Production Rates for Oxyfluorides SOF2, SO2F2, and SOF4 in SF6 Corona Discharges.

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.