U.S. patent application number 11/548753 was filed with the patent office on 2007-04-12 for production of high-purity niobium monoxide and capacitor production therefrom.
Invention is credited to Thomas J. Fonville, Brian J. Higgins, Charles A. Motchenbacher, James W. Robison.
Application Number | 20070081937 11/548753 |
Document ID | / |
Family ID | 33310401 |
Filed Date | 2007-04-12 |
United States Patent
Application |
20070081937 |
Kind Code |
A1 |
Motchenbacher; Charles A. ;
et al. |
April 12, 2007 |
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 temperatures greater than about 1800.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 e.g., capacitor anodes. The NbO product
is unusually pure in composition and crystallography, highly dense,
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.
Inventors: |
Motchenbacher; Charles A.;
(Robesonia, PA) ; Robison; James W.; (Lititz,
PA) ; Higgins; Brian J.; (Reading, PA) ;
Fonville; Thomas J.; (Reading, PA) |
Correspondence
Address: |
Richard A. Paikoff, Esq.;Duane, Morris LLP
One Liberty Place
Philadelphia
PA
19103
US
|
Family ID: |
33310401 |
Appl. No.: |
11/548753 |
Filed: |
October 12, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10428430 |
May 2, 2003 |
7157073 |
|
|
11548753 |
Oct 12, 2006 |
|
|
|
Current U.S.
Class: |
423/594.17 |
Current CPC
Class: |
C01P 2004/51 20130101;
H01G 9/0525 20130101; C01P 2004/61 20130101; C01P 2006/14 20130101;
C01P 2006/12 20130101; C01P 2004/03 20130101; C01P 2006/40
20130101; C01P 2006/80 20130101; C01P 2004/62 20130101; C01P
2002/72 20130101; C01G 33/00 20130101; C01P 2006/17 20130101 |
Class at
Publication: |
423/594.17 |
International
Class: |
C01G 31/02 20060101
C01G031/02 |
Claims
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, wherein the niobium
oxide and metallic niobium are present in powder or granular form;
b) forming a compact of the mixture; c) reacting the mixture with a
heat source, so that a mixture temperature greater than about
1800.degree. C. is reached; d) solidifying the reacted mixture to
form a body of material; and e) fragmenting the body of material to
form the NbO powder.
2. The niobium monoxide powder as recited in claim 1, wherein the
weight ratio of Nb.sub.2O.sub.5 to metallic niobium in the mixture
is about 1:1.
3. The niobium monoxide powder as recited in claim 1, wherein the
weight ratio of NbO.sub.2 to metallic niobium in the mixture is
about 1.3:1.
4. The niobium monoxide powder as recited in claim 1, wherein the
weight ratio of Nb.sub.2O.sub.3 to metallic niobium in the mixture
is about 2.5:1.
5. The niobium monoxide as recited in claim 1, wherein the niobium
oxide is Nb.sub.2O.sub.5.
6. The niobium monoxide as recited in claim 1, wherein the heat
source is an electron beam furnace.
7. The niobium monoxide as recited in claim 1, wherein the heat
source is a plasma-arc furnace.
8. The niobium monoxide as recited in claim 1, wherein the heat
source is an induction furnace.
9. The niobium monoxide as recited in claim 1, wherein the heat
source is an electric resistance furnace.
10. The niobium monoxide as recited in claim 1, wherein electronic
valves are produced from the niobium monoxide powders.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S.
application Ser. No. 10/428,430, filed May 2, 2003.
FIELD OF THE INVENTION
[0002] The present invention relates to methods of producing
niobium monoxide powders 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 long recognized that niobium monoxide (NbO) has
some unusual electrical properties that make it well-suited for the
manufacture of electronic capacitors. For example, it is of much
lower flammability than equivalent tantalum powders, is less costly
than tantalum, and has a 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
potentially harmful as well. In order to be useful in a valve
application, the niobium monoxide should be in a finely divided
form, i.e., a fine powder or agglomerates formed from small
particles, typically 1-2 microns in diameter, or finer. In order to
meet these prerequisites, the electronics industry has produced
niobium monoxide by reacting niobium pentoxide or niobium dioxide
(possibly 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
oxide to be preserved in the niobium monoxide.
[0004] 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, similarly at temperatures of approximately 1000.degree.
C. This results in a "spongy" niobium monoxide-magnesium oxide
mixture. After leaching the magnesium oxide, the resultant product
is a high-surface area, agglomerated mass of niobium monoxide.
[0005] Because of the low processing temperatures used in these
methods of producing niobium monoxide, there is inadequate
opportunity to remove impurities in either the niobium oxide or the
reducing agent feedstock. The purity requirements of the niobium
monoxide dictate the purity required of the feedstock. The surface
area requirements of the product niobium monoxide further dictate
the particle size distribution and morphology of the niobium
pent-or-dioxide required for the process. These requirements
severely limit the availability of suitable raw materials. In
addition, 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.
[0006] 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 further to the use of such powders in
the production of capacitors.
SUMMARY OF THE INVENTION
[0007] The present invention relates to a high-purity niobium
monoxide powder, produced by a process comprising:
[0008] (a) combining a mixture of niobium pentoxide, niobium
trioxide and/or niobium dioxide and coarse niobium metal powder in
effective amounts stoichiometrically calculated to yield a product
with a fixed atomic ratio of niobium to oxygen, the ratio being
preferably close to 1:1;
[0009] (b) forming a compact of the mixture by cold isostatic
pressing or other appropriate techniques;
[0010] (c) exposing the compact to a heat source sufficient to
elevate the surface temperature above the melting point of the
product niobium monoxide, i.e., greater than about 1800.degree. C.
in an atmosphere suitable to prevent uncontrolled oxidation;
[0011] (d) allowing the mixture to react exothermically to produce
the desired niobium monoxide;
[0012] (e) solidifying the mixture to form a solid body of niobium
monoxide; and
[0013] (f) fragmenting the body to form the desired particle size
of niobium monoxide.
[0014] Capacitor anodes can thereby be produced from niobium oxide
particles, by techniques common to the capacitor industry.
[0015] In preferred embodiments, the weight ratio of
Nb.sub.2O.sub.5 to metallic niobium in the mixture is about 1:1;
the weight ratio of NbO.sub.2 to metallic niobium in the mixture is
about 1.3:1; and the weight ratio of Nb.sub.2O.sub.3 to metallic
niobium in the mixture is about 2.5:1. The heat source is
preferably an electron beam furnace, a plasma-arc furnace, an
induction furnace, or an electric resistance furnace.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings illustrate preferred embodiments
of the invention as well as other information pertinent to the
disclosure, in which:
[0017] FIGS. 1 a-c are graphs of x-ray diffraction patterns for NbO
produced by the present invention (FIGS. 1 a-b), and NbO produced
by a commercial, solid-state reaction (FIG. 1c).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] 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 1800 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.
[0019] The present invention also relates to the production of a
high-purity niobium monoxide 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 presence of a
liquid state may be exploited to remove major impurities, including
iron, aluminum, and various other elements other than oxygen and
refractory metals.
[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 would also be effective.
Three such bars were prepared.
[0021] The compacts of Nb.sub.2O.sub.5 and niobium metal (weight
ratio 1:1) 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. A
production rate of 100 pounds an hour was established. 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 anticipated that other energy sources capable of heating the
materials to at least 1800.degree. C. could also be used,
including, but not limited to, cold crucible vacuum induction
melting, plasma inert gas melting, and electrical impulse
resistance heating.
[0023] The resultant ingot was allowed to cool under vacuum, and
the apparatus was vented to atmosphere. 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.
[0024] 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, (edge sample in FIG. 1a, top sample in
FIG. 1b) and NbO produced by a commercial, solid-state reaction
(FIG. 1c). The solid-state reaction product had numerous lines not
originating with NbO, indicating the presence of other, undesirable
phases.
[0025] The ingot was then degraded to powder by conventional
crushing, grinding and milling techniques. 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. All of 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.
[0026] Four additional experimental runs were performed using less
pure feedstock and altering the sizing of the feedstock used to
make the compacts. In each run, the product was NbO free of other
compounds and free of metallic niobium. This indicated that the
subject process was robust and not dependent on particular sources
of oxides or niobium metal. In one experimental run, the 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 process of the present
invention, the NbO was analyzed and found to contain less than 100
ppm of iron. This indicated a reduction of at least 50% in the iron
content during the process.
[0027] 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.
[0028] The process of the present invention also serves 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 most contaminants, even when such
contaminants are present as fine or micro-fine powders or
particles.
[0029] The formation of niobium monoxide by melt phase processing
lends itself to the recovery and remelting of niobium monoxide
solids, including but not limited to powders, chips, solids, swarf
(fine metallic filings or shavings) 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.
[0030] While the present invention has been described with respect
to particular embodiments thereof, it is apparent that numerous
other forms and modifications of the invention will be obvious to
those skilled in the art. The appended claims and this invention
generally should be construed to cover all such obvious forms and
modifications, which are within the true spirit and scope of the
present invention.
* * * * *