Production of S₂F₁₀, S₂OF₁₀, and S₂O₂F₁₀ from Spark and Negative-Corona Discharges in SF₆ and SF₆/O₂ Gas Mixtures

Abstract

The rates for production of the compounds S₂F₁₀, S₂OF₁₀, and S₂O₂F₁₀ have been measured both in spark and continuous, constant-current negative glow corona discharges generated using point-to-plane electrode gaps in 'pure'SF₆ and SF₆/O₂ gas mixtures containing up to 10% oxygen by volume fraction. In the case of corona discharges in pure SF₆, the S₂F₁₀ concentrations were measured as a function of time during discharge operation using a gas chromatograph-mass spectrometer for gas pressures in the range of 100kPa to 500kPa and at discharge currents between 2μA and 80μA. The charge rate-of-production of S₂F₁₀ from negative corona is observed to drop with decreasing discharge current, and the yield curves exhibit nonlinearities in the early stages of the discharge associated with "conditioning" of the point electrode. The initial nonlinearities become more pronounced with increasing gas pressure. The absolute yields of S₂OF₁₀ and S₂O₂F₁₀ were measured as a function of O₂ content in SF₆ for both negative glow corona (40μA and 200kPa) and spark discharge (80J/spark and 100kPa). The gas analysis in the case of spark discharges was performed after each spark using a cryogenic enrichment chromatographic technique. When O₂ is added to the gas, there is a dramatic drop in the S₂F₁₀ yield from both types of discharges with a corresponding increase in S₂OF₁₀ yield from the spark and S₂O₂F₁₀ yield from the corona discharge. The results can be explained within the framework of a plasma-chemical model from considerations of the competition among the reactions of SF₅ radicals produced by dissociation of SF₆ in the discharge with SF₅ itself as well as with O₂ and O, and the relative degree of O₂ dissociation in the two types of discharges.