Nano-structured carbon obtained by chlorination of NbC

New carbon materials have been synthesized by chlorinating niobium carbide at different temperatures. During the reaction, the volatile niobium chloride, mainly NbCl5, is formed and eliminated leaving the carbon in the shape of spherical particles. TEM examination of the remaining particles revealed that at 400 degrees C and 700 degrees C they are composed of a NbC core with an amorphous carbon shell outside. The NbC cores are very small (similar to 20 nm) at 700 degrees C and they are not observed at 900 degrees C. Carbon particles without the NbC core present a more ordered structure composed of concentric wavy graphene layers. This structure seems intermediate between carbon onions and carbon blacks. The 900 degrees C sample presents a very high BET surface area (1292 m(2) g(-1)) and the lower temperature samples exhibit a hysteresis phenomenon that can be attributed to the existence of large pores in the interspace between the NbC core and the carbon shell. (c) 2005 Elsevier Ltd. All rights reserved.