A new type cathode composed of “impregnated cathode” and “molded cathode” is investigated. In this cathode, excess Ba is supplied from inner impregnated porous tungsten to outer molded cathode.
Studies on the optimum manufacturing conditions suitable for this composite cathode indicate that the two parts-molded part and impregnated part-should be made under the following conditions: (1) Molded part; (Ba·Sr)CO
3: Ni=3:7 by weight, compressing pressure: 10 ton/cm
2, sintering condition: 900°C 10min.+1050°C 10 min. (2) Impregnated part; specific gravity of W: 10_??_12, impregnants: 3 BaO·Al
2O
3·1/2CaO, etc.
Zero field emission at 830°C(Br. ) and the work function of the cathode are 2_??_3 A/cm
2 and 1_??_1.1 ev respectively. In D. C. operation while the current of 0.6 A/cm
2 was being drawn at 820°C (Br. ), no significant decay of emission was seen for over 10, 000 hrs. This composite cathode is expected to have an extremely long life because the Ba supply to the molded part from the impregnated tungsten is made at a relatively low temperature.
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