Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
PROCESSES FOR PRODUCING TANTALUM ALLOYS AND NIOBIUM ALLOYS
TECHNICAL FIELD
[0001] This specification relates to processes for the
production of
tantalum alloys and niobium alloys. This specification also relates to
tantalum alloy
and niobium alloy mill products and intermediates made using the processes
described in this specification.
BACKGROUND
[0002] Tantalum is a hard, ductile, acid-resistant, and highly conductive
metal with a density of 16.65 g/cm3. Tantalum has a high melting point
temperature
of 3020 C. Tantalum is often used as an alloy additive and is frequently
combined
with niobium to increase niobium's corrosion resistance properties. When mixed
with
metals such as niobium, tantalum has excellent resistance to a wide variety of
.. corrosive environments, including mineral acids, most organic acids, liquid
metals,
and most salts.
[0003] Niobium has physical and chemical properties similar to
tantalum, including similar hardness, ductility, acid-resistance, and
conductivity,
although niobium is less dense (8.57 g/cm3) than tantalum (16.65 g/cm3).
Niobium
has a melting point temperature of 2477 C. As noted above, niobium and
tantalum
can be alloyed together or with other elements to make niobium-base or
tantalum-
base alloys. Niobium and tantalum alloys have properties suitable for a
variety of
applications, for example, in the aerospace, chemical processing, medical,
superconducting, and electronics markets, among others.
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SUMMARY
[0004] In a non-limiting embodiment, a process for the
production of
tantalum alloys comprises conducting an alum inothermic reaction to reduce
tantalum
pentoxide powder to tantalum metal.
[0005] In another non-limiting embodiment, a process for the
production of niobium alloys comprises conducting an alum inothermic reaction
to
reduce niobium pentoxide powder to niobium metal.
[0006] In another non-limiting embodiment, a process for the
production of a tantalum alloy comprises conducting alum inothermic reactions
using
a reactant mixture comprising: tantalum pentoxide powder; at least one of
iron (Ill)
oxide powder and copper (II) oxide powder; barium peroxide powder; and
aluminum
metal powder.
[0007] In another non-limiting embodiment, a process for the
production of a tantalum alloy or a niobium alloy comprises conducting
aluminothermic reactions using a reactant mixture comprising: tantalum
pentoxide
powder and/or niobium pentoxide powder; iron (III) oxide powder and/or copper
(II)
oxide powder; barium peroxide powder; aluminum metal powder; and at least one
of
tungsten trioxide powder, molybdenum trioxide powder, chromium (III) oxide
powder,
hafnium dioxide powder, zirconium dioxide powder, titanium dioxide powder,
vanadium pentoxide powder, and tungsten metal powder.
[0008] In another non-limiting embodiment, a process for the
production of a niobium alloy comprises conducting alum inothermic reactions
using a
reactant mixture comprising: niobium pentoxide powder; iron (Ill) oxide powder
and/or copper (II) oxide powder; barium peroxide powder; aluminum metal
powder;
and at least one of tantalum pentoxide powder, tungsten trioxide powder,
molybdenum trioxide powder, chromium (III) oxide powder, hafnium dioxide
powder,
zirconium dioxide powder, titanium dioxide powder, vanadium pentoxide powder,
and tungsten metal powder.
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[0009] In another non-limiting embodiment, a process for the
production of a tantalum alloy comprises conducting alum inothermic reactions
using
a reactant mixture comprising: tantalum pentoxide powder; at least one of iron
(III)
oxide powder and copper (II) oxide powder; barium peroxide powder; aluminum
metal powder; and at least one of niobium pentoxide powder, tungsten metal
powder, and tungsten trioxide powder.
[0010] In another non-limiting embodiment, a process for the
production of a tantalum alloy comprises positioning a reactant mixture in a
reaction
vessel. The reactant mixture comprises: tantalum pentoxide powder; at least
one of
iron (III) oxide powder and copper (II) oxide powder; barium peroxide powder;
aluminum metal powder; and at least one of niobium pentoxide powder, tungsten
metal powder, and tungsten trioxide powder. Aluminothermic reactions are
initiated
between the reactant mixture components.
[0011] In another non-limiting embodiment, a process for the
production of a tantalum alloy comprises forming a reactant mixture comprising
tantalum pentoxide powder, iron (III) oxide powder, copper (II) oxide powder,
barium
peroxide powder, aluminum metal powder, and tungsten metal powder. A
magnesium oxide powder layer is positioned on at least the bottom surface of a
graphite reaction vessel. The reactant mixture is positioned in the graphite
reaction
vessel on top of the magnesium oxide powder layer. A tantalum or tantalum
alloy
ignition wire is positioned in contact with the reactant mixture. The reaction
vessel is
sealed inside a reaction chamber. A vacuum is established inside the reaction
chamber. The ignition wire is energized to initiate aluminothermic reactions
between
the reactant mixture components. The aluminothermic reactions produce reaction
products comprising a monolithic and fully-consolidated alloy regulus and a
separate
slag phase. The alloy regulus comprises tantalum and tungsten. The slag phase
comprises aluminum oxide and barium oxide. The reaction products are cooled to
ambient temperature. The reaction products are removed from the reaction
vessel.
The slag and the regulus are separated.
[0012] It is understood that the invention disclosed and described in
this specification is not limited to the embodiments summarized in this
Summary.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Various features and characteristics of the non-limiting
and non-
exhaustive embodiments disclosed and described in this specification may be
better
understood by reference to the accompanying figures, in which:
[0014] Figure 1A is a flow diagram illustrating the flow of a
process for
the production of tantalum alloy mill products from a tantalum pentoxide
feedstock;
Figure 1B is a flow diagram illustrating the flow of a process for the
production of
tantalum alloy mill products from a tantalum metal feedstock;
[0015] Figure 2A is a photograph of aluminothermic reaction products
comprising a well-defined and separated regulus and slag phase; Figure 2B is a
photograph of the regulus shown in Figure 2A after removal of the slag phase;
[0016] Figure 3 is a cross-sectional schematic diagram (not to
scale) of
an aluminothermic reaction vessel;
[0017] Figure 4 is a cross-sectional schematic diagram (not to scale) of
an aluminothermic reaction vessel;
[0018] Figure 5 is a schematic diagram in perspective view (not
to
scale) of an alum inothermic reaction vessel;
[0019] Figure 6 is a schematic diagram in perspective view (not
to
scale) of an aluminothermic reaction vessel sealed inside a reaction chamber;
and
[0020] Figure 7 is a scanning electron microscopy (SEM) image of
the
microstructure of a tantalum alloy regulus produced by aluminothermic
reactions
involving a tantalum pentoxide reactant.
[0021] The reader will appreciate the foregoing details, as well
as
others, upon considering the following detailed description of various non-
limiting
and non-exhaustive embodiments according to this specification.
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DESCRIPTION
[0022] Various embodiments are described and illustrated in this
specification to provide an overall understanding of the function, operation,
and
implementation of the disclosed processes for the production of tantalum
alloys. It is
understood that the various embodiments described and illustrated in this
specification are non-limiting and non-exhaustive. Thus, the invention is not
necessarily limited by the description of the various non-limiting and non-
exhaustive
embodiments disclosed in this specification. The features and characteristics
illustrated and/or described in connection with various embodiments may be
combined with the features and characteristics of other embodiments. Such
modifications and variations are intended to be included within the scope of
this
specification. As such, the claims may be amended to recite any features or
characteristics expressly or inherently described in, or otherwise expressly
or
inherently supported by, this specification. Further, Applicant reserves the
right to
amend the claims to affirmatively disclaim features or characteristics that
may be
present in the prior art. The various embodiments disclosed and described in
this
specification can comprise, consist of, or consist essentially of the features
and
characteristics as variously described herein.
[0023] Also, any numerical range recited in this specification is
intended to include all sub-ranges of the same numerical precision subsumed
within
the recited range. For example, a range of "1.0 to 10.0" is intended to
include all sub-
ranges between (and including) the recited minimum value of 1.0 and the
recited
maximum value of 10.0, that is, having a minimum value equal to or greater
than 1.0
and a maximum value equal to or less than 10.0, such as, for example, 2.4 to
7.6.
Any maximum numerical limitation recited in this specification is intended to
include all
lower numerical limitations subsumed therein and any minimum numerical
limitation
recited in this specification is intended to include all higher numerical
limitations
subsumed therein. Accordingly, Applicant reserves the right to amend
this specification, including the claims, to expressly recite any sub-range
subsumed
within the ranges expressly recited herein.
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[0024] Applicants reserve the right to amend this specification to
expressly recite any subject matter, or portion thereof.
[0025] The grammatical articles "one", "a", "an", and "the", as
used in this
specification, are intended to include "at least one" or "one or more", unless
otherwise
indicated. Thus, the articles are used in this specification to refer to one
or more than one
(i.e., to "at least one") of the grammatical objects of the article. By
way of example, "a component" means one or more components, and thus,
possibly,
more than one component is contemplated and may be employed or used in an
implementation of the described embodiments. Further, the use of a singular
noun
includes the plural, and the use of a plural noun includes the singular,
unless the context
of the usage requires otherwise.
[0026] The metals tantalum and niobium may be initially obtained
from
tantalum-containing and niobium-containing mineral ores such as, for example,
tantalite and niobite (columbite): (Fe, Mn) (Ta, Nb)206. Generally speaking,
when
these mineral ores contain more tantalum than niobium, the ores are referred
to as
tantalite, and when the mineral ores contain more niobium than tantalum, the
ores
are referred to as niobite or colum bite. These mineral ores may be mined and
processed by crushing, gravity separation, and treatment with hydrofluoric
acid (HF) to
produce complex metal-fluorides such as H2(TaF7) and H2(Nb0F5). The tantalum-
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fluorides and the niobium-fluorides may be separated from each other through
liquid-
liquid extractions using water and organic solvents such as cyclohexanone. The
separated metal-fluorides may be further processed to produce industrial
feedstocks.
[0027] The tantalum-fluorides, for example, may be treated with
potassium fluoride salt to precipitate potassium heptafluorotantalate:
H2(TaF7) (aq) + 2 KF (aq) ---> K2(TaF7) (s) + 2 HF (aq)
The potassium heptafluorotantalate precipitate may be collected and reduced
with
molten sodium to produce refined and purified tantalum metal:
K2(TaF7)0)+ 5 Na (0-3 Ta (s) + 5 NaF +2 KF
Alternatively, the tantalum-fluorides may be treated with ammonia to
precipitate
tantalum pentoxide:
2 H2(TaF7) (aq) + 14 NH4OH (aq) Ta205 (s) + 14 NH4F (aq) + 9 H20
The production of tantalum pentoxide using ammonia is less expensive than the
sodium reduction process and, therefore, tantalum pentoxide is a less
expensive
commodity chemical than virgin sodium-reduced tantalum metal.
[0028] Similarly, the niobium-fluorides, for example, may be
treated
with potassium fluoride salt to precipitate potassium oxypentafluoroniobate,
which
may be collected and reduced with sodium, hydrogen, or carbon to produce
refined
and purified niobium metal. Alternatively, the niobium-fluorides may be
treated with
ammonia to precipitate niobium pentoxide:
2 H2(Nb0F5) (aq) + 10 NH4OH (aq) 3 Nb2O5 (s) + 10 NH4F (aq) + 7 H20
[0029] The production of niobium pentoxide using ammonia, like
the
production of tantalum pentoxide using ammonia, is less expensive than the
sodium,
hydrogen, or carbon reduction process and, therefore, niobium pentoxide is a
less
expensive commodity chemical than virgin reduced niobium metal
[0030] The refined and purified tantalum and niobium metals
produced
through reduction processes are primarily used for the commercial production
of
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electronic components such as capacitors and high-power resistors.
Accordingly,
the cost of virgin reduced tantalum and niobium metal as an industrial
feedstock is
relatively high, driven by the demand from the electronics industry and the
costs
associated with the reduction processes. This high cost may pose issues for
producers of tantalum and niobium alloys and mill products. The producers of
tantalum and niobium alloys and mill products do not necessarily require input
materials with the level of refinement and purity achieved by the reduction
processes. Furthermore, the alloying of tantalum and niobium with other metals
requires costly powder processing to produce a compact suitable for electron-
beam
melting to homogenize and refine the alloy chemistry.
[0031] Tantalum and niobium have a high melting point
temperature
compared with most metals. Therefore, alloying of tantalum and niobium with
each
other, and/or with other elements such as tungsten, molybdenum, zirconium,
titanium, hafnium, or vanadium, for example, which also have relatively high
melting
point temperatures, usually requires the use of an electron beam furnace to
melt a
compact comprising a hot pressed and sintered mixture of tantalum powder and
alloying element powder. Tantalum and niobium are also relatively ductile.
Therefore, unalloyed tantalum or niobium scrap or virgin metal produced
through
reduction processes, for example, usually must be embrittled by a hydriding
treatment before the tantalum or niobium can be crushed into a powder form.
The
hydrided tantalum powder or niobium powder usually also must be dehydrided
before the hot pressing and sintering with other alloying element powders to
produce
the input compact for an electron beam melting furnace. This hydriding-
dehydriding
(HDH) process, which requires significant capital and operational
infrastructure
including a hydriding furnace, a crusher, a compactor, a vacuum furnace, and
pressing/sintering equipment, adds significant additional costs to the
alloying of
tantalum and niobium over the already high costs of virgin reduced tantalum
metal or
niobium metal input material.
[0032] The downstream electron beam melting of pressed and
sintered
powder compacts comprising tantalum, niobium, and/or other alloying elements
may
involve additional issues. On a macroscopic scale, the tantalum and niobium
powders and other alloying element powders are homogeneously blended before
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pressing and sintering. However, the resulting compacts do not comprise a
homogeneous solid state solution comprising alloying elements completely
dissolved
in a tantalum matrix or niobium matrix. Instead, the compacts comprise
discrete and
isolated regions or inclusions of alloying elements such as, for example,
tungsten,
molybdenum, zirconium, titanium, hafnium, or vanadium, distributed in a
relatively
continuous region or phase of tantalum metal. The discrete alloying element
regions
and tantalum regions or niobium regions of this multi-phase microstructure
correspond to the respective powder particles that are metallurgically bonded
together to form the compact.
[0033] The electron beam melting of the compact is intended to
homogenize and refine the alloy composition and produce an ingot having a
uniform
microstructure, reduced levels of relatively volatile tramp elements, and
specified
alloying elements completely dissolved and uniformly distributed as a solid
state
solution in a tantalum matrix or niobium matrix. In practice, however, the
liquid
phase mixing of high-melting point materials, such as, for example, tantalum,
niobium, tungsten, molybdenum, zirconium, titanium, hafnium, or vanadium, may
be
difficult to achieve with electron beam melting. For instance, the relatively
small melt
pool and the lack of superheat in the melt pool may impede thorough liquid
phase
mixing. Moreover, the dripping of molten material from the compact into the
melt
pool in electron beam melting furnaces may lessen the dispersion of the alloy
constituents. Current industrial scale electron beam melting furnaces also
lack the
capability to induce supplementary physical agitation of the melt pool, which
would
improve alloy dispersion and homogenization of the alloy constituents.
[0034] The
processes described in this specification are directed to the
production of tantalum base alloys or niobium base alloys and mill products
from a
tantalum pentoxide or niobium pentoxide feedstock, as opposed the production
of
tantalum base alloys or niobium base alloys and mill products from a virgin
reduced
or scrap tantalum metal or niobium metal feedstock. In various embodiments, a
process for the production of tantalum alloys or niobium alloys may comprise
conducting an alum inothermic reaction to reduce tantalum pentoxide powder to
tantalum metal or to reduce niobium pentoxide powder to niobium metal. Figures
1A
and 1B are flow diagrams illustrating the operational infrastructure savings
provided
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by the aluminothermic reaction processes described in this specification
(Figure 1A)
as compared to processes using tantalum metal feedstocks for the production of
tantalum alloy mill products (Figure 1B). An analogous comparison can be made
between the aluminothermic production and powder metallurgical production of
niobium alloy mill products.
[0035] The aluminothermic reaction processes described in this
specification eliminate: (1) the need for relatively costly virgin reduced
tantalum
metal or niobium metal; (2) the costly HDH process; and (3) the pressing and
sintering operations needed to produce a powder compact for electron beam
melting. The processes described in this specification directly produce a
consolidated tantalum alloy regulus or niobium alloy regulus that may be
directly
input into an electron beam melting furnace for refinement of the tantalum
alloy or
niobium alloy composition. The tantalum alloy or niobium alloy reguli produced
according to the aluminothermic reaction processes described in this
specification
also comprise alloying elements completely dissolved into the tantalum matrix
or
niobium matrix, which facilitates the direct electron beam melting and casting
of
tantalum alloy or niobium alloy ingots having a uniform microstructure and
alloying
elements completely and uniformly distributed in the tantalum matrix or
niobium
matrix.
[0036] As used in this specification, the term "aluminothermic
reaction(s)" refers to high temperature exothermic oxidation-reduction
chemical
reactions between aluminum metal (functioning as a reducing agent) and metal
peroxide and/or metal oxides (functioning as oxidizing agents). Aluminothermic
reactions produce an aluminum oxide (A1203)-based slag and reduced metal
values.
As used in this specification, the term "regulus" (and its plural form,
"reguli") refer to
the consolidated and solidified metal or alloy portion of the reaction
products of
aluminothermic reactions.
[0037] Figure 2A is a photograph showing aluminothermic reaction
products comprising a well-defined regulus and a well-defined slag phase.
During
and/or after an aluminothermic reaction, the oxide reaction products may
coalesce
into a less dense slag phase and the metallic reaction products coalesce into
a
denser alloy phase. The phases may separate and solidify into a well-defined
alloy
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regulus and a separated slag phase, as shown in Figure 2A, for example. Figure
2B
is a photograph of the regulus shown in Figure 2A after removal of the slag
phase.
The metallic reaction products of alum inothermic reactions may coalesce and
solidify
to produce a monolithic, fully-consolidated, and non-brittle alloy regulus, as
shown in
Figure 2B, for example.
[0038] The use of alum inotherm ic reactions to produce
tantalum alloys
or niobium alloys involves the selection of reactants to produce: (1) the
specified
alloy constituents; (2) volatile (sacrificial) alloy constituents that
decrease the melting
point temperature of the resulting tantalum-base alloy intermediate or niobium-
base
alloy intermediate; and (3) sufficient heat to achieve reaction temperatures
that will
cause the metal reaction products to melt and coalesce into a tantalum-base
alloy or
niobium-base alloy, and also cause molten slag reaction products to phase
separate
from the molten metal reaction products so that the molten reaction products
solidify
to produce a monolithic, fully-consolidated, and non-brittle tantalum alloy or
niobium
alloy regulus and a separate slag phase.
[0039] Tantalum alloys that can be produced using the processes
described in this specification include, for example, binary tantalum-niobium
alloys
(e.g., Ta-40Nb (UNS R05240)) and binary tantalum-tungsten alloys (e.g., Ta-
2.5W
(UNS R05252) and Ta-10W (UNS R05255)). Ta-40Nb nominally comprises, by
weight, 40% niobium, balance tantalum and incidental impurities; Ta-2.5W
nominally
comprises, by weight, 2.5% tungsten, balance tantalum and incidental
impurities;
and Ta-10W nominally comprises, by weight, 10% tungsten, balance tantalum and
incidental impurities. Niobium alloys that can be produced using the processes
described in this specification include, for example, binary Nb-Ta alloys such
as, for
example, Nb-7.5Ta (nominally 7.5% tantalum by weight, balance niobium and
incidental impurities), binary Nb-Ti alloys comprising, for example, 40-55%
titanium
by weight, or any sub-range or value subsumed therein, such as, for example,
47-
53% titanium), binary Nb-Zr alloys, ternary Nb-Ti-Ta alloys, ternary Nb-Zr-Ta
alloys,
and multi-component alloys such as alloys comprising, in weight percent, 9.0-
11.0%
hafnium, 0.7-1.3% titanium, up to 0.7% zirconium, up to 0.5% tantalum, up to
0.5%
tungsten, balance niobium and incidental impurities.
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[0040] To produce a specified tantalum alloy or niobium alloy
chemistry
for example, in various embodiments, the reactants may comprise aluminum metal
powder (as the reducing agent), tantalum pentoxide powder (as the tantalum
source
and an oxidizing agent), and/or niobium pentoxide powder (as a niobium source
and
an oxidizing agent). In other embodiments, to produce a specified tantalum-
tungsten
alloy chemistry for example, the reactants may comprise aluminum metal powder
(as
the reducing agent), tantalum pentoxide powder (as the tantalum source and an
oxidizing agent), and tungsten trioxide powder (as a tungsten source and an
oxidizing agent). In other embodiments, to produce a specified tantalum-
tungsten
alloy chemistry for example, the reactants may comprise aluminum metal powder
(as
the reducing agent), tantalum pentoxide powder (as the tantalum source and an
oxidizing agent), and tungsten metal powder (as an inert tungsten source). In
other
embodiments, to produce a specified niobium-titanium alloy chemistry, for
example,
the reactants may comprise aluminum metal powder (as the reducing agent),
niobium pentoxide powder (as the niobium source and an oxidizing agent), and
titanium dioxide powder (as a titanium source and an oxidizing agent).
Reactive or
inert sources of other alloying constituents for tantalum-base alloys or
niobium-base
alloys produced by aluminothermic reactions may be determined by persons
skilled
in the art on the basis of the targeted alloy composition to be produced and
in view of
the information disclosed in this specification.
[0041]
Tantalum and tantalum-base alloys such as Ta-40Nb, Ta-2.5W,
and Ta-10W have relatively high melting point temperatures. For example, pure
tantalum melts at 3020 C, Ta-40Nb melts at 2705 C, Ta-2.5W melts at 3005 C,
and
Ta-10W melts at 3030 C. Niobium and niobium-base alloys have similarly high
melting point temperatures. Because of these relatively high melting point
temperatures, aluminothermic reactants may be selected to produce metal
products
that form volatile (sacrificial) alloy constituents. The volatile
(sacrificial) alloy
constituents facilitate the liquefaction and coalescence of the metal products
produced through the aluminothermic reactions into a tantalum-base alloy or a
niobium-base alloy by decreasing the melting point temperature of the alloy.
As
used herein, the term "volatile (sacrificial) alloy constituent(s)" refers to
elements
such as copper and iron that are relatively more volatile than the specified
constituents of tantalum alloys or niobium alloys (e.g., Ta, Nb, W, Mo, Ti,
Zr, Hf, V,
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Cr) and, therefore, may be readily reduced to incidental impurity levels in
tantalum-
base alloys or niobium-base alloys refined using electron beam melting. The
precursor reactant(s) used to produce "volatile (sacrificial) alloy
constituent(s)" may
be referred to as "sacrificial metal oxide(s)."
[0042] The addition of iron as an alloying element to tantalum or
niobium decreases the melting point temperature. For example, tantalum
containing
5% iron by weight melts at 2500 C as compared to 3020 C for pure tantalum.
Likewise, copper lowers the melting point temperature of tantalum, niobium,
tantalum
alloys, and niobium alloys. Iron and copper are also readily formed by the
aluminothermic reduction of iron (III) oxide and copper (II) oxide,
respectively, and
both alum inothermic reactions generate large amounts of heat, resulting in
high
reaction temperatures. Iron and copper are also relatively more volatile than
tantalum, niobium, tungsten, molybdenum, titanium, zirconium, and hafnium, and
are
therefore readily removed from a tantalum alloy matrix using electron beam
melting.
[0043] In various embodiments, sacrificial metal oxide reactants may
comprise iron (III) oxide powder, copper (II) oxide powder, or both. Other
sacrificial
metal oxide reactant powders that may be suitable for purposes of generating
reaction heat and producing volatile (sacrificial) elements that decrease the
melting
point temperatures of the resulting tantalum-base alloys include, for example,
manganese dioxide, nickel (II) oxide, cobalt (II) oxide, chromium oxides, and
molybdenum oxides. While these additional sacrificial oxides may be reactive
in
aluminothermic reactions, these oxides may be less suitable than iron (III)
oxide and
copper (II) oxide for the aluminothermic production of tantalum-base alloys or
niobium-base alloys because of the metal components of these additional oxides
are
relatively less volatile than iron and copper and, therefore, are not as
readily
removed by electron beam refining or otherwise. However, these additional
oxides
may alternatively function as non-sacrificial oxides that provide the metal
components as alloying additions to tantalum-base alloys or niobium-base
alloys
produced in accordance with this specification.
[0044] Like iron (III) oxide and copper (II) oxide, manganese dioxide
powder is reduced by aluminum powder with considerable release of reaction
heat.
Sacrificial manganese in a resulting tantalum-base alloy may also be readily
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removed using electron beam melting. However, the boiling point temperature of
manganese (2060 C) is significantly less than the boiling point temperatures
of
copper and iron (2562 C and 2862 C, respectively); therefore, manganese may
restrict the temperature of aluminothermic reactions involving tantalum
pentoxide,
which may result in inadequate alloy-slag phase separation. Nickel (II) oxide
and
cobalt (II) oxide do not react with aluminum as energetically as iron (III)
oxide and
copper (II) oxide. Nickel and cobalt metals also tend to form intermetallic
compounds with tantalum. Chromium oxides such as Cr2O3 may also be used in
various embodiments. Molybdenum metal has a significantly lower vapor pressure
as compared to the vapor pressures of iron and copper and, therefore,
molybdenum
may not be as readily removed from a tantalum alloy matrix as iron and copper
during electron beam melting, but, as noted above, may be used as a precursor
oxide that provides molybdenum alloying to tantalum-base alloys or niobium-
base
alloys.
[0045] To produce
sufficient heat to achieve reaction temperatures that
cause alloy formation and slag phase separation, in various embodiments, the
reactants may also comprise an aluminothermic accelerator. An aluminothermic
accelerator is a reactant compound that oxidizes aluminum and generates large
amounts of reaction heat, but does not produce a reduced metal value that
coalesces into a tantalum alloy matrix or a niobium alloy matrix. Examples of
thermal accelerator reactants include, for example, potassium chlorate and
barium
peroxide.
[0046] In various embodiments, the reactants may comprise barium
peroxide powder. Barium peroxide reacts with aluminum under aluminothermic
reaction conditions to produce barium oxide and aluminum oxide. Barium oxide
has
a favorable phase relationship with aluminum oxide and slags comprising a
mixture
of barium oxide and aluminum oxide have significantly lower melting point
temperatures than slags comprising mostly aluminum oxide. For example, a
composition of 32 mol% barium oxide in aluminum oxide has a melting point
temperature of 1870 C as compared to 2072 C for pure aluminum oxide.
Therefore,
slags comprising a mixture of barium oxide and aluminum oxide reaction
products
will more readily phase separate from liquefied and coalesced tantalum alloy
or
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niobium alloy under aluminothermic reaction conditions, which facilitates the
production of a monolithic, fully-consolidated, and non-brittle tantalum alloy
or
niobium alloy regulus and a separated slag phase. In various embodiments, the
reactants may be substantially free of potassium chlorate, which means that
potassium chlorate is present in the reactant mixture at no greater than
incidental
impurity levels.
[0047] A process for the production of tantalum alloys or
niobium alloys
may comprise conducting an aluminothermic reaction between reactants
comprising
aluminum metal powder (Al), tantalum pentoxide powder (Ta205), niobium
pentoxide
powder (Nb2O5), at least one of iron MO oxide powder (Fe2O3) and copper (II)
oxide
powder (Cu0), and barium peroxide powder (Ba02). The aluminothermic reactions
may proceed, for example, according to the following chemical equations:
3 Ta205+ 10 AI ¨> 6 Ta + 5 A1203
3 Nb205+ 10 Al ->6 Nb + 5 A1203
Fe203+ 2 Al ¨> 2 Fe + A1203
3 CuO + 2 Al 3 Cu + A1203
3 BaO2 +2 Al -+3 BaO + Al2O3
[0048] The products of the alum inothermic reactions may include
a slag
phase comprising a mixture of aluminum oxide (Al2O3) and barium oxide (BaO),
and
a separate monolithic, fully-consolidated, and non-brittle tantalum alloy
regulus or
niobium alloy regulus. A tantalum-base alloy may comprise niobium, iron,
copper,
aluminum, and balance tantalum and incidental impurities, and a niobium-base
alloy
may comprise tantalum, iron, copper, aluminum, and balance niobium and
incidental
impurities. The iron, copper, and aluminum may be reduced to incidental
impurity
levels by electron beam melting the tantalum alloy or niobium alloy regulus to
produce a refined tantalum alloy or niobium alloy ingot.
[0049] A process for the production of tantalum alloys may
comprise
conducting an alum inothermic reaction between reactants comprising aluminum
metal powder (Al), tantalum pentoxide powder (Ta205), tungsten trioxide powder
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(W03), at least one of iron (III) oxide powder (Fe2O3) and copper (II) oxide
powder
(CuO), and barium peroxide powder (Ba02). The aluminothermic reactions may
proceed, for example, according to the following chemical equations:
3 Ta205 + 10 Al - 6 Ta + 5 A1203
WO3 + 2 Al ---> W + A1203
Fe2O3 + 2 Al -->2 Fe + Al2O3
3 CuO + 2 Al --> 3 Cu + A1203
3 Ba02 + 2 Al ---> 3 BaO + A1203
[0050] The products of the alum inothermic reactions may include a slag
phase comprising a mixture of aluminum oxide (A1203) and barium oxide (BaO),
and
a separate monolithic, fully-consolidated, and non-brittle tantalum alloy
regulus. The
tantalum-base alloy may comprise tungsten, iron, copper, aluminum, and balance
tantalum and incidental impurities. The iron, copper, and aluminum may be
reduced
to incidental impurity levels by electron beam melting the tantalum alloy
regulus to
produce a refined tantalum alloy ingot.
[0051] A
process for the production of tantalum alloys may comprise
conducting an aluminothermic reaction between reactants comprising aluminum
metal powder (Al), tungsten metal powder (W), tantalum pentoxide powder
(Ta205),
at least one of iron (11I) oxide powder (Fe2O3) and copper (II) oxide powder
(CuO),
and barium peroxide powder (Ba02). The aluminothermic reactions may proceed,
for example, according to the following chemical equations:
3 Ta205 + 10 AI 6 Ta + 5 A1203
VV ---> W
Fe203 + 2 Al --> 2 Fe + A1203
3 CuO + 2 Al --> 3 Cu + Al2O3
3 Ba02 + 2 Al ¨> 3 BaO + Al2O3
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[0052] The products of the alum inothermic reactions may
include a slag
phase comprising a mixture of aluminum oxide (Al2O3) and barium oxide (BaO),
and
a separate monolithic, fully-consolidated, and non-brittle tantalum alloy
regulus. The
tantalum-base alloy may comprise tungsten, iron, copper, aluminum, and balance
tantalum and incidental impurities. The iron, copper, and aluminum may be
reduced
to incidental impurity levels by electron beam melting the tantalum alloy
regulus to
produce a refined tantalum alloy ingot.
[0053] A process for the production of tantalum alloys may
comprise
conducting an aluminothermic reaction between reactants comprising aluminum
metal powder (Al), tantalum pentoxide powder (Ta205), molybdenum trioxide
powder
(Mo03), at least one of iron (III) oxide powder (Fe2O3) and copper (II) oxide
powder
(Cu0), and barium peroxide powder (Ba02). The alum inotherm ic reactions may
proceed, for example, according to the following chemical equations:
3 Ta205+ 10 Al 6 Ta + 5 A1203
Mo03 + 2 Al Mo + A1203
Fe2O3 + 2 Al 2 Fe + Al2O3
3 CuO + 2 Al -4 3 Cu + A1203
3 BaO2 + 2 Al ¨*3 BaO + Al2O3
[0054] The products of
the aluminothermic reactions may include a slag
phase comprising a mixture of aluminum oxide (Al2O3) and barium oxide (BaO),
and
a separate monolithic, fully-consolidated, and non-brittle tantalum alloy
regulus. The
tantalum-base alloy may comprise molybdenum, iron, copper, aluminum, and
balance tantalum and incidental impurities. The iron, copper, and aluminum may
be
reduced to incidental impurity levels by electron beam melting the tantalum
alloy
regulus to produce a refined tantalum alloy ingot.
[0055] A process for the production of niobium alloys may
comprise
conducting an aluminothermic reaction between reactants comprising aluminum
metal powder (Al), niobium pentoxide powder (Nb2O5), molybdenum trioxide
powder
(Mo03), at least one of iron (III) oxide powder (Fe2O3) and copper (II) oxide
powder
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(CuO), and barium peroxide powder (Ba02). The aluminothermic reactions may
proceed, for example, according to the following chemical equations:
3 Nb205 + 10 Al -> 6 Nb + 5 Al2O3
Mo03 + 2 Al -> Mo + A1203
Fe203 + 2 Al --> 2 Fe + A1203
3 CuO +2 Al 3 Cu + Al2O3
3 BaO2 + 2 Al --> 3 BaO + Al2O3
[0056] The products of the alum inothermic reactions may include
a slag
phase comprising a mixture of aluminum oxide (Al2O3) and barium oxide (BaO),
and
a separate monolithic, fully-consolidated, and non-brittle niobium alloy
regulus. The
niobium-base alloy may comprise molybdenum, iron, copper, aluminum, and
balance
niobium and incidental impurities. The iron, copper, and aluminum may be
reduced
to incidental impurity levels by electron beam melting the tantalum alloy
regulus to
produce a refined niobium alloy ingot.
[0057] A process for the production of niobium alloys may
comprise
conducting an aluminothermic reaction between reactants comprising aluminum
metal powder (Al), niobium pentoxide powder (Nb2O5), zirconium dioxide powder
(ZrO2), at least one of iron (111) oxide powder (Fe2O3) and copper (II) oxide
powder
(CuO), and barium peroxide powder (Ba02). The aluminothermic reactions may
proceed, for example, according to the following chemical equations:
3 Nb205 + 10 Al -> 6 Nb + 5 A1203
3 ZrO2 + 4 Al -> 3 Zr +2 A1203
Fe2O3 +2 Al -*2 Fe + A1203
3 CuO + 2 Al -> 3 Cu + A1203
3 Ba02 + 2 Al 3 BaO + A1203
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[0058] The products of the aluminothermic reactions may include
a slag
phase comprising a mixture of aluminum oxide (A1203) and barium oxide (BaO),
and
a separate monolithic, fully-consolidated, and non-brittle niobium alloy
regulus. The
niobium-base alloy may comprise zirconium, iron, copper, aluminum, and balance
niobium and incidental impurities. The iron, copper, and aluminum may be
reduced
to incidental impurity levels by electron beam melting the niobium alloy
regulus to
produce a refined niobium alloy ingot.
[0059] A process for the production of niobium alloys may
comprise
conducting an aluminothermic reaction between reactants comprising aluminum
metal powder (Al), niobium pentoxide powder (Nb2O5), titanium dioxide powder
(ZrO2), at least one of iron (III) oxide powder (Fe2O3) and copper (II) oxide
powder
(Cu0), and barium peroxide powder (6a02). The aluminothermic reactions may
proceed, for example, according to the following chemical equations:
3 Nb205 + 10 Al 6 Nb + 5 A1203
3 TiO2 + 4 Al 3 Ti + 2 A1203
Fe2O3 +2 Al 2 Fe + A1203
3 CuO + 2 Al 3 Cu + A1203
3 BaO2 + 2 Al 3 BaO + A1203
[0060] The products of the aluminothermic reactions may include a slag
phase comprising a mixture of aluminum oxide (A1203) and barium oxide (BaO),
and
a separate monolithic, fully-consolidated, and non-brittle niobium alloy
regulus. The
niobium-base alloy may comprise titanium, iron, copper, aluminum, and balance
niobium and incidental impurities. The iron, copper, and aluminum may be
reduced
to incidental impurity levels by electron beam melting the niobium alloy
regulus to
produce a refined niobium alloy ingot.
[0061] A process for the production of niobium alloys may
comprise
conducting an aluminothermic reaction between reactants comprising aluminum
metal powder (Al), niobium pentoxide powder (Nb2O5), at least one of iron
(III) oxide
powder (Fe2O3) and copper (II) oxide powder (Cu0), barium peroxide powder
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(Ba02), and any combination or sub-combination of zirconium dioxide powder
(ZrO2),
titanium dioxide powder (ZrO2), hafnium dioxide powder (Hf02), tantalum
pentoxide
powder (Ta2O5), and tungsten trioxide powder (W03) and/or tungsten metal. The
alum inotherm ic reactions may proceed, for example, according to the
following
chemical equations:
3 Nb205 + 10 Al ¨> 6 Nb + 5 Al2O3
3 Zr02 + 4 Al ¨> 3 Zr + 2 A1203
3 TiO2 +4 Al ¨> 3 Ti + 2 A1203
3 Hf02 + 4 Al ¨> 3 Hf + 2 A1203
3 Ta205 + 10 Al ¨> 6 Ta + 5 A1203
W03 + 2 Al ¨> W + A1203
¨>
Fe2O3 +2 Al ¨>2 Fe + Al2O3
3 CuO + 2 Al ¨> 3 Cu + A1203
3 Ba02 + 2 Al ¨> 3 Ba0 + A1203
[0062] The products of the aluminothermic reactions may include
a slag
phase comprising a mixture of aluminum oxide (A1203) and barium oxide (BaO),
and
a separate monolithic, fully-consolidated, and non-brittle niobium alloy
regulus. The
niobium-base alloy may comprise zirconium, titanium, hafnium, tantalum,
tungsten,
iron, copper, aluminum, and balance niobium and incidental impurities. The
iron,
copper, and aluminum may be reduced to incidental impurity levels by electron
beam
melting the niobium alloy regulus to produce a refined niobium alloy ingot.
[0063] The alum inotherm ic reactant mixtures used in the
processes
described in this specification to produce tantalum alloys or niobium alloys
may
comprise aluminum metal powder, tantalum pentoxide powder and/or niobium
pentoxide powder, and any combination or sub-combination of alloying element
precursor powders, sacrificial metal oxide powders, and/or alum inothermic
accelerator powders. For example, the aluminothermic reactant mixtures may
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comprise any combination or sub-combination of reactant powders including
aluminum, tantalum pentoxide (Ta205), niobium pentoxide (Nb2O5), molybdenum
trioxide (Mo03), titanium dioxide (TiO2), zirconium dioxide (ZrO2), hafnium
dioxide
(Hf02), vanadium pentoxide (V205), tungsten trioxide (W02), chromium (III)
oxide
(Cr203), iron (III) oxide (Fe2O3), copper (II) oxide (Cu0), manganese dioxide
(Mn02),
nickel (II) oxide (NiO), cobalt (II) oxide (Co0), and/or barium peroxide
(Ba02). The
metal oxide alloying element precursor powders are chemically reduced by the
aluminum to the corresponding metal. In addition or as an alternative to metal
oxide
alloying element precursor powders, the aluminothermic reactant mixtures may
comprise any combination or sub-combination of aluminothermically inert
metallic
powders that provide alloying elements in addition to any allowing elements
provided
by the aluminothermically reduced reaction products. For example, the
aluminothermic reactant mixtures may comprise any combination or sub-
combination
of tungsten powder, molybdenum powder, titanium powder, zirconium powder,
hafnium powder, vanadium powder, and/or chromium powder.
[0064] The composition and relative amounts of the reactant
powders
(and inert powders, if used) may be based on the metallurgical composition of
a
specified tantalum alloy or niobium alloy target and the stoichiometry of the
aluminothermic reactions. For example, to produce a Ta-40Nb alloy target, a
60:40
.. Ta:Nb weight ratio, on a metal weight basis, may be specified in a reactant
feed
comprising tantalum pentoxide and niobium pentoxide. To produce a Ta-2.5W
alloy
target, for example, a 97.5:2.5 Ta:W weight ratio, on a metal weight basis,
may be
specified in a reactant feed comprising tantalum pentoxide and tungsten metal
or
tungsten trioxide. The relative metal weight ratios of the tantalum metal
precursor
(Ta205) and the specified alloying element precursors, such as, for example, a
niobium metal precursor (Nb2O5) or a tungsten metal precursor (W or W03), may
be
adjusted to account for yield losses to the slag phase, which may reduce the
relative
amount of a metal (e.g., Ta, Nb, or W) comprising the regulus product.
[0065] In
embodiments where the targeted alloy composition comprises
a tungsten-containing tantalum-base alloy such as Ta-2.5W, tungsten metal
powder
may be used as an inert tungsten precursor to provide the tungsten metal for
alloying
the tantalum metal produced from the aluminothermically reduced tantalum
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pentoxide precursor. A tungsten metal powder may be referred to as a
"reactant" or
"precursor for the provision of tungsten to alloy tantalum, notwithstanding
the fact
that the tungsten metal powder may be chemically inert under aluminothermic
reaction conditions and remain in a zero (elemental) oxidation state (W )
during the
reactions. The tungsten metal precursor in such embodiments does not
contribute to
any heat generation during the aluminothermic reactions. Instead, the tungsten
metal precursor functions as a heat sink in the reaction mixture, which
decreases the
otherwise available exothermic reaction heat energy and reaction temperature.
Accordingly, an excessive amount of tungsten in the initial reactant mixture
may
present an impediment to reactant conversion yield and alloy-slag phase
separation.
In various embodiments comprising a tungsten metal precursor in the reactant
mixture, the amount of tungsten may be limited to an amount up to 7% of the
reactant mixture on a total metal weight basis.
[0066] The relative amount of the sacrificial metal oxide powder
(such
as, for example, iron (III) oxide powder, copper (II) oxide powder, or both)
in the
initial reactant mixture is not determined by the metallurgical composition of
a
specified tantalum alloy or niobium alloy target because the resulting metal
reaction
products (e.g., Fe and/or Cu) of the aluminothermic reactions may be removed
or
reduced to incidental impurity levels in a tantalum alloy or niobium alloy
matrix by
downstream electron beam melting. Instead, the relative amounts of the
sacrificial
metal oxide powder reactants are determined by balancing the alloy melting
point
temperature reduction and the formation of undesired alloy phases due to the
presence of the sacrificial alloy constituents in the tantalum alloy or
niobium alloy
matrix.
[0067] As previously described, the addition of relatively low amounts
of iron to tantalum or niobium as an alloy constituent significantly decreases
the
melting point temperature of the alloy. The aluminothermic reduction of iron
(III)
oxide to iron also generates a relatively large amount of reaction heat as
compared
to the aluminothermic reduction of other metal oxides to elemental metals.
However,
at concentrations of 21% by weight or more, iron does not completely dissolve
in
tantalum and forms a brittle intermetallic TaFe compound that precipitates
from the
tantalum matrix and forms phases that severely embrittle the bulk alloy
material.
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Furthermore, as a sacrificial element, any iron present in a tantalum alloy or
niobium
alloy regulus produced by an aluminothermic reaction process may ultimately
need
to be removed or reduced to incidental impurity levels by downstream electron
beam
melting. Therefore, the relative amount of an iron (III) oxide powder reactant
may be
limited to ensure that a resulting tantalum alloy or niobium alloy regulus
comprises
less than 21% by weight of the alloy regulus.
[0068] Like
iron, the addition of relatively low amounts of copper to
tantalum or niobium as an alloy constituent decreases the melting point
temperature
of the alloy. The heat of reaction for the aluminothermic reduction of copper
(II)
oxide to copper metal is not as great as the heat of reaction for the
aluminothermic
reduction of iron (III) oxide to iron. However, unlike iron, copper does not
form any
detrimental intermetallic compounds with tantalum over the entire
compositional
range. Instead, at ambient temperatures, copper and tantalum are essentially
immiscible and form separate, relatively ductile metallic phases. In various
embodiments, copper (II) oxide powder may be used as a sacrificial metal oxide
reactant instead of or in addition to iron (III) oxide. Accounting for the
specified
tantalum-base alloy or niobium-base alloy composition to be produced by an
aluminothermic reaction process, suitable combinations of iron (Ill) oxide and
copper
(II) oxide powder reactants may be readily determined that: (1) facilitate
metal
liquefaction and coalescence of tantalum-base alloys or niobium-base alloys
under
aluminothermic reaction conditions; (2) do not result in the formation of
brittle
intermetallic phases in the solid tantalum alloy or niobium alloy regulus
product; (3)
facilitate alloy-slag phase separation; and (4) produce iron and/or copper
alloy
concentrations that are readily removed or reduced to incidental impurity
levels by
downstream electron beam melting of the regulus.
[0069] The
relative amount of an aluminothermic accelerator reactant,
such as, for example, barium peroxide, may be determined by the amount of heat
energy necessary to ensure liquefaction and coalescence of aluminothermically
reduced metals such as, for example, tantalum, niobium, iron, copper,
tungsten,
molybdenum, titanium, zirconium, hafnium, vanadium, chromium, manganese,
cobalt, nickel, or combinations of any thereof, and also the liquefaction and
coalescence of tungsten metal powder, if present, into the tantalum alloy or
niobium
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alloy matrix, The relative amount of an aluminothermic accelerator reactant
comprising barium peroxide may also be based in part on the melting point
depression of the resulting slag phase comprising aluminum oxide and barium
oxide
reaction products, which will more readily phase separate from liquefied and
coalesced tantalum alloy or niobium alloy under aluminothermic reaction
conditions.
[0070] As described above, the aluminum powder reactant
functions as
a reducing agent that is oxidized by at least the tantalum pentoxide and/or
niobium
pentoxide reactant, the sacrificial metal oxide reactant(s), and the
aluminothermic
accelerator reactant. Similar to iron, aluminum at concentrations of
approximately 4-
6% by weight or more does not completely dissolve in tantalum and forms a
brittle
intermetallic Ta2Alcompound that precipitates from the tantalum matrix, even
in a
molten state, and forms phases that severely embrittle the solidified bulk
alloy
material. Accordingly, it may be important control the amount of aluminum
powder in
an initial reactant mixture to ensure the presence of a stoichiometrically
sufficient
amount for the alum inotherm ic reactions, while also preventing excess
aluminum
from forming intermetallic Ta2Alcompounds in a resulting alloy regulus
product. In
various embodiments, the amount of aluminum powder in an initial reactant
mixture
may comprise up to 5.0% excess of the stoichiometric requirement on a mole
basis.
The amount of aluminum powder in an initial reactant mixture may comprise up
to
4.0% excess of the stoichiometric requirement on a mole basis. The amount of
aluminum powder in an initial reactant mixture may comprise from 0.0% to 5.0%
excess of the stoichiometric requirement on a mole basis, or any sub-range
subsumed therein, such as, for example, 1.0% to 5.0%, 2.0% to 5.0%, 3.0% to
5.0%,
1.0% to 4.0%, 2.0% to 4.0%, or 3.0% to 4.0%.
[0071] In various embodiments, a process for the production of a
tantalum alloy or a niobium alloy may comprise mixing a reactant mixture
comprising
aluminum metal powder, tantalum pentoxide and/or niobium pentoxide powder, an
alloying element precursor powder (e.g., tungsten metal, tungsten trioxide,
molybdenum trioxide, titanium dioxide, zirconium dioxide, hafnium dioxide,
and/or
vanadium pentoxide), at least one sacrificial metal oxide powder (e.g., iron
(III) oxide
and/or copper (II) oxide), and at least one aluminothermic accelerator powder
(e.g.,
barium peroxide). Reactant powders should be thoroughly dry to prevent the
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potential formation of steam during the aluminothermic reactions. For example,
in
various embodiments, the moisture content, determined as loss on ignition
(L01), for
= each reactant powder may be less than 0.5%, 0.4%, 0.3%, or 0.2%. The
reactant
powders should also be finely divided. For example, in various embodiments,
the
reactant powders may have a particle size distribution of greater than 85% by
weight
passing a 200 U.S. mesh (-200 mesh, <74 micrometer, <0.0029 inch).
[0072] The reactant powders may be individually weighed
and mixed
together using standard powder mixing equipment such as, for example, a double-
cone blender, a twin shell (vee) blender, or a vertical screw mixer. In
various
embodiments, the reactant powder may be mixed for at least 10 minutes, and in
some embodiments, for at least 20 minutes, to ensure macroscopically
homogeneous mixing. After mixing, the reactant mixture may be loaded into a
reaction vessel.
[0073] Referring to Figure 3, a reaction vessel 10
comprises vessel
sidewalls 12 and vessel bottom 14. The vessel sidewalls 12 and the vessel
bottom
14 may comprise a material that maintains structural integrity when subjected
to the
high levels of heat and high temperatures achieved during alum inotherm ic
reactions.
For example, the vessel sidewalls 12 and the vessel bottom 14 may be
fabricated
from extruded, compression-molded, or iso-molded graphite. The vessel
sidewalls
12 and the vessel bottom 14 may comprise coarse-grained, medium-grained, or
fine-
grained graphite.
[0074] For example, in various embodiments, reaction
vessel sidewalls
may comprise coarse-grained or medium-grained extruded graphite and a reaction
vessel bottom may comprise fine-grained iso-molded (i.e., isostatically
pressed)
graphite. While not intending to be bound by theory, it is believed that the
finer grain
size of fine-grained iso-molded graphite provides greater physical robustness
and
structural integrity to the reaction vessel bottom against erosion by the
molten
alum inothermic reaction products. The fine-grained iso-molded graphite is
also
believed to provide a contacting surface characterized by decreased porosity,
which
effectively excludes more molten material than coarser grained material. Fine-
grained iso-molded graphite is more expensive than coarse-grained or medium-
grained graphite and, therefore, cost considerations may dictate that the
reaction
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vessel bottom comprise fine-grained iso-molded graphite because of the
reactant
and product load bearing down onto the reaction vessel bottom, and the
reaction
vessel sidewalls comprise less expensive coarser grained graphite material.
Nevertheless, in various embodiments, the reaction vessel sidewalls may
comprise
fine-grained iso-molded graphite. Likewise, the reaction vessel bottom may
comprise coarser grained graphite material.
[0075] The thickness of the vessel sidewalls and the vessel
bottom
should be sufficient to maintain structural integrity when subjected to the
high heat
and temperatures produced during the aluminothermic reduction reactions. In
various embodiments, the vessel sidewalls and the vessel bottom may be at
least 1-
inch thick. The specific geometry (shape and dimensions) of the reaction
vessel is
not necessarily limited. However, in various embodiments, the specific
geometry of
the reaction vessel may be determined by the input configuration of a
downstream
electron beam melting furnace. In such embodiments, the specific geometry of
the
reaction vessel may be selected to produce a tantalum alloy or niobium alloy
regulus
having a geometry (shape and dimensions) that permits the regulus to be
directly
electron beam melted in an electron beam furnace to produce a refined tantalum
alloy or niobium alloy ingot.
[0076] Referring again to Figure 3, the vessel sidewalls 12 and
the
vessel bottom 14 may be mechanically fastened together to form the reaction
vessel
10. Alternatively, the reaction vessel 10, comprising the vessel sidewalls 12
and the
vessel bottom 14, may be formed as a monolithic and contiguous vessel
fabricated
from material such as graphite using compression molding or iso-molding
techniques, for example.
[0077] The reaction vessel 10 is positioned on top of a layer of
refractory material 18. The layer of refractory material 18 may comprise a
refractory
material such as, for example, fire clay bricks or other ceramic-based
materials used
for high temperature industrial applications. The layer of refractory material
18 may
be positioned on top of an elevated concrete slab 22. Alternatively, the layer
of
refractory material 18 may be positioned directly onto a suitable floor
surface (e.g.,
concrete) in a plant or shop (not shown).
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[0078] The reaction vessel 10 may comprise a layer of magnesium
oxide 16 positioned on at least the vessel bottom 14. The magnesium oxide
layer 16
provides a barrier between the vessel bottom 14 and the reactant mixture 20,
which
is positioned on top of the magnesium oxide layer 16, as shown in Figure 3.
[0079] While not intending to be bound by theory, during the
development of the processes described in this specification, cracking of
tantalum
alloy reguli produced through aluminothermic reactions was observed when the
reguli were removed from graphite reaction vessels. The observed cracking of
the
tantalum alloy reguli occurred notwithstanding the fact that the alloy
material itself
was subsequently determined to be relatively ductile. This behavior was
attributed,
at least in part, to a possible hot tearing mechanism wherein the alloy
material
produced by the alum inothermic reactions would stick to the interior surfaces
of the
graphite reaction vessel during liquefaction, coalescence, solidification, and
cooling.
Again, while not intending to be bound by theory, it is believed that this
possible hot
tearing may have resulted from the formation and growth of carbides at the
interface
between the newly-formed alloy material and the graphite reaction vessel. The
application of a magnesium oxide layer to the interior bottom surface of the
reaction
vessel was found to eliminate the observed cracking.
[0080] In various embodiments, a reaction vessel for the
aluminothermic production of tantalum alloys or niobium alloys may comprise a
layer
of magnesium oxide positioned on at least the interior bottom surface of the
reaction
vessel. The magnesium oxide layer functions as a barrier between the reactant
powder mixture and the bottom of the reaction vessel. The magnesium oxide
layer
may comprise a layer of magnesium oxide powder positioned on the bottom of the
reaction vessel. In various embodiments, a refractory grade magnesium oxide
powder in a heavy/dead-burned state (i.e., calcined at a temperature greater
than
1500 C to eliminate reactivity) may be used. A magnesium oxide powder layer
may
be positioned in the reaction vessel immediately before the reaction vessel is
loaded
with the reactant mixture.
[0081] A magnesium oxide layer may be positioned on at least the
interior bottom surface of a reaction vessel, but may optionally be applied to
the
sidewalls of a reaction vessel. Referring to Figure 4, a reaction vessel 10'
is shown
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comprising a magnesium oxide layer 16 positioned on the vessel bottom 14 and
the
vessel sidewalls 12.
[0082] In various embodiments, a layer of magnesium oxide may be
positioned in a reaction vessel as a thermally-sprayed coating layer applied
to the
sidewalls of the reaction vessel and/or the bottom of the reaction vessel. A
thermally-sprayed magnesium oxide coating layer may have advantages such as,
for
example, greater structural integrity, lower porosity, and uniform thickness.
In
various embodiments, a layer of magnesium oxide may be may be positioned in a
reaction vessel by applying a paint composition comprising magnesium oxide
particles to the sidewalls of the reaction vessel and/or the bottom of the
reaction
vessel. In various embodiments, a layer of magnesium oxide may be positioned
in a
reaction vessel by positioning magnesium oxide sheets or wallboards
immediately
adjacent to the sidewalls of the reaction vessel and/or the bottom of the
reaction
vessel.
[0083] While other ceramic materials may be used instead of a
magnesium oxide to provide a barrier layer in a reaction vessel, such other
materials
may not be as effective as magnesium oxide and may be reactive under
aluminothermic conditions. For example, refractory materials such as silicon
dioxide
and zirconium dioxide may be aluminothermically reduced by the aluminum metal
powder in a reaction mixture to silicon and zirconium, respectively. Like
magnesium
oxide, calcium oxide is inert toward aluminothermic reaction, and therefore
may be
suitable, but calcium oxide is sensitive to air exposure.
[0084] In various embodiments, a reactant powder mixture may be
loaded into a reaction vessel after positioning a magnesium oxide layer on the
sidewalls of the reaction vessel and/or the bottom of the reaction vessel. The
loading of the reactant powder mixture may comprise positioning the mixture in
the
reaction vessel on top of any magnesium oxide layer located on the interior
bottom
surface of the reaction vessel (see Figures 2 and 3, for example). After the
reactant
powder mixture is loaded into the reaction vessel, an ignition wire is
positioned in
contact with the reactant powder mixture in the reaction vessel.
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[0085] Referring to Figure 5, an ignition wire 28 is shown
submerged
into the reactant powder mixture 20 in the reaction vessel 10. The ignition
wire 28 is
connected to an electrical current source (power supply) 24 by lead and return
wires
26.
[0086] In various embodiments, the ignition wire may be directly
submerged into the reactant powder mixture in the reaction vessel, as shown in
Figure 5. For example, an ignition wire several inches in length may be looped
as
shown in Figure 5 and submerged at least two inches into the reactant powder
mixture in the reaction vessel. Alternatively, an ignition wire may be
positioned
inside a plastic starter bag (not shown) that contains aluminum metal powder
and
any one of or any combination of reducible metal oxides or peroxides such as,
for
example, tantalum pentoxide, niobium pentoxide, iron (III) oxide, copper (II)
oxide,
and/or barium peroxide. The starter bag may be positioned directly on top of
the
reactant powder mixture in the reaction vessel and does not necessarily need
to be,
but may be, partially or completely submerged into the reactant powder
mixture.
While not intending to be bound by theory, it is believed that the smaller
volume of
reactants inside a starter bag may provide a more reproducible environment for
reaction ignition than direct contact of an ignition wire submerged within the
entire
reactant powder mixture in a reaction vessel. Nevertheless, ignition wires may
be
positioned in contact with a reactant powder mixture by directly submerging
the wires
in the main reactant mixture or indirectly through starter bags.
[0087] The ignition wires may comprise tantalum, niobium, a
tantalum
alloy, or a niobium alloy, for example. Alternatively, the ignition wires may
comprise
any high-melting point metal or alloy that is intended to be present in a
targeted alloy
composition such as, for example, tungsten, tungsten alloys, niobium, and
niobium
alloys. In some embodiments, the ignition wires may be at least 12 inches in
length
and comprise a relatively narrow gauge of 20, for example, to create a
resistive
heating element to ignite the reactant mixture and initiate the aluminothermic
reactions. The ignition wire may be connected to a power supply using aluminum
wires or copper wires, for example, of sufficient length and gauge to provide
an
energizing current to the ignition wire. The connection between the ignition
wire and
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the wires connecting to the power supply may comprise a twisted wire
connection or
a metallic butt-connector, for example.
[0088] After an ignition wire is positioned in contact with the
reaction
mixture, the reaction vessel may be sealed inside a reaction chamber. The
specific
geometry and construction of a reaction chamber is not necessarily critical,
but a
reaction chamber should physically contain the reaction vessel and maintain
structural integrity when subjected to the heat and temperatures producing
during
the aluminothermic reactions. A reaction chamber should also be capable of
containing any reaction material ejected from the reaction vessel during the
reactions. A reaction chamber should also be capable of hermetically sealing
the
reaction vessel from the surrounding environment.
[0089] Referring to Figure 6, a reaction chamber 30 comprising a
lid
structure is shown sealing the reaction vessel 10 containing the reactant
powder
mixture 20. The reaction chamber 30 comprises a vacuum port 32 to connect to a
vacuum source (not shown), such as a vacuum pump, for establishing a vacuum
inside the reaction chamber. The lead and return wires 26 (connecting the
ignition
wire 28 and the power supply 24) are positioned through electrical ports (not
shown)
in the reaction chamber 30. After the reactant powder mixture 20 and the
ignition
wire 28 are positioned in the reaction vessel 10, the reaction vessel 10 is
sealed
inside the reaction chamber 30 by lowering the reaction chamber over the
reaction
vessel as indicated by arrow 34. The reaction vessel 30 engages a suitable
surface
such as a flat base plate with a machined flat edge, for example, or a
concrete slab
to provide a hermetic seal and permit a vacuum to be established inside the
reaction
vessel through vacuum port 32. After the aluminothermic reactions are complete
and the resulting reaction products have sufficiently cooled, the vacuum may
be
discontinued and the reaction chamber raised as indicated by arrow 34. The
lowering and raising of the reaction vessel 30 may be performed with suitable
plant
equipment such as, for example, a crane or hoist (not shown). The reaction
vessel
may comprise any suitable material of construction such as, for example,
steel.
30 [0090] The establishment of a vacuum is not necessarily required
for
the alum inothermic reactions. However, conducting the reactions under a
vacuum
provides advantages such as neutralizing pressure spikes in the reaction
mixture
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that may eject material from the reaction vessel. Conducting the reactions
under a
vacuum may also increase the quality of the tantalum alloy or niobium alloy
regulus
produced by the aluminothermic reactions by decreasing nitrogen and oxygen
contamination. The establishment of a vacuum inside a reaction chamber also
provides thermal insulation and extends the cooling time of the reaction
products,
which may further mitigate cracking of the tantalum alloy or niobium alloy
regulus
during solidification and cooling. Reasonable vacuum pressures are suitable
for
inside a reaction chamber. For example, a vacuum pressure of less than 100
millitorr may be used.
[0091] Initiation of the aluminothermic reactions may comprise
energizing the ignition wire. Initiation of the aluminothermic reactions may
occur
after the reaction vessel is sealed inside a reaction chamber and a vacuum
established inside the reaction chamber. Energizing the ignition wire may
comprise
activating a power supply and sending an electrical current of at least 60
amps
through the ignition wire. In various embodiments, the ignition wire may be
energized with at least 70 amps, at least 80 amps, at least 90 amps, or at
least 100
amps. In various embodiments, the ignition wire may be energized for at least
1
second, or in some embodiments, at least 2 seconds, at least 3 second, at
least 4
seconds, or at least 5 seconds.
[0092] After initiation, the aluminothermic reactions proceed very
rapidly and may be complete within 10 minutes of initiation, or in some
embodiments, within 5 minutes of initiation. However, the resulting reaction
products
comprising a slag phase and a tantalum alloy regulus may require 24 to 48
hours of
cooling to reach ambient temperature. Once the reaction products reach an
acceptable temperature, such as, for example, ambient temperature, the
reaction
chamber may be backfilled with air to remove the vacuum, the reaction chamber
may be opened, and the reaction product removed from the reaction vessel. In
various embodiments, the hot reaction products may be gas quenched by
backfilling
the reaction chamber with a gas, such as air or argon, for example, to
accelerate
cooling to ambient temperature. Backfilling with gas may be repeated multiple
times
to further accelerate cooling. However, gas quenching should only be
performed, if
at all, after the reaction products have solidified. Therefore, to ensure
solidification,
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gas quenching should not be performed until at least 12 hours after initiation
of the
aluminothermic reactions.
[0093] As described above, the reaction products of the
aluminothermic
reactions comprise a solidified slag phase and a tantalum alloy or niobium
alloy
regulus. The slag phase may comprise oxides such as barium oxide and/or
aluminum oxide, for example. The tantalum alloy or niobium alloy regulus may
comprise alloying elements dissolved in a tantalum matrix or niobium matrix,
wherein
the alloying elements are produced from the precursor reactants (e.g., Ta205,
Nb2O5,
Mo03, h02, ZrO2, 1-1f02, V205, W, or W03), the sacrificial metal oxide
reactants
(e.g., Fe2O3 and/or Cu0), and excess aluminum.
[0094] For
example, Table 1 below shows a reactant mixture that may
yield a 22.7-kilogram (50.0-pound) tantalum alloy regulus comprising 2.2
weight
percent tungsten, sacrificial iron and copper, and excess aluminum.
Table 1
Reactant Formula Amount (lbs) Weight Percent
tantalum pentoxide Ta205 65.6 56.10%
iron (III) oxide Fe2O3 2.9 2.50%
copper (II) oxide CuO 2.6 2.20%
aluminum Al 18.4 15.70%
barium peroxide Ba02 26.3 22.50%
tungsten W 1.1 1.00%
In various embodiments, the weight percentages shown in Table 1 may vary by
10%, 5%, + 2%, 1%, 0.5%, + 0.1%, 0.05%, or 0.01%.
[0095]
Additional target product weights may be obtained by scaling the
relative amounts of the reactants and maintaining the relative weight
percentages.
The resulting tantalum alloy regulus comprising 2.2 weight percent tungsten
may be
electron beam melted to reduce the copper, aluminum, and iron content of the
regulus material and produce a refined Ta-2.5W alloy ingot comprising 2.5
weight
percent tungsten, balance tantalum and incidental impurities.
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[0096] Alternative reactant mixture amounts for the
aluminothermic
production of niobium-containing tantalum-base alloy reguli, tantalum-
containing
niobium-base alloy reguli, tungsten-containing tantalum-base alloy reguli
having
different tungsten content, zirconium-containing niobium-base alloy reguli,
titanium-
containing niobium-base alloy reguli, molybdenum-containing tantalum-base
alloy
reguli, or other tantalum-base or niobium-base alloy compositions, including
more
highly alloyed compositions, may be determined in accordance with the
information
disclosed in this specification.
[0097] In various embodiments, a reactant mixture may comprise,
based on total weight of the reactant mixture: 55.1% to 57.1% tantalum
pentoxide
powder; 0% to 3.5% iron (III) oxide powder; 0% to 3.2% copper (II) oxide
powder;
21.5% to 23.5% barium peroxide powder; 14.7% to 16.7% aluminum metal powder;
and 0% to 15% tungsten metal powder. In other embodiments, a reactant mixture
may comprise, based on total weight of the reactant mixture: 55.6% to 56.6%
tantalum pentoxide powder; 2.0% to 3.0% iron (III) oxide powder; 1.7% to 2.7%
copper (II) oxide powder; 22.0% to 23.0% barium peroxide powder; 15.2% to
16.2%
aluminum metal powder; and 0.5% to 1.5% tungsten metal powder. In some
embodiments, a reactant mixture may comprise, based on total weight of the
reactant mixture: 56.0% to 56.2% tantalum pentoxide powder; 2.4% to 2.6% iron
(III)
oxide powder; 2.1% to 2.3% copper (II) oxide powder; 22.4% to 22.6% barium
peroxide powder; 15.6% to 15.8% aluminum metal powder; and 0.9% to 1.1%
tungsten metal powder.
[0098] In various embodiments, the processes described in this
specification may produce a tantalum alloy regulus having a tantalum yield of
at least
80%, on a metal weight basis, of the initial tantalum provided by the tantalum
pentoxide reactant, and in some embodiments, at least 85%, at least 90%, at
least
93%, or at least 95%, on a metal weight basis, of the initial tantalum
provided by the
tantalum pentoxide reactant. In various embodiments, the processes described
in
this specification may produce a tantalum alloy regulus comprising at least 80
weight
percent tantalum, and in some embodiments, at least 81%, at least 83%, at
least
85%, at least 87%, or at least 89% tantalum, based on the total weight of the
regulus. In various embodiments, the processes described in this specification
may
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produce a tantalum alloy regulus comprising at least 1.0 weight percent
tungsten,
and in some embodiments, at least 1.3%, at least 1.5%, at least 1.7%, at least
2.0%,
at least 2.1%, or at least 2.2% tungsten, based on the total weight of the
regulus.
[0099] The aluminotherrnic processes described in this specification
produce an oxide slag phase that may be completely separate from the metallic
alloy
regulus, which facilitates the separation and removal of the tantalum alloy or
niobium
alloy regulus from the slag. The tantalum alloy or niobium alloy reguli may be
washed to remove residual slag and then directly input into an electron beam
melting
furnace to refine the alloy composition and produce a tantalum alloy or
niobium alloy
ingot. In this manner, the tantalum alloy or niobium alloy reguli produced in
accordance with the processes described in this specification may function as
pre-
alloyed intermediates in the production of tantalum alloy or niobium alloy
ingots and
mill products. The tantalum alloy or niobium alloy reguli are monolithic,
fully-
consolidated, and non-brittle. The tantalum alloy or niobium alloy reguli also
comprise alloying elements completely dissolved into the tantalum matrix for
niobium
matrix, which facilitates the direct electron beam melting and casting of
tantalum
alloy or niobium alloy ingots having uniform microstructure, specified alloy
composition, and alloying elements completely and uniformly distributed in the
tantalum matrix or niobium matrix.
[00100] Referring back to Figure 1A, after electron beam melting the
tantalum alloy or niobium alloy reguli produced in accordance with the
processes
described in this specification, the resulting tantalum alloy or niobium alloy
ingots
may be forged, rolled, cut, annealed, and cleaned to produce mill products
such as
tantalum alloy or niobium alloy billets, rods, bars, sheets, wires, and the
like.
[00101] The non-limiting and non-exhaustive examples that follow are
intended to further describe various non-limiting and non-exhaustive
embodiments
without restricting the scope of the embodiments described in this
specification.
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EXAMPLES
Example 1:
[00102] A tantalum alloy regulus was produced by conducting an
aluminothermic reaction using the reactant powders and amounts listed in Table
2.
Table 2
Reactant Formula Amount (grams) Weight Percent
tantalum pentoxide Ta205 1800 56.16
iron (III) oxide Fe2O3 80 2.50
copper (II) oxide CuO 70 2.18
aluminum Al 505 15.76
barium peroxide Ba02 720 22.46
tungsten W 30 0.94
total 3205 100
[00103] The amount of aluminum metal powder was 4% excess of the
stoichiometric amount needed for reduction of the tantalum pentoxide, iron
(Ill)
oxide, copper (II) oxide, and barium peroxide according to the following
chemical
equations:
3 Ta205+ 10 Al --> 6 Ta + 5 A1203
1/11 1IV
Fe2O3 + 2 Al 2 Fe + Al2O3
3 CuO +2 Al -3 3 Cu + A1203
3 Ba02 + 2 AI 3 Ba0 + A1203
[00104] The
reactant powders were thoroughly dry (<0.2% L01) and
finely divided (85% by weight -200 mesh). The reactant powders were
individually
weighed and loaded into a double cone powder blender. The reactant powders
were
mixed in the blender for at least 20 minutes to provide a macroscopically
homogeneous reactant mixture. The reactant mixture was loaded into a reaction
vessel.
- 35 -
[00105] The reaction vessel was cylindrically-shaped with an
inside height
of 12-inches and an inside diameter of 4.25-inches. The reaction vessel was
fabricated
from an iso-molded fine-grained graphite sheet forming the bottom of the
reaction
vessel, and an extruded medium-to-coarse-grained graphite sheet forming
the cylindrical sidewalls. The bottom and sidewalls were approximately 1-inch
thick.
The reaction vessel was positioned on top of a layer of refractory bricks, and
the layer
of refractory bricks was positioned on top of a concrete slab. A layer
heavy/dead-
burned magnesium oxide powder was spread over the bottom interior surface of
the
reaction vessel and the reactant mixture was loaded on top of the
magnesium oxide powder layer. The magnesium oxide powder layer formed a
barrier between the reactant mixture and the graphite bottom surface of the
reaction
vessel.
[00106] A tantalum ignition wire was submerged into the reactant
powder
mixture in the reaction vessel. The ignition wire was connected to a power
supply by aluminum wires. The alum inotherm ic reactions were initiated by
sending
an electrical current of 100 amps from the power supply through the ignition
wire for five
(5) seconds. The reactions proceeded very rapidly and the reaction products
were
allowed to cool to ambient temperature over a period of 48 hours. The reaction
products
comprised a well-defined and separated regulus and slag phase. The
reaction products were removed from the reaction vessel and weighed to
determine
total material recovery. The total material recovery was determined to be
3145.6
grams (98% of the 3205 grams of initial reactant powders).
[00107] The regulus and slag phase were separated and analyzed for
chemical composition. Based on the stoichiometry of the chemical reactions,
and
assuming a complete yield, the theoretical alloy composition of the regulus
would be,
in percentages by weight, 1.2% aluminum, 3.4% iron, 3.4% copper, 1.8%
tungsten,
balance tantalum (90.2%). Taking into account that copper is essentially
immiscible in
tungsten at ambient temperatures, the theoretical alloy composition is
generally in
agreement with measurements of the actual alloy composition of the regulus
made
using Scanning Electron Microscopy / Energy-Dispersive Spectroscopy (SEM/EDS)
according to ASTM E1508 - 98(2008): Standard Guide for Quantitative Analysis
by
Energy-Dispersive Spectroscopy.
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The SEM/EDS analysis showed an actual alloy composition, in percentages by
weight,
of 3.4% aluminum, 8.4% iron, 2.0% tungsten, balance tantalum and incidental
impurities, The tantalum yield in the regulus was 90% of the initial tantalum
provided by
the tantalum pentoxide reactant (on a metal weight
basis). The slag phase comprised approximately 32% barium oxide and 68%
aluminum oxide, on a mole basis, and small amounts of tantalum-containing,
iron-
containing, and copper-containing by-products.
[00108] Figure 7 is an SEM image of the microstructure of the
tantalum
alloy regulus. The microstructure comprised two (2) observable phases: the
darker
phases labeled CA', and the lighter phases labeled CB', in Figure 7. Based on
SEM/EDS analysis, the A-phase is an aluminum- and iron-rich phase, and the B-
phase
is an aluminum- and iron-lean phase. Both phases (A and B) comprise tantalum
as the
predominant constituent and also comprise dissolved tungsten. The SEM/EDS
analysis
showed no phases comprising tungsten as the predominant
constituent. Indeed, the SEM/EDS analysis showed that the tungsten
concentration
only varied from 0.4% to 3.7%, by weight, in each distinct phase, and that the
average
tungsten concentration was 2.0% over the entire SEM/EDS field. This indicated
complete dissolution of the aluminothermically inert tungsten metal powder
into the
tantalum metal produced by the aluminothermic reduction of tantalum
pentoxide.
[00109] The tantalum alloy regulus was monolithic, fully-
consolidated,
non-brittle, and lacked any cracking. The tantalum alloy regulus could be
directly
input into an electron beam melting furnace for refinement of the tantalum
alloy
composition, including reduction of the aluminum, copper, and iron to
incidental
impurity levels, homogeneous dissolution of the tungsten into the tantalum
matrix,
and establishment of a tungsten concentration within specification for To-
2.5W.
Example 2:
[00110] A tantalum alloy regulus was produced by conducting an
aluminothermic reaction with the reactant powders and amounts listed in Table
3.
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Table 3
Reactant Formula
Amount (grams) Weight Percent
tantalum pentoxide Ta205 1800 55.42
iron (III) oxide Fe2O3 160 4.93
aluminum Al 518 15.95
barium peroxide Ba02 740 22.78
tungsten W 30 0.92
total 3248 100
[00111] The amount of aluminum metal powder was 4% excess of the
stoichiometric amount needed for reduction of the tantalum pentoxide, iron
(111)
oxide, and barium peroxide according to the following chemical equations:
3 Ta205+ 10 Al ¨> 6 Ta + 5 A1203
¨>
Fe203+ 2 Al ¨> 2 Fe +A1203
3 Ba02 + 2 Al ¨> 3 Ba0 + A1203
[00112] The reactant powders were thoroughly dry (<0.2% L01) and
finely divided (85% by weight -200 mesh). The reactant powders were
individually
weighed and loaded into a double cone powder blender. The reactant powders
were
mixed in the blender for at least 20 minutes to provide a macroscopically
homogeneous reactant mixture. The reactant mixture was loaded into a reaction
vessel.
[00113] The
reaction vessel was cylindrically-shaped with an inside
height of 12-inches and an inside diameter of 4.25-inches. The reaction vessel
was
fabricated from an iso-molded fine-grained graphite sheet forming the bottom
of the
reaction vessel, and an extruded medium-to-coarse-grained graphite sheet
forming
the cylindrical sidewalls. The bottom and sidewalls were approximately 1-inch
thick.
The reaction vessel was positioned on top of a layer of refractory bricks, and
the
layer of refractory bricks was positioned on top of a concrete slab. A layer
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heavy/dead-burned magnesium oxide powder was spread over the bottom interior
surface of the reaction vessel and the reactant mixture was loaded on top of
the
magnesium oxide powder layer. The magnesium oxide powder layer formed a
barrier between the reactant mixture and the graphite bottom surface of the
reaction
vessel.
[00114] A tantalum ignition wire was submerged into the reactant
powder mixture in the reaction vessel. The ignition wire was connected to a
power
supply by aluminum wires. The alum inotherm ic reactions were initiated by
sending
an electrical current of 100 amps from the power supply through the ignition
wire for
five (5) seconds. The reactions proceeded very rapidly and the reaction
products
were allowed to cool to ambient temperature over a period of 48 hours. The
reaction
products comprised a well-defined and separated regulus and slag phase. The
reaction products were removed from the reaction vessel and weighed to
determine
total material recovery. The total material recovery was determined to be
3216.6
grams (99% of the 3248 grams of initial reactant powders).
[00115] The regulus and slag phase were separated and analyzed
for
chemical composition. Based on the stoichiometry of the chemical reactions,
and
assuming a complete yield, the theoretical alloy composition of the regulus
would be,
in percentages by weight, 1.2% aluminum, 6.8% iron, 1.8% tungsten, balance
.. tantalum (90.2%). The slag phase comprised approximately 32% barium oxide
and
68% aluminum oxide, on a mole basis, and small amounts of tantalum-containing
and iron-containing by-products. The tantalum yield in the regulus was 88% of
the
initial tantalum provided by the tantalum pentoxide reactant (on a metal
weight
basis).
[00116] The tantalum alloy regulus was monolithic, fully-consolidated,
and non-brittle. The tantalum alloy regulus could be directly input into an
electron
beam melting furnace for refinement of the tantalum alloy composition,
including
reduction of the aluminum and iron to incidental impurity levels, homogeneous
dissolution of the tungsten into the tantalum matrix, and establishment of a
tungsten
concentration within specification for Ta-2.5W.
- 39 -
[00117] The processes and equipment for the production of tantalum
alloys described in this specification provide operational and economic
advantages
over processes that use tantalum metal feed stocks. The processes described in
this
specification eliminate: (1) the need for relatively costly virgin sodium-
reduced
tantalum metal; (2) the costly HDH process; and (3) the pressing and sintering
operations needed to produce a powder compact for electron beam melting.
Referring
to Figures 1A and 1B, the use of the less expensive tantalum pentoxide
feedstock and
the elimination of a number of unit operations results in a shorter and less
expensive
process flow for the production of tantalum alloy ingots and mill
products. The processes described in this specification directly produce a
monolithic, fully-consolidated, and non-brittle tantalum alloy regulus that
may be readily
isolated from a separate slag phase and directly input into an electron beam
melting
furnace for refinement of the tantalum alloy composition. The tantalum alloy
reguli
produced according to the processes described in this specification also
comprise alloying elements completely dissolved into the tantalum matrix,
which
facilitates the direct electron beam melting and casting of tantalum alloy
ingots
having uniform microstructure, specified alloy composition, and alloying
elements
completely and uniformly distributed in the tantalum matrix.
[00118] This specification has been written with reference to
various
non-limiting and non-exhaustive embodiments. However, it will be recognized by
persons having ordinary skill in the art that various substitutions,
modifications, or
combinations of any of the disclosed embodiments (or portions thereof) may be
made
within the scope of this specification. Thus, it is contemplated and
understood that this
specification supports additional embodiments not expressly set forth
herein. Such embodiments may be obtained, for example, by combining,
modifying,
or reorganizing any of the disclosed steps, components, elements, features,
aspects,
characteristics, limitations, and the like, of the various non-limiting and
non-exhaustive
embodiments described in this specification. In this manner, Applicant
reserves the right
to amend the claims during prosecution to add features as variously described
in this
specification.
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CA 3012230 2022-01-31
