U.S. patent application number 12/915681 was filed with the patent office on 2011-03-24 for tantalum based alloy that is resistant to aqueous corrosion.
This patent application is currently assigned to H.C. Starck Inc.. Invention is credited to Paul R. Aimone, Evan Hinshaw.
Application Number | 20110067524 12/915681 |
Document ID | / |
Family ID | 39619394 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110067524 |
Kind Code |
A1 |
Aimone; Paul R. ; et
al. |
March 24, 2011 |
TANTALUM BASED ALLOY THAT IS RESISTANT TO AQUEOUS CORROSION
Abstract
A tantalum or tantalum alloy which contains pure or
substantially pure tantalum and at least one metal element selected
from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, Mo, W and Re
to form a tantalum alloy that is resistant to aqueous corrosion.
The invention also relates to the process of preparing the tantalum
alloy.
Inventors: |
Aimone; Paul R.;
(Bridgewater, MA) ; Hinshaw; Evan; (Hickory,
NC) |
Assignee: |
H.C. Starck Inc.
Newton
MA
|
Family ID: |
39619394 |
Appl. No.: |
12/915681 |
Filed: |
October 29, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12109765 |
Apr 25, 2008 |
|
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12915681 |
|
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60914474 |
Apr 27, 2007 |
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Current U.S.
Class: |
75/10.13 ;
420/427; 75/10.19; 75/10.65 |
Current CPC
Class: |
C22C 27/02 20130101;
C22B 34/24 20130101; C22B 9/22 20130101; C22B 9/20 20130101 |
Class at
Publication: |
75/10.13 ;
420/427; 75/10.19; 75/10.65 |
International
Class: |
C22C 1/02 20060101
C22C001/02; C22C 27/02 20060101 C22C027/02 |
Claims
1. A tantalum alloy which comprises pure or substantially pure
tantalum or a tantalum alloy and at least one metal element
selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, Mo, W
and Re to form a tantalum alloy that is resistant to aqueous
corrosion.
2. The tantalum alloy as claimed in claim 1, wherein the tantalum
alloy is Ta-3W.
3. The tantalum alloy as claimed in claim 2, wherein the metal
element is platinum.
4. The tantalum alloy as claimed in claim 2, wherein the metal
element is ruthenium or rhodium or palladium or osmium or
iridium.
5. The tantalum alloy as claimed in claim 2, wherein the metal
element is molybdenum or rhenium.
6. The tantalum alloy as claimed in claim 2, wherein the metal
element is present in an amount of less than 10,000 ppm in the
alloy.
7. The tantalum alloy as claimed in claim 2, wherein the metal
element is present in an amount of less than 5,000 ppm in the
alloy.
8. The tantalum alloy as claimed in claim 2, wherein the metal
element is present in an amount of less 2,000 ppm in the alloy.
9. The tantalum alloy as claimed in claim 3, wherein the metal
element is present in an amount of less 2,000 ppm in the alloy.
10. The tantalum alloy as claimed in claim 4, wherein the metal
element is present in an amount of less 2,000 ppm in the alloy.
11. The tantalum alloy as claimed in claim 4, wherein the metal
element is present in an amount of less 2,000 ppm in the alloy.
12. A process to produce the tantalum alloy as claimed in claim 1
which is resistant to aqueous corrosion, which comprises
microalloying pure or substantially pure tantalum and at least one
metal element selected from the group consisting of Ru, Rh, Pd, Os,
Ir, Pt, Mo, W and Re.
13. The process as claimed in claim 12, wherein the tantalum alloy
is Ta-3 W.
14. The process as claimed in claim 12, wherein the metal element
is platinum.
15. The process as claimed in claim 12, wherein the metal element
is ruthenium or rhodium or palladium or osmium or iridium.
16. The process as claimed in claim 12, wherein the metal element
is molybdenum or rhenium.
17. The process as claimed in claim 12, wherein the metal element
is present in an amount of less than 10,000 ppm in the alloy.
18. The process as claimed in claim 12, wherein the metal element
is present in an amount of less than 5,000 ppm in the alloy.
19. The process as claimed in claim 12, wherein the metal element
is present in an amount of less 2,000 ppm in the alloy.
20. The process as claimed in claim 13, wherein the metal element
is present in an amount of less 2,000 ppm in the alloy.
21. The process as claimed in clam 13, wherein the metal element is
present in an amount of at least 150 ppm in the alloy
22. The process as claimed in clam 12, wherein the alloy is made
using laser additive manufacturing (LAM), vacuum arc remelting
(VAR), electron beam melting (EBM), or plasma arc melting (PAM).
Description
RELATED APPLICATIONS
[0001] This application claims benefit to U.S. Provisional
Application Ser. No. 60/914,474 filed Apr. 27, 2007 which is
incorporated by reference in its entirety for all useful,
purposes.
FIELD OF THE INVENTION
[0002] The invention is directed to tantalum or tantalum based
alloys that are resistant to aqueous corrosion, more particularly
to corrosion from acids and resistant to hydrogen embrittlement.
The tantalum or tantalum based alloy has superior resistance to
hydrogen absorption (and subsequent hydrogen embrittlement) as
compared to pure tantalum and Ta-3W (referred to as "NRC76").
BACKGROUND OF THE INVENTION
[0003] Pure tantalum and tantalum alloys begin to become
significantly hydrogen embrittled at hydrogen concentrations
greater than 100 ppm. In the chemical processing industry (CPI),
pure tantalum will absorb hydrogen and become embrittled when
exposed to hot HCl and hot H.sub.2SO.sub.4 at conditions
illustrated in FIGS. 2 and 3. Ta-3W has demonstrated better
resistance to hydrogen absorption than pure tantalum. Where
tantalum and tantalum alloys are used in the CPI to contain very
hot and concentrated acids, hydrogen embrittlement, rather than a
loss of wall thickness due to corrosion, is the predominant failure
mechanism.
[0004] U.S. Pat. No. 4,784,830 discloses that oxidation resistance
of alloys can be improved by a controlled addition and retention of
nitrogen. Put another way, it has been discovered that the
microstructure of the alloys of the type under consideration,
notably grain size, can be controlled or rendered relatively
structurally stable over extended periods at elevated temperature
through a microalloying addition of nitrogen. In addition, and most
advantageously, a special ratio of silicon to titanium should be
observed in seeking extended service life as will be shown
herein.
[0005] U.S. Pat. No. 3,592,639 relates to a ternary Ta--W alloy
which contains from 1.5 to 3.5 percent of tungsten. Niobium can
also be present in the alloy from 0.05 to 0.5 weight percent.
Molybdenum is limited to 0.5% maximum (less than 5000 p.p.m.) to
promote smaller grain size in the alloy.
[0006] U.S. Pat. No. 4,062,679 claims a wrought tantalum product
of, substantially pure tantalum containing less than 300 parts per
million of columbium, less than 200 parts per million of iron,
chromium and nickel combined, less than 50 parts per million of
tungsten, less than 10 parts per million of molybdenum, less than
30 parts per million of chromium, and less than 20 parts per
million of calcium, the improvement which comprises the inclusion
of from about 50 to about 700 parts per million of silicon in the
composition of said product whereby said product is improved in
resistance to embrittlement when exposed to elevated temperatures
in an oxygen-containing environment.
SUMMARY OF THE INVENTION
[0007] The inve ntion relates to a process of improving hydrogen
embrittlement resistance by microalloying at least one metal
element selected from the group consisting of Ru, Rh, Pd, Os, Ir,
Pt, Mo, W and Re with a pure or substantially pure tantalum or a
tantalum alloy.
[0008] One preferred embodiment of this invention would add
platinum to NRC76. The chemical process industry is seeking new
tantalum alloys that will permit greater operating temperatures in
their process equipment.
[0009] An object of the invention is to have an improved tantalum
alloy which is more resistant to aqueous corrosion and hydrogen
embrittlement.
[0010] At antalum alloy which comprises pure or substantially pure
tantalum or a tantalum alloy and at least one metal element
selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, Mo, W
and Re to form a tantalum alloy that is resistant to aqueous
corrosion.
[0011] The metal element(s) can be in an amount up to the
solubility limit of metal in the tantalum.
BRIEF DESCRIPTION OF THE FIGURES
[0012] FIG. 1 illustrates the addition of molybdenum since it has
the same crystal structure, a similar lattice parameter, and
complete solid solubility in both tantalum and tungsten.
[0013] FIG. 2 illustrates the conditions for the chemical
processing industry that pure tantalum will absorb hydrogen and
become embrittled when exposed to hot HCl.
[0014] FIG. 3 illustrates the conditions for the chemical
processing industry that pure tantalum will absorb hydrogen and
become embrittled when exposed to hot H.sub.2SO.sub.4.
[0015] FIG. 4 illustrates the results for corrosion rate and
hydrogen enrichment after short term corrosion tests in
hydrochloric acid.
[0016] FIG. 5 illustrates the results for corrosion rate and
hydrogen enrichment after long term corrosion tests in hydrochloric
acid.
[0017] FIG. 6 illustrates the results for corrosion rate and
hydrogen enrichment after long term corrosion tests in sulfur
acid.
DETAILED DESCRIPTION OF THE INVENTION
[0018] As used herein, the singular terms "a" and "the" are
synonymous and used interchangeably with "one or more."
Accordingly, for example, reference to "a metal" herein or in the
appended claims can refer to a single metal or more than one metal.
Additionally, all numerical values, unless otherwise specifically
noted, are understood to be modified by the word "about."
[0019] A tantalum or tantalum based alloy that is resistant to
aqueous corrosion, more particularly to corrosion from acids and
resistant to hydrogen embrittlement. The starting tantalum is pure
or substantially pure. Substantially pure tantalum would be a
tantalum alloy which has up to about 11% by weight of non-tantalum
components.
[0020] The tantalum or tantalum based alloys are preferably
prepared using a vacuum melting process. Vacuum arc remelting
(VAR), electron beam melting (EBM) or plasma arc melting (PAM) are
methods of vacuum melting that can also be used for alloying. To
formulate the actual alloy, at least one element selected from the
group consisting of ruthenium, rhodium, palladium, osmium, iridium,
platinum, molybdenum, tungsten, and ruthenium (Ru, Rh, Pd, Os, Ir,
Pt, Mo, W and Re) are added to the pure tantalum material or
substantially pure tantalum material or tantalum alloy using one of
the vacuum melting processes listed above. The tantalum alloy
preferably contains tungsten with platinum, molybdenum or rhenium
or mixtures thereof. Although it is noted that VAR, EBM or PAM
could all be used.
[0021] The preferred technique would be VAR.
[0022] Alternative embodiments of this invention could include
adding elements other than the elements listed above that improve
the corrosion and hydrogen embrittlement resistance. These
additional elements could include yttrium, gold, cerium,
praseodymium, neodymium, and thorium.
[0023] Each of the metals would preferably be less than 10,000 ppm
of the alloy, preferably less than 5,000 ppm of the total amount of
the alloy and more preferably less 2,000 ppm of the total amount of
alloy. The metal preferably would be added in an amount of at least
50 ppm, preferably at least 100 ppm, preferably at least 150 ppm,
preferably at least 200 ppm and preferably at least 250 ppm.
[0024] Examples of tantalum alloys that contain at least 89%
tantalum include, but are not limited to Ta-3W (tantalum-tungsten)
contains at about 3% tungsten), Ta-3W--Pt (tantalum-tungsten and
platinum alloy) which contains about 3% tungsten), the tantalum
Ta-3W--Mo (tantalum-tungsten and molybdenum alloy) which contains
about 3% tungsten), and Ta-3 W--Re alloys (tantalum-tungsten and
rhenium alloy) which contains about 3% tungsten). The Ta-3W--Pt,
Ta-3W--Mo and Ta-3W--Re would be formulated and manufactured in a
manner similar that used to make Ta-3W alloys. The alloys are
preferably made by microalloying the other metals with the Ta-3W
(tantalum-tungsten) alloy.
[0025] The addition of platinum would be the most preferred
embodiment since platinum has the greatest number of free electrons
to theoretically pull in additional oxygen atoms to close the holes
in the Ta.sub.2O.sub.5 oxide layer and/or provide sites of low
hydrogen overvoltage thereby stabilizing the Ta.sub.2O.sub.5 oxide
layer.
[0026] Another preferred embodiment would use the addition of
ruthenium, rhodium, palladium, osmium, and iridium (also known as
"platinum group metals, PGM) which also would provide sites of low
hydrogen overvoltage thereby stabilizing the Ta.sub.2O.sub.5 oxide
layer.
[0027] Still another preferred embodiment would use the addition of
molybdenum since it has the same crystal structure, a similar
lattice parameter, and complete solid solubility in both tantalum
and tungsten. This is shown in Table I and FIG. 1.
TABLE-US-00001 TABLE I Crystal Structure and Lattice Parameters for
Refractory Elements Lattice Parameter Element Symbol Crystal
Structure (.ANG.) Tantalum Ta body centered cubic (bcc) 3.296
Tungsten W body centered cubic (bcc) 3.16 Molybdenum Mo body
centered cubic (bcc) 3.15 Platinum Pt face centered cubic (fcc)
3.931 Rhenium Re hexagonal close packed (hcp) a = 2.761, c =
4.458
[0028] Another preferred embodiment would use the addition of
rhenium since rhenium has the same crystal structure and a similar
lattice parameter to tantalum and tungsten.
[0029] Tantalum ingots formulated using VAR or PAM would then be
used to produce plate, sheet, and tube products in a manner similar
to that used to manufacture these same products from pure tantalum
or Ta-3W alloy.
[0030] The plate, sheet, and tube products manufactured using the
Ta-3W--Mo, Ta-3W--Re, or Ta-3W--Pt alloys would be used in a manner
identical to that for from pure tantalum or Ta-3W alloys.
[0031] The advantages of the new alloys would be superior corrosion
and hydrogen embrittlement resistance over pure Ta-3W. The addition
of platinum would be the preferred embodiment since platinum has
the greatest number of free electrons to theoretically pull in
additional oxygen atoms and help close the holes in the
Ta.sub.2O.sub.5 oxide layer and/or provide sites of low hydrogen
overvoltage thereby stabilizing the Ta.sub.2O.sub.5 oxide
layer.
[0032] Samples were made using either a laser additive
manufacturing (LAM) or traditional vacuum arc remelting (VAR)
techniques. In the former technique, tantalum, tungsten, and
platinum powders were blended together in the desire composition
and then melted using and consolidated using a laser under inert
conditions. In these samples, the final tantalum alloy contained
2.8 weight percent tungsten with 500 ppm platinum. In the latter
technique, tantalum and platinum powders were blended together in
the desire composition, pressed into a powder leech, and welded to
the side of an NRC76 bar (this assembly herein referred to as the
"electrode"). The electrode was then melted using traditional
vacuum arc remelting (VAR) techniques. In these samples, the final
tantalum alloy contained 2.8 weight percent tungsten with up to
10,000 ppm platinum.
[0033] Corrosion tests in hydrochloric and sulfuric acids were
conducted for up to a four month time period. The platinum modified
alloy had a corrosion rate that was always lower than NRC76 with
almost no hydrogen enrichment.
[0034] FIG. 4 shows the results for short term corrosion tests in
hyrdrochloric acid. The platinum containing alloys have a
significantly lower corrosion rate than the NRC76 alloy. This
corrosion rate is reduced from approximately 16 mils per year (mpy)
for NRC76 to less than 4 mpy when platinum concentrations exceed
approximately 1000 ppm. In addition, the hydrogen concentration
after testing has dropped from 291 ppm to less than 4 ppm when when
platinum concentrations are between approximately 1000 ppm to
10,000 ppm.
[0035] FIG. 5 shows the results for long term corrosion tests in
hyrdrochloric acid. The platinum containing alloys had a corrosion
rate that was three times lower than the NRC76 alloy when platinum
concentrations exceed approximately 1000 ppm. In addition, the
hydrogen concentration after testing has dropped from 756 ppm to
less than 10 ppm when when platinum concentrations were greater
than approximately 1000 ppm.
[0036] FIG. 6 shows the results for long term corrosion tests in
sulfuric acid. The platinum containing alloys have a significantly
lower corrosion rate than the NRC76 alloy. This corrosion rate is
reduced from approximately 9.2 mils per year (mpy) for NRC76 to
less than 4 mpy when platinum concentrations exceed approximately
1500 ppm. In addition, the hydrogen concentration after testing has
dropped from 9 ppm to less than 2 ppm when when platinum
concentrations were greater than approximately 1000 ppm.
[0037] All the references described above are incorporated by
reference in its entirety for all useful purposes.
[0038] While there is shown and described certain specific
structures embodying the invention, it will be manifest to those
skilled in the art that various modifications and rearrangements of
the parts may be made without departing from the spirit and scope
of the underlying inventive concept and that the same is not
limited to the particular forms herein shown and described.
* * * * *