Cathode work function, sparking potentials and secondary ionization coefficients for oxide-coated cathodes in hydrogen

Abstract

The Kelvin vibrating electrode technique has been applied to measure the contact potential difference between oxide-coated cathodes and a gold reference surface in the presence of hydrogen. Special high vacuum (Alpert) techniques were used to ensure high gas purity. By the use of both calcium oxide and barium oxide cathodes, in various states of activation, it was possible to obtain a range of work function from 1.4 to 3.6 eV. Paschen curves were plotted for each of these oxide cathodes at room temperature, and minimum sparking potentials and secondary ionization coefficients were determined. A linear relation was found between the cathode work function and the minimum sparking potential. The slope of this line indicated that a 1 eV change in work function corresponded to a change of 55 V in the minimum sparking potential. The slope of the line was confirmed by independent work function measurements using the graph of the Richardson thermionic equation. The curves (ω/α) v (E/p) showed a rapid increase in ω/α with decreasing values of E/p at E/p < 100 V/cm mm of mercury.