GB783836A - Cathode structure for magnetrons - Google Patents

Abstract

783,836. Cathode constructions and materials. WESTERN ELECTRIC CO., Inc. Jan. 25, 1956 [Feb. 2, 1955], No. 2468/56. Class 39(1). A magnetron cathode includes a metallic core provided with an emissive coating in the form of a sintered matrix of nickel-coated tungsten particles interspersed with emissive material ; the amount of nickel on the particles is so related to the amount of tungsten that the coating expands on heating at the same rate as the core. A nickel submatrix may be provided between the core and the emissive coating. In this case the total amount of nickel on the particles and in the submatrix is related to the tungsten. Preferably the core is of molybdenum and there is a linear relation of tungsten to nickel of 4 to 1 taken along a radial line, out from the core. The method of manufacture may include the steps of moistening the tungsten particles with a plasticized nitrocellulose solution as a binder dusting a fine powder of nickel, nickel oxide, or both, on the tungsten particles while agitating them, and reducing the coated powder when dry in hydro. gen. Instead of by dusting, the coating may be applied by vapour deposition or by an electroplating technique. A cathode blank 15, Fig. 3, may have a spiral groove 27, and first receives a nickel submatrix 28 formed by painting on a suspension of fine nickel powder in a nitrocellulose solution. The nickel powder is fused at the entectic. temperature of the molybdenum and nickel to form an interdiffused layer between the submatrix and the core. A further coating of fine nickel powder is then applied followed by a thin deposit of coarse nickel powder. A permanent bonding is obtained by a hydrogen sintering treatment. The cathode blank with the nickel submatrix is then positioned in a mould of oxidized stainless steel, and the tungsten-nickel powder 16 is then applied. The blank is fired in hydrogen at 900‹-1000‹C., then removed from the mould and the matrix resintered at 1200‹-1300‹C. It is found that on interdiffused alloy, of nickel and tungsten, is also formed between the nickel submatrix and the nickel coated tungsten matrix. The emissive material 30, e.g., barium-strontium carbonate or one or more alkaline earth oxides, such as those of barium and strontium, is placed on the surface of the matrix 16 and soaks into it. The normal compressing of the blank and activation and aging then follow. The cathode 11, Fig. 2, has an internal heater 26 on an insulating core 25 which has a spacer and conductor 28. End portion 19 is a heat radiator; flange 21 is pole-piece member.