Neutral Decomposition Products in Spark Breakdown of SF6

The formation of decomposition by-products produced by electrical spark discharges in SF6 has been investigated by quadrupole mass spectrometry. The by-product SF4 was found to be a precursor to many of the long-lived decomposition by-products identified (SOF2, HF, SO2, and SiF4). The amount of SF4 formed was measured by "in situ" detection, utilizing a "threshold" technique for monitoring the SF4 ion (SF+3) in an SF6 background. The rate constant for the hydrolysis of SF4 was measured (at 350 K) and found to be ~2×10-19 cm3s-1. In addition to moisture, the effects of SiO2 and electrode material have been briefly examined. Quantification of the amounts of long-lived by-products of spark discharge in SF6 yielded the following ranking: SOF2 > SOF4 > SiF4 > S02F2 > SO2. The energy and pressure dependences in the ranges of 0.5 to 14.5 J/spark and 40 to 233 kPa respectively, of the amounts of the various by - products were examined.