Preparation of CNT-ceramic composites

Jiang and Gao22 reported the preparation of MWCNT-TiN and MWCNT-Fe2N composites using CCVD CNTs oxidized in nitric acid (140°C, 24 h). A mixed solution of Ti(OC4H9)4 and ethanol was added to an aqueous suspension of CNTs. The dried precursor was calcinated in N2 (450°C, 2 h) 

The third way to prepare CNT-ceramic composite powders is via the synthesis of CNT by a CCVD process, in situ in the ceramic powder. A ceramic powder which contains catalytic metal particles at a nanometric size, appropriate to the formation of CNTs, is treated at a high temperature (600-1100°C), in an atmosphere containing a hydrocarbon or CO. In the method reported in 1997 by the present authors,27 iron nanoparticles are generated in the reactor itself, at a high temperature ( 800°C), by the selective reduction in H2/CH4 (18% CH4) of an a-Al203 based oxide solid solution  

Many clusters of Fe atoms are formed both inside and at the surface of each alumina grain and progressively grow. When the Fe nanoparticles located at the surface of the alumina grains reach a size around 0.7-2 nm, they immediately catalyze the decomposition of CH4 and the nucleation and growth of CNTs of very small diameter  

The obtained CNT-Fe-Al203 powder is composed of clean isolated CNTs and small-diameter bundles of CNTs, surrounding all the oxide grains as a web. SEM and HRTEM studies have shown that most CNTs are SWCNTs or DWCNTs (80%), with only a small proportion of three- to six-walled CNTs, and have external diameters between 0.7 and 5 nm. The method has been extended to MgAl204 (Fig. 12.3) and MgO based powders, using Mg(i A.)MxAl204 or Mg,, M/) (M = Co, Fe or Ni) as starting materials.28,29 The products which were used to prepare dense composites were CNT-Fe- 

Another way to prepare catalytic metal nanoparticles in a ceramic powder is to impregnate the powder by a solution of a precursor salt. Weidenkaff et ai.32 impregnated a substituted L11C0O3 (Ln = Er, La) powder with a citrate, 

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