PLASMA CHEMICAL-MODEL FOR DECOMPOSITION OF SF6 IN A NEGATIVE GLOW CORONA DISCHARGE

A zonal plasma chemical model is proposed to account for the observed oxidation and decomposition of sulfur hexafluoride (SF6) by a negative, point-to-plane glow-type corona discharge in pressurized SF6/O2/H2O gas mixtures. The model yields dependencies of stable neutral oxidation by-products such as SOF2, SO2F2, SOF4, S2F10, and SO2 on time, discharge current, and O2 and H2O concentrations which are consistent with measured results. Electron-impact-induced dissociation of SF6 in the glow region of the discharge is the decomposition rate-controlling process. The relative roles played by different reactions involving neutral free radicals and ions in different zones of the discharge are examined, and in some cases, reaction rate coefficients have been adjusted within reasonable limits to give best fits to observed production rates of various by-products. Problems of uniqueness that arise because of gaps in our knowledge about important processes that should be included in the model are also discussed.