Two-layer cathode for electron gun

摘要

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 Ni4W fine crystal structure. An intermediate layer, such as Ba2SiO4, is dispersed in the Ni4W 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.