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Few-layer graphene (FLG) sheets with sizes exceeding several micrometers have been synthesized by exfoliation of expanded graphite in aqueous solution of ammonia under microwave irradiation, with an overall yield approaching 8 wt.%. Transmission electron microscopy (in bright-field and dark-field modes) together with electron diffraction patterns and atomic force microscopy confirmed that this graphene material consisted mostly of mono-, bi- or few-layer graphene (less than ten layers). The high degree of surface reduction was confirmed by X-ray photoelectron and infrared spectroscopies. In addition, the high stability of the FLG in the liquid medium facilitates the deposition of the graphene material onto several substrates via low-cost solution-phase processing techniques, opening the way to subsequent applications of the material.

C/C composites with improved mechanical strength were synthesized using a filler constituted by a carbon felt covered with catalytically grown carbon nanofibers (CNFs) and a carbonaceous matrix generated by the pyrolysis of a phenolic resin. First, the synthesis method of the filler allows the homogeneous deposition and anchorage of CNFs on the host microfilaments at a rapid densification rate. Carbon nanofibers grown this way lead to the formation of numerous micro- and nanobridges between the microfilaments, conferring a significant improvement of the mechanical resistance of the CNF/C system allowing one to tailor its dimensions and shape. Thus, further fabrication of C/C composites can be achieved: the CNF/microfilament structure was infiltrated with a phenolic resin and carbonized at 650 °C to generate a carbonaceous matrix by thermal decomposition. Similar experiments on the microfilaments carried out at the same synthesis time, without catalyst and at higher reaction temperatures led to the deposition of a pyrolytic carbon sheath and to poor mechanical enhancements. This clearly indicates the advantage of using CNF growth as an efficient densification process before infiltration. Such C/C composites exhibit high-quality bonding between the two carbon phases, the matrix and the CNF/microfilament filler, via the formation of a considerable amount of CNF interphase.

A self-supported carbon nanotubes (SSCNTs) with nanoscopic properties and controlled macroscopic shape were synthesized by a Chemical Vapour Deposition (CVD) method using a mixture of ethane/hydrogen and a Fe/Al 2 O 3 growth catalyst. The SSCTs were obtained in the form of beads of 6–8 mm in diameter, with a hollow core structure and a high and fully accessible specific surface area, i.e. 140–180 m 2 .g − 1 . In addition, the macroscopic shape and open structure of these SSCNTs allow them to be efficiently used as catalyst support either in a gas-phase or in a liquid-phase configuration.

Silicon carbide is a ceramic material that has been widely studied because of its potential applications, ranging from electronics to heterogeneous catalysis. Recently, a new type of SiC materials with a medium specific surface area and thermal conductivity, called β-SiC, has attracted overgrowing interest as a new class of catalyst support in several catalytic reactions. A primary electron tomography study, performed in usual mode, has revealed a dual surface structure defined by two types of porosities made of networks of connected channels with sizes larger than 50 nm and ink-bottled pores with sizes spanning from 4 to 50 nm. Depending on the solvent nature, metal nanoparticles could be selectively deposited inside one of the two porosities, a fact that illustrates a selective wetting titration of the two types of surfaces by different liquids. The explaining hypothesis that has been put forward was that this selectivity against solvents is related to the pore surface oxidation degree of the two types of pores. A new technique of analytical electron tomography, where the series of projections used to reconstruct the volume of an object is recorded in energy filtered mode (EFTEM), has been implemented to map the pore oxidation state and to correlate it with the morphology and the accessibility of the porous network. Applied, for the first time, at a nanoscale resolution, this technique allowed us to obtain 3D elemental maps of different elements present in the analysed porous grains, in particular oxygen; we found thus that the interconnected channel pores are more rapidly oxidized than the ink-bottled ones. Alternatively, our study highlights the great interest of this method that opens the way for obtaining precise information on the chemical composition of a 3D surface at a nanometer scale.

International audience; Magnetic nanowires of CoFe 2O4 were casted inside the channel of multiwall carbon nanotubes by mild chemical synthesis. A detailed investigation of these nanowires was performed using mainly the electron tomography technique; this study provides a complete characterization of their microstructure in terms of the spatial organization and the size distribution of individual particles forming the nanowire as well as its residual porosity. In particular, we have shown that the size of the CoFe 2O4 monocrystalline particles is closely dependent on the location of the particle within the nanotube, i.e., small particles close to the tube tip (5 nm) and bigger particles inside the tube channel (15 nm). As the theoretical critical size for superparamagnetic relaxation in CoFe 2O4 is estimated within the range of 4-9 nm, the size distribution obtained by 3D-TEM agrees with the Mossbauer study that suggests the presence of two different magnetic components inside the nanowire. We have shown also that, by using this preparation method and for this internal diameter of nanotube, the CoFe 2O4 nanowire exhibits a continuous structure along the tube, has a residual porosity of 38%, and can fill the tube at only 50%, parameters which influence in a significant manner the magnetic behavior of this system.

The location of palladium nanoparticles on and inside the multiwalled carbon nanotubes channel is presented for the first time using electron tomography (3D TEM). The palladium salt precursor was rapidly sucked inside the nanotube channel by means of capillarity that is favored by the hydrophilic character of the tube wall after acidic treatment at low temperature. Statistical analysis indicates that the palladium particles were well dispersed and the palladium particle size was relatively homogeneous, ranging from 3 to 4 nm regardless of their location within the nanotube, within the resolution limit of the technique for our experimental conditions, i.e., about 2 nm. Three-dimensional TEM analysis also revealed that introduction of foreign elements inside the tube channel is strongly influenced by the diameter of the tube inner channel, i.e., easy filling seems to occur with a tube channelor=30 nm , whereas with tubes having a smaller channel (15 nm), almost no filling by capillarity occurred leading to the deposition of the metal particles only on the outer wall of the tube.

Des composites à base de carbone présentant une tenue mécanique élevée et de faibles masses volumiques peuvent être élaborés par densification SPS (Spark Plasma Sintering). Ces composites sont réalisés en deux étapes : un précurseur C/C est synthétisé par croissance catalytique CVD de nanofibres de carbone (NFCs) sur une préforme de carbone (feutre ou tissu de graphite), puis le composite obtenu est soumis à un traitement de densification par SPS (frittage à 1750 ◦C sous pression de plusieurs dizaines de kN). La réaction CVD utilise des nanoparticules de métaux de transition comme catalyseurs et de l’éthane (C2H6) comme source de carbone. Cette voie de synthèse permet de conserver la mise en forme macroscopique et de rigidifier la structure du précurseur par le biais des nombreuses jonctions créées pendant la formation des NFCs. Une préforme composite C/C est ainsi obtenue et découpée en pastilles pour subir le traitement SPS. Le frittage peut être précédé d’une étape d’infiltration de résine phénolique afin de réaliser des composites C/C/C : cette étape permet de densifier les composites en adjoignant une matrice de carbone par la décomposition de la résine, ce qui favorise la cohésion de l’ensemble. La présence d’éléments de taille nanoscopique permet d’un côté d’améliorer la résistance mécanique en augmentant le transfert de charge, et d’un autre côté de faciliter le frittage et l’infiltration de la résine dans le composite.