BE483125A - - Google Patents

Description

       

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  Improvements made to metals coated with carbon and manufacturing process for these metals.



   The present invention relates to carbon coated metal for use where it is necessary to have good thermal emissivity or high heat radiating power, for example in vacuum devices such as electric discharge devices containing parts or parts. metal radiating heat in a vacuum during operation of the device. Such a "carbonaceous" metal is particularly suitable, in electronic discharge devices, for tube elements such as carbonaceous plates or anodes, for heat radiators such as grids and for similar uses.

   The invention also relates to metals or carbonaceous plates for the electrodes of electronic discharge devices, the methods of manufacture of these materials and the improved carbonaceous electrodes, such as plates or anodes,

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 used in thermionic discharge devices.



   In electronic discharge devices, metallic parts other than the electron emitting elements are usually kept as cool as possible. For this purpose, in thermionic discharge devices such as radio tubes, these other cold electrodes, such as grids, plates or other electrodes, which receive or are subjected to the influence of electric current during operation, are blackened. so as to increase their thermal emissivity or radiation power; is usually done by covering them with a layer of some form of carbon.

   In large productions, for reasons of economy, long metal strips for carbon electrodes are covered by a continuous process and the electrodes are then fabricated from the carbon metal. Nickel has very often been used as a metal for electrodes. Ferrous metals such as steel. Soft iron or iron alloys are less expensive than nickel and can be used if properly carbonated, but they have not been successfully carbonized. The usual gas "carbonation" process, the metal being heated in a hydrocarbon atmosphere to a temperature at which the hydrocarbons decompose and deposit carbon on the metal, is unsatisfactory when applied to ferrous metals. .

   The temperature required to get the right form of carbon in a hydrocarbon atmosphere is so high that carbonation becomes carburization or cementation of the ferrous metal, which is bad for several practical reasons. Carbonation gas hardens steel, even if it is coated with a thin layer of nickel, and decreases the strength of the metal. As the electrodes must be executed with great precision, stamping is a difficult operation if the carbon strip is not perfect -

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 ductile and virtually resilient. The less carburization of a strip of ferrous metal decreases the flexibility of the metal and hardens it to such an extent that the wear of the electrode stamping tools becomes excessive.



   It is difficult to obtain, by commercially acceptable methods, a carbon layer covering a metallic surface and adhering strongly thereto, because apparently no real bond between the carbon and the metal can be obtained by treatment. thermal. Various expedients such as sandblasting, etching, etching and others have been used to roughen the surface of the metal in order to increase the adhesion of the carbon. Experience has shown that the adhesion of the carbon layer to the metal and the thermal emissivity of the carbon coated electrode are a function and depend on the texture of the metal surface rather than on its ru- gosity.



   The main object of the invention is to form on a metal, such as material for plates or electrodes, a surface having a new texture to which a layer of carbon adheres more firmly than to surfaces obtained by usual methods. , and which, coated with carbon, especially carbon wholly or partially in the form of colloidal graphite, has a thermal emissivity or heat radiating power very greatly greater than that of the best commercial carbonaceous material of the conventional type , and getting very close to that of a black body.



   The invention also has the following objects: to provide on an annealed ferrous metal such as mild steel a very adherent carbon layer applied in such a way that the carbon does not affect or modify in any way the properties of the metal; to create a suitably carbonaceous and commercially useful electrode of ferrous or other metal which may, if desired, be

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 manufactured so as to have a thermal emissivity greater than 90% of that of a black body;

   create an electrode material consisting of strips or sheets of ferrous or other substantially soft metal, which can be easily stamped into precisely dimensioned electrodes, which has a relatively soft press-shaped surface, and which is preferably covered with a layer of carbon so firmly adherent that it can withstand the work of the material in the stamping dies of the electrodes; provide a simple, rapid and continuous process of treating a strip of steel or similar metal to form on its surface a porous novel-type texture layer or matrix such as a sponge to which a layer such as carbon adheres very firmly and with which a carbon layer forms a carbon metal having a thermal emissivity very close to that of a black body.



   In accordance with the present invention, a sheet of metal, preferably but not necessarily a ferrous metal such as mild steel, although some other metals such as nickel can be used, is covered by bonding to one or both of them. faces a porous layer firmly adhering to the metal and composed of fine metal particles welded to each other so as to leave between them voids forming fine pores.

   In the preferred embodiment the metal particles are metal sponges with crevices and microscopic pores, welded together and to the metal so as to form a coherent mass molecularly bonded to the metal and having a novel type texture with porosity or spongy condition due to porosity arising from the minute pores or voids between and between the particles welded to the metal and also arising from the microscopic porosity of the metal particles or sponges themselves. The layer can be, composed of particles having approximately all the same dimension

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 or else a mixture of particles of different dimensions.

   The surface of the layer covering the metal is usually rough and irregular with a multitude of tiny spikes and holes, the surface of porous sponges or metal particles also being covered with microscopic spikes. The layer of welded small porous particles or metal sponges has a novel texture and structure and is preferred because it retains a layer such as carbon more firmly than the porous layer formed with fine solid particles. of metal welded to each other and bonded to the base metal.



   The fine metal particles in the layer are best obtained by reducing, in a controlled manner, the fine metal oxide particles constituting the particles, when they are in place on the base metal. To obtain, for example, the preferred form of a layer composed of porous particles, finely ground metal oxide, preferably nickel oxide, is uniformly distributed over the entire surface of the metal so that it is in contact. with this one; oxide thus forms a layer of powdered oxide, the powder grains being in contact with one another and being kept applied to the metal by means of a binder which disappears when heated moderately.



  The oxide powder is reduced to the state of metallic nickel by heating in a reducing atmosphere the metallic strip carrying the layer of nickel oxide, hydrogen, for example, preferably at a temperature between 800 C and 1100 C. C, until the grains of nickel oxide are reduced, without melting, to tiny nickel sponges with microscopic pores and crevices. The temperature at which the nickel oxide is reduced is high enough to produce nickel sponges when the powdered nickel oxide grains are reduced, but too low to melt the reduced nickel oxide. a solid mass.

   These porous nickel sponges

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 individually hold each other despite being welded to each other and to the solid base metal.



  As a result, the base metal is covered with a surface layer of new-textured metallic nickel, which is soft, well bonded to the underlying metal and porous due to the tiny voids between the metal sponges. and because of the microscopic pores in the sponges themselves. The metal coated with the novel type layer forms a support which, when properly carbonated, produces a carbonaceous electrode superior to the current electrodes. A layer, such as carbon mainly comprising colloidal graphite, applied to and covering this porous layer turns out to be exceptionally adherent.

   The adhesion of the carbon particles to the porous layer is greater than the cohesion of these particles to one another; It follows that the carbon is not removed in the form of bands or peels, but only in the form of a carbon powder, the particles of which adhere very strongly to the support. Such a carbonaceous electrode retains the carbon layer extraordinarily well and has a thermal emissivity or heat radiating power which can reach 98% of that of a black body.



   The support strip is preferably produced by a continuous process: the metal strip, covered with a layer of nickel oxide powder, passes through a hydrogen furnace in which the oxide is reduced, preferably at a temperature such and under conditions such that the metal reduced nickel forms porous particles or nickel sponges welded to each other and to the metal strip, thereby producing a backing consisting of a metal strip covered with a layer having the desired texture and structure.



   The carbon can be applied to the support in various ways, preferably as a carbon paint consisting of very finely divided graphite, carbon black or.

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 another form of carbon suspended in a liquid binder. The carbon paint can be applied in any suitable manner such as spraying, brushing, dipping, but preferably by dipping or continuous dragging, the support with the new porous layer being in the form of a strip passing through a hanger. Liquid fusion of colloidal graphite in a vehicle such as alcohol to which a little nitrocellulose or a similar binder can be added. If you want a very black covering, you can also add a little carbon black.

   The suspension has a viscosity low enough to be quickly absorbed by the porous layer, as ink is absorbed by blotting paper; the layer is thus impregnated with very finely divided carbon, and its surface is covered with a layer of carbon paint. The support is dried and is thus covered with a thin layer of carbon or graphite paint, the exterior surface of which generally follows approximately the rough and irregular contour of the surface of the die. When the vehicle of the carbon paint has been removed, a layer of carbon remains on the carrier which is substantially bonded to the metal.



   The invention will emerge clearly from the description given below with reference to the accompanying drawing which shows, simply by way of example, one embodiment of the invention in the form of a carbon element, such as a plate or anode, of a thermionic tube, and also illustrates the best method of making the plate or anode material into which the completed plate or anode is constructed, in which:
FIG. 1 represents the surface of the porous layer as seen in photomicrography with an enlargement of 1000 diameters;
FIG. 2 shows the structure of the layer in photomicrographic section at an enlargement of 1000 diameters;

   

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Figure 3 shows, on a large scale, the surface of the layer composed of metal sponges welded to each other while leaving tiny voids and pores;
FIG. 4 shows, on a large scale, a section of the structure of the layer shown in FIG. 3;
Figure 5 shows part of the nickel oxide coated metal as seen in section in a photomicrograph;
Figure 6 shows in section the metal covered with a layer formed from the nickel oxide layer of Figure 5 (photomicrograph), simply by way of illustration of the carbon layer of the finished element;
Fig. 7 is a view of a carbon plate portion having two deep notches and four right angle bends, successfully manufactured in large quantities in accordance with the present invention;

   
FIG. 8 is a partial section of the strip as it leaves the apparatus, covered with a layer of carbon paint;
Figure 9 gives in part schematically an example of an apparatus suitable for the continuous manufacturing process, and
Figure 10 shows a detail. a characteristic embodiment of the invention consists of a carbonaceous plate or anode having, as the drawing indicates, a metallic support consisting of a base of non-porous metal 10, preferably a strip of ferrous metal such as iron. 'mild or cold-rolled steel of a thickness of approximately 5 thousandths of an inch (0.125 mm),

   covered with a porous metal layer 11 consisting mainly of metal sponges or porous nickel particles 12 having microscopic pores 13 and molecularly bonded to the base 10 while being welded together. Photomicrographs show that pores 13 usually have an average size of about a tenth of a micron.

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   The nickel sponges or metal particles generally retain their individuality, and are welded to each other with voids 14 between them which form tiny capillary pores 15, many of which extend through the layer to. base 10. These pores 15 are generally several times larger than the microscopic pores 13 of nickel sponges, and can often grow to the size of the nickel particles themselves.

   Experiments have shown that a carbon layer can be applied to the porous layer; preferably, but not necessarily, so thin that the outer surface follows the contour of the intermediate face between the porous layer and the carbon layer and therefore has substantially the same general contour as the surface of the porous layer 11; this surface serves as a finish to a carbonaceous electrode having a thermal emissivity or heat radiating power of about 90% to 98% of that of a black body, the carbon layer having such a characteristic and adhesion so firm that there is virtually no possibility of peeling, flaking, or noticeable loss of carbon occurring during use.



   The microscopic porous particles or nickel sponges 12 welded together form a novel texture layer attached to the base and bonding a layer such as carbon to the metal base more firmly than in the prior known methods which used. surfaces made rough by conventional means. The adhesion of carbon to metal does not depend solely on the degree or importance of the roughness of the metal surface. The kind of roughness and texture of the surface is much more important.

   The mechanical treatment of a metal surface by sandblasting or etching alone deteriorates the metal and decreases its ductility by strain hardening, while only obtaining a surface half as rough as that of the porous layer 11 and having a texture which binds carbon to metal much less well than porous layer 11 does.

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   Sandblasting increases tool wear because there are often fine particles of sandblasting material that adhere to the electrode material. By repeating sandblasting or etching to increase the roughness of the surface, the metal is increasingly deteriorated without improving the texture from the point of view of carbon adhesion, and it should be added that this process is not viable. because of its high cost and for other reasons.



  An oxidized strip of nickel or nickel-plated steel has a very smooth surface, and does not have the desired texture to hold carbon as well as the porous layer of the present invention.



  Repeated oxidations and reductions of nickel to some extent increase the roughness of the surface, without improving the texture in terms of carbon adhesion, make nickel brittle and largely not commercially justified. because of the price.



   The porous layer 11 composed of microscopic porous nickel sponges is best obtained by covering the metal 10 with a non-compacted layer of powdered nickel oxide with a binder, as shown in Figure 5, and then reducing nickel oxide under conditions and at a temperature such that the oxide is reduced without melting so as to form in place on the metal the nickel sponges and to weld them together while at the same time leaving tiny gaps between them. The nickel oxide layer can be formed on the metal in various ways, but preferably by means of a mixture or suspension of powdered oxide in a binder, and can be applied in various ways such as with a brush. , by spraying or dipping the metal in the suspension.

   Dry spraying gives a very rough surface, while wet spraying produces a smoother surface coat. The oxide will preferably be applied by soaking with train aging, the metal being covered by passing it through a bath containing the suspension, and then drying the layer. One can find in the oxy-

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 Suitable commercial nickel in the form of a mixture of nickel oxides NiO and Ni 2 O 3 assumed to come from natural ores after refining to remove sulfur and other impurities.

   The oxide is preferably ground in a ball mill to a powder so fine that most of the grains are 2 microns in diameter and only 5% of the grains are greater than 5. microns, although in some cases a small portion of the grains may be of much larger dimensions.



  An example of ball mill ground nickel oxide will contain 80% to 85% grain, particle size about 2 microns, 5% or more. particles between 2 and 5 microns, the remainder of the particles having a diameter ranging from 5 or 6 microns to 16 microns. These nickel oxide grains or particles 16 are reduced to the state of nickel sponges which are approximately the same size as the nickel oxide particles from which they originate. These welded sponges form a porous layer with a very even fine-grained surface (see fig.l), light gray in color and about twice as rough as a nickel sandblasted surface in one operation. Obviously, a porous layer with a rougher surface can be obtained by using larger oxide grains.

   To cover the metal with nickel oxide by dipping or dragging, good results have been obtained with a mixture of nickel oxide powder suspended in a volatile binder consisting of very volatile amyl or butyl acetate with a little nitrocellulose. Suitable proportions include: 1500 grams of nickel oxide powder per about 700 grams of amyl acetate and 35 grams of nitrocellulose at 40 seconds. A little methanol, such as 250 grams, can be added so that the binder has the desired viscosity. This suspension coats the metal evenly and when dried it leaves a suitable coating or layer of nickel oxide adhering to the metal.

   Experience has shown that good results are obtained when the binder has a

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 viscosity of about 30 to 35 c.p.s. at 23 C, or, with a standard pipette, 145 to 170 seconds per 100 cc. of binder at 23 C.



   Nickel oxide is preferably reduced by heating the oxide coated metal (see Fig. 5), in a reducing atmosphere, preferably hydrogen, for times and at temperatures between about 800 C and ten minutes and about 1100 C and half a minute; the particles 16 of nickel oxide are thus ordinarily reduced to the state of nickel sponges 12. A satisfactory and advantageous method is to heat at 900 ° C. for one minute. The preferred amount of reduced nickel forming the porous layer is about 5¸ milligrams per cm2 of the area covered by the layer, resulting in a layer thickness of about one thousandth of an inch on each side of the metal.

   Good metal sponges are obtained around 900 C, temperature below the processing temperature of mild steel base 11. If the steel base is a strip of mild steel, for example, of thickness of 5 thousandths of an inch, it can pass, through a reducing furnace of the conventional type about six feet long, at a speed of eight feet per minute, the furnace being maintained over its entire length at a temperature which heats up the tape at the recommended temperature. Under these conditions, the parent metal, particularly if it is mild steel, is almost completely annealed and quite soft, and has a usually negligible spring effect, from 18 to 20 degrees per. example, with respect to the resilient effect of about 50-60 degrees of gas carbonated nickel-coated steel strip.



  The resilian test is well known, one accepted test being described in a publication of "The American Society of Testing Materials", test B-155.



   With a temperature range of 800 C to 1000 C, nickel oxide is reduced without melting so as to form nickel sponges which weld together and are molecularly bonded to the base metal by means of a certain nickel-iron alloy which

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 forms nickel sponges and steel base at the contact surfaces. At temperatures above the processing point of most mild steels, which is around 930 C, there may be some deformation of the steel strip as well as a change in the properties of the steel, such as ductility.



  At these higher temperatures, the nickel oxide grains can be reduced to the state of solid metal particles, resulting in a porous layer because of the tiny voids between the solid particles suitably maintaining a carbon layer, but not so although a porous layer of nickel sponge. It is also possible to obtain a porous layer with solid particles at a lower temperature, such as 750 C, by reducing the nickel oxide for a much longer time, i.e. half an hour, which is not necessary. commercially admissible because of the price.

   During reduction there is some loss of volume in the nickel oxide layer due to the departure of oxygen and binder and the nickel particles weld together forming a similar porous matrix. to a canvas with tiny pores and voids.



   The porous layer of welded porous particles is rather soft and can be compressed to 50%, it does not contain hard abrasive particles. Such a porous layer of nickel can be deformed and polished by means of a polisher made of copper, nickel, brass or even softwood and can be strongly compressed by the pressure of the forming tools, so that the wear of the electrode shaping tools is minimal.



   A base metal coated with a porous layer in accordance with the present invention and without an additional layer is a very useful material in various fields, especially in electronic discharge devices. If the material is well annealed and cleared, it may be suitable for making wires and other elements of thermionic devices, and since it holds coatings very firmly, it may be suitable.

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 for charged elements such as carbon coated grids and if the base is nickel, for oxide coated cathode filaments and for cathode sleeves.



   The carbon layer 17 can be applied to the support by various known means. The nickel-based support 10 can give good results with gas carbonation. If the base 10 is a ferrous metal, such as mild steel or iron, either bare or with a light nickel plating, the carbon layer should be able to be applied without subjecting the base to heat treatment in the presence of carbon.

   Preferably, the carbon is applied by lining the porous layer with a thin suspension or slurry of carbon in the form of very finely divided carbon, such as colloidal graphite, in which, as the photomicrographs show, the particles have a size ranging from 1 micron to a small fraction well below a tenth of a micron, a large portion of these particles therefore being smaller than the microscopic pores 13 in nickel sponges.



  Good results have been obtained by dipping or dragging the base metal in a kind of carbon paint consisting of an alcoholic slurry, that is to say a suspension of colloidal graphite in alcohol, and a small quantity of nitrocellulose as a binder which disappears when brought to a moderate temperature, such as 200 C. As an example of a suitable carbon slurry, there may be mentioned an alcoholic slurry in an amount of 200 grams, ie 160 grams. methanol and 40 grams of colloidal graphite mixed with about 200 cc of a medium evaporative binder consisting of about 1 part by weight, when wet, of equal parts nitrocellulose at ¸ seconds and 40 seconds and about 12, 5 parts by weight of amyl acetate and diluted in about 250 cc of butyl acetate and 200 cc of methanol.

   The porous layer has such a degree and type of porosity that it absorbs the fine suspension of alcoholic slurry like blotting paper absorbs ink. With this mixture, the electricity

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 Carbonaceous trode manufactured has a highly efficient greyish black carbon coating. To obtain a blacker carbon layer approaching optimum heat radiation, 100 grams of alcoholic sludge and 100 grams of carbon black can be used instead of the 200 grams of alcoholic sludge. is completely impregnated with this mixture and dried, leaving (see Fig. 8) the metal covered with a thin, very adherent layer 18 of carbon paint comprising finely divided carbon and a small amount of binder.



   Tube elements, such as plates, are made from this coated metal, preferably by shaping them in presses, by the usual process. The dried carbon paint layer 18 adheres so firmly that it is not damaged in the tools, and usually no lubricant is required in the tools. If the electrode, in its final state, has a complicated shape, as shown in figure 7, with very re-entrant parts and sharp bends, it is good to lubricate the tools a little; in this case, a lubricant such as machine oil which does not soften the nitrocellulose can be used.



   The element with its coating is completed and ready for use after removal of the binder from the dried layer of carbon paint, which is preferably done by heating in a neutral or non-oxidizing medium. The binder disappears on heating at a moderate temperature, such as 200 ° C., and leaves a thin, very adherent layer of carbon on the tube element. The element may be heated while a vacuum is being made in the tube in which it is mounted, but it is preferably heated before it is mounted in the group of electrodes.



   In the preferred process the carbon coated shaped members are generally heated to about 800 ° C in a hydrogen atmosphere for about ten minutes as a finishing operation. By heating them in this way, the binder is first removed from the dried layer of carbon paint, and

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 then we clean and finish the element. At this temperature and under these conditions the cementation or transformation of the base metal by carbon is negligible. The result is a carbon element, like a plate, with a carbon layer whose adhesion to the base is greater than its cohesion.

   By brushing it, carbon powder may come off, but not peels or pieces, as often happens with carbon electrodes by the usual process.



   The carbon layer covering the finished electrode will preferably be as thin as possible so as to form a good black surface. For example, it has been found that a coating giving good results weighs in the region of 2 milligrams per cm 2 of base area. Since such a layer completely covers the porous layer to an appreciable thickness, it is firmly attached to the metal carrying the porous layer and can be so thin that its surface substantially follows the contour of the surface of the drill layer of the support. The carbon layer is so adherent that it is not possible to mechanically remove it from the carbonaceous anode by scraping without deforming the porous metal layer.

   It can be removed without altering the structure of the porous layer by heating the carbonaceous anode to about 1000 C for ten minutes in an atmosphere of hydrogen, such as industrial hydrogen, which contains a certain amount of vapor. of water. The porous layer 11 can thus be released from the carbonaceous anode without appreciable deformations.



   Carbon-coated anodes, for example, made by the above process have given, in comparative measurements, a much higher thermal emissivity than common carbon anodes. The thermal emissivity of a carbonaceous anode according to the present invention exceeds 90% and is usually between 95% and 98% of that of a black body, while the thermal emissivity of similar carbon anodes but typical commercial activities is between about 60% and

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 just under 90% of that of a black body. These comparative measurements, made in air at 200 ° C. in order to avoid possible oxidation, were carried out up to the temperatures usually reached by anodes in service.



   Although the preferred embodiment of the present invention uses a mild steel sheet as the base metal, a porous layer formed of metallic sponges and as a carbon coating a mixture of colloidal graphite and carbon black, it It is obvious that other metals can be used for the base or the porous layer, provided that the metallic particles of this layer can be reduced from the oxide state to the metal state when they sit in place on the base metal, and weld to the base and to each other while maintaining capillary voids, and other types of carbon coatings can be used as well.

   For example, the base can be nickel or nickel-plated steel, and part of the nickel oxide can be replaced by iron oxide where it is not necessary that all the particles have a spongy structure. .



   The present invention has marked commercial advantages, among others a significantly reduced cost price. With a single heat treatment in a hydrogen atmosphere, the oxide of the porous metallic layer is reduced on the final site and the reduced metallic particles are welded to each other and to the base; an inexpensive metallic base such as iron or steel can be used, and the carbon coating can be applied by a faster and cheaper process than gas carbonation, for example, especially because the particular porosity of the porous layer causes it to absorb the carbon slurry very quickly, as the blotter drinks the ink, thus forming on the finished product a thin, very adherent layer of carbon which completely covers the porous layer.

   Until now, - it was not possible to properly carbonize iron without a

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 heat treatment in the presence of carbon with the inevitable consequence of carburizing and alteration of the metal. With the present invention the carbonaceous iron is not altered, and is even improved in some respects by the degassing and annealing which it undergoes during the operation of reducing the nickel oxide.



   Among the structural and other features which distinguish the carbonaceous metal electrode according to the present invention from prior common carbonaceous metal electrodes, there should be mentioned a substantially fully annealed metal base which in the case of a ferrous metal such as mild steel, is practically quite soft and has a resilience halved or more than that of a gas carbonated nickel-plated steel base, a porous metallic layer of new texture on the base comprising particles of metal welded together and molecularly bonded to the base, and on the porous layer an exceptionally adherent carbon coating that does not peel or pieces.

   This carbonated electrode has an extraordinarily high thermal emissivity, which can be and usually is between 90% and 98% of that of a black body. The behavior of the carbonaceous plates according to the invention in thermionic tubes is so superior to that of the current carbonaceous plates that certain types of very useful tubes can be produced with them which cannot be executed successfully. by means of current carbon plates and that cannot be produced commercially without them.



   The preferred manufacturing process according to the invention consists of a continuous process by means of which, from a general point of view, a steel strip is covered by dragging or dipping with a slurry of nickel oxide, and the coating thereof. coated strip passes through a reduction furnace where the nickel oxide, being in place on the strip, is reduced so as to form the porous layer on

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 the strip and thereby produce the carrier which is then covered by sludge dragging or carbon paint so as to form the electrode material, with which tube elements can be produced quickly and economically , such as anodes, preferably in presses of form.



   The continuous process will become clear from the following more detailed description, with reference to the drawing and more particularly to Figures 9 and 10. In this process, the base 10, having the form of a mild steel strip, known commercially. ment under n.1010, 5 thousandths of an inch thick by convenience, unwinds from a reel 20, passing over a pulley 23 and into an oxide slurry chamber 24 containing the nickel oxide slurry recommended above for drag recovery.

   In order for the sludge to settle in a thin and uniform layer, the strip 10 passes over a pulley 25 in the chamber 24 and then exits the chamber and goes up into an equalizer 26 which (see fig. 10) can be a. pipe having two diametrically opposed grooves slightly wider than strip 10 which passes through the grooves with a slight clearance. The oxide sludge in chamber 24 continuously circulates, forced into the pipe by pump 27 and overflowing through the grooves in room 24.

   In order for the oxide layer to be uniform in the longitudinal direction of the strip, the oxide particles must be evenly dispersed in the suspension by the pump, and the slurry must have a constant viscosity, which can be carried out conveniently by adding, at the start of a reservoir 28 by a needle valve 29, a regular quantity of methanol or of another volatile agent, to the contents of the chamber 24.



   The strip covered with the oxide slurry exits the equalizer 26 and travels vertically through a vertical drying oven 30, which can be maintained at about 200 ° C and in which the volatile components of the binder evaporate, but where, the nitrocellulose does not disappear, because the oxide layer 1 -

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 of nickel and the strip are kept at too low a temperature. The strip, covered with a dried layer of ni- ckel oxide, passes from the drying oven into the vertical reduction oven 31 through a groove or opening, in the bottom, slightly wider than the strip and leaving only one just enough clearance so that the dried layer is not torn off the tape.

   The reducing furnace has an atmosphere of hydrogen or other reducing gas introduced through an inlet 31a at a pressure slightly above atmospheric pressure, and is maintained at a temperature such that the web in the furnace. is brought to a temperature between 800 C and 1100 C, which causes the decomposition of the nitrocellulose and the reduction of the nickel oxide. At the chosen temperature, the nickel particles resulting from the reduction weld together well and are molecularly bonded to the steel strip.

   The temperature of the strip in the furnace and its speed of movement are such that the reduced nickel adheres well to the steel thanks to the onset of melting of the iron-nickel alloy at the contact surface, while the coarse Part of the reduced nickel is in the form of a porous layer formed from microscopic porous nickel sponges. The oven 31 is of the standard type, about six feet long, and maintains itself at practically the same temperature throughout. The belt can pass through the oven at a rate of about eight feet per minute. The cold strip entering the hot oven at this speed is subjected to a rather sudden and significant increase in temperature. This high temperature gradient is advantageous from the point of view of obtaining the desired porous nickel layer structure.

   Water vapor, a byproduct of reduction, has a decarburizing and softening action on the steel.



   The strip 10 serves the furnace 31 as a support with a welded metallic nickel cover layer which is soft, highly porous, and bonded to the metal strip.

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  The extreme porosity of the product can be evidenced by depositing ink, which is almost completely absorbed, such as by blotting paper. With the known prior bands, the ink, after drying, marks on the surface and remains permanently visible as on paper. On leaving the oven, the strip with the nickel surface passes through a cooling chamber 32, over a pulley 33 enclosed in a gas-tight chamber and descends again into another cooling chamber 34, from where it comes out through a groove in the bottom at practically room temperature. The two cooling chambers and the enclosure for the pulley 33 are full of hydrogen coming from the furnace, the cooling chamber 32 opening onto the furnace on the one hand and into the enclosure of the pulley 33 of somewhere else.



   On exiting cooling chamber 34 the backing strip is ready to receive its coating, e.g. carbon. The strip can be stored, if desired, and the coating can be applied later in a separate subsequent operation. . It is preferable to pass the backing strip directly into the carbon application chamber 35, then over a pulley 36 in the chamber, and then upwards into another application chamber 37, similar to the equalizer 26, traversed by the carbon suspension, maintained at the right viscosity thanks to a small methanol reservoir 38 serving to send methanol through a needle valve 39, and driven into the application chamber 37 by means of a pump 40.

   The carrier tape coated with a coating of paint or carbon suspension which has penetrated the pores and crevices of the porous nickel-like ink layer is absorbed by blotting paper, then enters a drying oven 41 similar. wheat in the oven 30 and maintained at about 200 ° C. to obtain a dry layer 18 of carbon paint covering the matrix.



  The binder in the carbon suspension binds the particles of

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 carbon to each other on the surface, in the pores and crevices of the porous nickel coucke. The carbon can be either amorphous or graphitic, depending on the nature of the carbonemis in the suspension of the application chamber 35.



  The support strip with its layer of dried carbon 18 (see fig. 8) leaves the furnace 21 and passes through a pulley 22 on a spool, not shown, and can then be stored as an electrode material with which to manufacture. electrodes and tube elements. The carbon can, in this way, be applied to the surface layer web much faster than by gas carbonation processes, in which the carbon is applied by deposition of hydrocarbon gases. With the process according to the invention, a speed of eight feet per minute has been reached, which is ten times faster than the gas carbonation process.



   With a 5 thousandths of an inch steel strip, the layer formed on both sides by the porous layer of nickel and the carbon paint increases the thickness of the backing strip at most up to 7.5 thousandths of an inch . No difficulty will therefore be encountered in the manufacture of vacuum tube plates with toolings intended for a thickness of 5 thousandths of an inch, the backing strip constructed in accordance with the present invention with its layer of carbon paint, is easily compressed. in the tools. However, if desired, the carrier tape can be passed between rolls and compressed.

   It was thus possible to reduce the thickness of the layer on each side of the strip to a thickness of less than 1 thousandth of an inch without materially affecting the heat radiating characteristics of the finished electrode. It is possible, with the metal covered by the process of the present invention, compressed or not, to manufacture carbon electrodes whose heat radiation power or thermal emissivity is closer to that of a black body than carbonaceous metals.

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 obtained by any other known method.



   The present method has the additional advantage that the raw steel strip supplied by the manufacturer can be stored and used later without cleaning, the rust on the steel strip being reduced in the reduction chamber; an oil film can also be tolerated on the belt.



   The layer of carbon paint on the strip covered with a porous nickel coating, adheres very firmly to the nickel and does not accumulate in the tools during the manufacture of the tube elements. Tube elements made from this material can be heated in a hydrogen atmosphere at about 800 ° C for ten minutes, as usual, without the carbon shedding. The material for electrodes or plates according to the invention also has the advantage of being degassed and purified by virtue of this rather rigorous heating.



   The present method of reopening metals with carbon can be applied to various metals. It is suitable for both nickel-plated bands and ferrous metal bands.



   It can also be used to weld together two metal surfaces of different metals which cannot be joined to each other by electroplating or any other process. For example, nickel and copper which cannot be deposited together electrolytically are easily joined. It is also possible to add non-metallic substances to the metals, by mixing them in the suspension.


    

Claims (1)

R E V E N D I C A T I O N S 1) Carbonaceous metal element used in the manufacture of electronic discharge devices or the like, characterized in that it comprises a non-porous base metal sheet, a porous metal bonding layer consisting of adjoining particles of metal welded to each other in place on and bonded to the base, and a firmly adherent coating of finely divided carbon over the bond layer. <Desc / Clms Page number 24> age which it covers and fills the pores. 2) Carbon metal element according to claim 1, for electronic discharge devices, characterized in that the metal particles forming the bonding layer are welded to each other with voids or pores between these particles, these forming a spongy layer. 3) Carbon metal element according to claim 3 characterized by tiny pores in the metal particles forming the bonding layer. 4) Carbon metal element according to claim 1, 2 or 3, characterized in that the bonding layer is formed on the base metal by reduction without melting of a non-compact powder oxide coating of the selected metal. 5) Carbon metal element according to claim 1, 2, 3 or 4, characterized by a non-flaking carbon coating covering the asscormage layer and filling the pores thereof, the adhesion of carbon of this coating to said layer being greater than the adhesion of the particles of this coating to one another. 6) Carbon metal element according to any one of the preceding claims, characterized in that the base metal consists of a sheet of annealed ferrous metal, and in that the metal particles forming the bonding layer are par- ticles of nickel. 7) Carbon metal element according to claim 6, characterized in that the base metal consists of annealed soft steel t8le having a resilience between 15 and 25. 8) Carbon metal element according to any one of the preceding claims, characterized in that the carbon coating comprises colloidal graphite. 9) Carbon metal element according to claim 8, characterized in that the carbon coating consists of collordal graphite and very finely divided carbon black. <Desc / Clms Page number 25> 10) Carbon metal element according to claim 4, characterized in that the base carrying the bonding layer is obtained by covering a mild steel strip with a non-compact adherent layer of fine powder nickel oxide with a volatile binder at a temperature below the reduction temperature of this nickel oxide, passing this coated strip through a furnace having a reducing atmosphere and subjecting the coated strip, in the furnace, to a temperature below the steel transformation temperature and high enough that to reduce the nickel oxide to nickel particles on the strip and simultaneously solder these nickel particles to each other so as to form a spongy layer, and bond this layer to the strip. 11) Carbon metal element according to claim 10, characterized in that the carbon coating is formed by passing the metal strip in a suspension of very finely divided carbon suspended in a thin liquid binder so that this suspension can be absorbed by the spongy layer and so as to cover this spongy layer with a continuous coating of carbon. 12) Carbon metal element according to claim 10 or 11, characterized in that the mild steel strip covered with nickel oxide in fine powder is heated in a reducing atmosphere at a temperature of the order of 800 C to 1100 C, until this nickel powder is reduced to nickel particles welded together in the porous layer bonded to the base, these nickel particles generally having about the same dimensions as the nickel oxide particles from which they come by reduction. 13) Carbon metal element according to claim 12, characterized in that the steel strip with its layer is heated in a hydrogen atmosphere at temperatures and for <Desc / Clms Page number 26> time ranging from 800 C and ten minutes to 1100 C and half a minute. 14) Carbon metal element according to claim 12, characterized in that the steel strip with its layer is passed at a speed of eight feet per minute in a temperature zone of about 900 C in which it remains exposed to a hydrogen atmosphere for about one minute. 15) carbon metal element according to claim 4, characterized in that a layer of nickel oxide in fine powder is uniformly distributed on a base having the. form a strip, by causing a fine slurry of finely divided nickel oxide to flow vertically up and down over the surface of this strip in a volatile suspension containing a binder which evaporates at a temperature of 1 'order of 200 C to 500 C. 16) Carbon metal element according to claim 11, characterized in that the carbon suspension is applied to a base coated with the bonding layer, by causing this suspension to flow vertically simultaneously upwards and downwards on the surface of this layer.