEG-EPMA CAMECA SX FiveFE has been tested to determine their chemical composition which is well adapted to micrometer range analysis. The improved analytical resolution obtained with the FEG-EPMA made it possible to optimize the analysis of the micro particles, and to determine their chemical composition. The nature of the crystal phases was confirmed by EBSD electronic diffraction analysis coupled with SEM and approved the crystalline phases of apatite and cerianite measured by EPMA. To study in a more precise way the glass matrix near crystals, thin lamellas were prepared by ionic cut by FIB (Fig. 2). A microstructural analysis by TEM was performed to characterize the glass matrix and the inclusions and the chemical composition was settled by EDS quantification. This thin lamella were analyzed by EPMA in transmission with the microprobe CAMECA SX 100 to get a more complete analysis of elements, including especially some light elements such as Boron. The results of TEM EDS and EPMA analyses in transmission are self-consistent and confirm a peculiar enrichment in Zr of the glass matrix near crystals

Nouveaux regards sur Dominique Rolin

Francofonia consacre sa 68e livraison \ue0 la romanci\ue8re belgo-fran\ue7aise Dominique Rolin, d\ue9c\ue9d\ue9e en 2012 \ue0 l\u2019\ue2ge de 99 ans. En d\ue9pit (ou \ue0 cause ?) de sa tr\ue8s vaste production (40 livres publi\ue9s), les travaux critiques sur Rolin sont plut\uf4t rares. Dans ce num\ue9ro de Francofonia, diff\ue9rents auteurs essaient de poser un regard nouveau sur son \u153uvre

Direct Observations of Compositional Changes at the Early Stages of Er-doped Phase Separated Nanoparticles in Silicate Glasses

International audienc

Design and optimization of new simulated moving bed plants

The simulated moving bed (SMB) technology has attracted considerable attention for its efficiency as a chromatographic adsorptive separation. It has been increasingly applied to the separation of binary mixtures with low separation factors, namely to separate isomers. Although quite a vast amount of information has been published concerning the simulation and design of operating conditions of existing SMB plants, fewer works have addressed the question of design and optimisation of geometric parameters and operating conditions of a new adsorber, especially when mass transfer resistances are significant. The present work extends an algorithm developed elsewhere to design SMB equipment and optimize its operating conditions and applies it to the case of fructose-glucose separation using a cation-exchange resin as stationary phase in order to obtain nearly pure fructose in the extract and glucose in the raffinate. The constraints were set as 99% purity for both products. The objective function was chosen to be the adsorbent productivity. The algorithm attempted to find the minimum column lengths for increasing throughputs, which met the required purity constraint. Then, the best construction parameters and operating conditions were chosen as those for which the adsorbent productivity was maximum. The effects of the safety margins applied on the velocity ratios in sections 1 and 4 were examined and a heuristic rule for optimum eluent flowrate was derived. The effect of the purity requirements was also investigated. Finally, the calculated optimal operating points, in terms of flowrate ratios in SMB sections 2 and 3, were analysed in the frame of the equilibrium theory. Sound coherence was verified, which confirmed the accuracy and adequacy of the extended algorithm for the design and optimisation of a SMB adsorber with strong mass transfer effects