Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1996-03-28
2001-08-07
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C075S010330, C075S229000, C148S513000, C264S068000, C264S125000
Reexamination Certificate
active
06269536
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is a response to the problem of establishing high purity tantalum wire with under 100 ppm of oxygen impurity for use as an effective lead wire for sintered tantalum powder solid electrolytic capacitors. The invention also involves other metals and usage of such other metals and tantalum in applications other than as lead wires.
In working with tantalum and other reactive metals used for lead wires, and in similar application, problems arise out of the affinity of such metals to oxygen and the high temperatures normally associated with extrusion, forging and other fabrication of such metals. It is known that oxygen contents of several hundred ppm typically encountered with sodium reduced tantalum (i.e, reduction of K
2
TaF
7
or other salts of tantalum by sodium) will lead to difficulties in later working. The high temperatures of extrusion and/or encountered in the course of anneals and other softening treatments in the course of cold fabrication processes complicate the problem. See, e.g., Michaluk et al., “Characterization of Extruded and Forged Preforms,” 1992 paper for a book published that year by the Mineral, Metals and Materials Society.
It is the object of this invention to provide new and improved processing of tantalum and other reactive metals.
SUMMARY OF THE INVENTION
I have conceived of the approach of making wires via a powder metallurgy route using tantalum hydride powders that are packed into a shell. The powders are loosely filled into the shell and then dehydrided in situ while loosely contained in the shell. The shell is then closed in and used as an extrusion billet to produce a rod which can be used directly or subjected to further size reduction by forging, swaging and/or wire drawing or rolling steps to produce a final wire or sheet mill product and/or formed into a final fabricated part at that time or later. Both the extrusion step and later forming step(s) are made more effective by the original steps of provision of loose hydride powders into a container that will become an extrusion billet, dehydriding in situ and immediately sealing up the billet to prevent oxygen absorption and then extruding. After cooling, the extruded product, i.e. the resultant rod, can be cooled and the original can material now constituting a thin surface layer of the rod can be removed. The term “rod” as used herein includes all sizes of the rod and wire range practically achievable via extrusion as well as all cross-section forms.
The process as applied to tantalum includes the more specific steps:
(1) provision of a high purity tantalum body with an oxygen level under 50 ppm, preferably under 25 ppm, e.g. as an electron beam mealted ingot;
(2) hydriding the body by exposure to a vacuum chamber, back-fill of hydrogen to hydride-embrittle the body and preempting sites otherwise susceptible to oxygen pick up;
(3) pulverizing the hydrided body by crushing, grinding and screening to form a coarse powder preferably in a 44-250 mesh range and more preferably minus 120 mesh;
(4) forming an extrusion can with a back-plug and a conical leading nose end and a tube therein;
(5) filling the can via the tube with the hydride powder;
(6) dehydriding the powder by evacuation of hydrogen gas through the tube while maintaining a vacuum ambient by pumping and heating the can containing the loose hydrided powder at about 800° C. until hydrogen content of the scanned powder is under 10 ppm preferrably at a 1-2 ppm level;
(7) sealing the tube;
(8) preheating it, e.g. at 700-900° C. for the case of a copper can of six inches diameter for 4 hours;
1
(9) extruding the heated can in a single pass extrusion reduction of over 4:1, preferably about 16:1, and more preferrably in the 20:1 to 50:1 range, to consolidate the powder to a workable rod or wire;
(10) cooling the extruded product (rod) and removing a thin outer layer of it derived from the original can by turning or etching; and
(11) further processing the now exposed rod or wire, which at this point will have a maintainable low oxygen content, preferably under 100 ppm and more preferably below 50 ppm.
1
Longer times would be used for a longer diameter can on the basis of about 1 additional hour per additional inch of radius. The temperature would be higher for materials such as steel.
Apart from realization of a more feasible processing of the metal, the end product usages are substantially enhanced in a variety of applications including but not limited to electrolytic capacitor lead wire usage.
Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawing in which:
REFERENCES:
patent: 3295951 (1967-01-01), Fincham et al.
patent: 3779714 (1973-12-01), Nadkarni et al.
patent: 3884676 (1975-05-01), Nadkarni et al.
patent: 4141719 (1979-02-01), Haakko
patent: 4219357 (1980-08-01), Yolton et al.
patent: 4440572 (1984-04-01), Nadkarni et al.
patent: 5369088 (1994-11-01), Mukai et al.
patent: 5445787 (1995-08-01), Friedman et al.
patent: 5480601 (1996-01-01), Yamamoto et al.
Arbes Carl J.
Cohen Jerry
H.C. Starck Inc.
Perkins Smith & Cohen
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