Influence of O/sub 2/ and H/sub 2/O on the spark decomposition of SF/sub 6/ and SF/sub 6/+50% CF/sub 4/ mixtures

The spark decomposition of SF/sub 6/ and SF/sub 6/+ 50% CF/sub 4/ mixtures was studied at a gas pressure of 200 kPa. The sparks were generated between a point and a plane either under 50 Hz AC voltage (0.09 J per spark) or by discharging a capacitor (3.59 J per spark). The authors' attention was only focused on the gaseous SF/sub 6/ by-products: SOF/sub 2/+SF/sub 4/, SOF/sub 4/, SO/sub 2/F/sub 2/, S/sub 2/F/sub 10/, S/sub 2/OF/sub 10/, S/sub 2/O/sub 2/F/sub 10/ and S/sub 2/O/sub 3/F/sub 6/ which were assayed by gas chromatography. Their yields were studied varying the cell preparation technique, the metal constituting the plane electrode (aluminum, copper, stainless-steel) and the concentrations of two additives, O/sub 2/ (between 0 and 1%) and H/sub 2/O (between 0 and 0.2%). The cell preparation procedure had a strong effect on the formation of all products except SOF/sub 2/+SF/sub 4/. The aluminum led, whatever the procedure used, to the highest levels of products. With SF/sub 6/ as well as with the SF/sub 6/+50% CF/sub 4/ mixtures and whatever the spark energy, an increase of the oxygen content led to a decrease of SOF/sub 2/+SF/sub 4/ and S/sub 2/F/sub 10/ production rates and to an increase of that of SOF/sub 4/+SO/sub 2/F/sub 2/. Moreover, an increase of the H/sub 2/O content induced a lowering of the S/sub 2/F/sub 10/ production rate and an increase of those of SOF/sub 2/+SF/sub 4/ and SOF/sub 4/+SO/sub 2/F/sub 2/. With the SF/sub 6/+50% CF/sub 4/ mixture the by-products production rates were lower (10 to 50% depending on the by-product considered and on the O/sub 2/ or H/sub 2/O concentration) than those measured with pure SF/sub 6/.