Surface Treatment of Core Metal used for Oxide-coated Cathode

Abstract

In the oxide cathode coated with alkaline earth metal oxide on a nickel sleeve, it is generally known that the active material contained in the core significantly influences the thermionic electron emission. That is, the active material produces excess Ba through the reduction of oxide. The produced excess Ba diffuses in the oxide and appears on the cathode surface so as to enhance its thermionic activity. On the other hand, however, nickel sleeve is generally made by drawing method. Because of severe mechanical processings and heat treatments, the surface of the sleeve is subject more or less to contamination. As long as this surface contamination exists, the diffusion of the active material to the sleeve surface is impeded, whereby causing an inferior activity.
The following is the result of research showing the existence of these contaminated layers which exert some evil influences.