Development of a CVD silicon carbide-graphite-tungsten heat pipe structure

The operational capabilities of a trilayer structure of chemically vapor-deposited (CVD) tungsten and silicon carbide over graphite have been demonstrated by tests on a one-inch diameter hemispherical hot shell thermionic converter emitter. The tests consisted of operation in a natural gas-fired furnace for over 5000 hours at 1630 K and another 5900 hours at 1730 K. Additional tests demonstrated structural integrity under thermal shock and thermal cycling. A detailed description is given of the construction techniques used to fabricate such heat pipe devices, including the beam welding to tungsten end caps and the deposition of silicon carbide on the burnoff tube.