Carbon Nanotubes from Oxide Solid Solution: A Way to Composite Powders, Composite Materials and Isolated Nanotubes

Conclusions

We have demonstrated the ability to prepare C_NTS-metal-oxide powders that contain enormous amounts of C_NTs, most of which are SWNTs or small MWNTs with internal and external diameters in the 0.5-5 nm range. The results confirm that only the smallest metal particles (smaller than ca. 6 nm) may catalyze the formation of SWNTs and small MWNTs and underline the need that the catalyst is in the form of such nanoparticles at a temperature which is usually above 800°C in the catalysis methods. In this way, the reduction of oxide solid solutions allows to produce metal particles at a temperature which is high enough for the hydrocarbon gas to somehow interact with them so as to form the nanotubes prior to any exaggerate particle growth.

In the case of MgO-based materials, the oxide matrix and part of the Co catalyst can be dissolved by a combination of air oxidation and mild acid treatment that does not damage the C_NTS. The proposed method could be a real improvement in the low-cost, large-scale synthesis of C_NTS.

Dense materials can be prepared by hot-pressing the composite powders. These ceramic-matrix composites have acceptable mechanical properties and interestingly display an electrical conductivity owing to the dispersion of a network of C_NTS bundles, which could lead to some applications.