Improvement in preventing metal contamination from an electrode used for generating microwave plasma in liquid

The erosion of a conventional bare metallic electrode for generation of microwave plasma in liquid was investigated. The spectra of plasma, the surface temperature of the electrode and the erosion rate were measured by a spectroscope, a radiation thermometer and an analytical balance, respectively. The intensity of the spectral lines indicating the erosion of the metallic electrode and erosion rate depends upon the microwave power. To avoid metallic contamination, a coaxial electrode for generating microwave plasma on a dielectric material was developed. The metallic electrode is encased in an alumina closed tube. The side of the alumina closed tube is further covered with an open Teflon tube. It has been confirmed that the electric field is strongest at the point where the alumina closed tube, Teflon opened tube and liquid intersect as determined by the two-dimensional Finite-Difference Time-Domain (2D-FDTD) method. Synthesis of amorphous-carbon deposition in ethanol was conducted. The developed electrode enables synthesis with a smooth deposition.