MATERIALS FOR ELECTRIC

Future progress in electronic device technologywill depend on, among other things, developments in the field of cathodes characterized by high and stable, under conditions of intense electron bombardment, coefficients of secondary electron emission (CSEE) and controllable levels of thermionic emission. With some types of devices, thermionic emission should be virtually absent. In many cases, such requirements necessitate combining in one material a high CSEE, typical of some oxides, with the thermal and electrical conductivities of metals. In other cases, there may be a need for semifinished products and parts of complex profiles and configurations from difficult-to-for mmaterials. Recourse to powder metallurgy processes is very often the only possible solution to such problems. The main objectives of the investigation described below were to study the preparation and some properties of powder metallurgy alloys containing a beryllate phase, alloys of tungsten and rhenium with yttrium and gadolinium tetraborides, an alloy of tungsten with tantalum, and alloys of platinum, palladium, and nickel with barium, intended for use as thermal- and secondary-electr on emission cathode materials. As has already been noted by us earlier, powder metallurgy alloys containing beryllia are potentially useful secondary emission materials. The present tendency toward increased current loads raises the problem of improving the stability of beryllia-contain ing powder metallurgy alloys operating under conditions of intense electron bombardment. Preliminary tests have shown that the current resistance of cathodes can be effectively increased by introducing into metallic matrices complex beryllium-contai ning ceramic phases with oxides of the alkaline-earth metals [1]. In the production of test alloys and cathodes, use was made of a standard powder metallurgy process consisting of the following operations: preparation of a powder mix, cold pressing, and sintering (in this ~ case, in a vacuum). The compositions of the alloys investigated are listed in Table 1. One of the most important characteristics of effective secondary emission alloys is their resistance to prolonged electron bombardment. The variation of the CSEE of platinum powder metallurgy alloys under conditions of target bombardment (Tta r = 400 -~ 25~ with an electron beam having a density of 50 mA/cm 2