Preparation and properties of alumina composites modified by electric field-induced alignment of carbon nanotubes

Catalytic chemical vapor deposition (CVD) grown multi-walled carbon nanotubes (MWNTs) are treated with HF and deionized water and are then placed into alumina ceramics for improvement of both electrical conductivity and mechanical properties. In particular, an alternating current (ac) electric field is applied during the coagulation of the alumina slurries to induce the formation of aligned MWNT networks in the alumina matrix. The coagulated alumina matrix composite bases filled with 2 wt.% ac electric field-induced aligned MWNTs, are then sintered by hot pressing. The electrical conductivities of the prepared composites in directions both parallel and perpendicular to the MWNTs alignment, reach values of 6.2x10(-2)Sm(-1) and 6.8x10(-9)Sm(-1), respectively, compared with that of 4.5x10(-15)Sm(-1) for pristine alumina ceramics. The fracture toughness and flexing strengths of the prepared composites in the two directions are 4.66 +/- 0.66Pam(0.5), 390 +/- 70MPa and 3.65 +/- 0.46MPm(0.5), 191 +/- 5MPa, respectively, compared with 3.78 +/- 0.66MPm(0.5) and 302 +/- 50MPa for pristine alumina, 4.09 +/- 0.15MPam(0.5) and 334 +/- 60MPa for alumina filled with 2 wt.% MWNTs prepared without the effect of an electric field, respectively. The results indicate that the electric field leads to anisotropic behaviour. The properties of the composites along the direction of the MWNTs alignment are much improved with the addition of a small amount of CVD grown MWNTs.