Jin et al. Nanoscale Research Letters 2011, 6:515 http://www.nanoscalereslett.com/content/6/1/515 small sizes, and the TiCx stoichiometry formed at the combustion stage is low. Accordingly, the TiCx growth shape is octahedron. Frankly speaking, spending a great amount of metal (Al/Cu/Fe) to only synthesize the TiCx nanoparticles is really uneconomical. Nevertheless, considering that the TiCx particles reinforced metal matrix composites can be fabricated conveniently through following a pressing or forging treatment after the SHS [24], the real significance of this research is to provide a perspective to in situ synthesize the nano-TiCx particle reinforced composites more conveniently by using CNT. As known, the fabrica- tion of ceramic nanoparticles reinforced metal matrix is an important development direction for the development of composites, and many papers have been published on this issue from 2000. In 99% of these works, the nanopar- ticles were introduced into the metal matrix through external addition. In these methods, the mixing of nano- sized particles in metal liquid is usually lengthy, expen- sive, and energy consuming. In fact, in contrast with the external addition methods, the method with nanoparti- cles in situ synthesis has the advantages of a more homo- geneous distribution of the nanoparticles, clearer interface between nanoparticles and matrix, and lower chances to introduce impurity. However, when metal matrix is with high content (≥50 wt.%), the TiCx forma- tion reaction tends to be incomplete or even cannot be ignited by using traditional C sources such as C black or graphite. To solve this key question in the SHS, we used CNT as the C source in this paper. The results indicate that the samples with more than 70 wt.% metals can still be ignited easily because of the high activity of the CNT. In fact, in our following study, by using CNT as C source, we have successfully in situ synthesized the TiCx nano- particles in 97 wt.% Cu matrix, and the composite was fabricated conveniently by the SHS and a subsequent pressing or forging process. Moreover, our results sug- gest that other nano-sized transition metal carbides (such as SiC, ZrC, and NbC) and the corresponding reinforced composites could also be synthesized with using the high chemical activity of the CNT. Conclusions The using of CNT increases the reactivity in the Me (Cu, Al, and Fe)-Ti-CNT systems and makes SHS reac- tion more easily ignited. The sizes of the synthesized TiCx particles decrease with the increase in the Me con- tent. 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, respectively. The shapes of the nano-TiCx particles formed in the Cu- and Al-Ti-CNT systems are mainly octahedral, while those formed in the Fe-Ti-CNT system are mainly cubic Page 6 of 7 and sphere-like. This shape variation of the TiCx formed in different kinds of the Me liquid environment is believed to relate to the different stoichiometries of the TiCx formed during the combustion stage in these systems. Acknowledgements This work is supported by the National Natural Science Foundation of China (No. 51171071), National Basic Research Program of China (973 Program) (No. 2012CB619600), NNSFC (No. 50971065 and No. 50531030), the Project 985-High Performance Materials of Jilin University and Project 20092008 supported by Graduate Innovation Fund of Jilin University. Author details 1Key Laboratory of Automobile Materials, Ministry of Education, People’s Republic of China 2Department of Materials Science and Engineering, Jilin University, No. 5988 Renmin Street, Changchun 130025, People’s Republic of China Authors’ contributions All the authors contributed to writing of the manuscript. SBJ carried out the experiments under the instruction of QCJ. Competing interests The authors declare that they have no competing interests. Received: 1 June 2011 Accepted: 31 August 2011 Published: 31 August 2011 References 1. Kang YC, Chan SL: Tensile properties of nanometric Al2O3 particulate- reinforced aluminum matrix composites. Mater Chem Phys 2004, 85:438-443. 2. Liu YQ, Cong HT, Wang W, Sun CH, Cheng HM: AlN nanoparticle- reinforced nanocrystalline Al matrix composites: fabrication and mechanical properties. Mater Sci Eng A 2009, 505:151-156. 3. 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