Jin et al. Nanoscale Research Letters 2011, 6:515 http://www.nanoscalereslett.com/content/6/1/515 to about 40 nm (Figure 2k). As we have suggested before, in the Al-Ti-C system, the TiCx particles grow through the deposition and lateral stacking of the growth units on the (111) surfaces [22,23]. In contrast to the growth mode of the TiCx particles in the Al-Ti-CNT system, the TiCx particles growing in the Fe-Ti-CNT system have a differ- ent growth mode, i.e., the lateral stack along the (100) sur- faces (Figure 2m). Under this mode, the TiCx particles should grow into the cubic shapes. However, because of the round turning of the (100) surfaces, most of the TiCx particles in the Fe-Ti-CNT system show the sphere-like shapes (Figure 2l). When the Fe content increases, the sizes of the TiCx particles decrease and the cubic character of the TiCx particles becomes more and more distinct (Figure 2h). In the sample with 70 wt.% Fe, there are many TiCx particles with regular cubic shapes and sizes of about 200 nm (Figure 2o). Increasing the Fe content to 80 wt.% further decreases the sizes of the TiCx particles to approxi- mately 70 nm, with primarily cubic shapes (Figure 2q). Figure 3a gives the mean sizes based on the statistic analysis of a hundred of TiCx particles in the FESEM images for the Me-Ti-CNT systems. The decrease in the TiCx particle sizes with the increase in the Me content is easy to understand because of the decreasing combus- tion temperature. When the Me content increases to 80 wt.% for Cu, Al, and Fe, the sizes of the TiCx particles decrease to about 62+−6308, 36+−8200, and 68+−5480 nm, Page 4 of 7 respectively. Furthermore, it can be noticed that in the above Me-Ti-CNT systems, the TiCx particles formed in the Al-Ti-CNT samples are the finest, which could be attributed to the lowest combustion temperatures. Nevertheless, the TiCx particles formed in the Fe-Ti- CNT samples have the largest sizes even though their combustion temperatures are quite lower than those formed in the Cu-Ti-CNT samples. This phenomenon is meaningful to the discussion in the following paragraphs on the mechanism of the TiCx shape variation with the different kinds of the Me addition. Figure 4 gives the TEM images of the TiCx particles formed in the samples with 80 wt.% Me. The diffraction rings from inner to outer in the inserted images in Figure 4a, b, c match the (111), (200), and (220) planes of the fcc TiC. As we have mentioned, the shapes of the TiCx parti- cles vary considerably in the different kinds of the Me incorporated Ti-CNT systems, i.e., the TiCx particles formed in the Cu- and Al-Ti-CNT systems are mainly with the octahedral shapes, while those formed in the Fe-Ti-CNT system are mainly with the cubic and sphere-like shapes. In our pervious paper [23], we have suggested that the growth shapes of the TiCx particles in the Al-Ti-C system should be directly related to their stoichiometry (x), i.e., when the stoichiometry is low, the TiCx (111) surfaces are the most stable and the growth shape is octahedron, while when the Figure 3 Mean sizes and the size distribution of the TiCx particles. (a) Mean sizes calculated based on the statistic analysis of a hundred of TiCx particles in the FESEM images. (b, c, d) Size distribution of the TiCx particles formed in the samples with 80 wt.% Cu, Al, and Fe, respectively.