GB1023999A - Improvements in or relating to methods for impregnating tungsten dispenser cathodes - Google Patents

Abstract

1,023,999. Cathode materials and processing. SEMICON ASSOCIATES Inc. Nov. 8, 1963, No. 44237/63. Heading H1D. In manufacture of a cathode, a porous body of sintered tungsten is impregnated witha molten alkaline earth metal oxide in the absence of any diluent other than an alkaline earth metal tungstate which may be present in a mol ratio to the oxide of not more than 1 to 3, the impregnation being carried out in the presence of an auxiliary source of barium vapour. The porous tungsten body may be prepared by pressing tungsten powder to a density of 80 to 86% of the theoretical, sintering, impregnating with a plastic filler, e.g. methyl methacrylate, to facilitate machining, and heating to remove the plastic after shaping. The emissive mixture preferably comprises barium oxide, and one or more of barium, calcium or strontium tungstate, preferably strontium tungstate, in a mol ratio of 5 to 1, the ingredients being mixed in powder form and at least semi-fused before being reground and spread over the porous tungsten body. Impregnation may be effected by heating at 1850‹C. for 15 to 30 sees. in hydrogen, in the presence of an auxiliary source of barium vapour, which prevents corrosion of the porous tungsten and ensures more uniform emission characteristics. The cathode may be used in thermionic generators.