DE728589C - Process for the production of tubular tungsten incandescent cathodes for electron tubes - Google Patents

Description

Process for the production of tubular tungsten incandescent cathodes for Electron tubes To enlarge the cathode surface, there are already different ones Procedure became known. For example, tubes and larger cathodes , also tubes mostly made of nickel, in special cases also copper or tungsten as base metal used, on which a highly emissive layer (B.arium compounds) is applied will. Such cathodes are mostly indirect by means of an .isolated heating element heated. Tubular, directly heated cathodes are also already known. At half indirect heating of such tubes as hot cathodes is inside the tube a heating wire is arranged, while the tube itself is used to return the current. However, all these high-emission cathodes have the disadvantage that at high anode voltages, which are necessary for high-performance tubes, the dreaded spitting occurs and at the necessary high field strengths, particles. the applied emission layer loosen, which lead to the formation of arcs and thus to the destruction of the cathode can. In addition, when such cathodes are subjected to a high anode load, as a result of their Sensitivity to temperature fluctuations, strong re-heating effects, due to which the electron flow can rise like an avalanche and the tube can be destroyed.

Solid cathodes, e.g. B. paus tungsten, molybdenum, Tontal or thoriated Experience has shown that tungsten cathodes do not have the disadvantages mentioned above.

Even if it is already known, tubular cathodes from: the mentioned Manufacture of materials, the technical production is after the usual Drawing and hammering processes are very difficult because of the brittleness of these materials, Up to now impossible with thoriated tungsten, since the addition of thorium oxide removes the tungsten becomes even more brittle.

To now, in a simple manner, tubular tungsten incandescent cathodes for electron tubes produce, is, according to the invention on a with a wrapping of thoriated or pure tungsten wire with close together lying turns A tungsten powder with or without the addition of thorium oxide is applied to the core wire provided and sintered and the core wire chemically removed after sintering.

After removing the core wire, which is made of iron, for example or molybdenum, the resulting tube is below 200 to 300 ° C sintered at the tungsten melting temperature for a longer period of time, resulting in a stable tube in which the sintered crystal structure of the previously amorphous Powder connects intimately with the helix. During this process, the steams Thorium dioxide, which is firmly enclosed in the crystal structure of the thoriated tungsten wire located, only to a very small extent during sintering, so that for the operation of the cathode still sufficient thorium oxide is retained in the wire.

In the case of electron tubes that have to work without a getter, the use of undesired by thoriated tungsten cathodes. On the other hand, you want to be there too Use cathodes with a large emitting surface. As mentioned at the beginning, is the production of pure Wolframröhr chen according to the known method as a result The brittleness of the material is very difficult, especially when it comes to thin walls Tubes easily cracked.

It is also very advantageous here to use the method according to the invention To apply, since it has been shown that the wire helix applied to the core wire besides the aforementioned purpose of preventing the evaporation of thorium oxide also serves to give the cathode a stable, firm and crack-free structure.

In order to influence the grain growth of such tubes is expedient instead of tungsten powder with thorium oxide added tungstic acid, which is also with a binder is mixed, applied with thorium nitrate additive and reduced. During the reduction, which can take place in hydrogen, for example, is carried out by suitable choice of temperature levels influences the grain size of the tungsten powder; so that in the subsequent high sintering a suitable fine crystalline structure with the smoothest possible surface, which reduces the radiation and thus the heating power of the cathode is kept low.

The filament can be omitted for the production of pure tungsten cathodes and tungsten powder sprayed directly onto the core wire.

Fig. I shows a cathode manufactured according to the new process. On the core wire i is a winding of thoriated or pure tungsten wire applied with closely spaced turns 2, on which a tungsten powder 3 is applied with or without thorium oxide and sintered.

Fig. 2 shows a pure tungsten cathode, in which the filament - is omitted and the Wo-lfram powder er 3 is sprayed directly onto the core wire i has been.

Claims (3)

PATENT CLAIMS: i. Process for the production of tubular tungsten incandescent cathodes for electron tubes, characterized in that a tungsten powder with or without thorium oxide addition is applied and sintered to a core wire provided with a winding of thoriated or pure tungsten wire with closely spaced turns and that the core wire is chemically removed after sintering . 2. A method for the production of hot cathodes according to claim i, characterized in that characterized in that, instead of tungsten powder with thorium oxide added, tungstic acid is applied with thorium nitrate additive and reduced. 3. Use an after the method according to claim i or 2 produced tungsten tube as cathode body for indirectly or semi-indirectly heated cathodes.