US1808889A - Manufacture of metal having high emissivity - Google Patents

Description

June 9, 1931. Q G, PINK 1,808,889

MANUFACTURE oF METAL HAVING HIGH EMIssIvITY Filed June 21, 1924 MIX/NG Wl TH imam /40 TREA rllvq /N /g sara/Mu wmv AML/NE var/ons INVENTOR BY v ATTORNEY Patented June 9, 1931 COLIN G. FINE, 0F YONKERS, NEW' YORK MANUFACTURE OF METAL HAVING HIGH EMISSIVITY Application led June 21,

This invention relates to a process for the manufacture of a metal or alloy having relatively high electronic emissivity and more particularly to the manufacture of a metal adapted to be drawn into rods or filaments for use in electron discharge tubes and the like.

This invention has for its object generally to provide an improved and expeditious procedure for producing a metal or alloy adapted to be easily drawn into rods and filaments which have relatively high electronic emissivity.

Specifically an object of this invention is to provide an improved method of combining a metallic agent, adapted to provide a metallic frame or body having good working characteristics, with a second agent adapted to impart relatively high electronic emissivity to the resulting alloy or compound. l

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several Asteps and the relation and order of one or more of such steps with respect to each of the others thereof, which will be exempliiied in the rocess hereinafter disclosed, and the scope ofJ the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompan 'ng drawing, in which:

The gure shows schematically the character of the agents employed in this process, the mode of combining, and the relative order of the ,steps to be followedin practicin this invention.

n the practice of .this invention an agent which is adapted to provide a metallic frame or body is comblnedwith a second agent adapted to impart an electron-emitting property far in excess of that normally characteristic of the pure metals.

The agent supplying the metallic frame is for convenience hereinafter referred to simply as the metallic agent. This agent 1924. serial No. 721,493.

is to be very intimately mixed with the second agent which imparts the desired electron-emissivity to the resulting alloy or compound. The form in which the metallic agent is' preferably added is therefore one in which the subdivision of the mass can be carried to a very high order. Salts and oxides of the metallic agent are forms adapted for this purpose, the subdivision attainable being greater than for the pure metallic form. A soluble salt, however, is the more preferable, since by dissolving the agent, it may thus be subdivided into particles of substantially molecular dimensions. The metallic body of the alloy should be one capable of being heated to relatively high temperatures without fusing, should have relatively high electric resistance, and should also be relatively resistant to oxidation at high temperatures. The metallic agent of this invention, by preference comprises the highly refractory metals such as molybdenum', tantalum, tungsten and the like. Where molybdenum is to be the metallic frame employed, the formof the agent supplying this metal is preferably a soluble 'salt for example, ammonium molybdate (NH4)2MoO4. The oxides -of molybdenum may however be used.

Thev second agent that imparts the electron emitting properties will be hereinafter referred to as the emissive agent, and may be in the lform of a metallic compoun This second agent, however, should have as its base an element belongin to a chem- 85 ical group known to have high electron emitting properties, particularly in comparison with the refractory metal providing the body of the alloy or compound here produced.

In the metallurgy of the refractory metals difficulty has been experienced in thoroughly reducing the metals. As a consequence it is desirable that there' should be alloyed or'otherwise intimately mixed with 95 the metallic agent a substance which is readily susceptible to oxidation. The emissive agent according to this invention should be composed either wholly or in part of a metal that has the property of being highly sus# lic agent of oxygen, the presence of oxides .having been ascertained to be detrimental to the working and drawing properties of the alloy or compound produced.

The chemical group which is adapted to provide the second or emissive agent includes the rare earths and the radio active elements, for example, thorium, uranium, zirconium, and cerium. This agent is preferably added to the first in the form of a soluble salt or compound, forfexample, in the form of a chlorate, chloride or nitrate. Where thorium is the second agent used, thorium nitrate Th(NO3) 4, is a suitable salt for this purpose.

I have ascertained as set forth in my co pending application Serial No. 686,628, filed Jan. 16, 1924, inthe metallurgy of the refractory metals, that it is desirable to combine with such a relatively volatile agent which is yadapted to be boiled out as it were from the metallic body'during reduction thereby greatly facilitating the action of the hydrogen or reducing atmosphere in removing traces of oxygen from the metallic mass and otherwise freeing it ofintercrystalline impurities.

In the practice of this invention, there is accordingly added to the mixture of the above two agents a third or volatile agent which enables the reducing process to remove effectively the oxygen and intercrystalline impurities to a degree which results in a highly workable alloy or compound which may be readily drawn into rods and filaments adapted for copious electron emission in electron discharge tubes and the like. One or more volatile ingredients are added as the volatile agent in such quantities as substantially to insure their evaporization and complete boilin out from the metal under treatment during the step of reduction. The volatile agent includes preferably salts of metals having relatively low boiling points as compared with the melting temperatures of the metallic and emissive agents employed. Among suitable salts for this purpose are the volatile metallic chlorides, for example, cupric chloride, cuprous chloride, stanic chloride, stannous chloride, sodium chloride and cadmium chloride.

The agents of this invention are brought togetherl and mixed in such proportions that the emissive agent will substantially alloy with the metallic agent and form, as it were, a solid solution containin the emissive agent. This bringing toget er is symbolically indicated in the drawing. Where soluble salts are employed, the mixing as indicated is with advantage effected by the aid of a water solution.

The step of mixing is followed by the step of drying in order properly to condition the mixture for reduction. Where water solutions are to be prepared for reduction, this drying is preferably carried on in two stages. In the first stage the mixture is evaporated substantially to dryness. In the second stage the mixture is baked to remove the last traces of water of crystallization, the dry mass resulting being then preferably broken into pieces preparatory to reduction.

The step of reduction follows the step of drying, and -is preferably accomplished in a dry hydrogen atmosphere by the aid of an electric furnace. This step of reduction occupies several hours and is also preferably accomplished in two stages, namely, a preliminary stage in which the dry masses are brought to a temperature of 1200 C., and a final stage in. which the temperature is brought to a degree approaching the melting point. This latter stage of course occupies the greater portion of time allowed for this step. Between these two stages the fused parts are preferably pressed together tightly so that when finally heated in the electric mogeneous mass.

Following reduction is the step of drawin in which the reduced mass is made into suitable slugs, rods or filaments as the case msg' be.

uch rods and laments are preferably given a final treatment in order to remove the last trace of surface oxides or other impurities which may have developed during the drawing operation. Such step is indicated in the drawing as following the step of drawing, although the practice of this step is by no means essential to the practice` of this invention. This treatment is accomplished by the aid of a dry hydrogen atmosphere preferably saturated with the vapors of volatile hydrocarbon, for example, aniline, pyridine, etc., the rod or filament being brought substantially to incandescence during treatment by the aid of an electric current. Such current is made to pass for a period approximating thirty seconds.

The following is an example of the procedure followed in practising the process of this invention: v

1,000 grams of ammonium molybdate are mixed by the aid of a water solution with 7 5 grams of thorium nitrate; in this mixture is dissolved 10 grams of sodium chloride and from 10 to 15 grams of cadium chloride.

The drying of this mixture is here accomplished in'two stages, it being first evaporated to dryness and then baked and broken into suitable pieces.

furnace they become a sintered ho- The reduction is accomplished at high heat, by means of an electric furnace in a dry hydrogen atmosphere, preferably in two stages as above indicated.

The reduced mass from the electric furnace is then worked and drawn through dies` into ingots or slugs which mav be subsequently drawn into wires, rods and filaments.

These wires and filaments -are finally treated in an atmosphere of dry hydrogen,

more or less saturated with vapors of aniline; the finished wire being heated to incandescence for a brief period with an electric current.

The drawn wire manufactured by this process is readily workableand retalns its pliability for a relatively long time. The product is tough and quite resistant to shock, and is substantially an alloy of molybdenum and thorium, the thoriated molybdenum thus produced possessing an electron-emissivity many times greater than puredrawn molybdenum. The phenomenon of electron-emissivity is very marked when the thoriated molybdenum is at relatively low temperature, for example, 'that of a'dull red heat.

The electron-emissivity of the alloys of this invention is many thousand times greatei than that of pure refractory metals and mav be of the order of magnitude gf 100,00'0

- times greater.

Since certain changes may be made lin carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

It is. alsoto be understood that the following claims are intended t o cover all of the generic and' specific features of the invention herein described, and all statements of Athe scope of the invention which, as a matter of language, might 'be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. The process of producin tallic alloy having relatively emissivity, comprisin mixing `together with the aid of water solu le salts containing respectively a metallic` agent, an emissive igh electronic agent and a volatile agent, drying and re-.

a ductile me-..

lic agent and a volatile agent, evaporating the mixture to dryness, baking the dried mixture, and subsequently reduclng the mixture in an atmosphere of hydrogen, the final stage of reduction being at a temperature suiicient to assure alloying.

3. The process of producing a readily workable alloy having relatively high electronic emissivity comprising forming a solution in water of water soluble salts containing a metallic agent, an emissive metallic agent and a volatile agent, evaporating the mixture to dryness, baking the dried mixture, reducing the mixture in an atmosphere of hydrogen, pressing, completely sintering, the sintering temperature being suchas to assure alloying of the components, and drawing the reduced mass.

4. The process of -producing a readily workable refractory metallic alloy adapted to have relatively high electronic emissivity, comprising mixing in solution ammonium molybdate, thorium nitrate and volatile metallic salts, evaporating the mixture to dryness and baking, reducing in an atmosphere of hydrogen, the final stage of reduction being at a temperature suiiicient to assure alduced mass into filaments and the like.

5. The process of producing a readily workable refractory metal alloy adapted to have relatively high electronic emissivity, comprising mixing in solution ammonium molybdate, thorium nitrate, and a volatile metallic chloride, evaporating the mixture to dryness and baking, reducing in an atmosphere of hydrogen, the final sta e of reduction being at a temperature su cient to as'- sure alloyin ,working and drawing the re` duced mass into filaments and the like, and subsequently'treating the same to induce av desired temper.

6. The process of producing a readily workable alloy having relatively high electronic emissivity comprising forming a solution containing a metallic agent, an emis- `sive metallic vagent anda volatile agent, evaporating the mixture to dryness, baking the dried mixture, reducing in an atmosphere of hydrogen the baked mixture, pressing,

sintering, .the sintering temperature being such as to assure alloying of the components, drawing the reduced mass, and then treating the drawn rods in a dry hydrogen atmosphere while passing therethrough an electric current.

7. The process of producing a readily workable refractory metallic alloy adapted yto have relatively high electronic emissivity comprising mixingtogetheran agent conlOying, and subsequently drawing the resisting of a salt soluble in water containing molybdenum, a soluble agentv containing thorium, a soluble volatile a ent and water suilicient to produce a desire solution, drying and reducing the mixture in a. dry hydrogen atmosphere, the final stage of reduction being at a temperature suiment to cause alloyng, and subsequently working and 5 drawing the reduced mass.

ture.

COLIN G. FINK.

In testimony whereof I aIix my signa.-

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