Synthesis of diamond from carbon nanotubes under high pressure and high temperature

The investigation on elemental carbon has long been of nanotubes to diamond at 4.5 GPa and 13008C using a considerable interest because of its great importance in six-anvil high pressure apparatus with the existence of both science and technology. One of the most outstanding NiMnCo catalyst. The detailed characterization conducted achievements which occurred in carbon science was the shows that carbon nanotubes transform to quasi-spherical synthesis of diamond under high-pressure–high-temperaonion-like structures first and then to diamond crystals. It ture (HPHT) conditions [1,2]. Now, man-made diamond is is different from the phase transformation behavior of commercially available and plays an indispensable role in graphite to diamond under high pressure and high temperamodern industry for abrasives, tool coatings, microelecture conditions. tronics, optics and other applications. Another important For the experiments presented here, multiwalled carbon advance in carbon science was the discovery of fullerenes nanotubes with diameters of 20–50 nm produced by and carbon nanotubes [3,4]. These novel carbon phases catalytic chemical vapor deposition (CCVD) were used as have gained high visibility because they have the potential starting material (Fig. 1). A 63600 ton six-anvil high to exhibit unique structural variety and extraordinary pressure apparatus with an electric current heating device optical, mechanical, and electronic properties [5]. Recentwas employed for the high pressure experiments. In each ly, a number of studies relating to the behaviors of experiment, about 50 mg of carbon nanotubes placed fullerenes under high pressure have been reported which between two NiMnCo alloy flakes were put into the high were focused on probing the cage structure stability and pressure cavity and a cubic body with a cylinder sample looking for new novel structures [6–8]. Moreover, it has chamber of pyrophyllite was used as pressure seal and been demonstrated that fullerenes can convert to diamond transmitting medium. Before and after high pressure runs, by applying high pressure at either room temperature [9] or the samples were monitored by transmission electron high temperature [10]. However, only a few works have microscopy (TEM; H8100), scanning electron microscopy been so far focused on the structural stability and phase (SEM; S-4200) and Raman spectroscopy (T64000). Hightransformation of carbon nanotubes at high pressure resolution transmission electron microscopy (HRTEM) [11,12]. As we know, the transformation of graphite or investigations were carried out using a JEOL2010 micrographite-like materials to diamond is of great technological scope operating at 200 kV. importance and therefore remains an exciting field in both Fig. 1 shows the representative morphology of carbon experimental and theoretical studies. Therefore, a detailed nanotubes in the starting material. The carbon nanotubes study of the behaviors of carbon nanotubes at high exhibit typical concentric graphitic shell structure with a pressure is very necessary for further understanding their hollow core. The diameters of most carbon nanotubes in structures and properties and comparing with that of our sample are around 30–40 nm uniformly. No other graphite. forms of carbon can be detected in the sample by TEM In the present work we report the conversion of carbon study.