Analysis of slurry composition for the direct ink writing of mayenite electride for use in thermionic cathodes

Abstract

Thermionic cathodes, for use in electric propulsion thrusters, often utilize materials of low work function to decrease operating temperature and thus decrease power consumption. The ability to form these materials into complicated geometries allows for design of more efficient thermionic cathodes, such as multi-channel hollow cathodes. Mayenite electride, a calcium aluminate ceramic with a cage-like lattice structure that traps in electrons, has been identified as a low-work function ceramic that could be used for these thermionic cathodes. This thesis explores an additive manufacturing (AM) process for mayenite electride components, including the synthesis process for insulating mayenite and the development of an acetone-based slurry composition for direct ink writing (DIW). As the ink composition is critical to the success of any direct ink writing process, an in depth analysis was performed on mayenite slurries, which focused on different solvents, binders, and the dispersion of the ceramic particles. Water and acetone-based slurries were developed with mayenite, and printing tests showed that the printing mayenite with acetone as the solvent is viable, but greater dispersion of the mayenite powder within the slurry is necessary. In order to make quality components, the mayenite powder needs to be ground to a finer powder, the slurry needs to be mixed more thoroughly, or a dispersant must be added.