Carbon Nanotubes Synthesis via Arc Discharge with a Yttria Catalyst

A facile method is proposed to use a computer controlled Arc discharge gap between graphite electrodes together with an yttria-nickel catalyst to synthesize carbon nanotubes under an Ar-H2 gases mixture atmosphere by applying different DC currents and pressure. This produces carbon nanotubes with decreased diameters and increased length. XRD evidence indicated a shift toward higher crystallinity nanotubes. Yields of the CNTs after purification were also enhanced. 1. Introduction There has been intensive and increased research into the production of carbon nanotubes in recent years, as these novel nanoparticles with unique their properties are promising new advances and applications in a diverse number of areas, such as electronics, reinforced composite functionalized materials, and biomedical applications to name but a few. There are typically three major routes for such synthesis of carbon nanotubes: arc discharge, laser ablation, and chemical vapor deposition. The arc discharge technique involves an easy setup, and it is possible to obtain high yields [1]. This was the method originally used by Iijima [2] to produce multi-walled carbon nanotubes. The arc discharge is a very simple technique and is capable of massive production of both multiwalled CNTs and single-walled CNTs [3]. Arc discharge is a popular method for the production of SWNTs, and high quality SWNTs commonly collect around the cathode for easy harvesting after completion of the process [4]. The carbon arc technique for generating MWNTs appears very simple, but obtaining high yields of tubes can be difficult and requires careful control of the experimental conditions. In the most common laboratory scale production scheme, the direct current (DC) arc operates at a 1 to 4？mm wide gap between two graphite electrodes, which are typically between 6 and 12？mm in diameter and are vertically or horizontally installed in a water-cooled chamber filled with helium gas at subatmospheric pressure. Helium gas and DC current are important parameters to maximize the yield in the process [5]. Zhao et al. [6] used H2-Ar atmospheres comprising 60% Ar-40% H2 under a pressure of 266.6？mbar in their work, while Luo et al. [7] and Sun et al. [8] utilised high purity hydrogen at a pressure 799.9？mbar to optimize the yield in the process. Farhat et al. [9], Hai-yan et al. [10], and Sugai et al. [11] all successfully employed an Ar atmosphere to optimize the yield of the nanotubes produced. The position of the electrode axis does not noticeably affect the MWNT quality or quantity. The 50–250？mm long positive