Abstract A tungsten heater, covered with a thin alumina layer (about 1 mil), is potted inside a molybdenum cathode cup in a sintered mass formed from a mixture of fine particles (of the order of 1-5 microns) of molybdenum and nickel in the weight ratio of at least 40 percent molybdenum, but preferably about 90 percent moly. The emissive surface of the cup has a matrix of sintered nickel carbonyl filled with alkaline earth metal emissive oxides. The cup is supported by invar struts. The processing includes: (1) preparing a sintered nickel carbonyl matrix layer for the emissive surface of the cup; (2) ball-milling molybdenum-nickel mix with butyl carbitol, and after covering the heater therewith, inserting the heater in the cup, firing the assembly in hydrogen at between 1,150* to 1,350* C until sintered; and (3) impregnating the nickel carbonyl matrix with a mix of alkaline earth carbonates in methyl alcohol and using heat and ultrasonic vibration to compete impregnation. After assembly in tubes, activation and aging follows.
An indirectly heated cathode assembly according to claim 1, wherein said metals consist essentially of 90 percent molybdenum and 10 percent nickel.
Claim 2
Dependent Claim
75 words
An indirectly heated cathode assembly according to claim 1, wherein said cathode element is in the form of a cup of molybdenum having an outer concave curved surface and an inner curved surface, said emissive coating being of nickel carbonyl impregnated with an alkaline earth material and being on said outer surface, said heater being a planar winding potted in said mixture on said inner surface and having a curvature conforming to said inner surface.
Claim 3
Dependent Claim
39 words
An indirectly heated cathode assembly according to claim 1, further including a supporting member; and at least one strut of low thermal conductivity metal extending between and fastened to said supporting member and said cathode for mounting said cathode.
Claim 4
Dependent Claim
26 words
An indirectly heated cathode assembly according to claim 4, wherein said strut is formed of a material taken from the group consisting of invar and nichrome.
Claim 5
Dependent Claim
17 words
An indirectly heated cathode assembly according to claim 4, in which said supporting member is of molybdenum.
Claim 6
Dependent Claim
28 words
An indirectly heated cathode assembly according to claim 1, wherein said heater is of tungsten covered by a thin layer of alumina; and said cathode element is molybdenum.
Claim 7
Dependent Claim
99 words
In the process of manufacturing an indirectly heated cathode the steps comprising mounting a heater against the inner surface of a cathode element, preparing a homogeneous mixture of fine particles of the order of 1 to 5 microns of molybdenum and other refractory metal, said mixture consisting of 40 to 90 percent molybdenum; covering at least a portion of said heater mounted against said cathode with said mixture; and firing the assembly in a dry atmosphere of reducing gas at a temperature of between 1,150* to 1,350* C to sinter the metal and bond the heater to the cathode.