Vacuum Thermionic Work Functions of Polycrystalline Nb, Mo, Ta, W, Re, Os, and Ir

Experimentally measured effective vacuum thermionic work functions are reported for well-outgassed polycrystalline (but thermally preferentially oriented in many cases) surfaces of 70% (100)+20% (211)-oriented niobium (4.19 eV), 70% (100)+20% (211)-oriented molybdenum (4.0–4.3 eV), 70% (211)-oriented tantalum (4.25 eV), 96% (100)+4% (111)-oriented tungsten (4.52 eV), fairly randomly oriented rhenium (4.96 eV), randomly oriented osmium (4.83 eV), and 80% (111)+15% (100)-oriented iridium (5.27 eV) in a clean, 10−9 Torr background vacuum. Special techniques were employed to ensure accurate current, area, and temperature values. Purities, heat treatment histories, and x-ray crystallography measurements on the surfaces are included.