Origin of giant graphite balls including in the carbon nanohorns prepared by pulsed arc-discharge and their removal method

Abstract

Large sized spherical graphitic particles with the diameter as large as several micrometers, so called giant graphite balls (GGBs), are more or less included in the sample of carbon nanohorns (CNHs) which are prepared by the method of pulsed arc-discharge or laser ablation. For the use of CNHs in the application, it is needed to decrease such impurity from the sample. In order to find a way to decrease the GGBs content, we investigate the origin of GGBs and find a simple method for increasing the sample purity. The origin of GGBs is the exfoliated materials from the carbon rod, and such an exfoliation can be nearly avoided by the preheat treatment of the carbon rod up to 1000°C just in advance of the arc vaporization. According to this preheat, the quantity of GGBs in the sample can be reduced from 30 to 0.01 % (100 ppm) by weight. In addition, it was found that the simple two-staged purification which is combined with the centrifugation and filtration effectively works for removing such a small quantity of GGBs.