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Publication numberUS3335037 A
Publication typeGrant
Publication dateAug 8, 1967
Filing dateDec 27, 1963
Priority dateDec 27, 1963
Publication numberUS 3335037 A, US 3335037A, US-A-3335037, US3335037 A, US3335037A
InventorsDunn Cecil G, Webster Harold F
Original AssigneeGen Electric
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method for producing tantalum sheet
US 3335037 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

1967 c. G. DUNNVXETAL. 3,335,037

METHOD FOR PRODUCING TANTALUM SHEET Filed Dec. 27, 1953 /m ii 00 Inventors: Cecilpciig/ugm t Ha old e 8 er bywi Th (air A "Etc rm ey.

United States Patent Oke 3,335,037 METHOD FOR PRODUCING TANTALUM SHEET Cecil G. Dunn and Harold'F. Webster, Scotia, N.Y., as-

signors to General Electric Company, a corporation of New York Filed Dec. 27, 1963, Ser. No. 334,049 2Claims. (Cl. 14813.1)

This invention relates to a process for producing refractory metal bodies and more particularly to a process for producing tantalum foils having a (110) preferred grain orientation.

Tantalum metal has, as a result of increased knowledge of its properties and with improved production techniques, been used in widespread and diverse applications in recent years. It has a high melting point, good strength, chemical inertness to many strongly corrosive materials and it has been used as electrode material in diodes filled with cesium vapor.

The work function of a clean metal crystal, its adsorption properties, and its work function when thinly coated with cesium all are strongly dependent upon the crystallographic orientation of its surface. Thus, when a thermionic diode is built with its cathode and anode of polycrystalline metal with random grain orientation, the emission current density is non-uniform over the surface. Certain grains may emit as much as 100 times the current density emitted by the poorly emitting grains. When the diode is used to convert heat to electrical energy non-uniformity of the work function of the anode will also degrade the device efiiciency. If the electrodes can be made of many grains having approximately the same crystallographic orientation, the diode performance will be improved by having the entire electrode surface operating at maximum efficiency. The most strongly emitting grains of tantalum in cesium vapor are those having a (110) surface and. an electrode made up preferentially of grains of this crystal face will be the optimum cathode.

It is a principal object of this invention to provide a process for producing tantalum foil having a stable (110) grain orientation.

It is a further object of this invention to provide a process for producing tantalum foil having improved electrode work function properties in cesium filled diodes.

A further object of this invention is to provide a process for producing tantalum foil having the (110) preferred grain orientation.

Other objects and advantages of this invention will be in part obvious and in part explained by reference to the accompanying specification and drawings.

FIG. 1 of the drawings is a unit stereograph triangle referring to crystallographic directions normal to the rolling plane which schematically shows no (hkl) preferred orientation; i.e., the grains have random orientations;

FIG. 2 is a unit stereograph triangle identical to that of FIG. 1 but taken on tantalum processed according to the present invention; and

FIG. 3 is a unit stereograph triangle identical to that of FIG. 2 but made from a different tantalum sample.

Broadly, the process of this invention comprises providing a cold rolled body of tantalum foil of up to 6 mils thickness and subjecting this body to anneal at a temperature no lower than about 1950 C., and preferably from 2100 C. to 2200 C., in a vacuum no greater than about 10- mm. of Hg.

As a metal, tantalum has a slow rate of work hardening and is not diflicult to fabricate, standard methods and equipment being suitable for its shaping. Most fabrication is effected at room temperature, due at least in part 3,3 35,037 Patented Aug. 8, 1 967.

to tantalum, reactivity with the common gases when heated. Foil production is, of course, accomplished by cold rolling, the reduction in size per rolling stage generally ranging from 30 to 40 percent. Intermediate anneals are often used between rolling stages, the annealing temperatures being on the order of 1300 C. to 1400" C. for at least 1 hour.

Referring to FIG. 1 of the drawings, circles 10 represent crystallographic axes normal to the rolling plane or plane of tantalum foil having no preferred orientation. The absence of preferred orientation is indicated by the fact that circles 10 are evenly distributed in the unit triangle. Such is not the case in connection with tantalum produced by this process, as clearly evidenced by FIGS. 2 and 3 of the drawings where the material is indicated to have a (110) orientation.

Samples of tantalum foil were produced from two different sources of tantalum to produce (110) grain oriented foils of tantalum. The first of these was initially in the form of a V8 inch diameter tantalum rod initially 99.79 percent pure which was then refined further in four passes of zone melting. The rod was cold rolled to 0.0065 inch thickness and then annealed one hour at 1300 C. in a vacuum to 10'- mm. of Hg. This annealed strip was then cold rolled to .003 inch thickness and finally annealed for 2 hours at 2100" C. in a vacuum of 10' mm. of Hg. The large grains in the annealed foil specimen were then analyzed by means of X-ray diffraction patterns to determine whether or not grain orientation had been achieved. FIG. 2 of the drawings was obtained by plotting the results from the diffraction pattern studies, and it is clear that a (110) preferred orientation was in fact obtained since poles of (110) planes of most of the grains studied were within 5 degrees of an axis passing perpendicularly to the plane of the foil.

The second specimen was obtained using arc-melted tantalum of about the same purity as the zone-melted tantalum. This material which had previously been rolled to 0.010 inch thickness was annealed for 1 hour at 1400 C. in a vacuum to 10- mm. of Hg, then cold rolled to .003 inch thickness and finally annealed for 3 hours at 2200 C. The grain orientation of this specimen was studied in the same manner as that used in connection with the zone-melted tantalum and the stereograph triangle shown in FIG. 3 of the drawings was obtained. Here, once again, it is evident that a strong (110) preferred orientation had been obtained. 1

It is felt that in order to obtain the orientation, the tantalum material must be of high purity, i.e. at least 99 /2 percent pure, so that when subjected to the high temperature vacuum anneal, the grain boundaries within the material are free to migrate. It is felt that the (110) plane is one of lowest intrinsic energy so that given proper growth conditions and enough such (110) oriented grains, their growth will consume all other grains of different (hkl) orientation. The origin of such selective growth might best be described as an example of an (hkl) surface energy phenomenon. It will be understood, however, that the preceding is oifered by way of explanation and is not intended to be limiting to the invention, since other phenomena might prevail.

Although the present invention has been described in connection with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

" 1 The'pr ocess for producing tantalum foil having the References Cited (110) crystallographic orientation comprising, provid- UNITEDSTATES PATENTS ing cold-rolled tantalum foil of up to 6 mils thickness and of not less than about 99.5 percent purity, and angvelss nealing the tantalum foil in a vacuum no higher than 5 3166414 1/1965 Femme {'1 75*174 10- mm. of Hg at a temperature no lower than about 3203793 8/1965 g e a 1950 C. for a time sufficient to recrystallize the foil an and develop the (110) crystallographic orientation.

2. A process as described in claim 1 wherein the foil DAVID RECK"Pmary Exammer' is annealed at temperatures of from about 2000- C. to 10 DEAN, Assistant Examiner- 2300" C. for'not less than about 1 hour.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2451703 *May 2, 1945Oct 19, 1948Weiss Paul AlfredResilient tantalum tubes and a process for making same
US3156560 *Jun 5, 1959Nov 10, 1964Gen ElectricDuctile niobium and tantalum alloys
US3166414 *Jul 9, 1962Jan 19, 1965Westinghouse Electric CorpTantalum base alloys
US3203793 *Jan 28, 1963Aug 31, 1965Du PontPorous columbium and tantalum materials
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US6193821 *Jul 14, 1999Feb 27, 2001Tosoh Smd, Inc.Fine grain tantalum sputtering target and fabrication process
US6348113 *Nov 25, 1998Feb 19, 2002Cabot CorporationHigh purity tantalum, products containing the same, and methods of making the same
US6770154Sep 18, 2001Aug 3, 2004Praxair S.T. Technology, Inc.Textured-grain-powder metallurgy tantalum sputter target
US6893513Aug 6, 2001May 17, 2005Cabot CorporationHigh purity tantalum, products containing the same, and methods of making the same
US7081148Mar 26, 2004Jul 25, 2006Praxair S.T. Technology, Inc.Textured-grain-powder metallurgy tantalum sputter target
US7431782May 14, 2002Oct 7, 2008Cabot CorporationHigh purity tantalum, products containing the same, and methods of making the same
US7585380Dec 17, 2002Sep 8, 2009Cabot CorporationHigh purity tantalum, products containing the same, and methods of making the same
Classifications
U.S. Classification148/668, 148/422
International ClassificationC22C27/00, C22C27/02
Cooperative ClassificationC22C27/02
European ClassificationC22C27/02