Positive synergy of SF6 and HFO1234ze(E)

We measured mixtures of SF6and HFO1234ze(E) (C3H2F4) and determined the density-reduced critical electric field strength (E/N)critin a pulsed Townsend experiment. HFO1234ze(E) is an environmentally friendly alternative to SF6since contrary to SF6, its global warming potential is negligible. While SF6is unsurpassed in its efficiency of attaching thermal electrons, HFO1234ze(E) appears to moderate electron energies very efficiently. Electron attachment to HFO1234ze(E), on the other hand, is much weaker. We find a positive synergism in SF6/HFO1234ze(E) mixtures in the sense that the mixture of both compounds has a higher electric field strength than each gas separately. A maximum (E/N)critof 425 Td is reached for a mixture of 40% SF6and 60% HFO1234ze(E). A mixture of 90% HFO1234ze(E) and 10% SF6has a critical electric field strength of 360 Td, similar to pure SF6. We attribute this effect to the high efficiency of HFO1234ze(E) in moderating down the electron energies, which enhances electron attachment to SF6and reduces electron impact ionization.