US2453753A - Method of manufacturing cathodes of electric discharge tubes - Google Patents

Description

Patented Nov. 16,1948

, Marne!) oFMANUFAoTURING cArHoDEs j or ELECTRIC DISCHARGE TUBES] V .Robert Loosjes, Eindhoven, Netherlands, assig'nor to Hartford National Bank and, Trust Com:

- "pany, Hartford,- (;onn., as trustee No Drawing. Application February 8,1947, Se-

rial No. 727,303. In Belgium November 4, 1944 Section 1, Public Law .690, August 1 v Patent expires November 4, 1964 3 Claims.

In the manufacture of cathodes for electric discharge tubes, it is sometimes desirable to incorporate a method which permits of the cathode being manufactured outside the tube itself and of being exposed to the atmosphere for some time. This necessity particularly occurs in the case of cathodes that are manufactured, for example by the well-known azide-treatment as described in the Netherlandish Specification 19,215, more generally speaking in those methods, in which an alkaline earth metal is precipitated from the vapour phase, since in such cases there is the risk that the barium which evaporates from the azide or other compound or mixture would become deposited not only on the cathode but also on other areas or parts inside the tube and causes undue emission phenomena from those areas or parts, and in certain cases even cause short circuits. Also in the case of cathodes which are manufactured otherwise, for example by application and dissociation of an alkaline earth carbonate, it is important to incorporate a method in which the cathode is first manufactured in a separate space, in order to avoid the generation of large quantities of carbonic acid in the tube which must then be removed.

Th object of the present invention is to provide a method of manufacturing a cathode of an electric discharge tube, which consists in that an oxide cathode manufactured in any way in a separate space is coated with a copper, silver or gold film, is then removed from this space and finally incorporated in the actual tube, where the protecting outer layer is then vclatilized from the cathodes by heat.

This method provides a means of keeping the cathode for any length of time, for example in air, and in such cases it is not essential that the cathode should be manufactured inside of the tube in which it is to be used ultimately. It is desirable to use a protective layer which has no detrimental effect during volatilisation. Thus, for example, the protective metal films made of copper, silver or gold have advantages over the well-known layers made of a hydrocarbon, such as parafiin, polystyrene and similar substances, because the latter substances produce harmful gases during volatilisation, whereas the metals according to the invention practically have no detrimental effect. It is in many cases, even advantageous when a grid or an anode is coated with a copper, silver or gold film. The coating with copper, silver or gold can be readily effected by volatilization from a Wire Which is arranged in the proximity of the cathode. The protective film need only have a thickness of some few microns.

In order that the invention may be clearly understood and readily carried into effect, it will now be set out'more fully with reference to two embodiments, given by way of example, in which methods according to the invention are described in detail.

Barium-azide is heated and dissociated in a separate, exhausted space; next barium is volatilized and the vapour produced deposited on a core body, the surface of which is constituted by nickel oxide or copper oxide; an emissive layer of barium oxide is then formed by heat. Next, the barium oxide has a protective copper film applied to it by volatilization in the same space and the cathode, after being kept in the air for any length of time, is incorporated in the actual tube, the protective copper film being removed by volatilization.

In an alternative embodiment of the method according to the invention, a cathode core body is coated in known manner with a layer of a mixture of bariumand strontiumcarbonate; these carbonates are then dissociated, the carhome acid formed is pumped off and the alkaline earth oxide left on the core is coated with a silver film. The cathode is then removed from this space and after being kept in air for any length of time, is incorporated in the actual tube, the silver film being removed by volatilization.

What I claim is:

1. A method of manufacturing a cathode of an electric discharge tube, which comprises treating a cathode core with an alkaline earth material in an evacuated space to provide a layer of an alkaline earth metal oxide, coverin the layer with a film of a metal selected from the group consisting of copper, silver, and gold, removing the cathode thus formed from that space and disposing the cathode in the tube in which it is to be used, sealing the tube and removing the metal film from the cathode by volatilization of the metal.

2. A method of manufacturing a cathode of an electric discharge tube as claimed in claim 1, including heating and dissociating an alkaline earth metal azide in an exhausted space separate from the tube in which the cathode is to be used, depositing the alkaline earth metal vapour thus produced on a cathode core having a surface of nickel oxide or copper oxide, and then coating this body with a metal selected from the group consisting of copper, silver and. gold film, then removing the cathode thus obtained from the 3 said space and housing it in the actual tube where it is to be used, and then volatilizing the metal film.

3. A method of manufacturing a cathode of an electric discharge tube as claimed in claim 1, including the step of applying an alkaline earth carbonate to a cathode core body, then heating and dissociating the carbonate in an exhausted space separate from the tube in which the oathode is to be used, coating thealkaline earth oxide with a film of metal selected from the group-consisting of silver, copper and gold, removing the body thus obtained from the said space and housing it in the actual tube, and then removing the protective metal film by volatilization.

ROBERT LOOSJES.

REFERENCES CITED The following references-are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,936,334 Miesse Nov. 21, 1933 1,936,419 Asao et a1 Nov. 21, 1933 FOREIGN PATENTS Number Country Date 255,090 Great Britain June 9, 1927