US2014847A - Indirectly heated cathode - Google Patents

Description

Sept 17, 1935. J H. JQNKER 2,014,34?

INDIRECTLY HEATED CATHODE Filed July 20, 1954 INVENTOR JOHAN L.H. JONKER electron emitting material.

Patented Sept. 17, 1935 UNITED STAT A i'N'l' OFFICE INDIRECTLY HEATED CATHODE Application July 20, 1934, Serial No. 736,211 In Germany September 7, 1933 5 Claims.

This invention relates to an indirectly heated cathode for electric discharge tubes comprising at least a heating member and a cathode proper consisting of a metal carrier body coated with These cathodes may consist, for instance, of a heating member surrounded by and, if desired, insulated from the carrier body which carries the emitting layer.

With such cathodes the electron emitting material, such as a suspension of an alkali or alkaline earth compound, is sometimes applied by immersion to the surface of the carrier body. However, it is also possible to apply such a compound, or some other electron emitting material, by spraying, or by disintegration of the compound on the surface of the carrier body.

It has previously been known that it is important to reduce as much as possible the heat radiated by the carrier body and by the electron emitting material, which heat is consequently derived from the heating member, in order that the consumption of energy for heating the cathode to the required temperature be as small as possible. This might be done, as has already been proposed,

' by reducing as much as possible the thickness of the emissive layer applied to the carrier body. Furthermore it is possible, as has already been suggested, to reduce the loss of energy due to radiation of the carrier body and of the emissive layer by using a carrier body which is made of material with a very small heat radiating capacity, and on which the emitting material is applied in the form of a thin layer.

I have now found that the desired reduction in the amount of heat radiated from the cathode can be obtained in a very suitable manner by using an indirectly heated cathode constructed according to the invention. With this cathode, which consists of a heating member and a metal carrier body, the electron emissive layer or coating is applied in such a manner that it is discontinuous and parts of the surface of the carrier body are left uncovered or free between various parts of this emissive layer.

By this invention the result is achieved that the heat radiation of the cathode body itself, together with that of the electron emitting material, can be materially reduced. In fact, more particularly when using thin layers or coatings of electron emitting material, the sum of the heat radiation of both the cathode surface and the emitting layer surface is always involved, since the heat radiation of the cathode surface traverses the surface of the layer of emitting material. By means of the invention it is possible to reduce to zero the heat radiation of the emitting layer over part of the surface of the cathode. It will be appreciated that in this manner an improvement of the properties of such cathodes can be obtained. 5

In order to avoid affecting the electrical properties of discharge tubes equipped with cathodes made according to the invention, it has been found to be very advantageous to make the distances between the parts of the coating of emit- 10 ting material small relatively to the distance between the cathode and the first grid, for example, of the order of one-tenth of this distance. In the usual discharge tubes with the distance between the cathode and the grid about 0.5 mm., it has been found to be advantageous to make the distance between the discrete parts of the emissive layer about 0.05 mm.

It has turned out that the invention lends itself more particularly for use with indirectly heated cathodes in which the carrier body for the emitting material consists entirely or partly of a metal of less heat radiating capacity than that of nickel, and preferably a metal of the copper class, such as copper or silver. Even if, when using these metals, with which consequently the substratum of the emitting material has a very small heat radiating capacity, this emitting material is applied in the form of extremely thin layers, the heat radiation of the emissive layer plays in spite thereof such a part that when using the present invention a considerable improvement is obtained also with such cathodes.

The object of the invention may advantageously be attained by applying the emitting layer by spraying or by disintegration of suitable compounds. In this manner it is readily possible to make the electron emissive layer on the carrier body in such a way that it is discontinuous and that part of the surface of the carrier body remains uncovered between the discrete parts of the layer.

In the accompanying drawing, which shows as one example a cathode made according to the invention and manufactured according to the following method given by way of example, Figure 1 is a longitudinal section of the cathode, and Figure 2 a plan view of part of the cathode surface.

In the drawing, in which the cathode made according to the invention is represented very diagrammatically, I is the heating member of an indirectly heated cathode of which the carrier body consists of a metal tube 2. An insulator 3 is provided between the heater 1 and the carrier body 2.

On the outside of the carrier body 2 an electron emissive layer or coating 4 is applied in such a way that it is discrete or discontinuous and parts of the underlying metal surface between the many parts of this coating are left uncovered. The distance between the separated or discrete parts of the coating 4 is about 0.05 mm. The cathode is surrounded by a grid 5, which is spaced at a distance of about 0.5 mm. from the cathode, and which in turn is surrounded by an anode or plate 6.

The cathode referred to may be made as follows: Several cathodes which have not yet been provided with electron emitting material are introduced into a spraying, or coating mill. A coating consisting, for instance, of barium and strontium carbonate is applied to these cathodes in some well known manner, such as spraying. In order to insure a good distribution over the cathode surface the spraying is done with low air pressure, the solution or suspension containing a comparatively large quantity of solid material with respect to the liquid. The aperture discharge opening of the spray gun is comparatively large, for instance, 1.5 mm. so that a definite quantity of perfectly distributed barium and strontium carbonates can be readily applied on the cathode.

After the spraying operation, by which the coating is applied in such a way to the cathode that part of the cathode surface remains free and uncovered between the various parts of the emissive coating, the cathodes are removed from the spraying mill, and further finished and treated in the usual way.

It will be appreciated that the manufacture of the cathode according to the invention is not limited to the embodiment referred to above, but also includes many other methods of manufacturing such a cathode.

What I claim as new is:-

1. An indirectly heated cathode for electron discharge tubes consisting of a heating member, a metal carrier adjacent said heating memher, and a discontinuous electron emitting coating on said carrier composed of discrete parts distributed substantially uniformly over the surface of said carrier and spaced apart on said surface a distance of about 0.05 mm.

2. An indirectly heated cathode for electron discharge tubes consisting of a heating member and a carrier of a metal of the copper class mounted adjacent said heating member and coated with material of high electron emissivity distributed on the surface of said carrier to form a discontinuous coating of discrete parts spaced about 0.05 mm. to leave uncovered part of the surface of said carrier.

3. An indirectly heated cathode for electron discharge tubes consisting of a heating member, a carrier adjacent said heating member of copper, and a discontinuous electron emitting coating composed of discrete parts each containing barium and strontium compounds and distributed on said carrier to be spaced about 0.05 mm. and to leave uncovered part of the carrier surface between the discrete parts of the electron emitting coating.

4. An indirectly heated cathode for electron discharge tubes consisting of a heating member, and a metal carrier adjacent said heating member coated with alkaline earth metal compounds of high electron emissivity distributed on the carrier body to form a discontinuous electron emitting coating consisting of discrete spots of said compounds spaced about 0.05 mm. with the carrier surface between spots free of said compounds.

5. An electron discharge device comprising an indirectly heated cathode consisting of a heating member and a metal carrier adjacent said heating member, a grid electrode surrounding and spaced away from said carrier, and a discontinuous coating on said carrier of material of high electron emissivity distributed over the surface of said carrier in discrete parts with the distances between said discrete parts about one tenth of the distance between said carrier and said grid electrode.

J OI-IAN LODEWIJ K HENDRIK J ONKER.

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