The percolation of carbon nanotubes (CNT) in an electrical insulating ceramic is studied for the first time. The in situ synthesis of the CNT (0.2-25 vol%) by a CCVD route allows to achieve their homogeneous distribution in the spinel matrix. Up to 11 vol% CNT, the DC electrical conductivity (rÞ is well fitted by the scaling law of the percolation theory r ¼ kðp À p c Þ t with a low percolation threshold p c ¼ 0:64 vol%. At the threshold, r jumps over seven order of magnitude (from 10 À10 to 0.0040 S cm À1) and then reaches a maximum at 8.5 S cm À1. The results are discussed in relation with the characteristics of the CNT, their damaging during the hot-pressing at 1300°C and the microstructure of the composites. CNT-ceramic composites become attractive materials not only for their enhanced mechanical properties, but also for the possibility to tailor the electrical conductivity through the CNT content.

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International audienceThe synthesis of carbon nanotubes from an oxide solid solution foam is reported for the first time. A foam of Mg0.9Co0.1Al2O4 solid solution is prepared by the gelcasting-foam method using notably mono- and di-functional acrylate monomers. Using a surfactant in the alkylpolyglucoside family allows to prevent structure changes in the foam before the onset of polymerisation. The wet ceramic foam is dried in air, producing a foam with an open porosity. Total porosity is equal to about 98% and the diameter of the pores is in the range 25-300 mm, about 90% being smaller than 200 mm. The Mg0.9Co0.1Al2O4 foam is reduced in H2-CH4 atmosphere, giving rise to a CNTs-Co MgAl2O4 composite foam. Using the foam instead of the corresponding powder allows a fourfold increase in the production of carbon nanotubes, more than 95% of which have only 1 (70%) or 2 walls