GB408062A - Improvements in thermionic cathodes - Google Patents

Abstract

408,062. Thermionic cathodes. BENJAMIN, M., and ROOKSBY, H. P., c/o General Electric Co., Wembley, Middlesex. Dec. 6, 1932, Nos. 34544 /32 and 7367/33. [Class 39 (i).] An oxide coating for cathodes of the type in which a supporting body is coated with alkaline earth oxide or other compounds readily convertible into the oxide, or in which a selfsupporting mass of such material is formed comprises an inner layer relatively rich in barium and an outer layer relatively poor in barium. Preferably a substantially pure barium compound is deposited on a substantially pure strontium or calcium compound. If barium is present in the outer layer, the layer should consist of a solid solution, and not a polyphase mixture, of its ingredients. The proportion of barium present should be greater than that corresponding to two molecules of barium oxide to three of strontium oxide. A core may be dipped or sprayed with barium carbonate, dried, and dipped or sprayed with strontium or calcium carbonate, the latter layer being twice the thickness of the former layer. The usual heat treatment converts the carbonates to oxides. If the outer layer consists of a solid solution of strontium and barium compounds, this may be produced by precipitating the carbonates from the nitrates by ammonium carbonates. Specifications 17580/15, 221,851, 229,654, 280,236, 315,324, 316,015, [all in Class 39 (i)], 378,651, and 397,656 are referred to.