Analysis of plumes produced by novel ionic liquids in electrospray thrusters

A single emitter electrospray thruster was tested with four ionic liquids, which have not been tested before, in order to investigate the physics of ion emission. Two of these ionic liquids had metal/metalloid halides anions, similar to 1-ethyl-3-methylimidazolium tetrafluroborate, and were found to emit similar to greater currents than typically found with EMIBF4. 1-Ethyl-3-methylimidazolium tetrachloroferrate was found to emit up to +50.7/-33.6µA and 1-ethyl-3-methylimidazolium hexafluoroantimonate up to +12.6/-14.5 µA, compared to +18.3/-9.3 µA for 1-ethyl-3-methylimidazolium tetrafluoroborate. Two further propellants were investigated formed of very novel ionic liquids which have multiple charges on the ions within them, and hence termed multiply charged ionic liquids. These were found to emit reduced currents, with up to +11.4/-5.3 µA by bis(3-methylimidazolium) hexyltetrakis (hexathiocyanato) cobaltate and up to +2.1/-2.2 µA being emitted by tris(1-hexyl-3-methylimidazolium) dysprosium(III) hexathiocyanate. All four of these ionic liquids were shown to emit a purely ionic plume, despite having widely varying propellant properties.