Thermal electron emission from saline hydrides deposited on a metal surface

To study the thermionic property of saline hydride NaH, LiH, CaH2or SrH2., its powder ;3 mg. was deposited in the central part ;0.03 cm2.of a boat-type molybdenum ribbon, and the thermal electron current ;10y9–10y3 A. from each hydride was measured as a function of sample temperature ;600–900 K., elapsed time 0–10 h., or pressure ;10y6–10y4 Torr. of H2 or O2 introduced at a residual gas pressure of ;10y7 Torr, thereby yielding the following results. 1. Thermal decomposition such as LiH solid.ªLi solid.qH2 gas.r2 created those active spots mainly composed of Li.with low work function f.. 2. After activation above ;700 K for several hours, f’s of LiH, CaH2, and SrH2 were 3.1, 5.0, and 7.3 eV, respectively. 3. The active spots were destroyed by introduced H2or O2according to the deactivation reaction such as CaqH2ªCaH2or CaqO2r2ªCaO, thereby increasing f by up to ;0.5 eV. 4. NaH was thermally so unstable that f could not be determined. 5. CaH2 was most stable in current and longest in durability, safely recommended to be the best thermal electron source material among the hydrides. q1999 Elsevier Science B.V. All rights reserved