U.S. patent application number 10/834427 was filed with the patent office on 2005-01-06 for production of high-purity niobium monoxide and capacitor production therefrom.
Invention is credited to Fonville, Thomas J., Higgins, Brian J., Motchenbacher, Charles A., Robison, James W..
Application Number | 20050002854 10/834427 |
Document ID | / |
Family ID | 33310401 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050002854 |
Kind Code |
A1 |
Motchenbacher, Charles A. ;
et al. |
January 6, 2005 |
Production of high-purity niobium monoxide and capacitor production
therefrom
Abstract
The present invention relates to high-purity niobium monoxide
powder (NbO) produced by a process of combining a mixture of higher
niobium oxides and niobium metal powder or granules; heating and
reacting the compacted mixture under controlled atmosphere to
achieve temperature greater than about 1945.degree. C., at which
temperature the NbO is liquid; solidifying the liquid NbO to form a
body of material; and fragmenting the body to form NbO particles
suitable for application as capacitor anodes. The NbO product is
unusually pure in composition and crystallography, and can be used
for capacitors and for other electronic applications. The method of
production of the NbO is robust, does not require high-purity
feedstock, and can reclaim value from waste streams associated with
the processing of NbO electronic components. The method of
production also can be used to make high-purity NbO.sub.2 and
mixtures of niobium metal/niobium monoxide and niobium
monoxide/niobium dioxide. The method further is ideal for doping of
the product oxides to enhance particular characteristics of the
materials. The method further allows the production of single
crystal or directionally-solidified ingots. In contrast to the
spongy, highly porous agglomerates produced by other techniques,
the present invention produces solid, non-porous ingots that can be
fragmented to fine, non-porous angular particles suitable for
electronic applications.
Inventors: |
Motchenbacher, Charles A.;
(Robesonia, PA) ; Robison, James W.; (Lititz,
PA) ; Higgins, Brian J.; (Reading, PA) ;
Fonville, Thomas J.; (Reading, PA) |
Correspondence
Address: |
DUANE MORRIS, LLP
IP DEPARTMENT
ONE LIBERTY PLACE
PHILADELPHIA
PA
19103-7396
US
|
Family ID: |
33310401 |
Appl. No.: |
10/834427 |
Filed: |
April 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10834427 |
Apr 29, 2004 |
|
|
|
10428430 |
May 2, 2003 |
|
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|
Current U.S.
Class: |
423/594.17 |
Current CPC
Class: |
H01G 9/0525 20130101;
C01P 2004/03 20130101; C01P 2006/14 20130101; C01P 2006/12
20130101; C01G 33/00 20130101; C01P 2006/40 20130101; C01P 2006/80
20130101; C01P 2006/17 20130101; C01P 2002/72 20130101; C01P
2004/51 20130101; C01P 2004/61 20130101; C01P 2004/62 20130101 |
Class at
Publication: |
423/594.17 |
International
Class: |
C01G 033/00 |
Claims
What is claimed is:
1. A high-purity niobium monoxide (NbO) powder, produced by a
process comprising: a) combining a mixture of (1) a niobium oxide
selected from the group consisting of Nb.sub.2O.sub.5, NbO.sub.2,
and/Nb.sub.2O.sub.3, and (2) metallic niobium; b) forming a compact
of said mixture; c) reacting the mixture with a heat source such
that a temperature greater than 1945.degree. C. is achieved; d)
solidifying the reacted mixture to form a body of material; and e)
fragmenting the body to form niobium monoxide powder.
2. The niobium monoxide powder as recited in claim 1, wherein the
mass ratio of Nb.sub.2O.sub.5 to niobium metal powder or granules
in the mixture is about 1:1.
3. The niobium monoxide powder as recited in claim 1, wherein the
mass ratio of NbO.sub.2 to niobium metal powder or granules in the
mixture is about 1.3:1.
4. The niobium monoxide powder as recited in claim 1, wherein the
mass ratio of Nb.sub.2O.sub.3 to niobium metal or granules in the
mixture is about 2.5:1.
5. The niobium monoxide powder as recited in claim 1, wherein the
niobium oxide is Nb.sub.2O.sub.5.
6. The niobium monoxide powder as recited in claim 1, wherein the
heat source is an electron beam furnace.
7. The niobium monoxide powder as recited in claim 1, wherein the
heat source is a plasma-arc furnace.
8. The niobium monoxide powder as recited in claim 1, wherein the
heat source is an induction furnace.
9. The niobium monoxide powder as recited in claim 1, wherein the
heat source is an electric resistance furnace.
10. The niobium monoxide powder as recited in claim 1, wherein the
heat source is a vacuum arc remelting furnace.
11. The niobium monoxide powder as recited in claim 1, wherein the
reaction process achieves a temperature greater than or equal to
1945.degree. C.
12. The niobium monoxide powders as recited in claim 1, wherein the
mixture further comprises niobium monoxide revert, niobium metal
lead wire, or other niobium-containing waste products.
13. The niobium monoxide powders as recited in claim 1, wherein the
niobium oxide and metallic niobium are present in substantially
powder or granular form.
14. A method of producing niobium monoxide ingots or powder which
comprises: a) combining a mixture of (1) a niobium oxide selected
from the group consisting of Nb.sub.2O.sub.5, NbO.sub.2,
and/Nb.sub.2O.sub.3, and (2) metallic niobium, wherein the niobium
oxide and metallic niobium are present in powder or granular form;
b) forming a compact of said mixture; c) reacting the mixture with
a heat source such that a temperature greater than 1945.degree. C.
is achieved; d) solidifying the reacted mixture to form a body of
material; and e) fragmenting the body of material to form the NbO
powder.
15. The method as recited in claim 14, wherein the mass ratio of
Nb.sub.2O.sub.5 to niobium metal powder or granules in the mixture
is about 1:1.
16. The method as recited in claim 14, wherein the mass ratio of
NbO.sub.2 to niobium metal powder or granules in the mixture is
about 1.3:1.
17. The method as recited in claim 14, wherein the mass ratio of
Nb.sub.2O.sub.3 to niobium metal or granules in the mixture is
about 2.5:1.
18. The method as recited in claim 14, wherein the niobium oxide is
Nb.sub.2O.sub.5.
19. The method as recited in claim 14, wherein the reaction
achieves a temperature of 1945.degree. C. or greater.
20. The method as recited in claim 14, wherein the heat source is
an electron beam furnace.
21. The method as recited in claim 14, wherein the heat source is a
plasma-arc furnace.
22. The method as recited in claim 14, wherein the heat source is
an induction furnace.
23. The method as recited in claim 14, wherein the heat source is a
vacuum arc remelting furnace.
24. The method as recited in claim 14, wherein the mixture further
comprises niobium monoxide revert, niobium metal lead wire, or
other niobium-containing waste products.
25. A high-purity niobium monoxide (NbO) ingot, produced by a
process comprising: a) combining a mixture of (1) a niobium oxide
selected from the group consisting of Nb.sub.2O.sub.5, NbO.sub.2,
and/Nb.sub.2O.sub.3, and (2) metallic niobium; b) forming a compact
of said mixture; c) reacting the mixture with a heat source such
that a temperature greater than 1945.degree. C. is achieved; and d)
solidifying the reacted mixture to form a body of material.
26. The niobium monoxide ingot as recited in claim 25, wherein the
weight ratio of Nb.sub.2O.sub.5 to metallic niobium in the mixture
is about 1:1.
27. The niobium monoxide ingot as recited in claim 25, wherein the
weight ratio of NbO.sub.2 to metallic niobium in the mixture is
about 1.3:1.
28. The niobium monoxide ingot as recited in claim 25, wherein the
weight ratio of Nb.sub.2O.sub.3 to metallic niobium in the mixture
is about 1.25:1.
29. The niobium monoxide ingot as recited in claim 25, wherein the
niobium oxide is Nb.sub.2O.sub.5.
30. The niobium monoxide ingot as recited in claim 25, wherein the
heat source is an electron beam furnace.
31. The niobium monoxide ingot as recited in claim 25, wherein the
heat source is a plasma-arc furnace.
32. The niobium monoxide ingot as recited in claim 25, wherein the
heat source is an induction furnace.
33. The niobium monoxide ingot as recited in claim 25, wherein the
heat source is an electric resistance furnace.
34. The niobium monoxide ingot as recited in claim 25, wherein the
heat source is a vacuum arc remelting furnace.
35. The niobium monoxide ingot as recited in claim 25, wherein
electronic valves are produced from the niobium monoxide
ingots.
36. The niobium monoxide ingot as recited in claim 25, wherein
slices cut from ingots or parts of ingots are used as mounting
surfaces for electronic devices.
37. The niobium monoxide ingot as recited in claim 25, wherein the
mixture is adjusted to yield NbO.sub.2.
38. The niobium monoxide ingot as recited in claim 25, wherein the
niobium oxide and metallic niobium are present in powder or
granular form.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of application
Ser. No. 10/428,430, filed May 2, 2003.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of producing
niobium monoxide powder of high purity, and the use of such niobium
monoxide powders in the production of valve devices, i.e.,
capacitors.
BACKGROUND OF THE INVENTION
[0003] It has been recognized that niobium monoxide (NbO) has some
unusual electrical properties that make it well-suited for the
manufacture of electronic capacitors. It is of much lower
flammability than equivalent tantalum powders, is less costly than
tantalum, and has much larger potential supply than tantalum.
However, niobium monoxide capacitor powders require high levels of
purity, with not only foreign elements such as iron and copper
being deleterious, but other forms of niobium such as niobium
metal, niobium dioxide (NbO.sub.2), niobium trioxide
(Nb.sub.2O.sub.3) and niobium pentoxide (Nb.sub.2O.sub.5) being
harmful. In order to be useful in a valve application, the niobium
monoxide must be in a finely divided form, i.e., fine powder or,
preferably, agglomerates formed from small particles, such small
particles typically about 1-2 microns in diameter or finer. In
order to meet these requirements, the electronics industry has
produced niobium monoxide by reacting agglomerated and sintered
niobium pentoxide or niobium dioxide (optionally pre-reduced from
the pentoxide) with a metallic reducing agent under conditions in
which the niobium oxides remain in the solid state. This allows the
particle morphology of the original agglomerated oxide to be
preserved in the niobium monoxide. In one embodiment of this
process, niobium pentoxide is reacted at temperatures of
approximately 1000.degree. C. with finely-divided metallic niobium,
in such stoichiometric proportions as to produce primarily niobium
monoxide. In another embodiment, the niobium pentoxide or niobium
dioxide is reacted with gaseous magnesium, again at temperatures of
approximately 1000.degree. C. This results in a spongy, highly
porous niobium monoxide-magnesium oxide mixture. After leaching the
magnesium oxide, the resultant product is a porous, high-surface
area agglomerated mass of niobium monoxide.
[0004] Because of the low processing temperatures used in these
methods of producing niobium monoxide, there is virtually no
opportunity to remove any impurities in either the niobium oxide or
the reducing agent feedstocks. Moreover, impurities on the surface
of the feedstock particles remain on the surface through the
solid-state processing, resulting in potentially detrimental
concentrations of these impurities on the surface of the NbO
particles. The electronic characteristics of capacitors produced
from such surface-contaminated particles may be seriously degraded.
The purity requirements of the niobium monoxide dictate the purity
required of the feedstock. The surface area requirements of the
product niobium monoxide dictate the particle size distribution and
morphology of the niobium pent-or-di-oxide and niobium metal needed
for the process. These requirements severely limit the availability
of suitable raw materials. Further, because the reactions occur in
the solid state, the reactions are sluggish and often do not go to
completion. The product contains some higher oxides of niobium, and
often some niobium metal.
[0005] Thus, an object of the present invention is to produce
niobium monoxide (NbO) powder of high purity and sufficient surface
area to meet the requirements of NbO capacitors without the
constraints of raw materials purity and particle size imposed by
solid-state processes, and the use of such powders in the
production of capacitors. The present invention also can be used to
produce high-purity niobium dioxide, and to produce large,
(non-particulate) non-porous objects of both niobium monoxide and
niobium dioxide. The powders produced from such objects are
non-porous and angular in shape.
SUMMARY OF THE INVENTION
[0006] The present invention relates to a high-purity niobium
monoxide or niobium dioxide powder, produced by a process
comprising:
[0007] (a) combining a mixture of niobium pentoxide, niobium
trioxide, and/or niobium dioxide and coarse niobium metal powder in
amounts stoichiometrically calculated to yield a product with a
fixed atomic ratio of niobium to oxygen, said ratio being close to
about 1:1 in the case of niobium monoxide, or about 1:2 in the case
of niobium dioxide;
[0008] (b) forming a compact of said mixture by cold isostatic
pressing or other techniques known to those skilled in the art;
[0009] (c) exposing said compact to a heat source sufficient to
elevate the surface temperature above the melting point of the
product niobium monoxide or niobium dioxide, i.e., greater than
about 1945.degree. C. for niobium monoxide or about 1915.degree. C.
for niobium dioxide in an atmosphere suitable to prevent
uncontrolled oxidation;
[0010] (d) allowing the mixture to react exothermically to produce
the desired niobium monoxide;
[0011] (e) solidifying the liquid mixture to form a solid body of
niobium monoxide;
[0012] (f) fragmenting the body to form the desired particle size
of niobium monoxide; and,
[0013] (g) producing capacitor anodes from said niobium oxide
particles by techniques common to the capacitor industry.
[0014] For example, in order to produce niobium monoxide from
niobium pentoxide, the mixture of niobium pentoxide and metallic
niobium would have about a 1:1 ratio by weight. In order to produce
niobium dioxide from niobium pentoxide, the mixture of niobium
pentoxide and metallic niobium would have about a 5.7:1 ratio by
weight.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIGS. 1a-c display the x-ray diffraction patterns for NbO
produced by the present invention (FIGS. 1a-b) and NbO produced by
a commercial, solid-state reaction (FIG. 1c); and
[0016] FIG. 2 is an illustration of an ingot reduced to sharp,
angular, substantially non-porous individual pieces.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] The present invention relates to a method of producing
niobium monoxide powder which includes combining a mixture of
Nb.sub.2O.sub.5, Nb.sub.2O.sub.3, and/or NbO.sub.2, and niobium
metal; forming a compacted bar of the mixture; reacting the mixture
at a temperature greater than about 1945.degree. C.; solidifying
the reaction products; and fragmenting the solidified body to form
niobium monoxide powder. In a preferred embodiment of the present
invention, the weight ratio of niobium pentoxide to niobium metal
is about 1:1. Niobium dioxide powder can be made in the same
process by adjusting the ratio of niobium pentoxide to niobium
metal to about 5.7:1.
[0018] The present invention also relates to the production of a
high-purity niobium monoxide or niobium dioxide powder produced by
this process from impure niobium pentoxide and/or impure niobium
dioxide, and from impure niobium metal powder. In the present
invention, the high processing temperature, controlled atmosphere
and the presence of a liquid state can be exploited to remove some
major impurities, including iron, aluminum, and most other elements
other than refractory metals. Impurities on the surface of the
feedstocks (from crushing, grinding, milling, etc.) are dissolved
into the liquid NbO, producing a uniform distribution throughout
the particle and thereby reducing the harmful effects of such
impurities. The liquid state processing also allows other,
desirable elements to be added to the product.
[0019] The solid ingot produced by the present invention can be
sized to any desired size by comminution techniques well known to
those skilled in the art. This allows production of sizes from the
ingot down to sub-micron particles. Moreover, coarse particles of
niobium monoxide or niobium dioxide can be used as milling media to
produce fine powders free of the contamination introduced by
ordinary milling media.
EXAMPLE 1
[0020] In the testing of the present invention, a mixture of
commercially-available 99.99% pure Nb.sub.2O.sub.5 and
commercially-available electron-beam triple-refined dehydrided
niobium metal powder (50.times.80 US mesh) was blended and formed
into a bar by cold isostatic pressing, although other means of
compaction and resultant physical forms are acceptable. Three such
bars were prepared.
[0021] The compacts of Nb.sub.2O.sub.5 and niobium metal (weight
ratio 1:1.05) were each fed sequentially into the melting region of
an electron beam vacuum furnace, where each compact reacted and
liquefied when heated by the electron beam, with the liquid product
dripping into a cylindrical water-cooled copper mold. When the
electron beam initially struck the compact melting immediately took
place, with only a small increase in chamber pressure. With
experience, the production rate easily reached 100 pounds an hour.
Reaction was terminated before the final compact had been fully
consumed, leaving a layer of partially-reacted materials on the
face of the residual compact.
[0022] While an electron-beam furnace was used in this experiment,
it is obvious to those skilled in the metallurgical arts that other
energy sources capable of heating the materials to at least
1945.degree. C. could also be used, including, but not limited to,
cold crucible vacuum induction melting, plasma inert gas melting,
vacuum arc remelting, and electrical impulse resistance
heating.
[0023] The method of the present invention provides an opportunity
to add a wide range of dopant materials to the mixtures prior to
compaction, such additions melting into the liquid melt during the
melt-reaction process. Such dopants include, but are not limited to
tantalum, titanium, vanadium, and aluminum. Such dopants may be
added in amounts up to 40% by weight. While the usual purpose of
dopants is to improve the specific capacitance of capacitor
materials, they may provide other advantages, such as improved
long-term stability and reduced DC leakage.
[0024] A further advantage of the present invention relates to the
form of the ingot so produced. By applying well-known metallurgical
principles, it is possible to produce a single-crystal or
directionally-solidified ingot that may offer advantages in
applications beyond conventional capacitor powders.
[0025] The resultant ingot was allowed to cool under vacuum, and
the apparatus was vented to atmosphere. The ingot was a solid,
non-porous cylinder. The ingot was subsequently shattered by
impact. Samples were taken from the top one inch of the ingot (the
"top" samples), while "edge" samples were taken from lower
mid-radius locations in the ingot.
[0026] Subsequent analysis of the product NbO samples by x-ray
diffraction showed a clean pattern for NbO, with no additional
lines attributable to niobium metal, NbO.sub.2 or Nb.sub.2O.sub.3.
In FIG. 1, the x-ray diffraction patterns are shown for NbO
produced by the present invention (FIGS. 1a-b), and NbO produced by
a commercial solid-state reaction (FIG. 1c). The solid-state
reaction product has numerous lines not originating with NbO,
indicating the presence of other, undesirable phases. Gravimetric
analysis showed the material to be stoichiometric NbO, within the
limits of analytical precision.
[0027] It will be apparent to those skilled in the art that
alterations in the initial powder mixture allow the production not
only of high-purity niobium monoxide, but also of high-purity
niobium dioxide, and further of intimate mixtures of niobium
metal/niobium monoxide or niobium monoxide/niobium dioxide, as
illustrated in the Niobium--Oxygen phase diagram (see, "Binary
Alloy Phase Diagrams", American Society for Metals, Metals Park,
Ohio, 1990, p. 2749).
[0028] The ingot was then taken down to powder by conventional
crushing, grinding and milling techniques. Upon crushing the ingot
was reduced to sharp, angular, non-porous individual pieces, as
illustrated in FIG. 2. The morphology of these pieces was retained
by individual particles down to sub-micron sizes. The resultant NbO
powder had a Microtrac D50 of 2.38 microns and a B.E.T. surface
area of 2.06 m.sup.2/gram. When formed into a capacitor anode under
conventional conditions, (Forming Voltage 35 V; Forming current 150
mA/g, sintered at 1400.degree. C.) the anodes showed specific
capacitance at a 2-volt bias of 60,337 CV/g and a DC Leakage of
0.31 nA/CV. Tested with a 0 volt bias, the specific capacitance was
78,258 CV/g and the DC Leakage was 0.23 nA/CV. These values are
well within the normal range for commercial capacitors produced
from NbO made by solid-state reactions, as well as some tantalum
capacitors.
EXAMPLE 2
[0029] Four additional experimental runs were performed using less
pure feedstock and altering the sizing of the feedstock used to
make the compacts. In each case, the product was NbO free of other
compounds and free of metallic niobium. This indicates the subject
process is robust and not dependent on particular sources of oxides
or niobium metal. In one experimental run, the commercial-grade
niobium pentoxide used as feedstock contained approximately 400 ppm
of iron, and the niobium metal contained less than 50 ppm of iron.
After converting the feedstock to NbO by the subject process, the
NbO was analyzed and found to contain less than 100 ppm of iron.
This represents a reduction of at least 50% in the iron content
during the subject process. The subject process also offers the
opportunity to recover NbO values from waste streams associated
with production of powder-based NbO products, since the refining
action of the present invention can effectively remove or dilute
most contaminants, even when such contaminants are present as fine
or micro-fine powders or particles.
[0030] The NbO ingot from each of these four additional
experimental runs was reduced in size by conventional crushing,
grinding and milling to an average particle size under 2.5 microns,
formed into test anodes, and tested for capacitance and leakage
rates. The results in each case were similar to the initial results
described above, including anodes produced from NbO originating
from the high-iron feedstock as noted above. The specific
capacitance and DC leakage of NbO powder produced from such ingots
were 69,200 CV/g and 0.34 nA/CV, respectively. While the iron level
would normally be considered too high to permit good DC leakage
values, in these examples the iron has been uniformly
re-distributed throughout the particles. This re-distribution
results in a very low level of iron on the particle surfaces, so
that the iron does not degrade the leakage characteristics of the
NbO.
EXAMPLE 3
[0031] The formation of niobium monoxide by melt phase processing
lends itself to the recovery and remelting of niobium monoxide
solids in, but not limited to powder, chips, solids, swarf and
sludges. Off-grade powder, recycled capacitors and powder
production waste are among the materials that can be reverted to
full value niobium monoxide by this process. A compact was prepared
from "waste" NbO powders of various sizes and production states.
The compact was melt-reacted in the electron beam furnace to
produce a sound NbO ingot. Subsequent testing of the ingot showed
it to be indistinguishable in crystalline structure, purity, and
electronic characteristics (specific capacitance, DC leakage) from
earlier ingots produced from high-purity raw materials. Glow
Discharge Mass Spectrometry showed no elevated impurity levels
compared to earlier "high-purity" ingots.
EXAMPLE 4
[0032] Niobium pentoxide and metallic niobium powder were mixed in
proportions calculated to produce niobium dioxide, and the mixture
compacted and melt-reacted in the electron beam furnace as
described above. The ingot was sound, solid, and showed no obvious
defects. A sample taken from the ingot was analyzed to determine
the ratio of oxygen and niobium. Within the limits of analytical
precision, it was stoichiometric NbO.sub.2. NbO.sub.2 theoretically
contains 25.13% oxygen by weight. The NbO.sub.2 of this example
analyzed 25.14% oxygen.
[0033] Although the invention has been described and illustrated
with reference to specific illustrative embodiments thereof, it is
not intended that the invention be limited to those illustrative
embodiments. Those skilled in the art will recognize that
variations and modifications can be made without departing from the
spirit of the invention. It is therefore intended to include within
the invention all such variations and modifications which fall
within the scope of the appended claims and equivalents
thereof.
* * * * *