Combination of glow-discharge and arc plasmas for CF4 abatement

Abstract

Decomposition of CF4 by glow-discharge and arc plasmas was studied using a tubular quartz reactor, a disk type, and a T-type quartz reactor. The effects of different metal electrodes, input voltage, and reactor type on the efficiency of CF4 total destruction (DRE) were studied. The T-shape reactor was more efficient in CF4 destruction than either the disk or tubular type due to a combined effect of glow discharge and arc plasmas. Several hydrogen and oxygen sources, such as H2O, H2, O2, and CH4, were used to convert CF4. Using H2 and O2 as the hydrogen and oxygen sources presented better DRE than using H2O. The effect of different hydrogen and oxygen sources on the conversion of CF4 followed the trend: (H2 + O2) > (CH4 + O2) > H2O. The maximum DRE of 95% was observed with 0.5% CF4 using H2 and O2. A mass spectrometer and an emission spectroscope equipped with a charge-coupled detector (CCD) were used to characterize the products and intermediates. Mass spectrometric studies indicated that the reaction products were HF, CO2, and trace amounts of NO. N2 first negative and second positive emission lines were observed in the glow discharge plasmas as well as in the arc plasmas of N2. However, C and F intermediates were observed only in arc plasmas of CF4. Reactions occurring in the glow discharge plasmas and arcs seem to follow different mechanisms.