Hydrothermal synthesis of graphite tubes using Ni catalyst

Abstract

While many forms of carbon nanotubes and filamentous carbon have been reported, 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 diameter which were synthesized hydrothermally in the C–H–O–Ni system at 100 MPa and 730–800°C by first establishing a post-pyrolysis C–H–O equilibrium followed by an increase in pressure during which time growth of graphitic carbon occurred. Depending on the size of the Ni catalyst particles, flake-like graphite or carbon tubules were formed. Tubes were also synthesized 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 tube walls is demonstrated by straight and perfect lattice fringing in the tube walls and electron diffraction spot patterns free of diffuse amorphous rings. Raman spectral evidence shows high similarity to the spectra obtained from high purity natural graphite. The high integrity of hydrothermal nanotubes 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.