US1665636A - Activation of electron-emission material - Google Patents

Description

Patented Apr. 10, 1928 UNITED STATES PATENT OFFICE.

JOHN WESLEY MAEDEN, 01 EAST ORANGE, AND JOHN EDWARD CONLEY, OI BLOOI- FIELD, NEW JERSEY, ASSIGNORS T0 WESTINGHOUSE LAIP COMPANY, A CORPORA- TION OI PENNSYLVAN IA.

ACTIVATION OI ELECTBON-EIISSION MATERIAL.

No Drawing.

This invention relates to the activation of material for electrmi-emission purposes and more particularly to the activation of such material prior to introduction into an electron device.

An object of our invention is the preparation of refractory filamentary material with activating material incorporated therein during the course of manufacture.

Another object of our invention is the introduction. of carbon into filamentary material in a more compact form than heretofore, for activation purposes.

A further object of our invention is the preparation of filamentary material containmg the required amount of electron-emission material combined with carbon or mixed with a carbon compound, whereb the volume percentage of such admixe material may be reduced to facilitate the working of the filamentar material.

A still furt ier object of our invention is 7 electron-emission material for increasing the electron-emissivity thereof.

In the copending application of R. E. Myers, Serial No. 57 8,47 0, filed July 29, 1922, activation of thoriated filaments, and assigned to the Westinghouse Lamp Company, there is disclosed a method of preparing thoriated filamentary material with its surface so modified that upon heating, as an electron-emitting cathode, in an electron device, free thorium is developed on the surface thereof.

Briefly, the process comprises passing a thoriated filament, while heated, through a hydrocarbon atmosphere, comprising such compounds as benzene vapor or illuminating gas, whereby the thoria in the filament is either reduced to thorium, changed to thorium carbide or a mixture comprising one or more of the following materials is formed in or on the filament :--thorium, thorium carbide and tungsten carbide.

The process described in said application is only applicable for adapting material in Application fled February 81, 1928. Serial No. 820,485.

. heating, without further treatment, upon introduction to an electron device, carbon and thoria have been mixed with tun ten pow- 'der, which mixture was subsequent y pressed,

treated and drawn to filamentary form in accordance with usual practice.

The disadvantage in such a procedure lies in the fact that free carbon is relatively light and therefore occupies a relatively large volume in proportion to its weight. The introduction of more than a very small proportion of carbon in this manner makes 1t more difiicult to work the tungsten to filamentary form, because the difliculty in working tungsten, where foreign materials are added, is largely dependent upon the volume percentage of such foreign materials rather than on the percentage by weight.

To obviate the above noted difliculty, we propose to prepare activated filamentary material by mixing with tungsten powder, instead of a mixture of thoria and free carbon, either thorium carbide alone, or a mixture of thorium carbide and thoria or other thorium compound. If thorium carbide is used instead of free carbon, the volume percentage to be added for introducing the same weight of material is very much less than with free carbon. The volume percentage of thorium carbide necessary would be about A; that of free carbon.

As an'alternative, the mixture of thorium carbide and thoria may be used, in which case, they may be simply mixed with tungsten powder, pressed into a bar or slug,

sintered either by the ordinary method in hydrogen or in a vacuum, if desired. Thorium carbide may be conveniently prepared by heating the metal powderto about 900v C. in an atmosphere of illuminating as, benzene vapor or 'other hydrocarbon. or example, thorium carbide was prepared by heating thorium powder to about 900 C. for from two to three hours in a slow stream of illuminating gas, which was previousl dried bydpassingj through concentrated su phuric ac1 Thorium carbide, alone, may be mixed with tungsten powder, the mixture ressed, treated and worked to the desired lamenamount of carbide b tary form. In this instance, there will probably be enough oxide in the tungsten or enough oxidation introduced during the treatment, to at least partially decompose the thorium carbide to cause activation of the material. On the other hand, it is not necessary to have any free thorium present on com leting the working of the wire. If all of 51s thorium is then in the form of thorium carbide, it may be desirable to have it that wa because of its greater stability than free t orium.

When heated to a suficiently high temperature after introduction as a hot cathode m an electron device, the thorium carbide will either dissociate directly with the liberation of thorium, or will react with oxides present with the liberation of thorium.

In the following detailed description our invention is disclosed for producing activated tungsten but it is to be understood that we do not wish to be restricted to tungsten for substantially the same method is applicable for-producin activated molybdenum, tantalum and otier similar refracto metals.

i f it is desired to use thorium carbide alone for activating the tungsten, the same weight may be used as is ordinarily emp oye'd for manufacturi thoriated tungsten, for example, 1 or 2% or less, by weight, may be admixed with tun car ide and thorium axide or thoria are used, it is only necessary to employ about approximatel half the quantity of the different in ients.

The carbide or carbide and thoria are preferabl very intimately mixed with tungsten pow er, pressed into slugs of a convenient size, sintered or heat treated and finally swaged or rolled and drawn to the desired filamentary form. The same method of incorporating the carbide or carbide mixture may be used as is described and claimed in the copending ap lication of W. B. Gero, Serial No. 618,396, led February 10, 1923, manuated that the only change from the customen powder.- If a mixture of thorium,

ary metho'd of preglaring thoriated filamentary material, who is well known to those ski led in the art, is the addition of either thorium carbide alone, or admixed with thoria, instead of the usual proportion of c;

thoria.

After drawing to the desired size of wire, the same ma be introduced into an electron device, as t e hot cathode thereof. Upon heating to incandescence, thorium will be developed or liberated in the filament, either by decomposition of thorium carbide, interaction between thoriumcarbide and thorium oxide, or between thorium carbide and tlmgsten oxide. Whatever the precise reaction or combination of reactions, ood activation is produced because of t ie liberation or development of free thorium, at least on the surface of the filamentary cathode.

Although thorium has been disclosed as the preferred activating material, it is to be understood that our invention is applicable for activating by means of other electronemitters' such as uranium, zirconium and the like.

Although we have described what we now consider the preferred means of practicing our invention, it is to be understood that modifications will accur to those skilled in the art and we on] wish to be restricted within the spirit an scope of the appended claims.

What is claimed is:

1. The method of manufacturing tungsten in filamentary form for electron-emission purposes comprising mixing with tungsten wder, a small proportion of thorium caride, pressing said mixture to form a slug, heat-treating said slug and working to the desired filamentary form.

2. Themethod of manufacturing a refractory metal filament for electron emission purposes comprising mixing with the refractor metal power asmall-pro ortion of a car ide of a metal of good e ectron emissivit agglomerating said mixture into a bar, eat treating said bar and working and drawing the same to the desired filamentary orm.

In testimony whereof, we have hereunto 1o JOHN WESLEY MARDEN. JOHN EDWARD CONLEY.