Certain Refractory Compounds as Thermionic Emitters

Goldwater, Daniel; Haddad, R.

doi:10.1063/1.1699824

Cited by 35 publications

(1 citation statement)

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“…If such thermionic emitters are found, they may also be used as good field and thermal-field emitters. It has been suggested that some carbides are useful emitters from these points of view (Goldwater and Haddad, 1951;Eckstein et al, 1962;Ingold, 1963). We developed a new preparation method of refractory carbides of transition metals such as TaC, H E , NbC, and ZrC (Yada, 1982) and determined their emission properties from the measured brightness characteristics of the electron microscope cathodes (Yada and Shimoyama, 1985).…”

Section: Introductionmentioning

confidence: 99%

Studies of refractory carbides, nitrides, and borides as the thermionic emitters for electron microscopy

Yada

Masaoka

Shoji

et al. 1989

J. Elec. Microsc. Tech.

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Thermionic emission properties of several kinds of refractory carbides, nitrides, and borides of the transition metals in the form of powder were investigated with a newly developed measuring device and evaluated by the figure of merit defined as the ratio of the effective work function to the working temperature at which the vapor pressure becomes 1 x 10(-5) Torr. There are several materials whose thermionic emission properties are better than those of tungsten or compatible to those of tungsten among the carbides and borides, such as TaC, HfC, ZrC, LaB6, and CeB6, as judged by the figure of merit. New preparation methods for carburization, nitriding, and boriding of the wires of matrix metals and alloys were successfully developed for using these materials as the cathode of the electron microscope. Other necessary techniques such as spot welding and electrolytic etching were also developed. From the brightness characteristics, it was found that some of carbides, carbide solid solutions, and borides such as HfC, ZrC (Ta0.8-0.7Hf0.2-0.3)C, TaB2, and HfB2 are very good emitters comparable to LaB6. It is emphasized that the work functions of the carbide-solid solutions (Ta0.8Hf0.2)C and (Ta0.7Hf0.3)C, which have low rates of evaporation at high temperature, show no remarkable rise as compared with that of HfC, so that their figures of merit are better than that of HfC. Feasibility of providing good cathodes with HfC and (Ta0.8Hf0.2)C tips was demonstrated by taking high-resolution electron micrographs.

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Section: Introductionmentioning

confidence: 99%