Effects of additives on prebreakdown phenomena in liquid cyclohexane: II. Streamer propagation

Abstract

Streamer propagation in cyclohexane with various additives have been studied with fast impulses applied to a point-to-plane gap. The additives are perfluoro-n-hexane, N,N-dimethylaniline, 1-methylnaphthalene, di-n-propylether, 1,1-difluorocyclopentane and 1,4-benzoquinone, representing molecules with different electrochemical properties. We have used shadowgraphic imaging and a differential charge-measurement technique with a sensitivity of 0.1 pC to integrate currents induced to the point electrode during streamer propagation. The propagation is to various degrees facilitated by the additives. Perfluoro-n-hexane affects point cathode streamers, N,N-dimethylaniline and di-n-propylether affect point anode streamers, while 1-methylnaphthalene and 1,4-benzoquinone affect both point anode and point cathode streamers. 1,1-difluorocyclopentane is the only additive without a measurable effect in either point polarity. Largest effects are found for perfluoro-n-hexane, N,N-dimethylaniline and 1-methylnaphthalene, which are the only additives to produce a visible change in streamer appearances. In these cases, filaments become thinner and fewer, while propagating faster and sometimes further. The results follow expectations, considering point cathode streamers to be governed mainly by injection of thermal electrons from a gaseous phase, and point anode streamers to be governed mainly by more energetic electrons, extracted from the liquid at higher electric fields.