SF6 samples (PSF6=100 or 200 kPa) were submitted to point-to-plane dc negative polarity corona discharges in the presence of water [concentration=2000 ppmv (parts per million by volume)] or without the addition of water. The stable gaseous byproducts formed, (SO2F2, SOF2, and S2F10) were assayed by gas-phase chromatography. The variation of their yields against the charge transported (up to 10 C) was studied for two metals (aluminum and stainless steel) constituting the plane electrode, at various values of the SF6 pressure, the water content, the gap spacing (2.5 and 8 mm), and the discharge current [12≤Ī (μA)≤25]. The results indicate an important effect of the metal constituting the plane electrode and of the moisture conditions, particularly on the production of SOF2 and S2F10.

The study of the formation of Sulfur Hexafluoride (SF6) dissociation products under point to plane corona discharges was carried out at PSF6=300 kPa using different discharges production conditions (50 Hz ac voltage, dc negative polarity voltage, mean discharge current intensity Ī varying between 2 and 45 μA for dc negative polarity voltage), for two plane electrode materials (aluminum and stainless steel), and moisture levels (200 and 2000 ppmv H2O). The stable gaseous by-products formed (SO2F2, SOF4, SOF2, and S2F10) were assayed by gas-phase chromatography. The results indicate an important effect of the metal constituting the plane electrode and of the moisture conditions whatever the SF6 pressure (100–300 kPa), discharges intensity (Ī) and voltage type studied. An effect of the increase of SF6 pressure up to 300 kPa was mainly observed for S2F10 and corresponds to a greater formation of this compound with PSF6. The influence of the mean discharge current intensity on SF6 by-product formation carried out for a transported charge of 1 C showed that for Ī≤10 μA, the effect varies according to the compound considered and depends on the water content of the SF6 and/or on the plane electrode material, whereas for Ī≳10 μA, the levels of the four compound studied hardly vary with the current. Comparison of results obtained under ac and dc voltage for a cumulated charge of between 0.5 and 11 C showed that (SO2F2+SOF4) and SOF2 were formed in larger quantities with ac than with dc, unlike S2F10 for which the opposite effect was observed.

No abstract

The spark decomposition of and 50% mixtures (100 kPa) in the presence of a solid insulator struck by an electric arc is studied. The sparks were generated in a cylindrical Monel 400 cell between a stainless steel point and a stainless steel plane (gap space 0.9 mm) either under a 50 Hz ac voltage (90 J per disconnection) or by discharging a capacitor (3.59 J per spark). The gaseous by-products , , , , , , and were assayed by gas chromatography and their yields studied by varying the nature of the insulator material (Megelit, Kel-F (polytrifluorochloroethylene), Teflon, polypropylene, polyethylene, nylon) and the concentration of two additives: (0 and 0.2%) and (0 and 0.2%). As it becomes vaporized under the effect of the discharges, the insulator produces species that can trap the fluorine atoms released from decomposition and enhance the formation of by-products. This explains the main results of this work which can be summarized as follows. (i) Enhancement, by an order of magnitude or more, of by the insulators. (ii) A quantity of formed in the presence of the insulator proportional to the enhancement of . The ratio between the levels of these compounds proved to be the same regardless of the initial concentration of or added to the and the intensity of the sparks. (iii) Enhancement of the quantities of (up to fivefold), , and formed in the presence of an insulator whatever the gas sample studied. In the presence of an insulator, the - mixture led to results rather similar to those of concerning the levels of decomposition products formed. In all cases however, i.e. in the presence or absence of insulator or added or , the mixture led to decreased formation of the main products: and . Interference was seen to occur between the action of the insulator and that of and ; this is ascribed to reactions taking place between these molecules or their dissociation fragments.

This study concerns the production of , , , , and when is subjected to negative polarity corona discharges of varying durations (with transported charges of 1.5, 4 and 6 C) performed with a point-to-plane set-up using a stainless steel or aluminium plane electrode. During the experiments, the parameters varied were the way the measurement cell was prepared (clean and very clean), the pressure (50 to 400 kPa), the concentration of additives such as (0 to 50%) for total gas pressures of 200 kPa and 300 kPa, water (0 to 0.2%) and oxygen (0 to 1%) for a total pressure of 300 kPa. Analyses were carried out using gas phase chromatography. The mode of preparation of the cell proved to be representative of the action of impurities such as water and oxygen on each of the compounds studied. This effect was all the stronger when the pressure was low. In the very clean conditions (effect of and reduced to a minimum) we observed a decrease of the quantities of the main products formed as the pressure or the percentage of was increased. Concerning the effect of the small quantities of added water and oxygen studied in both pure and in the 50 - 50 - mixture, the results showed that, overall, the oxygen and the water enhance the production of all the sulphur oxyfluorides from the fragments (except for which is inhibited by oxygen to the benefit of ) and inhibit the production of . The presence of 50% , a fluorine source, inhibited the production of all the compounds studied independently of the transported charge, the metal used for the plane electrode and the percentages of impurities (, ) added.