US3056061A - Method of manufacturing nickel supports for oxide cathodes and cathodes provided with such supports - Google Patents

Description

Sept. 25, 1962 H. MELSERT 3,056,061

METHOD OF MANUFACTURING NICKEL SUPPORTS FOR OXIDE CATHODES AND CATHODES PROVIDED WITH SUCH SUPPORTS Filed Jan. 18, 1960 lY/c/re/ .I/eeve B Oxide coaizhg Era/H1219 surface 5 Passive IV! .Bound INVENTOR H. MELSERT AGEN .the supports of United States Patent Hans Melsert, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Jan. 18, 1960, Ser. No. 3,183 Claims priority, application Netherlands Mar. 6, 1959 Claims. (Cl. 313-346) It is known that the active nickel commonly used for oxide cathodes contains some impurities, inter alia magnesium, manganese, silicon, and iron, from which especially magnesium is favourable for the emission of electrons due to reduction of barium oxide. How ever, particularly magnesium has the disadvantage that it continuously evaporates from the cathode during opa mirror gives rise to a capacitance between the electrodes which becomes greater and greater. More particularly the resulting varying capacitance between the anode and the control grid is very troublesome for the performance of the device of which the tube forms part.

This disadvantage may be avoided by the use of nickel of high purity, wherein the impurities are present in less than 0.022% by weight. However, such nickel brings about .a lower emission of electrons due to the reduction The present invention permits of avoiding the troublesome evaporation of magnesium from the cathode support without the electron emission being detrimentally affected.

According to the invention, for this purpose, in the tubular support for an oxide cathode, which support consists of nickel containing inter alia magnesium as an im purity, steps are taken to ensure that, during heating to from 1000 C. to 1200 C., oxygen can diffuse into the nickel from the surface opposite to the surface intended as the support for the emissive layer, until at least the magnesium present in the nickel has been bound for the greater part, but not completely, by oxygen. magnesium remains free in the than half the wall thickness.

of the tubular support connected to tube means that communicate with the exterior of the oven chamber. The tube means may communicate with the oxygen contained in the surrounding air, or, in the alternative, for a more positive supply of oxygen for the dilfusion process the tube means may be connected to a gas circulating and/ or feeding system that pumps oxygen to the tube means and tubular support. It has been found that, if the support has a wall thickness of 0.1 mm., heating at 1100 C., for a period of 20 minutes yields the desired result. The outer surface of the tube is kept in a neutral atmosphere such as nitrogen, for example, by furnishing the interior of the oven chamher with a nitrogen atmosphere. The surface on which the electron-emissive material will be provided later on is then still active since it still contains free magnesium, but it has been found that in the part of the support-wall in which oxygen has penetrated, the magnesium is comis still present in the remaining part of the support-wall does not evaporate either.

Instead of being brought into contact with air, the said surface of the support with a wall thickness of 0.1 mm. may alternatively be covered with an oxide layer, for example a 0.1 mm. layer of nickel-oxide, from which oxygen can be freed for heating at 1100" C. during 10 min. and diffuse into the nickel in a neutral vacuo. This affords the advantage that the said surface is insulated with respect to the heater of the cathode and that the heating process can coincide with the heating carried out for activating the electron-emissive layer after the cathode has been mounted in a discharge tube. In fact, the temperature necessary for activating and disintegrating the emissive layer ordinarily consisting of equal parts barium oxide and strontium oxide, also lies between 1000 C., and 1200 C. In any case, the process of heating to the said temperature must not be continued until the Mg has been bound throughout the whole Wall thickness. Free magnesium must always remain present at the surface covered with the oxide layer.

The content of impurities is low. The Mg-content of the said nickel is, for example, from 0.05 to 0.06% by weight. The nickel further may contain 0.01% silicon; 0.02% iron and 0.101% manganese. However, impurities with a percentage of weight lower than 0.02% do not not react notably with the emitting oxides. Nickel containing such small percentages of impurities is therefore also said to be passive. From the said impurities only magnesium, and to a lesser degree also manganese, can give trouble due to evaporation.

In order that the invention may be readily carried into effect, it will now be described, by way of example, with reference to the accompanying drawing showing one embodiment thereof, viz., a cathode sleeve, partly in section, according to the invention.

In the FIGURE, a tubular sleeve 1 consisting of active nickel as mentioned above and having a wall thickness of 0.1 mm., is covered at the outer side with an oxide coating 2 consisting of equal parts barium carbonate and strontium carbonate. The inner surface of the sleeve has been covered with nickel oxide 3. During activation of the cathode in the discharge tube, the sleeve 1 is heated at 1100 C. for 10 min. whereby the carbonates are converted into oxides and oxygen from the NiO layer 3 difluses into the nickel of the sleeve 1, to about half its thickness, thereby completely converting the Mg and, possibly the other impurities, into oxides, so that part 5 of the sleeve becomes passive. The remaining part 4 remains active. It is desirable that the part 5 extends at least over half the wall thickness.

What is claimed is:

l. A method of manufacturing an oxide-coated cathode comprising the steps of providing a nickel support containing magnesium as an impurity, said support havsecond surface and leave free the remaining portion of said magnesium adjacent to said first surface.

2. A method of manufacturing an oxide-coated cathode comprising the steps of providing a nickel support containing magnesium as an impurity, said support havpredetermined part of said distance to cause a substansaid magnesium to become bound with said oxygen adjacent to said second surface and leave free the remaining portion of said magnesium adjacent to said first surface.

3. A method according to claim 2 wherein said nickel support comprises a tubular member having a lateral wall, said first and second surfaces comprising the interior an exterior surfaces, respectively, of said wall, and during said heating step said oxygen passes through the interior of said tubular member for said diffusion thereof and said first surface is maintained in a neutral .atmosphere.

4. A method according to claim 3 wherein during said heating step said support is heated from 1000 C. to 1200 C.

5. A method according to claim 3 heating step said support is heated at minutes.

6. A method according to claim 2, wherein said oxygen binds said magnesium adjacent to said second surface greater than one-half of said distance.

7. A method according to claim 2 further compris ing the step of covering said second surface with an oxide layer prior to said heating of said support to provide said oxygen for said diffusion.

8. A method according to claim 7 wherein said first surface is covered with said alkaline earth oxide prior to said heating, and said support is effected in a vacuum to provide simultaneously the aforesaid diffusion and emiswherein during said 1100 C. for twenty sive activation of said alkaline earth oxide of said first surface.

9. A nickel support containing magnesium as an impurity for supporting an electron emissive layer of an oxide-coated cathode comprising a first surface for support of an alkaline earth oxide, and a second lateral surface disposed a predetermined distance from said first surface, a substantial portion of the magnesium being bound adjacent to said second surface and the remaining portion thereof free adjacent to said first surface.

10. A nickel support containing magnesium as an impurity for supporting an electron emissive layer of an oxide-coated cathode comprising a hollow cylinder with a lateral wall having a predetermined thickness, said lateral wall having a first surface to support said emissive layer, and a second surface, a substantial portion of the magnesium being bound adjacent to said second surface and the remaining portion thereof being free adjacent to said first surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,778,970 Widell Jan. 22, 1957 2,912,611 Beck Nov. 10, 1959 FOREIGN PATENTS 213,179 Australia Feb. 7, 1957

Claims (1)

1. 9. A NICKEL SUPPORT CONTAINING MAGNESIUM AS AN IMPURITY FOR SUPPORTING AN ELECTRON EMISSIVE LAYER OF AN OXIDE-COATED CATHODE COMPRISING A FIRST SURFACE FOR SUPPORT OF AN ALKALINE EARTH OXIDE, AND A SECOND LATERAL SURFACE DISPOSED A PREDETERMINED DISTANCE FROM SAID FIRST SURFACE, A SUBSTANTIAL PORTION OF THE MAGNESIUM BEING BOUND ADJACENT TO SAID SECOND SURFACE AND THE REMAINING PORTION THEREOF FREE ADJACENT TO SAID FIRST SURFACE.

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