US1615994A - Electrode and method of degasifying the same - Google Patents

Description

Feb; 1, 1927.

M. MORRlSON ELECTRODE AND METHOD OF DEGASIFYING THE SAME Filed Dec. 1. 1921 I L I a I i FUSIBLE METAL R R E m H m m V 0 T R A mo 1 Patented Feb. 1, 1927.

Uhll'lED STATES PATENT Oil- HEE;

MONTFORD MORRISON, OF NEW YORK, N. Y.

ELECTRODE AND METHOD OF DEGASIFYING THE SAME.

Application filed December The present invention relates to electrodes and more particularly to those operated at an elevated temperature.

In the electrical and electro-chemical arts, electrodes are frequently employed in a manner which causes them to be raised to an elevated temperature. This is true, for example, of electrodes for are lights, electric furnaces and X-ray generating bodies. The heating of such electrodes should not, of course, be allowed to reach the melting point of the material of which they are composed.

To enable the electrodes to withstand high temperatures, refractory conducting materials and cooling means, such as circulating water for rapidly conducting the heat away from electrodes, have been used. The corn bination of refractory materials, and cooling means has, however, been made in such manner as to be disadvantageous or inappropriate for certain usages; for example, in the manufacture of X-ray targets, which are heated by electronic bombardment, it has been proposed to utilize a refractory metal for the target proper and to surround the target with a metal having high heat conductivity, such as copper, in order to keep the temperature of the target down to a minimum. This practice is open to certain objections; for example, being operated in an evacuated vessel in which a very high vacuum must necessarily be maintained ases which may be liberated from the copper inpair or destroy the operation' of the tube.

That gases are likely to be liberated from the copper, as now combined with the electrode, is ascribed to the fact that the meltingpoint of the later element is such that it may not be heated to a sufficiently high temperature to be completely degasilied. The comparatively low melting point of copper and of other metals of high heat coiuluctivity, as now employed in the con struction of electrodes, demands that a comparatively large body of such material be used if the destruction of the electrode by fusion is to be avoided.

From these considerations, it is an object of this invention to provide an electrode capable of withstanding high temperature and, at the same time, one that shall have high heat conductivity.

Another object of the invention is the provision of an electrode which will with.

1, 1921. Serial No. 519,154.

stand a temperature sufiiciently high to thoroughly degasify it.

A further object of the invention is the provision of a method for degasifying an electrode.

A special object of the invention is the provision of a comparatively small anode for an X-ray device which may, at the same time, be operated at a. comparatively high temperature.

Other Objects of the invention Will be ap parent from a reading of the following description in connection with the accompanying drawing, the single figure of which illustrates an embodiment of my invention in the form of an electrode for the generation of X-rays, shown partly in section.

While my invention pro ides an electrode applicable in many arts, it will be set forth, for the purpose of illustration, as embodied in an electrode especially adapted for the generation of Roentgen or X-rays.

According to my invention, an elect-rode 1, usually constituting an'anode, at which X-rays are generated, comprises a body or shell 2 of refractory material having the usual focal spot 8 consisting of a material of high atomic weight and enclosing a solid, liquid, or gaseous body 4, of high heatdissipating capacity in such manner that the latter may be held intact in a molten condition. Preferably, the refractory material 2, which may be tungsten, is a hollow body of any suitable configuration partly or wholly filled with a metal 4 of high heat conductivity, such as copper.

It is well known that all bodies in their natural state, being porous, and being in contact with gases, such as the atmosphere, contain occluded gases, and that these gases are slowly liberated if the bodies are placed in a vacuum or under reduced pressure and at a faster rate if they are heated to an elevated temperature under such conditions. It is, therefore, necessary to degasify bodies which are to function in devices in which it is necessary to maintain the pressure of the residual gas below a low limiting value. This is especially true of materials used in modern X-ray devices which operate with a substantially pure electron discharge, a necessary condition for which is that an extremely low gaseous pressure exist in the tube.

In order to degasify the electrode of my invention, as employed in an X-ray tube,

the electrode 1 may be heated to a high temperature by any one of several well known methods while the pressure of the inner space of the tube is maintained below that of the atmosphere, preferably a vacuum. The occluded gases are thus liberated and are preferably exhausted from the tube as released. The electrode may be heated by high-frequency induction currents generated by'surrounding the-electrode with a conduct-- ing body carrying a high-frequency current. In this treatment, the temperature of the electrode is preferably raised to a degree just short of the melting point of the enclosing refractory material 2, at which temperature the enclosed material st of high heat-dissipating capacity, a solid body, becomes molten. When it remembered that the occluded gases are more quickly and completely disengaged by heating the electrode to the highest possible temperature, the advantage of heating a part of the electrode to and beyond its melting point will be appreciated.

Inasmuch as an electrode constructed according to my invention may be more thoroughly degasitied than those of the prior art, it may be operated at a higher temperature, without the risk of having gas disengaged therefrom. From its ability to withstand a higher temperature, it follows that a smaller electrode may be used 'for a given power input, or a larger input may be employed for an electrode of a given size. This quality'makes my invention valuable for the manufacture of electrodes for devices such as; X-ray tubes wherein the heat capacity of the electrodes is the limiting feature of the time which the device may be run with out destruction.

While I have described in detail one em bodiment of my invention and the method of utilizing the same, minor modifications may undoubtedly be made therein which, however, would employ the same underlying principle and it is therefore desired that it be understood that such modifications come within the scope of this invention.

hat is claimed is:

1'. An electrode comprising a container of refractory metal closed at one end and fill-ed with a metal of high heat conductivity, solid at room temperatures but of lower melting point than the refractory metal.

2. An anode for an X-ray device comprising a shell of tungsten filled with copper.

3. The method of de 'asifying an electrode comprising a body of refractory material filled with solid metal of high heat conductivity but lower melting point than the refractory material, which consists in heating the electrode to a temperature at which the enclosed metal melts, and pre venting the I e-absorption by the electrode of gases liberated therefrom by heat.

4-. The method of degasi-fying an electrode comprising a shell of refractory metal filled with solid metal of high heat conductivity and lower melting point than said shell, which consists in heating the electrode in a vacuum toa temperature at which the enclosed metal melts, and preventing the re-absorption by the electrode of gases driven off during the heat treatment by enhausting said gases as they are liberated.

In testimony whereof, l have hereunto subscribed my name this 28th day of Nd vember 1921.

MONTFOBD MORRISON.

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