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Carbon onion production by arc discharge in water

<Arc discharge in water is a simple method to fabricate high-quality nanoparticles including spherical carbon onions and elongated fullerene-like nanoparticles similar to nanotubes in large quantities without the use of vacuum equipment. The nanoparticles are obtained in the form of floating powder on the water surface following the arc discharge between two graphite electrodes submerged in water.
Carbon onions can only be produced in minute quantities by various methods such as electron beam irradiation of amorphous carbon using a transmission electron microscope, annealing nanodiamonds, implantation of high voltage carbon ions in silver or copper, radio frequency plasma enhanced chemical vapor deposition and shock wave treatment of carbon soot. But an economical method to produce carbon onions in bulk quantities is by using an arc in water.
The widely used methods to fabricate carbon nanomaterials suffer in bulk production from not only the high investment and running costs of the vacuum equipment but also from low yield of the desired products unwanted contaminants, time consuming and costly purification steps must be carried out to successfully produce nanotubes. Higher purity high concentration nanoonions can be obtained as floating powder on the water surface while the rest of the product emitted is found at the base of the water.
In this method, a direct current dc arc discharge was generated in de-ionized water between two carbon electrodes. The arc discharge in water was found to be stable. The plasma can also be seen to surround the anode. In addition, fine black powder emitted from the plasma ball region carbon plasma is generated by thermal evaporation of the anode and the powder floats on the water surface.
The floating powder shows two types of onion structure; well crystallized onion structure with well defined concentric shells which is promising material for gas storage and not so well crystallized onions along with elongated fullerene-like structures.

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