A thermionic cathode (FIG. 1) comprises an emitter (3) comprising a matrix (4) of tungsten impregnated with an alkaline earth activator. The matrix is coated with a coating (5) of about 20-30% osmium fully alloyed with tungsten formed by cosputtering osmium and tungsten onto the matrix. A diffusion barrier (6) of osmium may be interposed between the matrix 4 and coating (5) (FIG. 2) and, optionally, osmium may be diffused into the matrix (4). Alternatively the whole matrix may comprise a mixture of about 20-30% osmium fully alloyed with tungsten (FIG. 3). Alternative to osmium and tungsten may be used, and various modifications may be made, and other methods of making the emitter may be used. In particular the proportion of osmium may be about 40%.
An indirectly heated cathode structure for electron tubes comprises a cathode supporting sleeve, an electron emission section fitted on a part of the supporting sleeve, and a heater arranged inside the supporting sleeve, the supporting sleeve being an alloy containing niobium as a main component, more particularly more than 85 weight % of niobium. As an additive, at least one metal selected from titanium, zirconium, hafnium, vanadium, tantalum, molybdenum and tungsten is used.
A method of manufacturing a thermionic cathode structure comprises the steps of: (1) forming a mixture of (a) tungsten powder, (b) at least one of the group comprising alumina or zirconia or yttrium oxide powder, (c) alkaline earth metal carbonate powder, and (d) a binder, (2) pressing the mixture isostatically causing the mixture to adhere to form an electrically insulating body, (3) sintering the body in a dry hydrogen ambient thereby reducing the carbonate, and (4) coating the surface of the body or a portion of the surface with a poly-crystalline metal layer.
A long life high current density cathode is made from a mixture of tungsten nd iridium powders using a barium iridiate as the impregnant by processing the mixture of powders with an activator into a porous billet, and then impregnating the billet with a barium iridiate by firing the billet in a dry hydrogen furnace at a temperature at which the impregnant melts.
An impregnated thermionic cathode includes a porous matrix of sintered tungsten-alloy particles containing less than six percent iridium and/or other platinum-group metal. The pores of the matrix are impregnated with a temporary process impregnant such as molten copper or an organic monomer, and upon solidification is machined to a desired shape. Thereafter the temporary process impregnant is removed, and the matrix pores again infiltrated with a barium oxide such as molten barium aluminate, or other alkaline earth. A thin, iridium-rich surface activating layer, preferably of about 50% iridium, is then applied to the emitting surface. The diffusion of surface activating iridium is substantially blocked; superior emission and lifetime is provided; and the cathode is relatively low cost and easy to fabricate.
A four-piece, easily manufactured dispenser cathode capable of current densities up to and exceeding 10 Amperes per square centimeter is particularly adapted for CRT applications because of its surprisingly low cost. A refractory material reservoir contains a pellet of tungsten and barium calcium aluminate and is sealed by a pellet of porous tungsten or tungsten mixture. The reservoir/pellet assembly is contained in a support cylinder to which the porous tungsten pellet may be welded. The inventive process includes the steps to prepare the pellets and assemble the four elements of the cathode.
