US1733813A - Composite body and method of producing the same - Google Patents

Description

Patented oct. 29, 1929 V V UNITED STATES JOHN WESLEY MARDEN AN D HARVEY CLAYTON RENTSCHLER, OF EAST ORANGE, NEW JERSEY, ASSIGNORS TO WESTINGHOUSE LAMP -COMP. ANY, A. CORPORATION OF PENNSYLVANIA COMPOSITE BODY AND METHOD OF PRODUCING THE SAME No Drawing.

a process for the production of composite posite bodies geneous material,

bodies of refractory metals and to the articles produced thereby.

It is necessary or advantageous in many arts to employ, in lieu of a single homocomposite bodies consisting of consolidated materials having differ.- ent properties. Conditions making such comdesirable arise, for instance, when a small amount of comparatively expensive material, used in combination with a cheaper material, will serve the same purpose'as a body or article consisting entirely of the former. As an example of such combination, the coating of a common metal with platinum for use as electrodes in the electro chemical arts may be cited. x

Other circumstances requiring a composite body arise when a material having valuable properties can, only with difiiculty, be fabricated sin ly to adapt it for practical use but may be more readily worked as one of the elements ofa combination. An example of such character is present when it is desired to utilize metallic thorium as electron-emisson material .in'electrical devices, such as vacuum tubes used in wireless apparatus, hot-cathode rectifiers of the Rectigon type and X-ray tubes, all of which require a heated filament and preferably one having high electron emissivity at temperatures not incompatible with a long-burning life. For such purposes, the thorium should be drawn into wire form to adapt it; to be heated by the electric current. It has been found-possible by employing the process hereinafter described, to readily produce a composite wire comprising a base material, such as molybdenum. coated with thorium. which, as electron-emission material, is as valuable as a wire consisting entirely of -metallic thorium.

In other circumstances a composite body is superior to a homogeneous body. For example, an X-ray target at which X-rays are generated preferably consists of a refractory metal of high atomic Weight and another metal of high heat-dissipating capacity, the

Applicatioii filed August 1, 1921. Serial No. 489,108.

former being necessary for the generation of powerful X-rays and the latter so that the heat generated by electronic bombardment of the target may be dissipated rapidly enough to prevent the temperature from rising to the melting point of the material of which the target is composed. Such composite tar et may consist of a metal of high atomic weig t, such as thorium, consolidated with a body having a high heat-dissipating capacity, such as copper, chromium or other metal. The composite bodies for such purposes may be very conveniently prepared by the process of the present invention. It is, therefore, an object of the present invention to provide a process for the production of composite bodies and, more particularly, for the production of such bodies consisting of at least one refractory metal.

Another object of our present invention is the provision of a composite body consisting, at least in part, of a metalof high electron emissivity.

A further object of the invention is the pro-- vision of composite bodies which shall be valuable in increasing the efliciency and the burning life of electric devices, such as incandescent electric lamps and the like.

Other objects of the present invention will be apparent from a reading of.the following specification.

In order to secure the advantages of composite bodies, well-known methods such as rolling, drawing and electrolytic deposition have been employed. These methods have often been successful when the materials to be united were malleable, ductile, or did not easily combine chemically with other elements. When, however, the materials sought to be combined did not possess the requisite properties for such methods of fabrication, combinations of certain materials having valuable properties were not available. For example, the combination of a non-ductile metal, such as zirconium, could notbe drawn in connection with another material as a base. Up to the present time it has been found successful attempt was made to coat a tungsten wire with thorium by surrounding the former with a quantity of thorium powder. The two metals, in contact, were heated in a high vacuum to a temperature which would 'be" thought suflicient to cause a union of the two metals. The resultant product, however, when tested for electron emissivity did not give results characteristic of thorium, showing that, if a small quantity of the latter metal did adhere to the tungsten, it very probably was left in such physical condition that it was quickly oxidized when exposed to the air.

Other experiments conducted by us have shownthat compounds of certain metals cannot be made to form a composite body with another material by applying a compound of the metal to another material as a base, attempting to reduce the metallic compound and subjecting the materials to a heat treatment with a view to effecting a union between the reduced metal and the base material.

That part of our present invention which relates to the method of producing composite bodies is particularly valuable for the utilization of those metals which have such a strong chemical. afiinity for other elements that they should preferably be Worked, in combination with another material, in a very high vacuum in order to obtain them in adense, coherent and adherent mass. and it is still more valuable when dealing with such metals having a hi h melting point and also in combining with other. material metals which, in addition to possessing a strong chemical affinity and a refractory nature,

1 are also diflicultly. workable by such proc-' plies a very satisfactory methodof produc"-' ing composite bodies, utilizing one or more of suchmetals.

We have also utilized the present invention for producing composite bodies of refractory materials suitable for use as filaments in incandescent lamps. In this case. a base material may be coated by any suitable method with a metal or mixture of metals or alloys having desirable properties such, for example, as selective light emissivity.

Another part'of ourinvention' consists in the discovery that metals having certain properties are valuable as agents for purifying other materials and for removing or converting from the active phase, materials which act deleteriously under certain circumstances, such as gases or vapors in vacuum and gas filled tubes which employ an incanlamp. such metals are especially valuable in removing deleterious gases, such as oxygen, and vapors, such as that of Water, which quickly damageincandescent bodies. Water vapor is particularly injurious, inasmuch as the interaction between water vapor and the incandescent filament is a cyclic process, the

When employed in electrical first step in which is the decomposition of? 1 the water vapor by the filament, resulting in the formation of a metallic oxide and free hydrogen. The oxides pf many metals, being volatile at the high temperature at which the filament operated, are thereby vaporized and are subsequently reduced by the hydrogen to produce the original quantity of water vapor and the metal of which the filament consists. The water vapor, being thus renewed again reacts with the incandescent filament, and the. cycle described is continuously repeated until the filament burns out.

It will thus be seen that, in order to eliminate water vapor and harmful gases from such devices, metals such as zirconium, thorium, uranium, titanium, chromium, metals of the .rare earths, aluminum and magnesium or a combination of two or more of the same, which react with them to form stable compounds therewith and especially those which form compounds not reducible by hydrogen, are efiective in maintaining the efiiciency and prolonging the burning life of such devices. In the lamp-making art, materials which perform such functions are known asclean-up agents and hereinafter.

will be referred to as such in referring to incandescent lamps and similar devices.

3 Various methods may be employed for introducingmetallic. clean-up agents into incandescent lamps and similar devices but a.

very convenient method is found to be the placement of the clean-'up'agent on the filament to form 'a composite body. Preferably,

after the lamp has been exhausted and sealed to the atmosphere, the filament is then, for the 'first time, lighted .to incandescence and the clean-up agent is thus activated, that is, made to combine with the residual gases and vapors. Part of the clean-up agent may be ing,

Up to the present time, we have found it best for producing composite bodies consistfor example, of two materials, to have one of them in the form of particles or in a pulverulent condition, While the material with which it is to be consolidated, may or may not be a dense, coherent mass. The material in comminuted form gives best results if it is placed in a medium or vehicle which is preferably a liquid or at least is in a plastic state. The material placed in the vehicle may, in some cases, be dissolved in the latter while, in other instances, the vehicle should be of such nature that it will not dissolve the added material but merely hold it in suspension without reacting chemically therewith. The material added to the vehicle should be thoroughly distributed throughout the latter to obtain a homogeneous mixture. This mixture, in any desired concentration, is then applied to a material or body of any suitable nature, form or size, with which it .is desired to unite the added material to produce a composite body. The combination thus obtained is then treated by any suitable means, such as mechanical working or by heating, to cause the applied material to permanently adhere to the other body and iii to cause the particles of the applied material to form a permanently coherent body. During this step in the process, the vehicle should in most cases, be removed but, in other conceivable conditions, it may not be necessary to do so. In dealing with many materials it is necessary to give this treatment in an inert environment to avoid a change in the nature of the materials dealt with. In some cases, the atmosphere in contact with the materials employed may be an inert gas while the treatment of other materials requires the operations to be carried out in a vacuum and in still other instances an exceedingly high vacuum such, for example, as that obtained in a high-vacuum X-ray tube will give the best results.

Since it has been stated that one of the objectsof this invention is the provision of a process for producing a composite body consisting, in part at least, of a metal of comparately high electron emissivity, it will be shown in suiiicient detail how such a body may be produced. Thorium will be selected as a metal representative of the class of metals possessing and also as a member of the group of refractory metals. It is, moreover, a representative of that class of metals whose oxides are not reducible by hydrogen and of which'c lass zirconium, uranium, beryllium, etc. are also members. Such metals, we have found, are particularly advantageous for increasing the efiiciency and maintaining the candle power high electron emissivityof incandescentelectric lamps, as explained above.

Molybdenum will be assumed as the base material to which the thorium is to be united. Thorium, in a powdered eondition and in any desired quantity, may be mixed with a vehicle consisting of a solution of nitro cellulose in amyl acetate until a homogeneous mixture results. This mixture is then applied to a body of molybdenum which may, for example, be of wire form, by passing the molybdenum wire through the mixture. The quantity of thorium deposited on the wire will obviously depend on such factors as the concentration of thorium in the mixture, the rate at which the wire is passed through it, and the nature of the vehicle.

The coated wire is then preferably placed inan air-tight vessel and connected therein to electrical conducting terminals sealed into the vessel. The latter is subsequently exhausted to a very high degree of vacuum by means of a pump which is preferably of the diffusion type. While maintaining the high vacuum in the vessel, electric current is passedthrough the coated wire which is thus heated to a temperature sufficiently high to remove the vehicle by volatilization and to cause the particles of thorium to be agglomerated and form a dense, coherent mass permanently adherent to the molybdenum base. The electric current passing through the wire is then cut out and the wire is allowed to cool before it is withdrawn from the vessel.

It is to be understood that the composite bodies produced according to the present invention may consist of two or more consolidated materials and that each component part may consist of mixtures or alloys. For example, a mixture of powdered thorium and powdered aluminum may be applied to a wire of molybdenum or tungsten, and the aluminum will then serve as a clean-up agent, preserving the thorium unoxidized to act as an electron emitter. Other variations in the products and process of this invention will be apparent to those skilled in the art but we desire it to be understood that such are part of our invention as set forth in the appended claims.

What is claimed is:

1. A composite refractory metal body, com prising molybdenum as a base and thorium consolidated therewith, said thorium having been first applied thereto as a suspension in a binder liquid and subsequently permanently consolidated thereto by heat in an inert environment.

2. A composite body comprising a base of molybdenum having thorium consolidated thereto, said thorium having been first applied to said base as a suspension in a binder liquid and subsequently permanently consolidated thereto by heat in an inert environment.

3. Electron emission material comprising a base of molybdenum coated with thorium in a coherent and homogeneous state.

4. Electron-emission material comprising afilamentary body with a coating thereon ofa powdered mixture of one of the group of metals consisting of thorium, zirconium, uranium, titanium and vanadium as the active electron-emitter and one of the group of metals consisting of aluminum, magnesium, chromium and the rare earth metals as a cleanup agent and protector of the active electronemitter.

5. As an article of manufacture, a composite metallic body comprised of a molybdenum metal base member surfaced at least in part with an adherent, coherent, homogeneous coating of thorium.

In testimony whereof, We have hereunto subscribed our names this 30 day of July, 1921. v

JOHN WESLEY MARDEN.

HARVEY, CLAYTON RENTSCHLER.