US 3127641 A
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A ril 7, 1964 K. S. G. PERTWEE TUNGSTEN TUBE MANUFACTURE Filed Oct. 5, 1961 W49; $1,, #0 H260 2 f M M J 7 5 T /2 A? 1TWVTTTOTI Kenne th SGPev b-wee b3 fl/ZK I-Iis A t to neg United States Patent 3,127,641 TUNGSTEN TUBE MANUFACTURE Kenneth S. G. Pertwee, South Euclid, Ohio, assign'or .to General Electric Company, a corporation of New York FiledOet. 5, 1961, Ser. No. 143,197 6 Claims. (Cl. 22-204) This invention relates to a method of making tungsten tubing, and more particularly to the manufacture of seamless tungsten tubing by vapor deposition.
Tungsten tubing is useful for such purposes as resistance heating elements, lamp filaments, etc. However, to the best of myknowledge seamless tungsten tubing has not been heretofore commercially available. It 'has been possible to purchase tungsten tubing formed by first preparing tungsten in sheet form and then rolling it to tubular form, but such tubing is very expensive. It has been proposed to form tungsten tubing by the decomposition of tungsten hexachloride in an evacuated enclosure to deposit tungsten onto a metallic core member heated by the passage of electric current therethrough, followed by dissolving the core member in a suitable acid. However, the uniformity of wall thickness of tungsten tubing made in that manner cannot be accurately controlled, and the process is quite expensive.
It is therefore a principal object of this invention to provide a relatively inexpensiveprocess of making seamless tungsten tubing of readily controlled and uniform wall thickness.
Samples of tungsten metal in 'massive form and of high purity have been made heretofore by passing a mixture by hydrogen and tungsten hexafiuoride through the interior of a copper tube heated in a furnace to a. temperature sulficient to cause a chemical reaction of the hydrogen and tungsten hexafluoride to yield tungsten which is deposited on and virtualy fills the interior of the tube. The copper tube is then removed by dissolving in nitric acid.
When it is attempted to make tungsten tubing by this method, the wall thickness is non-uniform since the tungsten builds up much more heavily on the leading end of the reaction tube at which the gaseous mixture enters. Clogging of the leading end of the reaction tube may be alleviated by periodically shifting the tube. However, that procedure causes lamination to be formed in the tungsten deposit corresponding to the position of the tube at each shift. The laminations contain a blue, partly reduced tungsten compound.
In accordance with the invention, I have found that a dense, homogeneous tungsten tube of substantially uniform wall thickness is formed by progressively heating the copper reaction tube in a longitudinally narrow annular zone which is moved slowly along the length of the tube at a uniform rate. The thickness of the tungsten tubing can be controlled by repeatedly passing the heated zone back and forth along the length of the copper reaction tube.
Further features and advantages of the invention will appear from the folowing detailed description, and from the drawing wherein:
FIG. 1 is a diagrammatic representation of a tube forming apparatus;
FIG. 2 is a fragmentary longitudinal section showing the copper reaction tube and the inner vapor deposited tungsten tube prior to stripping the reaction tube;
FIG. 3 is a side elevation showing a coiled reaction tube for forming a coiled tungsten tube; and
FIG. 4 is a fragmentary longitudinal section of a reaction tube with an enclosed tungsten wire coil serving as a base for the formation of a vapor deposited tungsten tube.
Referring to FIG. 1 of the drawing, the copper reaction tube l is supported by and connected to spaced tube .members 2 and 3, preferably of copper, by suitable couplings or fittings 4 and 5, the tube members 2 and 3 being cooled by water jackets 6 and 7. The'inlet tube 2 is supplied with the reaction gases from a mixing chamber 8 into which is fed the hydrogen from a supply tube 9,
and the tungsten hexafluoride froma supply tube 10. The mixture of H and WE, therefore flows from the mixing chamber 8 through the inlet tube 2, reaction tube 1, and
outlet tube 3, and is removed by-a suitable exhaust system.
Tungsten is caused to deposit on the inside of the copper reaction tube 1 by heating the tube to 'a sufficiently high temperature. Although the reaction ofH and WF starts at approximately 450 C., the reaction tube is preferably heated to a temperature in the range of about 600 to 800 C. to insure a high degree of recovery. In accordance with the invention, the tube 1 is heatedin a "longitudinally narrow annular zone, not over about 2 inches long and preferably between land 2 inches, and the heated Zone is moved slowly along the tube at a uniform rate, preferably about 1 inch per minute, to achieve a deposit of tungsten in a layer 11 (FIG. 2) of "substantially uniform thickness.
Although the heating of the copper reaction tube 1 may convenient manner, as by an electric motor-driven carriage traveling along a track below the tube 1. The thickness of the tungsten tubing 11 can be controlled by repeatedly passing the furnace 12 back and forth along the length of the'tube 1. When the desired number of passes have been made the copper tube 1,-with its adherent layer of tungsten tubing 11, is removed from the apparatus,
and the copper tube is stripped off the tungsten tubing,
conveniently by dissolving it away in nitric acid.
Tungsten tubing may be made by this method in any reasonable size and wall thickness. For example, tubing has been made ranging in size from about /2 inch outside diameter to about inch outside diameter, and in uniform wall thicknesses ranging from .001 inch to about .020 inch. The tungsten is dense, specific gravity 19.25, and non-porous.
The quantity of hydrogen in the reaction mixture should be in excess of that which will combine stoichiometrically with the tungsten hexafluoride, preferably at least four times, by volume, of H to WF The rate of flow of the mixture into the reaction tube 1 is quite important, being substantially greater for the larger tubing than for the smaller. If the rate is too high it causes a turbulent deposit which builds up across the reaction tube. By way of example, when using a copper reaction tube 1 of inch outside diameter and 10 mil wall thickness, good results are obtained with a hydrogen flow of 1175 cc. per minute and a tungsten hexafluoride flow of 200 cc. per minute. At these flow rates, the tungsten tubing is formed at a rate of approximately 1 mil thick for each pass of the furnace 12.
The tungsten tubing may be made in the form of a helical coil by forming the reaction tube as a helical coil. This is illustrated in FIG. 3 where the helically coiled copper reaction tube In is shown connected to the outlet tube 3a by suitable fittings 5a.
When it is desired to make the tungsten tubing physically stronger, this may be done by re-enforcing with tungsten wire. As illustrated in FIG. 4, the wire, in the form of a helical coil 13, is fitted snugly in the interior of the copper reaction tube 1. The deposition of tungsten is carried out as described above. The deposit builds up on the inside of the coil 13 and also fills in between the turns of the coil to form a strong finished tube.
It may be desirable in some cases to make the ends of the tungsten tubing thicker, for example for added strength where it is to be clamped at its ends and the main portion is quite thin. This may be done conveniently by holding the furnace 12 stationary at each end of the reaction tube 1 for a time sufficient to build up the deposit of tungsten to the desired thickness.
While the reaction tube 1 may be made of functionally equivalent metals such as molybdenum and nickel, it is preferred to use copper for reasons of economy. Iron or steel is not suitable because of failure of the tungsten deposit to adhere to it.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. The method of making tungsten tubing which comprises flowing a mixture of hydrogen and tungsten hexafluoride through the interior of a copper reaction tube while progressively heating the tube to a temperature of about 600-800 C. in a longitudinally narrow annular zone thereof which moves slowly along the length of the reaction tube at a substantially uniform rate to thereby elfect chemical reaction of the hydrogen and tungsten hexafluoride and deposition of tungsten in a layer on the interior of said reaction tube, controlling the thickness of the tungsten layer by repeatedly moving the heated annular zone back and forth along the length of the reaction tube while continuing the flow of hydrogen and tungsten hexafluoride, and subsequently removing the reaction tube.
2. The method of making tungsten tubing as set forth in claim 1 wherein the heated annular zone is moved along the reaction tube at a rate of about one inch per minute.
3. The method of making tungsten tubing as set forth in claim 1 wherein the smaller heating zone is not longer than about two inches.
4. The method of making tungsten tubing as set forth in claim 1 wherein the annular heating zone is not longer than about two inches and is moved along the reaction tube at a rate of about one inch per minute.
5. The method of making tungsten tubing as set forth in claim 1 wherein, prior to deposition of the tungsten, a helical tungsten wire coil is fitted snugly in the interior of the reaction tube and, during subsequent deposition, the tungsten deposit builds up on and between the turns of the said tungsten wire coil.
6. The method of making tungsten tubing which comprises fiowing into the interior of a copper reaction tube a mixture of hydrogen and tungsten hexafluoride at a rate of about 1175 cc. per minute of hydrogen and 200 cc. per minute of tungsten hexafluoride While progressively heating the tube to a temperature of about 600800 C. in an annular zone about one to two inches long which moves along the length of the reaction tube at a substantially uniform rate of about one inch per minute to thereby effect chemical reaction of the hydrogen and tungsten hexafluoride and deposition of tungsten in a layer on the interior of said reaction tube, controlling the thickness of the tungsten layer by repeatedly moving the heated annular zone back and forth along the length of the reaction tube While continuing the flow of hydrogen and tungsten hexafluoride, and subsequently dissolving the reaction tube in a selective solvent therefor.
References Cited in the file of this patent UNITED STATES PATENTS 2,689,807 Kempe et al. Sept. 21, 1954 2,783,164 Hill Feb. 26, 1957 2,834,690 Marvin May 13, 1958 3,004,866 Bolton et al. Oct. 17, 1961 3,031,338 Bourdeaw Apr. 24, 1962 3,072,983 Brenner et al. Jan. 15, 1963 FOREIGN PATENTS 792,589 Great Britain Apr. 2, 1958 742,304 Great Britain Dec. 21, 1955 OTHER REFERENCES Vapor Deposition, Iron Age, vol. 69, issue 15, pages 113-117, published April 10, 1952, copy in Division 3. 22/203.