Date of Award
2025
Document Type
Open Access Master's Thesis
Degree Name
Master of Science in Materials Science and Engineering (MS)
Administrative Home Department
Department of Materials Science and Engineering
Advisor 1
Paul G. Sanders
Committee Member 1
Timothy J. Langan
Committee Member 2
Sriram Vijayan
Abstract
This project seeks to optimize a rare-earth hexaboride cathode material for thermionic emission Hall-effect thruster in an air breathing electric propulsion system for the very low earth orbit (VLEO). The main atmospheric constituents in VLEO are nitrogen and atomic oxygen. The presence of oxygen causes the Hall-effect thruster cathode to poison, sharply decreasing its electron emission, thus reducing thrust. Two cathodes used for thermionic emission are dispenser cathodes and lanthanum hexaboride (LaB6) cathodes, with the LaB6 cathodes having better resistance to oxygen poisoning. It is desired to develop a cathode that can better tolerate the oxygen environment than LaB6, so the alloys of LaB6 and other rare-earth hexaborides are explored with respect to their:
- Work function, determined via the Hashimoto approximation
- Stable oxide formation at operation temperature and pressure, assessed with Ellingham diagrams
- Pilling-Bedworth ratio using the most stable oxide to evaluate the oxide’s protectiveness of the cathode surface.
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.
Recommended Citation
Brylinski, Sophia G., "THERMIONIC EMISSION COMPUTATIONAL DESIGN OF RARE-EARTH HEXABORIDE CATHODES IN AN OXYGEN ENVIRONMENT", Open Access Master's Thesis, Michigan Technological University, 2025.