Carbon nanotubes-ceramic composites

The use of carbon nanotubes (CNTs) as reinforcing elements in polymer-, metal- or ceramic-matrix composites is widely studied. However, the dispersion of the CNTs within the matrix is a critical step in the preparation of these composites. We have shown that a very homogeneous dispersion of the CNTs can be achieved by their synthesis in-situ inside an alumina-based powder. Our CCVD method produces single- and double-walled CNTs, individual or gathered in small bundles, forming a network surrounding the oxide grains. We have recently developed the synthesis of CNTs from oxides solid solution foams, prepared by the gelcasting-foam method. This preparation allows a four-fold increase in the amount of CNTs compared to the corresponding powder catalyst. Dense CNT-Fe-Al2O3 composites were prepared by hot-pressing as well as CNT-FeCo-MgAl2O4 and CNT-Co-MgO composites. Despite some pull-out during the fracture, a real reinforcement has not been evidenced. The CNTs provide to the composites an electrical conductivity between 0.2 and 4 S.cm^-1. We managed to align the CNTs within the ceramic by hot-extrusion, thus leading to an electrical conductivity anisotropy.