JPS61264624A - Impregnated type cathode - Google Patents

Abstract

PURPOSE:To achieve good electron emission characteristic for long term by adhering a film mainly composed of mixture of specific alloy and compound onto the surface. CONSTITUTION:The pellet 1 as cathode material is composed of porous W basic material 11 having porosity of 20-25% where Ba-Ca aluminate is impregnated in the voids 12. Then the pellet 1 is mounted on a tantalum Ta cup 2 and secured through laser welding to Ta sleeve 3. The film to be adhered onto the surface of cathode material is mainly composed of mixture of at least one of Os, Ir, Ru, Re or their alloy and at least one of alumina, yttrium, scandium, oxide or their compound. Consequently, good electron emission characteristic can be maintained stably for long term.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an impregnated cathode used as a high current density cathode in an electron tube or the like.

[Background of the invention]

Conventionally, this type of impregnated cathode is constructed by impregnating a porous substrate made of a high-melting point metal such as Ta/Gesten, Molybdenum GMo) with an electron-emitting substance such as Ba-Ca aluminate. However, in order to further improve the electron emission characteristics, a thin film mainly made of noble metals is sometimes attached to the cathode surface, and osmium (Oa) and iridium (Ir) are effective materials for improving such electron emission characteristics. , ruthenium (Ru), rhenium (R.), etc. (Vacuum Vol. 3, p. 718 (Va)
Cuum.

Vol. 3 (1983), p718)).

These thin films are gradually alloyed and lost with the underlying metal substrate material during operation of the cathode, with concomitant deterioration of electron emission properties.

Therefore, in order to maintain good electron emission characteristics for a long time, it is necessary to form a thin film sufficiently thick. However, when the thickness of the thin film is increased in this manner, the effect of improving the electron emission characteristics generally decreases, and in some cases, the effect of improving the electron emission characteristics may be even worse than that of a case where no thin film is formed.

[Purpose of the invention]

Therefore, an object of the present invention is to provide an impregnated cathode that provides good electron emission characteristics over a long period of time.

[Summary of the invention]

For this purpose, the present invention provides a coating film to be attached to the surface of the cathode material, which is composed of at least one of Oas Ir-, Rus Re, or an alloy mainly composed of them, and alumina (A
t20g), yttria (YxOs), and scandium oxide (Sagos), or a mixture thereof with a compound mainly composed of them.

[Embodiments of the invention]

The figure is a sectional view showing one embodiment of the present invention. In the figure, 1 is a pellet serving as a cathode material. This pellet 1 is composed of a porous W substrate 11 with a porosity of 20-25%, and the pores 12 are impregnated with Ba--Ca aluminate. And this Beret 1 is tantalum (
T1) Attached to cup 2 and further attached to Ta sleeve 3
It is fixed by laser welding.

Here, on the pellet 1, an Os-Atx Os film 4 containing about 4 wt% of curvature O3 is formed to a thickness of about 800 OA by sputtering. The pellet 1 is heated by a heater 5 made of a W core wire 51 coated with an alumina film 52.

Using a cathode with such a configuration, the anode has a width of approximately 5μ and a frequency of 1o using a cathode-anode diode system.
A high voltage pulse of oaz was applied and the saturation current density was measured.

As a result, the electron emission characteristics of the cathode of this example were the same as or about 1.2 times that of the cathode in which the Os film without At snow 03 was deposited to a thickness of 400 OA.
The thickness was about 1.5 times or more than that of a cathode on which a txo*-free Os film was deposited to a thickness of 600 OA.

Although the example in which the Os film contained in ALsOs' is attached has been described above, Ir, Ru, and Re, which are conventionally used for the same purpose, may be used as substitutes for Obata, or alloys mainly composed of these may be used. , e.g. Os-Ru, Os-I
r, 0s-W, etc. may also be used. Further, Os whose surface is covered with t-Ir is also used to prevent oxidation. On the other hand, A4
Y for 0s! Similar results can be obtained by using 03.5c20s, h, or a compound mainly composed of these.

Note that a film may be formed in a metal state, that is, At% Y% Sc, and then converted into an oxide. In addition, in order to sufficiently improve the electron emission characteristics, these
It is desirable to set it at t* or more, and it is also desirable to set it at about 20 vrt% or less to suppress the increase in resistance value.

Further, the thickness of such a coating varies depending on the required life span, but if it is too thick, the cost will increase and activation will take time, so it is preferably about 2 pIn or less.

〔Effect of the invention〕

As explained above, according to the present invention, alumina is added to the coating for improving electron emission characteristics that is attached to the surface of the cathode material.
By adding at least one of yttoria and scandium oxide, or a compound based on them, the oil coating can be made thicker without reducing its effect of improving electron emission properties. Therefore, good electron emission characteristics can be stably maintained over a long period of time.

[Brief explanation of drawings]

The figure is a sectional view showing one embodiment of the present invention. 1...Six Sword Pellet, 411・il @ OB
-A 40s membrane, 11... Porous W substrate, 12...
・Φ・Vacancy. ,・・′−・,

Claims (1)

[Claims] In an impregnated cathode in which a porous base made of a high-melting point metal is impregnated with an electron-emitting substance, the surface is coated with at least one of osmium, iridium, ruthenium, and rhenium, or an alloy mainly composed of them, and alumina, yttria, 1. An impregnated cathode characterized by being coated with a coating mainly composed of at least one type of scandium oxide or a mixture with a compound mainly composed of scandium oxide.