Figure 2: Wet processes for CNT-based TCFs fabrication [Sandeep et al., 2018]

Arc discharge

Electric current is used as the energy source in arc discharge synthesis of CNTs. The method uses temperatures usually above 1700oC and obtains CNT growth with fewer structural defects. The arc-discharge method was the first method by which CNTs were produced. The setup consist of a furnace, graphite electrodes, a stainless steel vacuum chamber, a water cooled trap and high voltage power supply. The two graphite electrodes are placed in a case filled with inert gas at low pressure and subject to arc vaporization, end-to-end with a slim clearance of almost 1 mm. A DC current of 50-100A at a potential difference of almost 20V will achieve this high-temperature arc discharge. The arc usually exceeds 3000oC which helps to vaporize the plasma in carbon atoms. When anode material is used for the doping of metal catalyst-graphite rods, soot-like SWCNTs are achieved. Researches have been done by varying the current source to AC and bipolar sources delivering currents at various peak frequencies. It is found that the soot production rate (SWCNT production rate) increases with increase in current supplied. However, the quality of SWCNTs almost remains the same. MWCNTs are found deep inside cathode deposits and on the top surface. Researches have proven that a hydrogen arc obtained by using a gas that contains hydrogen in place of inert gas is more effective due to its high temperature and high activity.