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.
Measurements of the photoconductivity of liquid n -pentane, n -hexane, cycJopentane, cycJohexane, neopentane, neohexane, and tetramethylsilane induced by far UV radiation (7 5,hv 5, lOeV) have been performed. We have studied the influence of the incident photon energy, of the applied electric field strength, and of the concentration of two electron scavengers (carbon tetrachloride and perfluoromethylcycJohexane). Our results show that in going from the gas phase to the liquid phase, the ionization energy threshold values of these low dielectric constant liquids are lowered by about 1.6 eV. The introduction of an electron scavenger reduces drastically the solvent photocurrent. Our results are consistent with the quenching, by the scavenger, of a solvent expanded excited state, precursor of the geminate ion pair, and not with an epithermal electron scavenging as in high energy photon irradiation.
The spark decomposition of and of mixtures was studied principally 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). Our attention was only focused on the gaseous by-products: and which were assayed by gas chromatography. The last three compounds were principally observed under the higher energy sparks. Their yields were studied varying the cell preparation technique, the metal constituting the plane electrode (aluminium, copper, stainless steel) and the concentrations of two additives, (between 0 and 1%) and (between 0 and 0.2%). The cell preparation procedure had a strong effect on the formation of all products except ; the yield was for example multiplied by when the cell was carefully dried and outgassed and with an aluminium electrode. The aluminium led, whatever the procedure used, to the highest levels of products. Under the high-energy sparks an increase of the oxygen content of or of the mixture led to a decrease of the and formation rates and to an increase of that of the other compounds. An increase of the content had very little effect on production and led to increased production of and and to a lowering of the formation of other compounds. Under the low-energy sparks the addition of to or to the mixture led to a lowering of the and yields like under high-energy sparks and to an increase of (which became observable) and of . Addition of water resulted in an increase of the and yields, in a lowering of and had no effect on which remained unobservable. Finally it should be noted that the addition of 50% of to the had very little effect on the rates of formation of the gaseous by-products except under low-energy sparks where the mixture led to lower production rates for and .
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