Multi-walled carbon nanotube–Al2O3 composites: Covalent or non-covalent functionalization for mechanical reinforcement

Multi-walled carbon nanotube–Al2O3 composites are prepared using carbon nanotubes (8 walls, 1.5 μm long or 20 walls, 10 μm long) previously submitted to either covalent or non-covalent functionalization. High-energy sonication mixing, freeze-drying and spark plasma sintering lead to dense composites. The shorter CNTs are better dispersed than the longer ones, whatever the functionalization. Crack-bridging by CNTs is evidenced only when non-covalent functionalization is used and is correlated with a high fracture toughness for composites with the longer CNTs.