Improved Thermal and Mechanical Properties of [Ca₂₄Al₂₈O₆₄]⁴⁺(4e⁻) Electride Ceramic by Adding Mo Metal

Abstract

The low‐work function material [Ca24Al28O64]4+(4e−)—named as C12A7:e‐ or electride—is a promising candidate to replace established materials such as BaO–W or LaB6 electron emitters because of its good reported electron emission in plasma environments and decent chemical inertness. However, it has poor thermal conductivity and low mechanical behavior. Therefore, cracks due to thermal shock occur in applications under thermal load, when used as a thermionic emitter. The addition of a metal with high thermal conductivity to create a ceramic–metal composite (CerMet) is evident. Molybdenum has a very high thermal conductivity and a coefficient of thermal expansion comparable to C12A7:e‐. This allows the crack‐free sintering of a composite ceramic made of C12A7:e‐ and Mo with improved thermal and mechanical properties as well as still low work function of the C12A7:e‐. Herein, the C12A7:e‐/Mo CerMets are characterized in terms of their thermal conductivity, thermal expansion coefficient (CTE), hardness, toughness K1C, and strength as a function of Mo content. The CerMets have been tested in a plasma‐based cathode with disk‐shaped emitters for electron emission characteristics. An optimal range of the Mo content for the stability of the plasma discharge and the required discharge potential has been evaluated.