Two-layer cathode for electron gun

Abstract

A cathode for use in an electron gun includes a base metal comprising Ni as a principal component and a two-layer electron emissive material disposed on the base metal. The inner layer is comprised of an alkaline earth metal oxide and 1-30 wt. % W and may further include 0.1-5 wt. % of a rare earth metal oxide. The outer layer is comprised of an alkaline earth metal oxide and may further include 0.1-5 wt. % of a rare earth metal oxide. The outer electron emissive layer provides stability for the cathode. In the degassing and activation process, W and Ni react at high temperatures to form a Ni W fine crystal structure. An intermediate layer, such as Ba SiO , is dispersed in the Ni W fine crystal structure in operation. Free barium is produced in reactions between the various cathode components to provide a high current density for the cathode. The normalized electron emission current value of the cathode does not decrease with use, even over extended periods of operation. While W has heretofore been used as a reducing agent in impregnating cathodes as well as in the base metal, it has not heretofore been used in an outer layer of a cathode.