GB1139766A - Improvements in or relating to supply cathodes for electrical discharge tubes - Google Patents

Abstract

1,139,766. Cathode materials and processing. SIEMENS A.G. 21 April, 1966 [22 April, 1965], No. 17395/66. Addition to 1,120,969. Heading H1D. The dispenser cathode as claimed in the parent Specification, in which a supply chamber containing a charge of barium oxide is covered by a porous emissive-substance carrier, has applied to the surface of the carrier facing the supply chamber a coating of an oxide of aluminium, beryllium, hafnium, magnesium, or zirconium, or of titanium or thorium dioxide, or of niobium trioxide, or vanadium tetroxide, or of niobium pentoxide, the coating being a thermally converted hydroxide layer. The coating tends to equalize the pore diameter in the carrier and so regularizes the barium evaporation, and also inhibits the penetration of solder into the carrier. The hydroxide layer in the form of a voluminous colloidal gel may be precipitated from a suitable salt on to the carrier surface and then thermally reacted and sintered to convert it to the oxide. The layer may be formed by lightly pressing the carrier against a moist gel film so that plastic hydroxide gel penetrates the pores of the carrier, this being aided by a vacuum the other side of the carrier, or the carrier may be moistened and then exposed to a jet of a vapour of a metal alkyl compound to form the hydroxide. The above oxide coatings have various melting points and are chosen according to the highest temperature the cathode is likely to experience during manufacture and operation. Any surface of the carrier not to be coated may be masked by a template or a removable layer of nitrocellulose or a depolymerizable synthetic resin, or the surface coating may be machined off.