Solid materials subjected to partial-discharge activity in pure SF 6 and mixtures with CF4

This work aimed at characterizing the surface modifications of solid materials, when subjected to partial discharges in SF₆/CF₄. Samples of high-purity copper and Teflon were used. The experiment was conducted under negative DC, producing negative corona-discharge conditions. The gas pressures ranged from 300 to 400 kPa, and SF₆/CF₄ mixtures containing 50% of CF₄ were utilized. Corona currents were varied as well as the exposure time of the samples. X-ray photoelectron spectroscopy (XPS) was used for characterizing the bulk sample surface. On-line sampling of the gas was done throughout. In both dealing with pure SF₆ and the mixture, it was experimentally found that SOF₂ and SO₂F₂ were the predominant by-products. Surface modifications were qualitatively detected for both the conductor and insulating materials. The gas medium used in the discharge brought about some differences. In particular, in presence of SF₆/CF₄ , less oxygen and sulfur were detected on the discharged surface