Study of Non-Thermal DC Arc Plasma of CH₄/Ar at Atmospheric Pressure Using Optical Emission Spectroscopy and Mass Spectrometry

Non-thermal C/H/Ar plasmas are widely applied to carbonaceous material production and processing. In this work, plasma parameters and gaseous species of the atmospheric non-thermal C/H/Ar plasmas produced by an atmospheric-pressure DC arc discharge generator in CH₄/Ar were investigated. The voltage-current characteristics were measured for different CH₄/Ar ratios. Optical emission spectroscopy was employed to analyze the electron excitation temperature, gas temperature and electron density under various discharge conditions. The hydrocarbon molecules produced in the CH₄/Ar plasmas were detected with photoionization mass spectrometry. The optical spectral results demonstrated that the electron excitation temperature was 0.4-1 eV, the gas temperature was 2800-4200 K and the electron density was in the range of (5-20)×10¹⁵ cm⁻³. The mass spectrum indicated that a variety of unsaturated hydrocarbons (C₂H₄, C₃H₆, C₆H₆, etc.) and several highly unsaturated hydrocarbons (C₄H₂, C₅H₆, etc.) were produced in the non-thermal arc plasmas. (paper)