Preparation And Properties Of CNTs-ceramic Composites

Ceramics are widely applied in aerospace, automobile industries and daily life due to their superior hardness, abrasive resistance, chemical inertness and mechanical strength. However, the toughness problem of ceramics hinders the applications in structural areas. Adding carbon nanotubes (CNTs) into ceramics matrix will be an effective method to increase the toughness of ceramics owing to excellent mechanical, electrical and thermal properties of CNTs.CNTs were modified by the mixed acid to attach with oxygenic functional groups, which attracted positive Al2O3 particles due to the attractive electrostatic forces. As a result, the CNTs were homogeneously dispersed in the matrix and the interfacial compatibility between CNTs and ceramic matrix was improved. CNTS-Al2O3 composites have been fabricated by hot-pressing method. Mechanical measurements reveal that, compared with the pure alumina, adding 1.5wt.% CNTs into the Al2O3 matrix results in 38% and 35% simultaneous increases in flexure strength(403.6MPa) and fracture toughness (4.21MPa·m1/2), respectively. Continuing to increase CNTs contents, the mechanical properties of composites drop due to CNTs aggregation.CNTs-AlN composites have been prepared by a hot-pressing method. Raising the sintering temperature, the properties of CNTs-AlN composites increase. Compared with the pure aluminum nitride, when sintered at 1750℃ for 1h, the fracture toughness of AlN-1wt.%CNTs composites is 3.89 MPa · m1/2, which shows 16% increase in fracture toughness. Continuing to increase CNTs contents, the mechanical properties of composites drop.The microstructural observations of CNTs-ceramic composites show that the tight bonding between CNTs and ceramic matrix, the pullout of CNTs from matrix, CNTs bridging and crack deflection lead to the improvement of the fracture toughness.