SU680670A3 - Cathode material for electronic instruments - Google Patents

Description

(54) CATALOD MATERIAL FOR ELECTRONIC INSTRUMENTS

palladium, platinum, rhodium and ruthenium in the reduction of oxides of rare-earth elements.

It is preferable to use oxides of yttrium and lanthanum as an active additive. Entering one or several diffusion-promoting metals, such as palladium, platinum, rhodium and ruthenium into the carrier metal carbide system as a reducing agent, allows to obtain cathodes with reduced power and high emission.

The invention is explained in the example and execution of the experiments.

Example 1. 98 wt.% Molybenum powder (isar grain at 1.2 m.mk) is mixed with 2 wt.% Of sour lanthanum () i which is previously ground in a wet mill mill in a wet state (grain size 0.5 mmk) for 30 Inut in a vibromixer. After this, the mixture of the powder, in the first operation, is cut onto an isostatic resin in a cylindrical rubber form under a pressure of 3000 bar to obtain a preform. Then, in the second step, the billet is preliminarily reduced in flowing hydrogen at a temperature of 12 hours, to remove oxygen from the moliene. In the third step, the billet is inductively heated for one hour in a vacuum furnace filled with hydrogen and sintered to a density of 98% of the theoretical density. In the fourth operation, the sintered blanks are cut by the electric-spark method using plates of 5-1 to 12 mm, 1, the surface of which is polished. In the next sixth operation, a plate coating is deposited on the cut plates in an electroplating bath. As a means of accelerating diffusion, the coating thickness is 1-10 mmk. The plate equipped with this coating undergoes diffusion glowing in a vacuum or a protective atmosphere for a few minutes at a temperature of about seven; ISOO C. Then, during the eighth operation, the carbide is exposed to the plate. The plate is exposed to a mixture of benzene with hydrogen at 1700e for 10 minutes, so that a layer of molybdenum carbide (Mo2C) forms between a layer of platinum on one side and a core of molybdenum and lanthanum oxide on the other hand.

Example 2. The procedure is the same as in Example 1, but the eighth step (carbidizing with benzene and hydrogen) is performed before the sixth Operation, i.e. before platinum plating.

Example 3. Molybdenum powder with 2 wt.% Lanthanum oxide (LajO) is mixed with 0.5 wt.% Platinum black with a grain size of 0.5 µm. In the first operation, the mixture is isostatically compressed under a pressure of 3000 bar. To obtain a stockpile. In the second operation, the billet is subjected to recovery within five hours at a temperature of 1000 ° C in flowing hydrogen. Thereafter, the preform is baked for one hour at 1000 ° C, with 99.8% of the theoretical density being achieved. From the sintered block, in the fourth operation, a plate of size 5 1 12 mm is cut by an electric spark method. In the fifth operation, the plate is carbidated for 10 minutes in a mixture of benzene and hydrogen at a temperature of 1700 ° C.

Example 4. High purity tantalum powder with a grain size of 1 mmk is mixed with 2 wt.% Yttria powder with a grain size of 0.2 mmk and then in the first operation is pressed isostatically in a cold state under a pressure of 3000 bar to obtain a preform. In the second operation, to obtain a mat from a blank, it is sintered for one hour in vacuum at a temperature of 2300 ° C. At that, a density of 89% of the theoretical density is reached. In the third operation, a plate of mm size is cut out from this disc by the method of electroerosion. In the fourth step, the plate is carbidized in a mixture of benzene and argon for 15 minutes at a temperature of 1700 ° C. A layer of β-tantalum carbide is formed on the surface of the plate. In the fifth operation, a palladium layer with a thickness of 10 MMK is galvanically applied to the surface of the plate. In the next sixth operation, the plate is annealed in vacuum for two hours at 1600 ° C, with the palladium diffusing into tantalum.

The value of placing a compound forming a monolayer and a means of accelerating diffusion inside the carrier or on the carrier was investigated. The following options were explored.

First, on the surface of the carrier of the refractory metal, a zone is obtained containing a compound forming a monolayer, in some cases with the addition of a reducing agent. After that, a means of enhancing (causing) diffusion is applied in the form of an outer zone. Although the latter, thus, first of all, is obtained in the outer layer, it exhibits its specific effect on deeper or shallower depths, due to which penetration is required

means of accelerating diffusion into deeper cathode zones. This can be achieved as described in example 1 by diffusion firing (glowing) in the manufacture of the cathode. In another embodiment, on the outer surface of the carrier, a zone of diffusion accelerating agent is obtained, on which a compound forming a monolayer is placed, which ensures the location of the diffusion accelerating means in the intermediate zone. Usually, penetration of the diffusion accelerating agent into the zone of the monolayer compound is required. In both of the above cases, the layer. containing the accelerated diffusion of the medium, is a form for storing the appropriate amount necessary to compensate for the losses occurring during evaporation during operation. In the third embodiment, the means for accelerating the diffusion is dispersed in the carrier, and the compound forming the monolayer is preferably in the outer zone. In the fourth embodiment, the monolayer forming compound is dispersed in the carrier, and the diffusion accelerating agent is preferably located in the outer zone. Both of these options, especially the latter, have advantages in manufacturing, however, diffusion roasting is usually required in both of these options. In the fifth embodiment, both the activator and the mobilizer are dispersed in the carrier. This design, from the point of view of material processing, should be considered optimal. From the point of view of the quantitative composition of the cathode, the following, the most favorable limits of the content of the main components are determined: a compound forming a monolayer from 0.05 to 10 wt.%; diffusion accelerating agent - from 0.01 to 5 wt.%. The optimal values, from the point of view of the density of the emission current, electrons, service life and processability, the cathode material into a wire will be as follows: the chemical compound of the activator is from 0.5 to 3 wt.%; mobilizer from 0.3 to 0.6 wt.%.

Claims (2)

1. A cathode material for electronic devices containing a refractory metal as a carrier, a rare earth metal oxide as an active additive and a reducing agent, characterized in that, in order to increase the current density. emission and durability of the cathode; in addition, at least one of the metals - palladium, platinum, rhodium, ruthenium - is introduced in the amount of O, O If 5. 2. The material according to claim 1, wherein the content of the additionally introduced metal is 0.01-0.75% by weight, and the content of the rare earth metal oxide is 0.2-15% by weight. 3. The material according to claim 2, characterized in that it contains one of the additionally introduced metals in an amount of 0.25-0.6 wt.%, And rare earth metal oxides in an amount of not more than 3 wt.%. 4. Material according to claims 1-3, characterized in that it contains one of the additionally introduced metals in dispersed form in the carrier. 5. Material according to claims 1 to 3, characterized in that it contains one of the additionally introduced metals, preferably in the outer zone of the cathode. Sources of information taken into account in the examination 1. Oxide cathode, ed. B.N. Tsareva, M., NIL, 1957, p. 43338. 2. Kudintsev G.A. et al. Thermoelectronic cathodes. Energy, M.-L., 1966, p.281.