Production rates for oxyfluorides SOF2, SO2F2, and SOF4 in SF6 corona discharges

Abstract
The most abundant, long-lived stable gaseous species generated by corona discharges in SF6 gas containing trace levels of O2 and H2O are the oxyfluorides SOF2, SO2F2, and SOF4. Absolute energy and charge rates-of-production of these and the minor products SO2, OCS, and CO2 have been measured at different total gas pressures from 100 kPa to 300 kPa and for discharges of different current, power, and polarity. Oxyfluoride yields for SF6/O2 mixtures containing up to 10% O2 have also been measured. The results indicate that oxyfluoride production is not controlled by the concentrations of either O2 or H2O at levels below about 1%, and the rate controlling factor is the dissociation rate of SF6 in the discharge. The discharge current and time dependence of the production rates are discussed in terms of gas-phase mechanisms that have been proposed to explain previous observations of electrical, thermal, and laser-induced decomposition of SF6 and SF6/O2 mixtures. Upper limits on the total SF6 decomposition rate in low-current discharges have been estimated. Details of the chemical analysis procedures are given, and application of the results to the design of chemical diagnostics for SF6-insulated, high-voltage apparatus is discussed.

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