U.S. patent application number 13/104334 was filed with the patent office on 2011-09-08 for method for the production of tantalum powder using reclaimed scrap as source material.
Invention is credited to Craig F. Hafner, Joseph Smokovich.
Application Number | 20110214534 13/104334 |
Document ID | / |
Family ID | 40532887 |
Filed Date | 2011-09-08 |
United States Patent
Application |
20110214534 |
Kind Code |
A1 |
Smokovich; Joseph ; et
al. |
September 8, 2011 |
METHOD FOR THE PRODUCTION OF TANTALUM POWDER USING RECLAIMED SCRAP
AS SOURCE MATERIAL
Abstract
A process for obtaining tantalum powder from tantalum containing
scrap material is provided. The process includes selecting source
material, such as from sintered anodes for capacitors, hydriding
the source material, milling to desired particle size and surface
area, dehydriding, deoxidizing, agglomerating, sifting, and acid
treating to obtain tantalum powder of a desired size and
purity.
Inventors: |
Smokovich; Joseph; (Old
Field, NY) ; Hafner; Craig F.; (Bridgewater,
NJ) |
Family ID: |
40532887 |
Appl. No.: |
13/104334 |
Filed: |
May 10, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12248350 |
Oct 9, 2008 |
7981191 |
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13104334 |
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60979949 |
Oct 15, 2007 |
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Current U.S.
Class: |
75/353 |
Current CPC
Class: |
B22F 2998/10 20130101;
B22F 2009/001 20130101; C22B 7/002 20130101; Y02P 10/24 20151101;
B22F 9/023 20130101; Y02P 10/20 20151101; C22B 34/24 20130101; B22F
2998/10 20130101; B22F 9/023 20130101; B22F 9/04 20130101; B22F
1/0096 20130101; B22F 1/0088 20130101; B22F 2201/10 20130101; B22F
9/04 20130101; C23F 1/00 20130101 |
Class at
Publication: |
75/353 |
International
Class: |
B22F 9/20 20060101
B22F009/20 |
Claims
1. A method for producing tantalum powder from tantalum containing
source material comprising the steps of: hydriding the source
material; crushing and milling the hydrided source material to form
a powder; dehydriding and agglomerate the powder to form
agglomerates; deoxidize the agglomerated powder; and, optionally
crushing and sifting the agglomerates to a desired particle
size.
2. The method of claim 1 further comprising the step of acid
treating the deoxidized crushed agglomerated powder.
3. The method of claim 1 further comprising the step of crushing
and sifting the deoxidized crushed agglomerated powder to a desired
particle size.
4. The method of claim 1 further comprising the step of treating
the scrap material to remove contaminates prior to the step of
hydriding the scrap material.
5. The method of claim 1 wherein the step of crushing and milling
the hydrided scrap form a powder with a surface area between about
0.5 and 2.0 m.sup.2/g.
6. The method of claim 1 wherein agglomerates are formed of about
100 microns.
7. The method of claim 1 further comprising the step of crushing
and sifting the agglomerates prior to the step of deoxidizing the
agglomerates.
8. The method of claim 1 wherein the step of deoxidizing the
agglomerated powder is performed by mixing the agglomerates with
Magnesium metal and heating under an inert gas.
9. The method of claim 1 where the tantalum containing source
material is tantalum scrap comprising one or more of Tantalum
capacitor anodes and manufacturing scrap from sheet and wire.
10. The method of claim 1 further comprising the step of
identifying impurities in the source material prior to the step of
hydriding the source material.
11. The method of claim 1 further comprising the step of removing
impurities prior to the step of hydriding the source material.
12. The method of claim 11 further wherein the impurities are
removed by acid treating the source material.
13. (canceled)
14. (canceled)
15. (canceled)
16. The method of claim 2 further comprising the steps of rinsing
the acid treated anodes to remove acid residue and drying the
rinsed anodes.
17. The method of claim 1 further wherein the capacitor anode
contains a oxide film and further comprising the step of removing
the oxide layer by heating with Mg at sufficient temperature and
time to at least partially remove the oxide layer before the step
of hydriding.
18. The method of claim 1 further comprising the initial steps of
sampling the source material to determine initial contamination
levels and treating the source material to remove
contamination.
19. The method of claim 18 wherein the treating the source material
is done by acid leaching the source material.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/979,949, filed Oct. 15, 2007, the
entirety of which is hereby incorporated by reference into this
application.
FIELD OF THE INVENTION
[0002] The invention relates to metal tantalum powder. More
particular the invention relates to processes for the production of
tantalum powder
DESCRIPTION OF THE RELATED ART
[0003] Capacitors have been produced from tantalum powder for many
years. For example, tantalum powder may be manufactured by molten
sodium reduction of potassium heptafluorotantalate,
K.sub.2TaF.sub.7 which is produced by digesting tantalum ore or
tantalum scrap in hydrofluoric acid, separating the tantalum values
by solvent extraction and precipitating K.sub.2TaF.sub.7. Another
method involves milling of hydrided ingot. The ingots are typically
melted in an electron beam furnace under vacuum to achieve the very
high melting temperature of tantalum, about 3000.degree. C.
[0004] Such conventional methods are expensive. Additionally, the
use of hydrofluoric acid poses a hazard to technicians and
equipment. Improvements to the process for producing tantalum
powder are constantly desired in the marketplace. Tantalum
capacitors are used for a wide range of applications from very high
reliability military and medical applications to commercial
applications and consumer electronics.
[0005] It would be desirable to have a more cost effective method
to produce tantalum powder. It would be desirable to have a method
and process to produce commercial grade capacitor powder from
reclaimed tantalum scrap that does not require hydrofluoric acid
digestion or re-melting the material into ingots.
SUMMARY OF THE INVENTION
[0006] Methods for converting processed tantalum source material
into usable capacitor grade powder are described. The material may
be from a variety of sources but is preferably from tantalum scrap.
Such tantalum scrap includes tantalum anodes made from sintered
powder, deoxidized tantalum anodes or from other high purity
tantalum scrap such as fabricated sheet made from ingot.
[0007] The use of scrap material to obtain tantalum powder presents
several challenges as compared to virgin material, including the
presence of varying amounts of impurities, some of which must be
removed prior to processing. The powder is prepared by first
sorting material, removing contaminants below acceptable levels,
processing to achieve the desired surface area and then further
treating to form an agglomerated capacitor powder.
[0008] The invention has many advantages over conventional
processes to obtain tantalum powder. Commercial grade capacitor
powder from tantalum scrap is obtained by the inventive processes
without using hydrofluoric acid digestion or having to initially or
subsequently re-melt the source material to ingots. The elimination
of the these steps from conventional processes is significantly
more economical, saves time and reduces the considerable hazards
associated with chemicals such as hydrofluoric acid.
[0009] In one embodiment method for producing tantalum powder from
tantalum containing source material is provided. The method
comprises the steps of hydriding the source material, crushing and
milling the hydrided source material to form a powder, dehydiding
and agglomerate the powder to form agglomerates, deoxidize the
agglomerated powder; and optionally crushing and sifting the
agglomerates to a desired particle size. Optionally, the method
includes additional steps depending on the source material and the
requirements of the final powder. These steps include, among
others, acid treating the deoxidized crushed agglomerated powder,
crushing and sifting the deoxidized crushed agglomerated powder to
a desired particle size, treating the scrap material to remove
contaminates prior to the step of hydriding the scrap material.
[0010] In one embodiment the step of crushing and milling the
hydrided scrap forms a powder with a surface area between about 0.5
and 2.0 m.sup.2/g. In another embodiment the agglomerates are
formed of about 100 microns. The agglomerates may be crushed and
sifted prior to the step of deoxidizing the agglomerates. The step
of deoxidizing the agglomerated powder may be performed by mixing
the agglomerates with Magnesium metal and heating under an inert
gas.
[0011] The tantalum containing source material can be in a variety
of forms. In one embodiment the tantalum scrap comprises tantalum
capacitor anodes and/or manufacturing scrap from sheet and
wire.
[0012] A method is provided of producing powder from reclaimed
capacitor anodes that are sintered tantalum powder around a central
tantalum wire. The method includes the steps of hydriding the
material by heating the material in vacuum then backfilling with
hydrogen, lightly milling the hydrided anodes to liberate the
tantalum wire, sifting the milled anodes to separate the tantalum
wire from the powder, heat treating the powder in two or more steps
to dehydride, deoxidize, and agglomerate the powder and crushing
the agglomerates and sifting to produce a particle size
distribution capable of being pressed and sintered to re-form
capacitor anodes.
[0013] Optionally, the initial steps of sampling the anodes to
determine initial contamination levels and acid leaching the anodes
to remove metallic contamination is performed. The acid treated
anodes are then rinsed to remove acid residue and the rinsed anodes
are dried. In an another embodiment the step of removing the oxide
layer by heating with Mg at sufficient temperature and time to at
least partially remove the oxide layer before the step of hydriding
is included.
DETAILED DESCRIPTION OF THE INVENTION
[0014] A process for obtaining tantalum powders from selected
source material is provided. The source material must have a high
concentration of tantalum but need not be in the form of ingots as
is required by conventional techniques. The selection of source
material is based on the form of the material and the amount and
type of chemical contamination. The source material is thin,
preferably less than about 2 mm, such as sheet or wire. Thin source
material allows for easier and more complete hydriding. Acceptable
forms include, but not limited to, thin sheet, sintered powder
compacts (anodes), de-oxidized anodized anodes from capacitors and
wire.
[0015] One preferred source material is tantalum scrap, such as
various recycled tantalum materials including tantalum capacitor
anodes, manufacturing scrap from high purity sheet and wire as well
as other high purity tantalum scrap. One important feature of the
invention is that the form of the source material need not be
altered or changed to any specific form prior to treatment. For
example, when the tantalum source material is scrap, the scrap need
not be digested with HF acid and ultimately reduced with molten
Sodium metal to form powder, or alternately melted at 3000.degree.
C. in an electron beam furnace to form ingots, both of which
processes have high associated costs as well as hazards.
[0016] Once selected, the source material is subjected to a process
that includes a number of steps to produce the tantalum powder. In
one embodiment, the selected source material is initially
chemically treated to remove contaminants. The specific treatment
depends on the specific contaminates present in the scrap and also
depends on the desired purity of the final tantalum powder. For
example, for many contaminates, the contamination can be leached or
dissolved to sufficiently low levels by conventional means such as
acid leaching in Hydrochloric, Nitric, or Sulfuric Acid or
combinations of these acids, with or without additional oxidizing
agents.
[0017] The treatment will also depend on the desired purity of the
finished tantalum powder. In some instances, if the starting source
material is of sufficient purity in relation to the desired final
powder, no initial treatment is required. Those skilled in the art
will readily be able to determine what treatment is necessary for
the intended source material.
[0018] The source material is then hydrided using conventional
techniques. For example, source material is heated in vacuum and
then backfilled with Hydrogen. Hydriding makes the source material
brittle and more easily crushed and milled, which is the next step
in the process. Those skilled in the art will readily be able to
determine an operative temperature/time profile to yield a high
degree of Hydrogen uptake. Generally, the greater the Hydrogen
uptake, the more brittle the source material and the easier it is
to mill. The thicker the source material, the more difficult it
becomes to hydride as there is typically a gradient of Hydrogen
concentration from the surface to the interior of thick pieces.
[0019] Once hydrided, the hydrided material is crushed and milled
to a powder. The equipment used for crushing and milling is that
typically used for milling metal. The specific process for crushing
and milling the material will depend on the desired properties for
the finished powder. For example, if the finished powder is
intended to be commercial grade tantalum powder for, then the
hydrided material is preferably milled to a fine powder with a
relatively high surface area between about 0.5 and about 2.0
m.sup.2/g. By "commercial grade," it is generally understood to
mean non-military, usually consumer products requiring a lower
degree of reliability and a wider operating specification. For
example handheld devices: cell phones, games, etc are included in
consumer grade applications. The finer the powder the more
capacitance per gram, CV/g., which is one of the major price
factors in Ta powder.
[0020] The crushed and milled powder is then dehydrided. Preferably
the Tantalum is heated to about 1300.degree. F., in a vacuum to
dehydride the powder. Under the right conditions the dehydrided
powder will agglomerate to produce agglomerates. For example, if
the temperature is then increased to 2000.degree. F. agglomeration
will occur. Such agglomerates will typically be of about 50 microns
to about 250 microns; preferably the agglomerates are about 100
microns as these agglomerates have good flow characteristics, which
is important for filling the small molds used to press the powder
into anodes.
[0021] The agglomerated powder is then optionally crushed and
sifted to remove undersized and oversized material thereby
obtaining a sifted powder. This step is done to improve the
uniformity of the powder. Again uniformity of material size is an
important property when the powder is to be used for producing
anodes. In other instances when uniformity is not as critical, the
powder need not be crushed or sifted.
[0022] Preferably, the sifted powder is subsequently deoxidized.
This is done to lower the oxygen content in the powder. In many
common applications of tantalum powder, it is desirable to minimize
the amount of dissolved oxygen in the tantalum powders. In one
embodiment, deoxidizing the powder is performed by mixing the
powder with magnesium metal and heating under inert gas at elevated
temperature, such as about 1,200.degree. F. to about 1,600.degree.
F., preferably about 1,450.degree. F. In many instances when high
purity is desired, the deoxidized powder is acid treated, such as
for example with warm Hydrochloric, Sulfuric Acid and Peroxide,
Nitric Acid and Hydrochloric, or Niric Acid and Hydroflouric. This
removes the magnesium and other metallic impurities added during
milling and deoxidizing.
[0023] The deoxidized and acid treated powder is again crushed and
optionally sifted to a desired particle size to obtain a tantalum
powder. In one embodiment, the powder is crushed and sifted to a
particle size of about 1.0 m.sup.2/g, as this size is readily
obtainable, easily deoxidized, and produces a good CV/g in the 15 k
to 30 k range.
[0024] In alternate embodiments of the invention, one or more
optional steps are included for producing tantalum powder from a
tantalum containing source material. The specific form of the
source material and the specific content and concentration of
contaminates often require different steps to produce tantalum
powder.
[0025] For example, in one embodiment, the source material includes
reclaimed capacitor anodes comprising sintered tantalum powder
around a central tantalum wire. In this embodiment, the process
includes testing and selecting the source material. Samples of
source material are tested to determine initial contamination
levels of the source material. The testing is done by conventional
testing methods known to those skilled in the art. The testing may
reveal that certain samples contain too much of a particular
contaminate and therefore not used.
[0026] For example, high levels of Nb, W, or Si are difficult to
remove and therefore, materials containing these contaminates are
typically not suitable for most applications. For another example,
high levels of Mo typically require further testing to determine if
the Mo is on the surface only, or in the interior of the material.
For another example, high levels of Carbon also require further
testing to determine the most effective removal efficiency. Most
other normally present contamination can be removed by conventional
methods know to those in the art. Depending on the results of the
testing, the material may be subjected to acid leaching to remove
metallic contamination identified in the testing. If acid treated,
the material is then rinsed to remove acid residue and then
dried.
[0027] The dried material is hydrided as described above, for
example by heating the material in vacuum then backfilling with
hydrogen. The hydrided material is milled, preferably light milling
to liberate any tantalum wire. Tantalum wire typically contains a
high silica content. If the wire does have high silica content, it
is preferably separated from the powder so as not to contaminate
the powder. The wire can be separated from the usable powder by
sifting. The powder is heat treating to dehydride, deoxidize, and
agglomerate the powder. The heat treatment is preferably performed
in one or more steps, such as in two or more steps, or in several
steps.
[0028] In one embodiment the steps of dehydriding, deoxidizing, and
agglomerating is performed in a single step. The hydrided powder is
pre-blended with Magnesium and put in a vacuum oven. A vacuum of
about (7.5.times.10.sup.-4 Torr) is pulled and heated to 1300F
until outgassing stops (dehydriding). The heat is increased to a
temperature of about 1650.degree. F. for about 3 hours
(deoxidizing) and then increased to about 2000.degree.
F.-2400.degree. F. for about 30 minutes (agglomerating).
[0029] Finally the agglomerates are crushed and optionally sifted
to produce a particle size distribution capable of being pressed
and sintered to re-form capacitor anodes.
[0030] In a further embodiment, the source material is capacitor
anodes that have been anodized. The anodized capacitor anodes have
an oxide film which serves as a dielectric between the anode and
the cathode in tantalum capacitors. The oxide film must be removed
to a sufficient degree prior to the step of hydriding. In this
further embodiment, the process for making metal powder from this
type of source material may comprise the step of removing the oxide
layer from the anodized capacitor anodes. This can be accomplished
by heating the capacitor anodes with magnesium for a sufficient
temperature and time to remove enough of the oxide layer to permit
hydriding during the hydriding step. This step may be performed as
a preprocessing step discussed above, or may be performed at any
point in the process prior to the hydriding step discussed
above.
[0031] In another aspect of the invention, a process is provided to
manufacture tantalum powder from source material that is thin
sheet. For example, the source material may be a thin sheet formed
by rolling pure tantalum ingot into sheet material. Preferably,
such sheet material has a thickness less than about 15 mm, and more
preferably less than about 5 mm, and most preferably in a range
from about 0.001 mm to about 5 mm.
[0032] The tantalum powder reclaimed through the processes
described herein is can produce high quality powder such as that
acceptable for use as sintered anodes for capacitors. As such, the
processes may be adapted to produce agglomerated capacitor powder.
Application of the processes described herein to obtain tantalum
powder having properties, such as size and purity, for applications
other than to capacitors are also within the scope of the
invention.
[0033] The following Examples are provided to illustrate
embodiments of this invention. Other specific applications of the
teachings in this patent application can be used without departing
from the spirit of this invention. Other modifications of the
methods can be used, and are considered to be within the scope of
this invention.
Example 1
[0034] 25 kg of sintered, not anodized, gray anodes were washed to
remove carbon residue, acid treated in 50% HNO.sub.3 followed by
HCI to remove metallic contamination. Subsequently the anodes were
thoroughly rinsed and dried. The clean anodes were then sampled and
analyzed. The results are provided in Table 1.
TABLE-US-00001 TABLE 1 Contaminate Concentration C 65 ppm Cr 15 ppm
Fe 133 ppm Mn 1 ppm N 77 ppm Ni <10 ppm O 0.318% Zr <1
ppm
[0035] The sample was hydrided by backfilling a vacuum oven to a
positive pressure with Hydrogen at 482.degree. C. for 3 hours. The
hydrided sample was wet milled with tantalum media for 30 minutes
then sifted to separate the Ta wire from the remaining material.
The remaining material was milled for an additional 6 hrs to form a
powder. The powder was rinsed and dried at 100.degree. C. for 24
hours. The powder was tested with a Fischer SubSieve Sizer and had
a particle size of 1.1 .mu.m and a BET surface area of 1.1
m.sup.2/g.
[0036] This powder was then dehydrided at 700.degree. C. and
agglomerated at 1300.degree. C. for 30 minutes. The resulting
agglomerates were crushed, sifted to -80 mesh, blended with Mg
turnings and deoxidized at 900.degree. C. for 6 hours.
[0037] The resulting power was acid treated with 50% HNO.sub.3
followed by conc. HCI to remove residual Mg. The powder was then
rinsed and dried and then tested for particle size distribution.
The mean diameter was 45 .mu.m with 94% being 100 .mu.m or less.
The powder was pressed and sintered and tested for wet leakage. At
60 V the anodes had a wet leakage of 1.5 nA/CV.
Example 2
[0038] 25 kg of thin Tantalum Sheet with an average thickness of 2
mm and a starting Oxygen content of <100 ppm was hydrided and
milled as in Example 1. The final particle size and BET surface
area was 2.5 .mu.m and 0.79 m.sup.2/g respectively.
[0039] There will be various modifications, adjustments, and
applications of the disclosed invention that will be apparent to
those of skill in the art, and the present application is intended
to cover such embodiments. Accordingly, while the present invention
has been described in the context of certain preferred embodiments,
it is intended that the full scope of these be measured by
reference to the scope of the following claims.
* * * * *