U.S. patent application number 11/576320 was filed with the patent office on 2008-05-08 for magnesium removal from magnesium reduced metal powders.
Invention is credited to Aanastasia M. Conlon, Leonid Lanin, Leonid N. Shekhter.
Application Number | 20080105082 11/576320 |
Document ID | / |
Family ID | 39358584 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080105082 |
Kind Code |
A1 |
Shekhter; Leonid N. ; et
al. |
May 8, 2008 |
Magnesium Removal From Magnesium Reduced Metal Powders
Abstract
A method of producing a refractory metal powder that includes
providing a metal powder containing magnesium tantalate or
magnesium niobate; and heating the powder in an inert atmosphere in
the presence of magnesium, calcium and/or aluminum to a temperature
sufficient to remove magnesium tantalate or magnesium niobate from
the powder and/or heating the powder under vacuum to a temperature
sufficient to remove magnesium tantalate or magnesium niobate from
the powder, the heating steps being performed in any order. The
metal powder can be formed into pellets at an appropriate sintering
temperature, which can be formed into electrolytic capacitors.
Inventors: |
Shekhter; Leonid N.;
(Ashland, MA) ; Lanin; Leonid; (Belmont, MA)
; Conlon; Aanastasia M.; (Canton, MA) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Family ID: |
39358584 |
Appl. No.: |
11/576320 |
Filed: |
September 19, 2005 |
PCT Filed: |
September 19, 2005 |
PCT NO: |
PCT/US05/33291 |
371 Date: |
June 16, 2007 |
Current U.S.
Class: |
75/255 ; 75/343;
75/366 |
Current CPC
Class: |
H01G 9/0525 20130101;
B22F 9/20 20130101; B22F 2999/00 20130101; B22F 2999/00 20130101;
B22F 2201/20 20130101; B22F 2201/10 20130101; B22F 9/20
20130101 |
Class at
Publication: |
75/255 ; 75/343;
75/366 |
International
Class: |
B22F 9/22 20060101
B22F009/22; B22F 1/00 20060101 B22F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2004 |
US |
10/593163 |
Claims
1. A method of producing a refractory metal powder comprising: (A)
providing a metal powder containing magnesium tantalate or
magnesium niobate; and (B) heating the powder in an inert
atmosphere in the presence of a reducing agent to a temperature
sufficient to remove magnesium tantalate or magnesium niobate from
the powder (reduction step) and/or heating the powder under vacuum
to a temperature sufficient to remove magnesium tantalate or
magnesium niobate from the powder (heating under vacuum step), the
reduction step and heating under vacuum step can be performed in
any order.
2. The method according to claim 1, wherein the metal powder is
free-flowing.
3. The method according to claim 1, wherein the reducing agent in
step (B) is selected from the group consisting of magnesium,
aluminum, calcium, and combinations thereof.
4. The method according to claim 1, wherein the temperature in (B)
is a temperature at which the magnesium tantalate or magnesium
niobate is unstable.
5. The method according to claim 1, wherein step (B) is only the
heating under vacuum step.
6. The method according to claim 1, wherein step (B) is only the
reduction step.
7. The method according to claim 1, wherein the reduction step in
(B) is conducted in the presence of an inert gas.
8. The method according to claim 7, wherein the inert gas is
selected from neon and argon.
9. The method according to claim 1, wherein the temperature in the
reduction step in (B) is from 800.degree. C. to 1,300.degree.
C.
10. The method according to claim 1, wherein the temperature in the
heating under vacuum step in (B) is from 1,100.degree. C. to
1,400.degree. C.
11. The method according to claim 1, wherein the heating under
vacuum step in (B) is carried out by heating the powder to
800.degree. C. to 1,000.degree. C. for from 1 to 6 hours.
12. The method according to claim 1, wherein the reduction step in
(B) is carried out by heating the powder under vacuum at
1,100.degree. C. to 1,400.degree. C. for from 15 minutes to 6
hours.
13. The method according to claim 1, wherein step (B) is carried
out by i) heating the metal powder under vacuum at 1,100.degree. C.
to 1,400.degree. C. for from 15 minutes to 6 hours, and ii) heating
the powder in the presence of a reducing agent at 800.degree. C. to
1,300.degree. C. for from 1 to 6 hours.
14. The method according to claim 1, wherein step (B) is carried
out by i) heating the powder in the presence of a reducing agent at
800.degree. C. to 1,300.degree. C. for from 1 to 6 hours; and ii)
heating the metal powder under vacuum at 1,100.degree. C. to
1,400.degree. C. for from 15 minutes to 6 hours.
15. The method according to claim 13, wherein the heating step (ii)
is conducted in the presence of an inert gas.
16. The method according to claim 15, wherein the inert gas is
selected from neon and argon.
17. The method according to claim 14, wherein the heating step (i)
is conducted in the presence of an inert gas.
18. The method according to claim 17, wherein the inert gas is
selected from neon and argon.
19. The method according to claim 1, wherein the magnesium
tantalate and/or magnesium niobate in (A) are present at from 0.02
wt. % to 7 wt. % based on the weight of the metal powder.
20. The method according to claim 1, wherein after step (B), the
magnesium tantalate and/or magnesium niobate are present at less
than 500 ppm.
21. A refractory metal powder prepared according to the method of
claim 20.
22. The method according to claim 1, further comprising forming the
refractory metal powder into pellets at an appropriate sintering
temperature.
23. The method according to claim 22, further comprising forming
the sintered pellets into electrolytic capacitors.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the production of tantalum,
niobium and other refractory or valve metal powders, as well as
metal suboxide powders or alloys thereof.
BACKGROUND OF THE INVENTION
[0002] Refractory metals are members of a group of elements that
are difficult to isolate in pure form because of the stability of
their compounds, such as oxides, chlorides and fluorides. Since the
manufacturing of refractory metals is very complex, we will use
tantalum extractive metallurgy as an example to illustrate the
development of this technology.
[0003] State of the art tantalum powder production is based on the
process of reducing potassium heptafluorotantalate
(K.sub.2TaF.sub.7) with sodium (sodium reduction). The modern
method for manufacturing tantalum was developed by Hellier and
Martin (U.S. Pat. No. 2,950,185). A molten mixture of
K.sub.2TaF.sub.7 and a diluent salt, typically NaCl, KF and/or KCl,
is reduced with molten sodium in a stirred reactor. The
manufacturing process requires the removal of the solid reaction
products from the retort, separation of the tantalum powder from
the salts by leaching with dilute mineral acid, and treatments like
agglomeration and deoxidation to achieve specific physical and
chemical properties. While the reduction of K.sub.2TaF.sub.7 with
sodium has allowed the industry to make high performance, high
quality tantalum powders primarily used in solid tantalum capacitor
manufacturing; there are several drawbacks to this method. It is a
batch process prone to the inherent variability in the system; as a
result, batch-to-batch consistency is difficult. Using diluent
salts adversely impacts the throughput. The removal of chlorides
and fluorides in large quantities presents an environmental issue.
Of fundamental significance, the process has evolved to a state of
maturity such that a significant advance in the performance of the
tantalum powder produced is unlikely.
[0004] Over the years, numerous attempts were made to develop
alternate ways for reducing tantalum compounds to the metallic
state (U.S. Pat. Nos. 1,602,542; 1,728,941; 2,516,863; 3,647,420;
and 5,356,120). Among these was the use of active metals other than
sodium, such as calcium, magnesium, and aluminum, and raw materials
such as tantalum pentoxide and tantalum chloride.
[0005] Kametani et al. (GB 2231883) developed a process for
reducing gaseous titanium tetrachloride with atomized molten
magnesium or sodium in a vertical type reactor in the temperature
range of 650-900.degree. C. Though the reaction was very
exothermic, it was not self-sustaining due to a special effort
designed to avoid the formation of titanium-iron intermetallic
compounds at high temperatures (the melting point of Fe--Ti
eutectic is 1080.degree.).
[0006] U.S. Pat. Nos. 1,602,542, 3,658,507 and 2,881,067 suggest
the use of gaseous magnesium to better control the process
parameters. The gaseous reducing agent was generated in-situ from a
mixture of metal oxide and reducing agent, or outside the reactor
enclosure. Patentees managed to produce at bench scale fine
zirconium, titanium, tungsten, molybdenum and chromium powders. The
method was of batch type. The only controlled parameter was the
magnesium (calcium) partial pressure. The kinetics and the
temperature of the charge were a function of the gaseous magnesium
(calcium) flow rate and were impossible to control due to the
condensation of magnesium (calcium) on the cold parts of the
reactor. Since both melting and evaporation of Mg (Ca) without
condensation on the cold parts was practically impossible, the
process had to be periodically stopped for the removal of the
buildup. Therefore, continuous operation could not be carried
out.
[0007] Numerous attempts have been made to produce tantalum and
niobium powders by metalothermic reduction of their oxides with Mg,
Al or Ca in a bomb type reactor (U.S. Pat. Nos. 1,728,941 and
2,516,863). A blend of finely-divided oxide and metal reducing
agent was placed into a reactor and then ignited. The temperature
could not be controlled and therefore it was not possible to
achieve reproducible physical and chemical properties of the metal
powders. The residual Mg (Al, Ca) content was high due to the
formation of tantalates and niobates. The process was found to be
unsuitable for manufacturing high quality capacitor grade
powders.
[0008] Shekhter et al. (U.S. Pat. No. 6,171,363) described a method
for controlled reduction of tantalum and niobium oxide with gaseous
magnesium to produce capacitor grade tantalum and niobium powders
(batch magnesium reduction). The key is control of the reaction
process to achieve essentially isothermal conditions. The batch
magnesium reduction process requires excess amount of magnesium to
compensate for its condensation on the cold parts of the
furnace.
[0009] The process disclosed by Shekhter et al. was advantageous
compared to the traditional sodium reduction process. For example,
there are no fluorine bearing compounds and there is no need to use
any diluent salt.
[0010] U.S. Patent Application Publication Nos. 2002/0066338 and
2004/0163491, both to Shekhter et al., disclose a method of making
high purity refractory metals suitable for use in electrical,
optical and mill product/fabricated parts produced from their
respective oxides by metalothermic reduction of a solid or liquid
form of such oxide using a reducing agent selected from magnesium,
calcium, and aluminum that establishes (after ignition) a highly
exothermic reaction, the reaction preferably taking place in a
continuously or step-wise moving oxide such as gravity fall with
metal retrievable at the bottom and an oxide of the reducing agent
being removable by leaching or in other convenient form and
unreacted reducing agent derivatives being removable by leaching or
like process.
[0011] Unlike metal after sodium reduction, the magnesium reduced
powders contain tangible amounts of magnesium after magnesium
reduction. Depending on the reduction conditions used, i.e., excess
Mg, temperature, residence time, oxide/magnesium particle size,
etc., the magnesium content in the powder can vary from 0.02 to 7%
by weight.
[0012] According to X-ray diffraction analysis in tantalum/niobium
powders, the magnesium does not exist in the elemental form but
forms complex oxide compounds referred to as magnesium
tantalate/niobates. In particular, the X-ray diffraction pattern
was used to identify the chemical formula of a particular oxide
present as Mg.sub.4Ta.sub.2O.sub.9. Tangible quantities of
magnesium tantalate/niobates can adversely affect physical,
chemical, and electrical properties, thus, the conversion of
magnesium tantalate/niobates into metals is an important issue.
[0013] It is a principle object of the present invention to provide
a new process for producing high performance, high quality
tantalum, niobium, and other refractory metals and blends or alloys
thereof by reducing solid/liquid metal oxides in a steady,
self-sustaining reaction zone, thereby eliminating one or more, and
preferably all, of the problems associated with the traditional
double salt reduction and other processes described above, while
minimizing or eliminating the presence of magnesium
tantalate/niobates.
SUMMARY OF THE INVENTION
[0014] The present invention is directed to a method of producing a
refractory metal powder that includes providing a metal powder
containing magnesium tantalate or magnesium niobate; and heating
the powder in an inert atmosphere in the presence of magnesium,
calcium and/or aluminum to a temperature sufficient to remove
magnesium tantalate or magnesium niobate from the powder and/or
heating the powder under vacuum to a temperature sufficient to
remove magnesium tantalate or magnesium niobate from the powder,
the heating steps being performed in any order.
[0015] The present invention additionally provides refractory metal
powder obtained according to the above-described method.
[0016] The present invention is also directed to forming the
above-described powder into pellets at an appropriate sintering
temperature and forming the sintered pellets into electrolytic
capacitors.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Other than in the operating examples or where otherwise
indicated, all numbers or expressions referring to quantities of
ingredients, reaction conditions, etc., used in the specification
and claims are to be understood as modified in all instances by the
term "about." Various numerical ranges are disclosed in this patent
application. Because these ranges are continuous, they include
every value between the minimum and maximum values. Unless
expressly indicated otherwise, the various numerical ranges
specified in this application are approximations.
[0018] The present invention provides a method of producing a
refractory metal powder that includes: [0019] (A) providing a metal
powder containing magnesium tantalate or magnesium niobate; and
[0020] (B) heating the powder in an inert atmosphere in the
presence of magnesium, calcium and/or aluminum to a temperature
sufficient to remove magnesium tantalate or magnesium niobate from
the powder and/or heating the powder under vacuum to a temperature
sufficient to remove magnesium tantalate or magnesium niobate from
the powder, the heating steps being performed in any order.
[0021] The metal powder containing magnesium can be obtained by
methods known in the art, as a non-limiting example, by the methods
disclosed in U.S. Pat. Nos. 1,602,542, 1,728,941, 2,516,863,
2,881,067, 2,950,185, 3,647,420, 5,356,120, and 6,171,363, U.S.
Patent Application Publication Nos. 2002/0066338 and 2004/0163491,
as well as GB 2231883, the relevant portions of each are
incorporated herein by reference.
[0022] Depending on the reduction conditions used, i.e., excess Mg,
temperature, residence time, oxide/magnesium particle size, etc.,
the magnesium content in the powder resulting from the process can
vary from 0.02 to 7%.
[0023] In an embodiment of the invention, the process involves
blending a metal powder with 1-15 percent magnesium and heating to
achieve the reduction process. The magnesium is in the molten state
during a portion of the heating time. In this case, the objective
is to remove 1000-3000 ppm oxygen and only a low concentration of
MgO is produced. However, when a much greater quantity of tantalum
oxide is reduced a large quantity of magnesium oxide is generated.
The resulting mixture of magnesium, tantalum oxide and magnesium
oxide can form tantalum-magnesium-oxygen complexes that are
difficult to separate from the tantalum metal.
[0024] Different types of equipment can be used to run the
reduction process, in some cases continuously, such as a vertical
tube furnace, a rotary kiln, a fluid bed furnace, a multiple hearth
furnace, and an SHS (self-propagation high-temperature synthesis)
reactor.
[0025] According to X-ray diffraction analysis in tantalum/niobium
powders, the magnesium does not exist in the elemental form but
forms complex oxide compounds referred to as magnesium
tantalate/niobates. As a non-limiting example, X-ray diffraction
patterns obtained from tantalum powders have been used to identify
the chemical formula of a particular oxide present as
Mg.sub.4Ta.sub.2O.sub.9. Tangible quantities of magnesium
tantalate/niobates can adversely affect physical, chemical, and
electrical properties, thus, the conversion of magnesium
tantalate/niobates into metals is an important issue.
[0026] The present process provides for both agglomeration (heating
under vacuum) and deoxidation (heating in the presence of a
reducing agent such as magnesium, calcium and/or aluminum), which
causes the decomposition of the magnesium tantalate/niobates. This
result is surprising as there are no thermodynamic data that
predict the thermal stability of the complex oxides, i.e., no prior
art could be found that provided any insight as to the stability or
instability of the magnesium tantalate/niobates, yet it has now
been established that these compounds can be decomposed and removed
during downstream processing. As a result, the magnesium content in
the resulting niobium/tantalum powder can be significantly reduced
to, in many cases, undetectable levels.
[0027] Agglomeration or heating under vacuum, according to the
present invention is carried out by heating the metal powder under
vacuum at from 1,100.degree. C. to 1,400.degree. C., in some cases
from 1150.degree. C. to 1350.degree. C., in other cases from
1200.degree. C. to 1300.degree. C., and in some situations from
1225.degree. C. to 1375.degree. C. for from 15 minutes to 6 hours,
in some cases from 15 minutes to 5 hours, in other cases from 30
minutes to 4 hours, and in some instances from 30 minutes to 2
hours.
[0028] Deoxidation or reduction according to the present invention
is carried out by heating the metal powder at a temperature of from
800.degree. C. to 1,300.degree. C., in some cases from 850.degree.
C. to 1050.degree. C., and in other cases from 875.degree. C. to
925.degree. C. in the presence of a reducing agent such as
magnesium, calcium and/or aluminum, which can be carried out for
from 15 minutes to 6 hours, in some cases from 30 minutes to 5
hours, in other cases from 1 hour to 4 hours, and in some instances
from 2 hours to 4 hours.
[0029] In the reduction step, the reducing agent is used at a level
of at least 0.01%, in some cases at least 0.1% and in other cases
at least 1% based on the weight of the metal powder. Also, the
reducing agent can be used in an amount up to 15%, in some cases
5%, and in other cases up to 2% based on the weight of the metal
powder. The amount of reducing agent will be an amount sufficient
to sufficiently remove magnesium tantalate/niobates from the metal
powder under the reduction conditions employed. The amount of
reducing agent used can be any value or can range between any of
the values recited above.
[0030] In an embodiment of the invention, the resulting metal
powder is free-flowing.
[0031] The downstream processing (heating) steps can be performed
in various types of equipment, in some cases continuously.
Non-limiting examples of suitable equipment include a rotary kiln,
a fluid bed furnace, a multiple hearth furnace, a pusher furnace,
vacuum furnaces, vacuum pusher furnaces and combinations
thereof.
[0032] In an embodiment of the invention, the present method of
producing a refractory metal powder can include forming a
magnesium-containing metal powder by (a) combining (i) an oxide
particle component and (ii) a reducing agent; (b) forming a mixture
of (i) and (ii); (c) continuously feeding the mixture into a
furnace; (d) igniting the mixture at a reaction zone and starting a
reaction that is sufficiently exothermic to form a high temperature
flash; (e) starting a reaction that is sufficiently exothermic to
form a high temperature self-sustaining flash; (f) producing a
free-flowing metal powder containing magnesium tantalate or
magnesium niobate; and (g) heating the metal powder under vacuum
and/or performing a reduction step as described above, in any order
at a temperature sufficient to remove magnesium tantalate or
magnesium niobate from the metal powder.
[0033] Typically, the metal powder resulting from (f) contains
magnesium tantalate and/or magnesium niobate at a level of from
0.002 wt. % to 7 wt. %, in some cases 0.01 wt. % to 6 wt. % and in
other cases at a level of from 0.1 wt. % to 5 wt. % based on the
weight of the powder.
[0034] In an embodiment of the invention, the heating in step (g)
is analogous to the heating step (B) as described above.
[0035] In a particular embodiment of the invention, the heating
step (B) is a reduction step and is carried in the presence of Mg,
Ca, and/or Al, out at a temperature of from 800.degree. C. to
1,300.degree. C., in some cases from 850.degree. C. to 1050.degree.
C., and in other cases from 875.degree. C. to 925.degree. C., which
can be carried out for from 15 minutes to 6 hours, in some cases
from 30 minutes to 5 hours, in other cases from 1 hour to 4 hours,
and in some instances from 2 hours to 4 hours. In another
embodiment of the invention, the reduction step is conducted in the
presence of a suitable inert gas. Any suitable inert gas can be
used. Suitable inert gases include, but are not limited to neon and
argon.
[0036] In another particular embodiment of the invention, the
heating step (B) is performed under vacuum, which can be carried
out by heating at from 1,100.degree. C. to 1,400.degree. C., in
some cases from 1150.degree. C. to 1350.degree. C., in other cases
from 1200.degree. C. to 1300.degree. C., and in some situations
from 1225.degree. C. to 1375.degree. C. for from 15 minutes to 6
hours, in some cases from 15 minutes to 5 hours, in other cases
from 30 minutes to 4 hours, and in some instances from 30 minutes
to 2 hours. Typically, when heating under vacuum, no reducing agent
is present.
[0037] In a particular embodiment of the invention, step (B)
involves two steps and is carried out by [0038] i) heating the
metal powder under vacuum at 1,100.degree. C. to 1,400.degree. C.
for from 15 minutes to 6 hours, and [0039] ii) heating the powder
in the presence of a reducing agent at 800.degree. C. to
1,300.degree. C. for from 1 to 6 hours.
[0040] In another particular embodiment of the invention, step (B)
involves two steps and is carried out by [0041] i) heating the
powder in the presence of a reducing agent at 800.degree. C. to
1,300.degree. C. for from 1 to 6 hours; and [0042] ii) heating the
metal powder under vacuum at 1,100.degree. C. to 1,400.degree. C.
for from 15 minutes to 6 hours.
[0043] After heating step (B), the magnesium content of the metal
powder is typically less than 500 ppm, in most cases less than 100
ppm, in some instance less than 50 ppm and in other instances less
than 25 ppm.
[0044] A particular embodiment of the invention provides a method
of producing a refractory metal powder. The method includes: [0045]
(a) combining (i) an oxide particle mixture containing oxide
particles selected from refractory metal oxide particles,
refractory metal alloy oxide particles, refractory metal suboxide
powders, refractory metal alloy suboxide powders and mixtures
thereof and (ii) a reducing agent selected from magnesium,
aluminum, calcium and mixtures thereof; [0046] (b) forming a
substantially uniform mixture of (i) and (ii); [0047] (c)
continuously feeding the mixture into a furnace; [0048] (d)
igniting the mixture at a reaction zone and starting a reaction
that is sufficiently exothermic to form a high temperature flash;
[0049] (e) producing a free-flowing metal powder selected from
refractory metal powders, refractory metal alloy powders, and
mixtures thereof; where the mixture is introduced at a consistently
constant rate and the second temperature remains substantially
constant; and [0050] (f) performing a reduction step and/or heating
under vacuum, as described above, in any order.
[0051] A further particular embodiment of the invention provides a
method of producing a refractory metal powder that includes: [0052]
(I) combining (i) an oxide particle mixture containing oxide
particles selected from refractory metal oxide particles,
refractory metal alloy oxide particles, refractory metal suboxide
powders, refractory metal alloy suboxide powders and mixtures
thereof and (ii) a reducing agent selected from magnesium,
aluminum, calcium and mixtures thereof; [0053] (II) forming a
substantially uniform mixture of (i) and (ii); [0054] (III)
reducing the free-flowing mixture in a reaction zone by heating the
mixture in a reaction vessel to create a highly exothermic
reaction, the exothermic reaction being triggered by heating the
mixture to an ignition temperature or by adding a further reagent
or catalyst; [0055] (IV) recovering a high surface area powder,
containing magnesium tantalate and/or magnesium niobate, which is
selected from refractory metal powders, refractory metal alloy
powders, refractory metal suboxide powders and refractory metal
alloy suboxide powders; and [0056] (V) performing a reduction step
and/or heating under vacuum, as described above, in any order.
[0057] In the various embodiments of the invention, the refractory
metal oxide component can be selected from tantalum pentoxide,
niobium pentoxide, niobium suboxide, tungsten trioxide, chromium
trioxide, molybdenum trioxide, titanium dioxide, vanadium pentoxide
and niobium oxide, mixtures of at least one of the foregoing and
zirconium dioxide, and mixtures thereof.
[0058] Also, in the various embodiments of the invention, the
refractory metal powder and the refractory metal alloy powder can
be selected from tantalum, niobium, molybdenum, tungsten, vanadium,
chromium, titanium and combinations thereof.
[0059] Additionally, in the various embodiments of the invention,
the reducing agent in the mixture can be provided in an amount
substantially equal to the stoichiometric quantity required to
react with the refractory metal oxide component.
[0060] In an embodiment of the invention, the powder can be formed
into pellets at an appropriate sintering temperature. Further to
this embodiment, the sintered pellets can be formed into
electrolytic capacitors.
[0061] The present invention is more particularly described in the
following examples, which are intended to be illustrative only,
since numerous modifications and variations therein will be
apparent to those skilled in the art. Unless otherwise specified,
all parts and percentages are by weight.
EXAMPLES
Example 1
[0062] Niobium pentoxide was blended with solid magnesium to form a
substantially uniform mixture. The mixture was continuously fed to
a vertical tube furnace at 10 kg/hr. The flash temperature in the
furnace was near, but less than, the melting point of niobium
pentoxide. The procedure produced a metal powder as with the
properties described in Table 1.
Example 2
[0063] Tantalum pentoxide was blended with solid magnesium to form
a substantially uniform mixture. The mixture was continuously fed
to a vertical tube furnace at 20 kg/hr. The flash temperature was
near, but less than, the melting point of tantalum pentoxide. The
procedure produced a metal powder with the properties as described
in Table 1.
TABLE-US-00001 TABLE 1 Surface Area C Si H Mg (m.sup.2/g) O (ppm) N
(ppm) (ppm) (ppm) (ppm) (ppm) Example 1 5.9 19150 115 120 20 210
825 Example 2 8.8 53000 500 210 390 -- 1160
[0064] Vacuum heated samples of the powders from Examples 1 and 2
were obtained by heating under vacuum in a SUPER VII.RTM. High
Temperature Vacuum Furnace, Centorr Vacuum Industries, Nashua, N.H.
(1 kg). Reduced samples were obtained by magnesium reduction (100%
excess) conducted in a horizontal tube furnace (500 g). Conditions
and results are summarized in Table 2 (vacuum heating) and Table 3
(reduction).
TABLE-US-00002 TABLE 2 Vacuum Heating Starting Temp Time Surface
Area O N C Si H Mg Powder (.degree. C.) (hrs.) (m.sup.2/g) (ppm)
(ppm) (ppm) (ppm) (ppm) (ppm) A-1 Example 1 1300 1 0.6 19700 70 70
20 80 <20 A-2 Example 2 1100 0.5 4.5 69100 580 135 430 -- 580
A-3 Example 2 1200 0.5 2.3 70600 410 155 680 -- 260
TABLE-US-00003 TABLE 3 Reduction Starting Temp. Time Surface O N C
Si Mg Powder (.degree. C.) (hrs.) Area (m.sup.2/g) (ppm) (ppm)
(ppm) (ppm) (ppm) D-1 A-2 950 2.0 6.1 17600 460 200 460 66 D-2 A-2
1000 2.0 4.4 12900 520 200 455 32 D-3 A-3 950 2.0 4.9 14800 470 260
460 66 D-4 A-3 1000 4.0 4.1 9970 415 240 435 40
[0065] The results show that both heating under vacuum and
reduction downstream processing steps result in significantly less
magnesium tantalate/niobate in the resulting metal powder. The
results demonstrate that the magnesium tantalate/niobates can be
eliminated using downstream processing. As a result, magnesium
content is significantly reduced in the resulting niobium/tantalum
powder.
[0066] It is to be understood that the above-described embodiments
are simply illustrative of the principles of the invention. Various
and other modifications, changes, details and uses may be made by
those skilled in the art which will embody the principles of the
invention and fall within the spirit and scope thereof.
* * * * *