Carbon nanotubes as part of composites: synthesis of powders and dense materials, microstructure and properties
Ch. Laurent, E. Flahaut, A. Peigney, A. RoussetCarbon nanotubes (CNTs)-metal-oxide powders are prepared by reduction in H2-CH4 of solid solutions between a non-reducible oxide (Al2O3, MgO, MgAl2O4) and transition metal (Fe, Co, Ni) oxide(s). The powders contain enormous amounts of SWNT and MWNT with a diameter in the 0.8 - 15 nm range, mostly arranged in small bundles up to 100 micrometer long forming a web-like network around the metal-oxide grains. The in-situ synthesis, which obviates a mechanical mixing, allows to obtain a very homogeneous dispersion of the CNTs. Dense composites are prepared by hot-pressing the nanocomposite powders. The fracture strength and fracture toughness are usually lower than those measured for metal-oxide composites, although electron microscopy observations seem to indicate that some fracture energy is absorbed by the CNTs. The network of CNTs also confers an electrical conducting character to the composite (s = 0.1 - 2 S/cm). In an attempt to align the CNTs, dense composites are prepared by hot-extrusion. A strong conduction anisotropy (by a factor of 107) is observed.
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