X-ray diffraction as a tool for the determination of the structure of double-walled carbon nanotube batches

The average structure of double-walled carbon nanotube DWCNT samples can be determined by x-ray diffraction XRD. We present a formalism that allows XRD patterns of DWCNTs to be simulated and we give researchers the tools needed to perform these calculations themselves. Simulations of XRD patterns within this formalism are compared to experimental data obtained on two different DWCNT samples, produced by chemical vapor deposition or by peapod conversion i.e., high-temperature peapod annealing. For each sample, we are able to determine structural aspects such as the number of walls, the diameter distribution of inner and outer tubes, the intertube spacing, and the bundled structure

Percolative superconductivity in La2CuO4.06 by lattice granularity patterns with scanning micro X-ray absorption near edge structure

The simplest cuprate superconductor La2CuO4+y with mobile oxygen interstitials exhibits a clear phase separation, but only recently a bulk multiscale structural phase separation has been observed by using scanning micro X-ray diffraction. Here we get further information on the structural phase separation, using local probe X-ray absorption near edge structure. The spatial distribution of superconducting units is a key parameter controlling percolative superconductivity in complex matter with dispersed superconducting units. These oxides form super-molecular architectures made of superconducting atomic monolayers intercalated by spacers. Oxygen interstitials enter into the rocksalt La2O2+y spacer layers forming oxygen interstitials rich puddles and poor puddles. Their spatial distribution has been determined by using scanning La L3-edge micro X-ray absorption near edge structure. Percolating networks of oxygen rich puddles are observed in different micrometer size portions of the crystals. Moreover, the complex surface resistivity shows two jumps associated to the onset of intra-puddle and inter-puddles percolative superconductivity. The similarity of oxygen doped La2CuO4+y, with the well established phase separation in iron selenide superconductors is also discussed.Comment: 9 pages, 6 figure

Systèmes unidimensionnels de fullerènes C60 et C70 confinés dans les nanotubes de carbone : transformations structurales et dynamique

This thesis in dedicated to the structural and dynamical properties of the one dimensional structures of C60 and C70 fullerenes, respectively spherical and ovoid, confined inside carbon nanotubes, as function of the temperature and the pressure. Peapods structures are studied by x rays diffraction and electron diffraction. Simulation of the experimental diffraction patterns allows characterizing the structural parameters of the carbon nanotubes (mean radius (0.7nm), distribution of radius), the filling rate of fullerenes inside carbon nanotube and the one dimensional lattice parameter of the fullerenes chains. According to the C70 peapods, the fullerene orientation as a function of the nanotube radius is studied and the critical nanotube diameter of the changing of orientations is determined. The structural evolutions of the fullerenes chains (thermal expansion, polymerization, and coalescence) as function of temperature and/or of pressure are studied and compared for the two kinds of fullerenes. Differences are observed according the polymerization under high pressure and high temperature. C60 fullerenes polymerize by [2+2] cyclo-addition inside carbon nanotubes but not the C70 ones. This result is explained by the confinement of the carbon nanotube. Structure of the double wall carbon nanotubes, synthesized by the fullerenes chains coalescence of C60 and C70 peapods at high temperature, seems to be independent of the kind of fullerenes. The inner radius is estimated to be about 0.36nm and the mechanism of the inner tube formation is discussed. Finally, dynamics of fullerene peapods are studied by inelastic neutron scattering. High orientational mobility of the C60 fullerenes is evidenced until relatively low temperature. This result is interpreted considering the strong one dimensional behavior of the fullerenes chains.Ce travail de thèse est consacré à l'étude des propriétés structurales et dynamiques, en fonction de la température et de la pression, des structures unidimensionnelles des fullerènes C60 et C70, respectivement de formes sphériques et ellipsoïdales, confinés dans les nanotubes de carbone. Ces nano-hybrides sont communément appelées peapods. La structure des peapods est étudiée à l'aide de la diffraction des rayons X et de la diffraction électronique. La simulation des diagrammes de diffraction permet de déterminer la structure des nanotubes de carbone (rayon moyen (0.7nm), distribution de rayons) ainsi que le taux de remplissage des nanotubes par les fullerènes et le paramètre de maille des chaînes de fullerènes. Dans le cas des peapods de C70, l'orientation des molécules en fonction du diamètre des nanotubes est analysée et la valeur du diamètre « critique » de changement d'orientation est déterminée. Les évolutions de la structure des chaînes de fullerènes (dilatation thermique, polymérisation, coalescence) en fonction de la température et/ou de la pression sont étudiées et comparées pour les deux sortes de fullerènes considérés. Des différences sont observées entre fullerènes C60 et C70 quant à la polymérisation à hautes pressions et températures. Les molécules de C60 polymérisent par cyclo-addition [2+2] dans les nanotubes, mais pas celles de C70, ce résultat étant expliqué par le confinement par le nanotube de carbone. La structure des nanotubes bifeuillets obtenus par la coalescence des chaînes de fullerènes des peapods C60 et C70 à très haute température semble indépendante de la nature des fullerènes. Le rayon moyen des nanotubes internes est estimé à 0.36 nm. Le mécanisme de formation du tube interne est discuté. Finalement la dynamique des peapods est étudiée par diffusion inélastique des neutrons. Une forte mobilité orientationnelle des fullerènes C60 est mise en évidence jusqu'à assez basses températures. Celle-ci est interprétée en considérant le caractère fortement unidimensionnel des chaînes de fullerènes

Systèmes unidimensionnels de fullerènes C60 et C70 confinés dans les nanotubes de carbone (transformations structurales et dynamique)

ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Orientation of C70 molecules in peapods as a function of the nanotube diameter

cited By 34International audienceEncapsulated C70 molecules packed in single-walled carbon nanotubes display different orientations depending on the nanotube radius. We present x-ray scattering data obtained on a powder of nanotubes filled with C70 molecules. Analytical expressions for calculating the diffraction diagram taking into account fullerene orientations are developed. The comparison between calculations and experiments allows us to conclude that the change from the lying to standing orientation-corresponding to the molecule long axis parallel and perpendicular to the tube axis, respectively-takes place when nanotubes reach a diameter of about 1.42 nm. Energy calculations are performed using a Lennard-Jones (6-12) potential, leading to a calculated reorientation diameter in good agreement with that determined experimentally

Bone quality around bioactive silica-based coated stainless steel implants: analysis by Micro-Raman, XRF and XAS techniques

Surface modification of surgical stainless steel implants by sol gel coatings has been proposed as a tool to generate a surface that besides being protective could also create a ‘‘bioactive’’ interface to generate a natural bonding between the metal surface and the existing bone. The aim of this work is to analyze the quality and bone formation around hybrid bioactive coatings containing glass-ceramic particles, made by sol–gel process on 316L stainless steel used as permanent implant in terms of mineralization, calcium content and bone maturity with micro Raman, X-ray microfluorescence and X-ray absorption techniques. Uncoated implants seem to generate a thin bone layer at the beginning of osseointegration process and then this layer being separated from the surface with time. The hybrid coatings without glass-ceramic particles generate new bone around implants, with high concentration of Ca and P at the implant/tissue interface. This fact seems to be related with the presence of silica nanoparticles in the layer. The addition of bioactive particles promotes and enhances the bone quality with a homogeneous Ca and P content and a low rate of beta carbonate substitution and crystallinity, similar to young and mechanical resistant bone.Fil: Ballarre, Josefina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Universidad Nacional de Mar del Plata; Argentina;Fil: Desimone, Paula Mariela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Universidad Nacional de Mar del Plata; Argentina;Fil: Chorro, Matthieu. Synchrotron SOLEIL. LUCIA Beamline; Francia;Fil: Baca, Matías. Hospital Interzonal General de Agudos ‘‘Oscar Alende’’. Traumatología y Ortopedia; Argentina;Fil: Orellano, Juan Carlos. Hospital Interzonal General de Agudos ‘‘Oscar Alende’’. Traumatología y Ortopedia; Argentina;Fil: Cere, Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Universidad Nacional de Mar del Plata; Argentina

Alteration of nuclear glass in contact with iron and claystone at 90 °C under anoxic conditions: Characterization of the alteration products after two years of interaction

The present study investigates the alteration of a fractured glass block in contact with iron and Callovo-Oxfordian claystone at 90 °C under anoxic and water-saturated conditions. The alteration rates and the nature of glass alteration products at the different compact interfaces (glass-clay, glass-iron) and in cracks were assessed by solution chemistry and microscopic-scale techniques (scanning electron microscopy coupled with energy-dispersive X-ray microscopy, microRaman spectroscopy, and X-ray absorption fine structure spectroscopy). A significant but modest (two-fold) increase in glass alteration in contact with steel was observed, leading to an average alteration rate over the experiment of about 0.007–0.014 g/m2/d. This rate is significantly lower than forward rate r0 in clay-equilibrated groundwater (1.7 g/m2/d), indicating that a decrease of the alteration rate was not hindered by the steel presence. The corrosion–alteration interface was made up of successive layers of corrosion products in contact with iron, a layer of Fe silicates, and an altered glass layer enriched in Fe. Characterization of the glass block in direct contact with claystone revealed that the thickness of altered glass was much more important than at the glass-iron interface. The altered glass layer in contact with clay was slightly enriched in Fe and Mg, and depleted in alkali cations. Altered glass layers in cracks were usually limited to fringes thinner than 2 μm, with a thickness decreasing from the crack mouth, indicating that alteration is controlled by transport in the cracks. The fractures were partially filled with calcite and lanthanide hydroxocarbonate precipitates. These results contribute to the understanding of nuclear vitrified waste-iron-corrosion products interactions in a deep geological repository

Corrosion of metal iron in contact with anoxic clay at 90 degrees C: Characterization of the corrosion products after two years of interaction

International audienceChemical and mineralogical properties of solids formed upon free corrosion of two iron probes (one massive iron rod, and one model overpack made by two pipes covering the ends of a glass rod) in saturated clay rock (Callovo-Oxfordian formation, East of Paris Basin, France) at 90 degrees C over two years were investigated by microscopic and spectroscopic techniques (X-ray tomography, scanning electron microscopy coupled with energy-dispersive X-ray analysis, Raman microspectroscopy, micro-X-ray diffraction, and micro-X-ray Absorption Fine Structure spectroscopy). The corrosion rate of the massive rod was monitored in situ by electrochemical impedance spectrometry, and found to decrease from about 90 mu m/year during the first month of reaction, to less than 1 mu m/year after two years. X-ray tomography revealed the presence of several fractures suggesting the presence of preferential flow and diffusion pathways along the iron samples. Microscopic observations revealed similar corrosion interfaces for both samples. Corrosion heterogeneously affected the interface, with damaged thickness from similar to 0 to 80 mu m. In extensively damaged areas, an inner discontinuous layer of magnetite in contact with metal, an intermediate chukanovite (Fe2CO3(OH)(2)) layer (only when magnetite is present, and only for the overpack), and an outer layer of poorly ordered Fe phyllosilicate were observed. In areas with little damage, only the Fe-silicate solids are observed. The clay transformation layer is predominantly made of ankerite ((Fe,Ca,Mg)CO3) forming a massive unit near the trace of the original surface, and intermixed with clay minerals towards the bulk matrix. The average thickness of oxidized iron, as measured by the average of distances from the original to the final metal surface, was 13 +/- 1 and 15 +/- 1 mu m for the massive rod and the micro-overpack, respectively. The corresponding Fe amount is about twice the amount of Fe present in the corrosion products. Thus a significant Fe fraction migrated in the nearby clay, likely as Fe-(II), and could act as a significant buffer of the electrochemical potential

Discriminated structural behaviour of C60 and C70 peapods under extreme conditions

cited By 15International audienceWe studied structural changes in C60 and C70 peapods - i.e. C60 and C70 chains inserted inside single-walled carbon nanotubes - when submitted to high pressure and temperature conditions. X-ray diffraction experiments showed that while C60 molecules polymerize inside nanotubes at pressures and temperatures consistent with polymerization in bulk C60 phases, no polymerization is observed in C70 peapods, even at pressures and temperatures above the threshold for polymerization in bulk C70. Tubular confinement in the nanotube container prevents the monomers to rearrange in the way needed for polymerization. This result testifies for the strong influence of confinement on the behaviour of C70

Substantial Improvement of Nanotube Processability by Freeze-Drying

As-produced carbon nanotubes often contain a fraction of impurities such as metal catalysts, inorganic supports, and carbon by-products. These impurities can be partially removed by using acidic dissolution. The resulting nanotube materials have to be dried to form a powder. The processability of nanotubes subjected to regular (thermal vaporisation) drying is particularly difficult because capillary forces pack and stick the nanotubes irreversibly, which limits their dispersability in polymeric matrices or solvents. We show that this dramatic limitation can be circumvented by using freeze-drying instead of regular-drying during nanotube purification process. In this case, the nanotubes are trapped in frozen water which is then sublimated. As a result the final powder is significantly less compact and, more important, the nanotubes can be easily dispersed with no apparent aggregates, thereby greatly enhancing their processability, e.g., they can be used to make homogeneous composites and fibers. Results from coagulation spinning from water-based dispersions of regularly-dried and freeze-dried nanotubes are compared. We also show that freeze-dried materials, in contrast to regularly-dried materials, can be dissolved in organic polar solvents using alkali-doped nanotubes. High resolution TEM and XRD analysis demonstrate that the nanotube structure and quality are not affected at the nanoscale by freeze-drying treatments