An in situ emission microscopy study of barium supply to the surface of scandium-coated porous tungsten

The transport of Ba to the surface of a porous tungsten disk packed with barium oxide powder is observed directly with emission microscopy. The W disk surface is patterned with sputter deposited scandium metal squares. Thermionic electron emission is observed from the Ba/Sc/W areas at temperatures below those required for thermionic electron emission from the non-Sc coated areas. The ldquodispensingrdquo process is observed directly, in situ.