Thermionics

Fabricated thermionic diode with hot shell tri-layer CVD structure of SiC and W deposited on graphite. Diodes operate at 1400C in a natural gas –fired furnace for over 18,000 hours demonstrating stable operation. Multiple thermionic diodes are fabricated in 1” and 2” diameter geometries. Diodes are fabricated by CVD W deposited on the inside of graphite shell followed by a CVD SiC coating on the outer side of graphite shell completely encapsulating the graphite. Diagram shows cross section of hot shell with W emitter, Ni collector, Cs reservoir, brazed flange and SiC oxidation protection coating

Drawing of diode

Thermionic diode heated by induction coil in air to 1200C being quenched by LN2. No cracks in CVD SiC coating resulted from this thermal shock test. Test was repeated over 100 times and the thermionic diode remained vacuum leak tight.

Copper coid with white vapor

Thermionic diode heated by induction coil in air to 1200C being quenched by spray of water. No cracks in CVD SiC coating resulted from this thermal shock test. Test was repeated over 100 times and the thermionic diode remained leak tight. Thermal gradient on hot shell tri-layer dome between water impingement area greater than 1000C/inch.

Copper coil with dark spot