I’m looking for material capable to act as filament of thermionic emitter in open air. Classical tungsten filament is not capable, because it readily oxidizes. We experimented with filaments made from SiC and ZrO2 (Yttria stabilized). At 1900K SiC provides certain degree of emission, but it is rapidly blocked by formation of SiO2 layer on filament surface. ZrO2 doesn’t emits at all, despite low work function and good electrical conductivity when hot. We heated it up to 2200K. We guess that it simply has no free electrons available for emission, as its conducts by circulation of oxygen ions. Can somebody recommend material which can be used ? Does anybody have experience with LaCrO3 for such application ?