DE2104062A1 - Fine machining of sintered refractory metal bodies - to produce storage cathodes for electrical discharge devices - Google Patents

Abstract

Fine-working of porous sintered bodies of refractory metals of gps. IVa, Va and VIa, such as W, Mo, Ta, Hf, Nb, etc., is facilitated by deposition of metals of gp. VIIa or VIIIa; such as Re, Os, Ir, etc., followed by heating to effect diffusion and partial alloying. The residual deposit remaining on the surface after the working is removed mechanically or by thermal diffusion. The presence of residual amounts of these metals does not interfere with the emission of the cathode, in contrast to Ca normally used for this purpose.

Description

?? Process for the machining of sintered bodies with high melting points Metals for electrical discharge vessels "The invention relates to a method for machining of porous sintered bodies of refractory metals from groups IVa, Va and VIa such as tungsten, Mo, Ta, Hf, Nb or the like, in particular for toroidal cathodes of electrical discharge vessels.

It is of particular importance for supply cathodes, especially metal capillary cathodes, in which a porous sintered, for example tungsten body, either with a active substance, usually barium, is impregnated or a corresponding supply in a container and in which the surface serves as an emission surface. Such sintered bodies are predominantly made purely metallurgically by pressing and sintering manufactured. However, there are always cases in which machining post-processing, mostly fine machining, is required, e.g. B. with complicated body shapes or Bodies with very small contours.

It is already known1 for this purpose the porous sintered body, such as B. immersed tungsten body in molten copper, which is in question Avidly fills pore volume with copper. After machining the copper is then removed either by chemical leaching or by evaporation removed again. The known procedure has however the disadvantage that this process is very tedious and never takes place quantitatively and on the other hand, that the machining is still quite difficult and only with hard metal or Vidia tools is possible. Particularly disturbing and disadvantageous, however, is the fact that such processed Electrodes when used in electrical discharge vessels in a heated state Re-vaporize copper for as long as you like and thereby usually cause malfunctions.

The object on which the invention is based is therefore to use metals for the aforementioned purpose, which considerably increase the machinability facilitate more, practically only to be attached to the surface and if of it Residues remained on the surface, mostly practically no disruptive effect have or are easy to remove.

This is achieved with a procedure described in the first paragraph for the machining of porous sintered bodies according to the invention, that on the surface to be processed, partial surface or the like, another other Group VIia or VIIIa refractory metal such as W, Re, Os, Ir or the like deposited by annealing a diffused and partially alloyed and that after-the machining of it possibly disturbing residues a.l of the surface each removed mechanically or by diffusion annealing, depending on the extent.

The deposition takes place chemically reductive with particular advantage, ie currentless, ao that after diffusion a penetrated or alloyed zone 2 - 3 tenths of a mm deep is available. The application of the metal can also by vapor deposition, but with less strength. Of the applied Re diffuses metals very well; Os, on the other hand, is much slower. With that in addition applied metal is an expansion of the base metal grid z. B. of the tungsten lattice, so that the loosening involved makes it easier to work with will. After machining become remnants of the additional metal either mechanically removed or, in the case of small quantities, diffused into the base material.

In the case of porous tungsten sintered bodies for supply cathodes, the presence is of residues of the additional metals in question are not disruptive as these Metals consistently even improve the quality of the cathode in question.

4 claims

Claims (4)

Claims 0Method for the machining of porous sintered bodies of refractory metals from groups TVa, Va and VIa such as W, Mo, Ta, Hf, Nb or the like, especially for supply cathodes electrical Discharge vessels, characterized in that on the surface to be processed, partial surface or the like another other refractory metal of group VIIa or VIIla, such as W, Re, Os, Ir or the like deposited, diffused in by annealing and is partially alloyed and that after the machining of it possibly disturbing residues on the surface mechanically or by diffusion annealing, depending on the extent removed. 2. The method according to claim 1, characterized in that when carried out a stronger machining process this in partial threading and accordingly the metal separator inserted in the meantime, also several times he follows. 5. The method according to any one of several of claims 1-2, characterized characterized in that the deposition takes place electroless, namely chemically reductive. 4. The method according to one or more of claims 1-3, characterized characterized in that the deposition takes place by vapor deposition.