US1565724A - Filament and method of manufacture thereof - Google Patents

Description

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mensa Dec. 1s, 1'925.

UNITED STATES PATENT OFFICE.

GOBTON E. FONDA, OF SCHENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

FILAMENT AND METHOD OF MANUFACTURE THEBEOF.

Application led July 29, 1920. Serial No. 399,798.

To all whom tmay concer/n.-

Be it known that I, GoR'roN R. FONDA, a citizen of the United States, residing at Schenectad in the county of Schenectady,

' 6 State of 4ew York, have invented certain new and useful Im rovements in Filaments and Methods of anufacture Thereof, of which the following is a specification.

The present invention relates to the production of ilamentary or wire-shaped bodies, strips, sheets or the like, of tungsten alloy, as, for example, filaments for incandescent lamps, electron discharge devices and the like.

Although metallic tungsten cannot be worked mechanically by the metallurgical methods applied to other metals, it can be rendered ductile and drawn into fine filamentary form by the methods described in `il() Coolidge Patent 1,082,933. It is advantaeous to constitute filaments for incandescent amps, or other devices, of an alloy of tungsten. For example, in my prior Patent 1,496,457, 'issued June 3, 1924, I have described lamentary conductors consisting of Y tungsten Vcontaining iron not in excess ofl about one or two per cent of the total. In some cases, the mechanical working of alloys of tungsten, such, for example, as tungstenironalloys, is attended with diiiculties.

` In accordance with my present invention, I have provided a new method of preparing wires or filaments of alloys, or solid solutions, of a refractory metal, for example, tungsten, and one or more alloying metals.

As described more fully hereinafter, filamentary bodies are'prepared in accordance with this invention by depositing alloying metal by electrolysis or other convenient 40 method on a clean surface of a bod of refractory metal, which has alrea yy been drawnor otherwise worked either into final desired form or into a form suitable for sub-v sequent working.

As" illustrative of my invention, I will describe in detail a continuous processlfor carrying outthe preparation of alloy filaments of tun ten and iron, although it to be un erstood that my invention is l0 applicable to alloys of tungsten or other refractory' metal with elements other than wish surface impurities, such as grease and carbon, for example, by heating the filament in a protective environment to a temperature of about 1000 to 13000 C., preferably to aboutv 12000 C. As illustrated in Fig. 1, a filament or -wire 1 may be drawn from a reel 2 over revolving electrical contacts 3, 4 in a container 5 into which a protective gas, such, for example, as hydrogen, is introduced by a conduit 6. A suitable heating current for the wire 1 is conveyed to the contacts 3, 4, by the conductors 7 8, which may be connected to a source S.

The cleansed wire or filament is introduced into a suitable electrolyte, for example, a solution of ferrous chloride or ferrous ammonium sulphate. Although proportions may be varied, I prefer to use by weight about 200 parts of ferrous chloride or of ferrous ammonium sulphate to 1000 parts of water. Preferably 50fparts of magnesium sulphate and 5 parts of sodium bicarbonate may also be added to the electrolyte. As further illustrated diagrammatically in the drawing, the wire l1 to be coated with iron is slowly passed through electrolyte over pulleys 9, 10 supported by a standard 11. The wire 1 is connected as cathode to a suitable source of direct current G by the conductor 12, the anode 13 consisting of iron, carbon, or other suitable material, being connected to the positive conductor 14. The current is chosen to produce a current density of about 0.003 amperes per square centimeter of surface. The coated wire or filament is passed over another pulley 15 into a receptacle 16 vcontaining pure water. It is then dried as by passing through a dryer 16 and finally wound upon a spool 17 driven by a motor 18 through suitable speed reducing gears 19. The coated wire is pliable and rugged. It desired, it may be stored forfuture use.

As shown in Fig. 2, the coating 20 upon the core 21 represents such relatively inconsiderable part of the total mass of the Wire or filament that the production by the described method of a homogeneous alloy is surprising, articularly so as the alloying metal is app ied externally. I do not intend to represent exact proportions of core and coating. In fact, the proportions-may be varied, but l mean to show only roughly the general relative magnitudes of the core and coating. As indicated, the core largely preponderates in mass over the coating. My investigations indicate that the coating metal diffuses uniformly throughout the core metal during the alloyin step. The resistance characteristics of t e resulting alloy correspond to the characteristics of a homogeneous alloy of the same proportions. The small diameter or thinness of a filament or ribbon favors this result. Contrary to what might be expected, the alloying step in the case of the present process requires a materially shorter time than the process of making alloy filaments or the like described in my prior Patent No. 1,496,457, referred to above, according to which the alloying metal is mixed in a state of fine subdivision with the refractory metal.

Alloyage of the core and coating is produced by heating the composite Wire to a temperature of at least about 15009 C. A1- though preferable, it is not absolutely essential in all cases that this alloying step be carried out separately preparatory to the manufacture of a lamp or other device in Which the Wire or filament is to be used. ln the case of the finer filaments particular- 1y, the composite filament may be mounted in a lamp bulb in the usual Way and the lamp may be exhausted and sealed. When the lamp is put into use the heating of the filament to incandescence at the usual operating temperature or sometimes by a preliminary heating at a lower temperature Will cause cementation or absorption of the iron coating by the tungsten core. For example, l have obtained good results by heating a four mil filament for five minutes to about 1600o C. which is above the melting point of irorli The resulting filaments are operable in mps at a highlighting efficiency Without blackening.

y invention is not restricted to the electr ytic deposition of an alloying metal; for example, when it is desired to produce an alloy of tungsten With zirconium the desired amount-of zirconium may be deposited on a filament of ductile tungsten by heating the' filament in a mixture of zirconium chloride an\d hydrogen to a temperature high enough to cause reduction of the zirconium chloride to the metal and the consequent formation of a coating of zirconium on the tungsten filament. The resulting composite filament may be subsequently converted into a homogeneous zirconium alloy by heatineI it to a sufficiently high temperature to produce diffusion of the zirconium into tun sten. My application Serial No. 735,075 fi ed August 30, 1924 constitutin a continuation in part of the present app ication contains claims based on the latter modification of my invention. Y What I claim as new and desire to secure by Letters Patent of the United States, is 1. rlhe process of pre aring tungsten laments containing iron w ich consists in producing by mechanical workin filamentary bodies of ductile tungsten, eating said bodies in hydrogen to a temperature of about 1000 to 1300 C. to remove surface impurities, electroplating the cleaned tungsten `body With iron, removing excess electrolyte,

and finally producing a homogeneous alloy by heating to a temperature of at least about 1600o C.

2. The process of preparing a li hting filament consisting or tungsten an iron which is homogeneous throughout which* consists in providing u on a tungsten filament a coating of metal ic iron in measured amount and thereupon heating the coated filament to a temperature of about 1600 C. for a suliicient length of' time to produce diffusion of the iron throughout the tungsten.

3. The process of preparing a filament constituted of a' homogeneous predetermined alloy of tungsten and iron Which consists in removing surface impurities from a filament of ductile tungsten, electroplating the cleaned filament with iron in desired proportion, removing excess electrolyte and heating to a temperature of at least about 1600o C. for a sufficient length of time to produce uniform diffusion of the iron throughout the tungsten.

4. The process of preparing a filamentary body consisting of a homogeneous, predetermined mixture of tun sten'and iron which vconsists in electroplatmg a `layer of iron upon the surface of a tungsten Wire and heating said plated Wire to a temperature sufficiently high to produce penetration of the iron throughout said tungsten Wire.

5. The method of producing a Wire consisting of a preponderant amount of a refractory metal and a metal alloyable therewith and capable of diffusing therethrough Which consists in providing a Wire consisting of a refractory metal with a coating of the alloyable metal and then heatin the coated Wire to a tempera-ture sufliclently high to cause alloyage and diffusion of the coating metal throughout said wire.

6. The method of producing a wire consisting of a preponderant amount of a tungsten wire with a coating of iron and 10 tungsten and a metal alloyable therewith, heating said coated wire to a temperature which consists in co'atin a wire consistin suiiciently high to produce penetration and of the tungsten with t e alloyablc met alloyage of the iron throughout the tungsten and then heatin the coated wire to a temwire. perature at whic alloyagc and diffusion of In witness whereof, 1 have hereunto set the coating throughout said wire occurs, my hand ths28th day of July, 1920.

7 The process of preparing tungsten wire n containing iron which consists in providing GORTON R. FONDA.

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