GB824902A - Improvements in cathodes and emissive material therefor - Google Patents

Abstract

824,902. Cathode materials and processing. GENERAL ELECTRIC CO. April 2, 1958 [April 29, 1957], No. 10567/58. Class 39(1). A cathode, particularly for photographic flash tubes, comprises a conductive core and an emissive coating thereon of barium aluminate and barium corresponding to the formula (xBaO.Al 2 O 3 ).yBa wherein x lies between extends from 0À1 but is less than 1 and y is between 0À5x and 2À6x. The preferred mixture lies in the range between BaO.Al 2 O 3 .0À48 Ba and 0À34 BaO. Al 2 O 3 . 0À89 Ba. Such an emissive material may be made by mixing the requisite amount of aluminium powder having a grain size of 3Á with a barium aluminate compound which may contain excess BaO, for example 1À76 BaO. Al 2 O 3 . The mixture may then be coated on a cathode body such as a nickel grid, an iron cup or a tungsten coil by dipping the body into the dry powder, or into a slurry of the mixture with butylacetate or by inserting particles or pellets of the pressed mixture into the cathode. The cathode is activated by heating to a temperature between 600‹C. nd 1200‹C., preferably to 660‹C. at which temperature the aluminium reacts with some of the barium oxide to form Ba and Al 2 O 3 , no gases being evolved. The activation may be carried out by the usual methods such as heating by radiation, passing current through the cathode coil, low pressure arc or glow discharge in argon or by conduction from a hot surface, in particular by heat conducted from a source used to seal the cathode in a glass tube. The activation may also take place in an atmosphere of hydrogen or an inert gas or in a vacuum.