Hydrothermal synthesis of graphite tubes using Ni catalyst

While many forms of carbon nanotubes and filamentous carbon have been repor ted, both a large inside diameter and highly graphitic wall structure have not been created. This paper describes such tubes from 70 to 1300 nm in dia meter which were synthesized hydrothermally in the C-H-O-Ni system at 100 M Pa and 730-800 degreesC by first establishing a post-pyrolysis C-H-O equili brium followed by an increase in pressure during which time growth of graph itic carbon occurred. Depending on the size of the Ni catalyst particles, f lake-like graphite or carbon tubules were formed. Tubes were also synthesiz ed without water, i.e., in the C-H-Ni system, but these tubes had multiple internal caps while those produced with water present had very few internal obstructions and a large inside diameter. The exceptional quality of the t ube walls is demonstrated by straight and perfect lattice fringing in the t ube walls and electron diffraction spot patterns free of diffuse amorphous rings. Raman spectral evidence shows high similarity to the spectra obtaine d from high purity natural graphite. The high integrity of hydrothermal nan otubes is demonstrated by the existence of liquid inclusions trapped inside the tubes during synthesis. The properties of hydrothermal graphite tubes suggest their use in nano-fluidic devices and as lightweight reinforcement for composites. (C) 2001 Elsevier Science Ltd. All rights reserved.