U.S. patent number RE45,899 [Application Number 12/507,605] was granted by the patent office on 2016-02-23 for low temperature, extrudable, high density reactive materials.
This patent grant is currently assigned to Orbital ATK, Inc.. The grantee listed for this patent is Daniel B. Nielson, Nikki Rasmussen, Richard M. Truitt. Invention is credited to Daniel B. Nielson, Nikki Rasmussen, Richard M. Truitt.
United States Patent |
RE45,899 |
Nielson , et al. |
February 23, 2016 |
Low temperature, extrudable, high density reactive materials
Abstract
A reactive material for use as a reactive liner in penetrating
(shape-charge) warheads and for use in reactive fragments in
fragmenting warheads is disclosed. The reactive material comprises
an oxidizing agent and a metal filler or metal/metal oxide filler.
The oxidizing agent comprises a fluoropolymer having high fluorine
content, a low melt temperature, and a high mechanical strength.
Preferably, the fluoropolymer is a thermoplastic fluoropolymer,
such as a polymer of tetrafluoroethylene, hexafluoropropylene, and
vinylidene fluoride. The metal filler comprises a high density,
reactive metal. Preferably, the metal filler is hafnium or
tantalum. The reactive material is safely processed at temperatures
significantly below the thermal autoignition point of the reactive
material.
Inventors: |
Nielson; Daniel B. (Tremonton,
UT), Truitt; Richard M. (Champlin, MN), Rasmussen;
Nikki (Logan, UT) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nielson; Daniel B.
Truitt; Richard M.
Rasmussen; Nikki |
Tremonton
Champlin
Logan |
UT
MN
UT |
US
US
US |
|
|
Assignee: |
Orbital ATK, Inc. (Plymouth,
MN)
|
Family
ID: |
55314854 |
Appl.
No.: |
12/507,605 |
Filed: |
July 22, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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09789479 |
Jul 15, 2003 |
6593410 |
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60368284 |
Mar 28, 2002 |
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60184316 |
Feb 23, 2000 |
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Reissue of: |
10386617 |
Mar 12, 2003 |
6962634 |
Nov 8, 2005 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F42B
12/32 (20130101); C08K 3/08 (20130101); C06B
27/00 (20130101); C09D 127/18 (20130101); F42B
1/032 (20130101); C08K 3/08 (20130101); C08L
27/12 (20130101); C09D 127/18 (20130101); C08K
3/08 (20130101) |
Current International
Class: |
C06B
45/10 (20060101); C06B 27/00 (20060101); F42B
1/032 (20060101); F42B 12/32 (20060101) |
Field of
Search: |
;502/211 |
References Cited
[Referenced By]
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|
Primary Examiner: Lopez; Carlos
Attorney, Agent or Firm: TraskBritt
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
.[.This.]. .Iadd.The present application is a reissue of U.S. Pat.
No. 6,962,634, issued Nov. 8, 2005. The present
.Iaddend.application claims the benefit of U.S. Provisional Patent
Application Ser. No. 60/368,284, filed Mar. 28, 2002, for LOW
TEMPERATURE EXTRUDABLE, HIGH DENSITY REACTIVE MATERIALS.
.Iadd.Additionally, this application is a continuation-in-part of
U.S. patent application Ser. No. 09/789,479, filed Feb. 21, 2001,
now U.S. Pat. No. 6,593,410, issued Jul. 15, 2003, for HIGH
STRENGTH REACTIVE MATERIALS, which claims the benefit of U.S.
Provisional Patent Application Ser. No. 60/184,316, filed Feb. 23,
2000..Iaddend.
.Iadd.The present application is also related to U.S. Provisional
Application No. 60/184,316, filed Feb. 23, 2000, entitled "High
Strength Reactive Materials," now abandoned; U.S. Pat. No.
6,593,410, issued Jul. 15, 2003, entitled "High Strength Reactive
Materials;" U.S. Pat. No. 7,307,117, issued Dec. 11, 2007, entitled
"High Strength Reactive Materials And Methods Of Making;" U.S.
patent application Ser. No. 10/801,946, filed Mar. 15, 2004,
entitled "Reactive Compositions Including Metal," now abandoned;
U.S. patent application Ser. No. 11/620,205, filed Jan. 5, 2007,
entitled "Reactive Compositions Including Metal," now U.S. Pat. No.
8,075,715, issued Dec. 13, 2011; U.S. Pat. No. 8,361,258, issued
Jan. 29, 2013, entitled "Reactive Compositions Including Metal;"
U.S. Provisional Application No. 60/553,430, filed Mar. 15, 2004,
entitled "Reactive Material Enhanced Projectiles and Related
Methods," now abandoned; U.S. Pat. No. 7,603,951, issued Oct. 20,
2009, entitled "Reactive Material Enhanced Projectiles and Related
Methods;" U.S. patent application Ser. No. 10/801,948, filed Mar.
15, 2004, entitled "Reactive Material Enhanced Munition
Compositions and Projectiles Containing Same," now abandoned; U.S.
patent application Ser. No. 12/127,627, filed May 27, 2008,
entitled "Reactive Material Enhanced Munition Compositions and
Projectiles Containing Same," now U.S. Pat. No. 8,568,541, issued
Oct. 29, 2013; U.S. patent application Ser. No. 14/062,635, filed
Oct. 24, 2013, entitled "Reactive Material Compositions and
Projectiles Including the Same;" U.S. Provisional Application No.
60/723,465, filed Oct. 4, 2005, entitled "Reactive Material
Enhanced Projectiles And Related Methods," now abandoned; U.S.
patent application Ser. No. 11/538,763, filed Oct. 4, 2006,
entitled "Reactive Material Enhanced Projectiles And Related
Methods," now U.S. Pat. No. 8,122,833, issued Feb. 28, 2012; U.S.
patent application Ser. No. 13/372,804, filed Feb. 14, 2012,
entitled "Reactive Material Enhanced Projectiles and Related
Methods;" U.S. Pat. No. 7,614,348, issued Nov. 10, 2009, entitled
"Weapons And Weapon Components Incorporating Reactive Materials And
Related Methods;" U.S. patent application Ser. No. 11/697,005,
filed Apr. 5, 2007, entitled "Consumable Reactive Material
Fragments, Ordnance Incorporating Structures For Producing The
Same, And Methods Of Creating The Same," pending; and U.S. patent
application Ser. No. 11/690,016, filed Mar. 22, 2007, entitled
"Reactive Material Compositions, Shot Shells Including Reactive
Materials, and a Method of Producing Same," now U.S. Pat. No.
7,977,420, issued Jul. 12, 2011..Iaddend.
Claims
What is claimed is:
1. A composition for a reactive material, .[.comprising.].
.Iadd.consisting of.Iaddend.: .[.an oxidizing agent comprising.]. a
fluoropolymer selected from the group consisting of a thermoplastic
terpolymer of tetrafluoroethylene, hexafluoropropylene, and
vinylidene fluoride, a thermoplastic copolymer of
tetrafluoroethylene and perfluorovinylether, a thermoplastic
copolymer of tetrafluoroethylene and ethylene, and a thermoplastic
copolymer of tetrafluoroethylene and hexafluoropropylene; and at
least one metal filler.Iadd., the fluoropolymer present in the
composition at from approximately 15% by weight to approximately
90% by weight.Iaddend..
.[.2. The composition of claim 1, wherein the fluoropolymer is
present in the reactive material at approximately 15-90% by
weight..].
3. The composition of claim 1, wherein the fluoropolymer is present
in the .[.reactive material.]. .Iadd.composition .Iaddend.at
.Iadd.from approximately 25% by weight to .Iaddend.approximately
.[.25-75%.]. .Iadd.75% .Iaddend.by weight.
4. The composition of claim 1, wherein the oxidizing agent has a
fluorine content of greater than approximately 45% by weight.
5. The composition of claim 1, wherein the at least one metal
filler comprises a metal having a density approximately equal to or
greater than the density of magnesium.
6. The composition of claim 1, wherein the at least one metal
filler is present in the .[.reactive material.]. .Iadd.composition
.Iaddend.at .Iadd.from approximately 10% by weight to
.Iaddend.approximately .[.10-85%.]. .Iadd.85% .Iaddend.by
weight.
7. The composition of claim 1, wherein the at least one metal
filler is selected from the group consisting of magnesium,
aluminum, magnesium/aluminum alloys, iron, copper, zirconium,
titanium, zinc, manganese, tin, boron, silicon, hafnium, tungsten,
depleted uranium, and tantalum, and metal carbides, oxides, and
nitrides thereof.
8. The composition of claim 1, wherein the at least one metal
filler is a metal/metal oxide thermite or a metal/metal
intermetallic.
9. The composition of claim 1, wherein a processing temperature of
the reactive material is substantially below a thermal autoignition
temperature of the reactive material.
10. An article .[.comprising a liner formed from a reactive
material, the reactive material.]., comprising: .Iadd.a reactive
material liner consisting of:.Iaddend. .[.an oxidizing agent
comprising.]. a fluoropolymer selected from the group consisting of
a thermoplastic terpolymer of tetrafluoroethylene,
hexafluoropropylene, and vinylidene fluoride, a thermoplastic
copolymer of tetrafluoroethylene and perfluorovinylether, a
thermoplastic copolymer of tetrafluoroethylene and ethylene, and a
thermoplastic copolymer of tetrafluoroethylene and
hexafluoropropylene; and at least one metal filler.Iadd., the
fluoropolymer present in the reactive material liner at from
approximately 15% by weight to approximately 90% by
weight.Iaddend..
11. The article of claim 10, wherein the at least one metal filler
comprises a metal having a density approximately equal to or
greater than the density of magnesium.
12. The article of claim 10, wherein the at least one metal filler
is selected from the group consisting of magnesium, aluminum,
magnesium/aluminum alloys, iron, copper, zirconium, titanium, zinc,
manganese, tin, boron, silicon, hafnium, tungsten, depleted
uranium, and tantalum, and metal carbides, oxides, and nitrides
thereof.
13. The article of claim 10, wherein the at least one metal filler
is a metal/metal oxide thermite or a metal/metal intermetallic.
14. The article of claim 10, wherein the at least one metal filler
is present in the reactive material at approximately 10-85% by
weight.
15. The article of claim 10, wherein a processing temperature of
the reactive material is substantially below a thermal autoignition
temperature of the reactive material.
.[.16. The article of claim 10, wherein the fluoropolymer is
present in the reactive material at approximately 15-90% by
weight..].
17. The ice of claim 10, wherein the fluoropolymer is present in
the reactive material at approximately 25-75% by weight.
18. A method of processing a reactive material, comprising: mixing
at least one metal filler with .[.an oxidizing agent.]. .Iadd.a
fluoropolymer .Iaddend.to form a reactive material .Iadd.consisting
of the at least one metal filler and the fluoropolymer.Iaddend.,
the .[.oxidizing agent comprising a.]. fluoropolymer selected from
the group consisting of a thermoplastic terpolymer of
tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride,
a thermoplastic copolymer of tetrafluoroethylene and
perfluorovinylether, a thermoplastic copolymer of
tetrafluoroethylene and ethylene, and a thermoplastic copolymer of
tetrafluoroethylene and hexafluoropropylene.Iadd., and the
fluoropolymer present in the reactive material at from
approximately 15% by weight to approximately 90% by
weight.Iaddend.; and processing the reactive material at a
temperature that does not exceed a thermal autoignition temperature
of the reactive material.
19. The method of claim 18, wherein mixing at least one metal
filler with an oxidizing agent comprises mixing the at least one
metal filler selected from the group consisting of magnesium,
aluminum, magnesium/aluminum alloys, iron, copper, zirconium,
titanium, zinc, manganese, tin, boron, silicon, hafnium, tungsten,
depleted uranium, and tantalum, and metal carbides, oxides, and
nitrides thereof, with the oxidizing agent.
20. The method of claim 18, wherein mixing at least one metal
filler with an oxidizing agent comprises mixing at least one
metal/metal oxide with the oxidizing agent.
.[.21. A method of processing a reactive material, comprising:
mixing a metal filler with an oxidizing agent to form a reactive
material, the oxidizing agent comprising a fluoropolymer selected
from the group consisting of a thermoplastic terpolymer of
tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride,
a thermoplastic copolymer of tetrafluoroethylene and
perfluorovinylether, a thermoplastic copolymer of
tetrafluoroethylene and ethylene, and a thermoplastic copolymer of
tetrafluoroethylene and hexafluoropropylene; and processing the
reactive material at a temperature substantially below a thermal
autoignition point of the reactive material..].
22. An artillery projectile .[.comprising a liner formed from a
reactive material, the reactive material.]..Iadd.,
.Iaddend.comprising: .[.an oxidizing agent comprising a
fluoropolymer selected from the group consisting of a thermoplastic
terpolymer of tetrafluoroethylene, hexafluoropropylene, and
vinylidene fluoride, a thermoplastic copolymer of
tetrafluoroethylene and perfluorovinylether, a thermoplastic
copolymer of tetrafluoroethylene and ethylene, and a thermoplastic
copolymer of tetrafluoroethylene and hexafluoropropylene; and at
least one metal filler.]. .Iadd.a reactive material liner
consisting of:.Iaddend. .Iadd.a fluoropolymer selected from the
group consisting of a thermoplastic terpolymer of
tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride,
a thermoplastic copolymer of tetrafluoroethylene and
perfluorovinylether, a thermoplastic copolymer of
tetrafluoroethylene and ethylene, and a thermoplastic copolymer of
tetrafluoroethylene and hexafluoropropylene; and at least one metal
filler, the fluoropolymer present in the reactive material liner at
from approximately 15% by weight to approximately 90% by
weight.Iaddend..
23. A warhead .[.comprising fragments or a liner formed from a
reactive material, the reactive material.]..Iadd.,
.Iaddend.comprising: .[.an oxidizing agent comprising a
fluoropolymer selected from the group consisting of a thermoplastic
terpolymer of tetrafluoroethylene, hexafluoropropylene, and
vinylidene fluoride, a thermoplastic copolymer of
tetrafluoroethylene and perfluorovinylether, a thermoplastic
copolymer of tetrafluoroethylene and ethylene, and a thermoplastic
copolymer of tetrafluoroethylene and hexafluoropropylene; and at
least one metal filler.]. .Iadd.reactive material fragments or a
reactive material liner, the reactive material fragments or the
reactive material liner consisting of: a fluoropolymer selected
from the group consisting of a thermoplastic terpolymer of
tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride,
a thermoplastic copolymer of tetrafluoroethylene and
perfluorovinylether, a thermoplastic copolymer of
tetrafluoroethylene and ethylene, and a thermoplastic copolymer of
tetrafluoroethylene and hexafluoropropylene; and at least one metal
filler, the fluoropolymer present in the reactive material
fragments or the reactive material liner at from approximately 15%
by weight to approximately 90% by weight.Iaddend..
24. A warhead for use in a projectile, comprising: a case; an
explosive material; an initiator; and a liner or fragments, the
liner or fragments formed from a reactive material .[.comprising.].
.Iadd.consisting of .Iaddend.at least one metal filler and .[.an
oxidizing agent, wherein the oxidizing agent comprises a.].
.Iadd.from approximately 15% by weight to approximately 90% by
weight of a fluoropolymer, the .Iaddend.fluoropolymer selected from
the group consisting of a thermoplastic terpolymer of
tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride,
a thermoplastic copolymer of tetrafluoroethylene and
perfluorovinylether, a thermoplastic copolymer of
tetrafluoroethylene and ethylene, and a thermoplastic copolymer of
tetrafluoroethylene and hexafluoropropylene.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a reactive material suitable
for use as a shape-charge liner in a penetrating warhead and in
reactive fragments in a fragmentary warhead. More specifically, the
invention relates to a reactive material comprising a fluoropolymer
and a metal filler. This reactive material is capable of being
safely processed at temperatures significantly below the thermal
autoignition point of the reactive material.
2. State of the Art
A penetrating warhead 2 used in a projectile or missile typically
comprises a case 4, an explosive material 6, an initiator, and a
liner 8, as shown in FIG. 1A. The case 4 is generally a cylindrical
tube comprised of steel, plastic, or a composite material. At least
a portion of the case 4 is typically filled with the explosive
material 6. When the explosive material 6 in the warhead 2 is
detonated, the liner 8 forms a high-velocity jet that has a high
kinetic energy capable of penetrating solid objects, such as a
target. The liner 8 is formed from a solid material that is formed
into a jet responsive to detonation of the explosive charge. The
liner material is typically a high density, ductile material, such
as a metal, a metal alloy, a ceramic, or a glass. The metals
commonly used in liners include copper, aluminum, depleted uranium,
tungsten, or tantalum. In addition to penetrating warheads 2,
fragmentary warheads 10 are commonly used. As illustrated in FIG.
1B, the fragmentary warhead 10 typically comprises fragments 12 of
material that are projected at a target upon detonation of the
explosive material 6 of the warhead 10. The fragments 12 must be
able to withstand the explosive force of the detonation, otherwise
the force commonly breaks up the fragments, thereby reducing their
ability to penetrate the target.
Depending on the mechanical strength characteristics of the target,
penetration by the liner 8 or fragments 12 may heavily damage or
destroy the target. However, if the target is an armored vehicle or
other heavily armored target, the liner 8 or fragments 12 may not
cause the desired degree of damage. To improve the destructive
capability of the warhead, the liner 8 or fragments 12 may be
provided with the ability to produce secondary reactions that cause
additional damage. These secondary reactions commonly include
incendiary reactions. As disclosed in U.S. Pat. No. 4,807,795 to
LaRocca et al., pyrophoric metals are added to the liner to provide
the desired incendiary effects. In LaRocca et al., a double-layered
liner is disclosed, where a layer of dense metal provides the
penetration ability and a layer of light metal, such as aluminum or
magnesium, produces the incendiary effects.
While metals have been commonly used in liners, reactive materials
have also been used. As known in the art and used herein, the term
"reactive material" refers to a material comprising a metal that
reacts with an oxidizing agent. Upon impact with a target, the
reactive material of the liner produces a high burst of energy. A
known reactive material includes an aluminum and
polytetrafluoroethylene ("PTFE") material, referred to herein as an
"Al/PTFE" reactive material. PTFE is available from DuPont under
the tradename TEFLON.RTM.. PTFE has the highest fluorine content of
all fluoropolymers, is the most resistant fluoropolymer to chemical
attack, and requires high processing temperatures to achieve its
maximum strength. PTFE is used in reactive materials because its
high fluorine content makes it a strong oxidizing agent. The
Al/PTFE reactive material has good penetration ability in light
armor or thin-skinned targets, such as aircraft, due to the density
of the aluminum. The Al/PTFE reactive material also provides
incendiary reactions because the reactive material ignites upon
penetration into the target.
To form Al/PTFE high strength components, such as reactive
fragments 12 for fragmentary warheads 10, the reactive material is
pressed into billets or pressed preforms. The pressed preforms are
then sintered and annealed at high temperatures, typically
350-390.degree. C. Due to PTFE's high melting temperature of
342.degree. C., these high sintering temperatures are necessary to
form reactive materials using PTFE. The currently preferred
technique for forming Al/PTFE fragments comprises blending the PTFE
and aluminum in a solvent. The solution of Al/PTFE is spread on a
tray and dried in an oven. The dried composition is then
conditioned to 185.degree. F. and pressed in a 185.degree. F.
heated die. The pressed preform is then heated to 350-390.degree.
C. for sintering. Since the PTFE is highly viscous at this
temperature range, it maintains its approximate shape. The sintered
preform is then cooled at a set rate to minimize cracking and
maximize the mechanical properties of the Al/PTFE reactive
material. The mechanical properties of the Al/PTFE reactive
material are inversely related to the degree of crystallinity in
the PTFE. In general, high crystallinity in the PTFE results in low
tensile strength and high elongation. The current processing
techniques available to form high strength components from Al/PTFE
are limited due to PTFE's high viscosity at the 350-390.degree. C.
temperatures required for sintering.
To further increase the penetration ability of warheads, reactive
materials comprising PTFE and metals with a higher density than
aluminum have been produced. These higher density metals included
tantalum and tungsten, which are more chemically reactive with PTFE
at the sinter temperatures than aluminum. These Ta/PTFE and W/PTFE
reactive materials were processed, using the same conditions as the
Al/PTFE reactive material, to form 3.5-inch diameter and 1-inch
diameter pucks. However, under these reaction conditions, the
Ta/PTFE and W/PTFE reactive materials exhibited undesirable grain
cracking resulting from volatile chemical reactions during the
sintering process. The tungsten and tantalum reacted with trace
amounts of hydrofluoric acid ("HF") present at the temperatures
used during the sintering process to produce highly volatile
reaction products. The Ta/PTFE reactive material formed volatile
tantalum fluoride compounds that were extremely exothermic.
Accelerated Rate calorimetry ("ARC") testing of the Ta/PTFE
material revealed an exotherm that occurred at only a few degrees
higher than the sintering temperature. This exotherm occurred at
375.degree. C. In addition, the strong exothermic reaction caused
the Ta/PTFE reactive material to autoignite at 307.degree. C.
during an experimental sinter cycle. The W/PTFE reactive material
off-gassed during the sintering process due to the formation of
highly volatile tungsten fluoride compounds (such as WF.sub.6 and
WOF.sub.4) that caused severe cracking of the pressed preforms.
These highly exothermic reactions raised concerns regarding the
safety of processing the Ta/PTFE reactive materials at the high
temperatures necessary to process PTFE. The highly exothermic
reactions also raised concerns regarding the quality of the W/PTFE
reactive materials due to the observed cracking.
Reactive materials comprising a metal and a fluoropolymer have also
been used in military pyrotechnics. In U.S. Pat. No. 5,886,293 to
Nauflett et al., a process of producing energetic materials for use
in military pyrotechnics is disclosed. The energetic material
comprises a magnesium fluoropolymer, specifically
magnesium/TEFLON.RTM./Viton.RTM. ("MTV"). Viton.RTM. is a copolymer
of vinylidenefluoride-hexafluoropropylene. The resulting energetic
material is used to produce rocket motor igniters and aircraft
decoy flares.
In light of the processing and safety problems associated with
Ta/PTFE and W/PTFE reactive materials, it would be highly desirable
to develop a reactive material having a high penetration ability
that can be safely processed at temperatures lower than the
350-390.degree. C. temperatures required to process PTFE. Ideally,
the desired reactive material would be processed at temperatures
below the autoignition temperature at which volatile metal fluoride
compounds form.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a reactive material comprising at
least one metal filler and an oxidizing agent. The oxidizing agent
comprises a fluoropolymer having a high fluorine content, a low
melt temperature, and a high mechanical strength. Preferably, the
fluoropolymer is a thermoplastic fluoropolymer, such as a polymer
of tetrafluoroethylene, hexafluoropropylene, and vinylidene
fluoride. The metal filler comprises a high density, reactive
metal, such as hafnium, tantalum, magnesium, titanium, tungsten,
aluminum, magnesium/aluminum alloys, or zirconium. The metal filler
may be a metal/metal oxide filler or an intermetallic filler. The
reactive material is processed at temperatures significantly below
the thermal autoignition point of the reactive material.
The present invention also relates to an article, such as a
warhead, comprising the reactive material.
In addition, the present invention relates to a method of safely
processing a reactive material. The method comprises mixing at
least one metal filler with an oxidizing agent to form the reactive
material. The reactive material is then processed at a temperature
below the thermal autoignition point of the reactive material.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing
out and distinctly claiming that which is regarded as the present
invention, the advantages of this invention can be more readily
ascertained from the following description of the invention when
read in conjunction with the accompanying drawings in which:
FIGS. 1A and 1B schematically illustrate a penetrating warhead and
a fragmentary head;
FIG. 2 shows ARC temperature and pressure v. time plots for a step
heat run performed on a composition of Ta/THV 220;
FIG. 3 shows ARC temperature and pressure v. time plots for a
250.degree. C./24 hour isothermal age run performed on a
composition of Ta/THV 220;
FIGS. 4 and 5 show ARC temperature and pressure v. time plots for a
200.degree. C./24 hour isothermal age run performed on different
sample sizes of a composition of Ta/THV 220;
FIG. 6 shows ARC temperature and pressure v. time plots for a step
heat run performed on a composition of Hf/THV 220;
FIG. 7 shows ARC self-heat rate v. temperature plots for a step
heat run performed on a composition of Hf/THV 220; and
FIG. 8 shows thermal stability results for a 200.degree. C./24 hour
isothermal age run performed on a composition of Hf/THV 220.
DETAILED DESCRIPTION OF THE INVENTION
The reactive material of the present invention may be used as a
reactive liner 8 in penetrating (shape-charge) warheads 2 and in
high strength reactive fragments 12 in fragmentary warheads 10, as
illustrated in FIGS. 1A and 1B. The reactive material comprises an
oxidizing and at least one metal filler and may be safely processed
at temperatures significantly below the thermal autoignition point
of the reactive material. The reactive fragments 12 and reactive
liners 8 are able to penetrate solid targets and produce incendiary
effects after the fragments/liners have penetrated the target,
thereby increasing the destructive effect of the warheads.
The oxidizing agent may provide strength to the reactive material
so that the reactive material survives detonation of the warhead.
In addition, the oxidizing agent may be a strong oxidizer so that
secondary reactions, such as incendiary reactions, occur when the
reactive material penetrates its target. The incendiary reactions
may also be due to afterburning of the metal filler, which is
caused by a reaction between the metal filler and atmospheric
oxygen. The oxidizing agent may accelerate the rate of metal
filler/atmospheric oxygen reaction. Preferably, the oxidizing agent
is a fluoropolymer or fluoroelastomer with a high fluorine content,
a low melt temperature, and a high mechanical strength. More
preferably, the oxidizing agent is a thermoplastic
fluoropolymer.
The high mechanical strength of the fluoropolymer may provide the
reactive material with the strength to survive the detonation or
explosive launch of the warhead. The mechanical strength of the
fluoropolymer may be particularly important in fragmentary warheads
10 because coherent fragments 12 must survive the detonation in
order to impact the target. The high fluorine content of the
fluoropolymer may provide the necessary oxidizing strength to
produce incendiary reactions with the metal filler when the
reactive material penetrates its target. The heat generated when
the reactive material penetrates the target may cause the fluorines
in the fluoropolymer to be liberated from the hydrocarbon chain of
the fluoropolymer and to exothermically react with the metal
filler. The low melt temperature of the fluoropolymer may help to
ensure that the reactive material may be processed at a temperature
below which the rate of metal reacting with trace amounts of HF is
greatly reduced or eliminated.
By reducing the temperature at which the reactive material is
processed, the safety concerns identified previously may be
eliminated or greatly reduced. In order to improve the safety of
processing the reactive materials, the melting temperature of the
fluoropolymer may not exceed the autoignition temperature of the
reactive material (the fluoropolymer/metal filler composition). In
other words, the reactive material may not produce an exotherm or
exotherms at or below the processing temperature. The processing
temperature of the reactive metal may vary depending on the melting
point of the fluoropolymer and the amount of metal filler present.
To provide an adequate margin of safety, the processing temperature
may be no higher than 50.degree. C. below the thermal autoignition
point of the reactive material or the temperature at which an
exotherm occurs. However, depending on the acceptable degree of
risk in processing the reactive materials, this 50.degree. C.
margin of error may be reduced as long as the melting temperature
of the fluoropolymer does not exceed the autoignition temperature
of the reactive material.
The fluoropolymer of the reactive material may be selected based on
its low-temperature processing capability, cost, availability,
fluorine content, mechanical properties of the unfilled
fluoropolymer, melting point, viscosity at desired processing
temperature, and compatibility of the fluoropolymer with reactive
metal fillers. Properties of selected commercially available
fluoropolymers are shown in Table 1. These fluoropolymers are
available from Dupont, Dyneon LLC, and Asahi Glass Co., Ltd. The
fluoropolymer of the present invention may include, but is not
limited to, a thermoplastic terpolymer of tetrafluoroethylene,
hexafluoropropylene, and vinylidene fluoride ("THV"), a
thermoplastic copolymer of tetrafluoroethylene and
perfluorovinylether ("PFA"), a thermoplastic copolymer of
tetrafluoroethylene and ethylene ("ETFE"), or a thermoplastic
copolymer of tetrafluoroethylene and hexafluoropropylene
("FEP").
TABLE-US-00001 TABLE 1 Properties of Selected Fluoropolymers
Tensile (%) Fluorine Strength Elonga- Melting Content (psi) tion at
Point (% by Polymer at 23.degree. C. 23.degree. C. (.degree. C.)
Solubility weight) Polytetrafluorethylene PTFE 4500 400 342
Insoluble 76 (TEFLON .RTM.) TFM 1700 5800 650 342 Insoluble 76
Modified PTFE Fluoroelastastomers (Gums) Viton A 2000 350 260
Soluble in 65.9 (Fluorel 2175) ketones/esters FEX 5832X 2000 200
260 Soluble in 70.5 terpolymer ketones/esters Fluorothermoplastic
Terpolymer of Tetrafluoroethylene, Hexafluoroproplyene, and
Vinylidenefluoride THV 220 2900 600 120 Soluble in 70.5 ketones/
Esters (100%) THV X 310 3480 500 140 Soluble in 71-72
ketones/esters (partial) THV 415 4060 500 155 Soluble in 71-72
ketones/esters (partial) THV 500 4060 500 165 Soluble in 72.4
ketones/esters (partial) HTEX 1510 4800 500 165 Insoluble 67.0
Fluorothermoplastic Copolymer of Tetrafluoroethylene and
Perfluorovinylether PFA 4350 400 310 Insoluble 76
Fluorothermoplastic Copolymer of Tetrafluoroethylene and
Hexafluoropropylene FEP 2900-4300 350 260 Insoluble 76
Fluorothermoplastic Copolymer of Tetrafluoroethylene and Ethylene
ETFE 6700 325 260 Practically 61.0 insoluble
In addition to using one fluoropolymer as the oxidizing agent, it
is also contemplated that a combination of at least two
fluoropolymers may be used. For sake of example only, a combination
of PTFE and THV 220 or a combination of two different THV polymers
may be used. At least two fluoropolymers may be present in
percentages sufficient to provide the high fluorine content, the
low melt temperature, and the high mechanical strength to the
reactive material.
The fluorine content of the fluoropolymer is preferably greater
than approximately 45% by weight. However, a fluoropolymer having a
lower fluorine may be used depending on the mechanical properties
of the fluoropolymer. In other words, a fluoropolymer having a
fluorine content less than approximately 45% by weight may be used
if the fluoropolymer has a high tensile strength and a high
percentage of elongation, in addition to the desired low melt
temperature.
Preferably, the fluoropolymer of the reactive material is THV 220,
available from Dyneon LLC (Oakdale, Minn.), because THV 220 is easy
to process due to its complete solubility in conventional solvents
and its low melt temperature. THV 220 has a melt temperature of
222.degree. C. below the melt temperature of PTFE. Conventional
solvents include ketones and esters and, more specifically, acetone
and ethyl acetate. The low melt temperature of THV 220 allows the
reactive material to be processed at temperatures significantly
below the thermal autoignition point using conventional batch
mixers. THV 220 is further preferable because the sintering process
required to produce PTFE reactive materials may be eliminated,
thereby increasing production efficiency.
In addition to THV 220, other THV polymers including, but not
limited to, THV X 310, THV 415, THV 500, and HTEX 1510, all
available from Dyneon LLC, may be used as the fluoropolymer of the
reactive material. The primary advantage offered by THV polymers is
the significantly reduced process temperature and the elimination
of the sintering process required in PTFE processing. Other
fluoropolymers may also be used in the reactive material as long as
these fluoropolymers have the desired properties of a high fluorine
content, a low melt temperature, and a high mechanical
strength.
The metal filler of the reactive material may be a reactive, high
density metal that provides the requisite penetrating power and
energy release for the warhead. The metal filler may be magnesium,
aluminum, magnesium/aluminum alloys, iron, copper, zirconium,
titanium, zinc, boron, silicon, manganese, tin, hafnium, tungsten,
depleted uranium, or tantalum, or metal carbides, oxides, or
nitrides of these metals. The metal filler may have a density that
is approximately equal or greater than the density of magnesium
(1.74 g/cm.sup.3). In addition, the metal filler may be at least as
reactive with the oxidizing agent as magnesium or aluminum.
Preferably, the metal filler is hafnium, tantalum, magnesium,
titanium, tungsten, aluminum, magnesium/aluminum alloys, or
zirconium. The metal fillers may be combined with the reactive
material in powdered form. However, intermetallic thermitic and
incendiary mixes of the metal filler may also be used within the
scope of the invention. The metal filler may also be a combination
or blend of two or more of these metals. For example, the metal
filler may be a blend of hafnium and tantalum. In addition, the
metal filler may be a metal/metal oxide filler (a thermite), such
as Fe.sub.2O.sub.3/aluminum, Fe.sub.2O.sub.3/zirconium,
CuO/aluminum, Fe.sub.2O.sub.3/titanium, tantalum/iron oxide,
manganese dioxide/aluminum, or other thermite compositions.
Intermetallic fillers that include a blend of two or more of the
metals may also be used. The intermetallic fillers may include a
blend of unreacted metals that have differing numbers of molar
ratios of each of the two or more metals, such as one mole of
hafnium and two moles of aluminum; one mole of hafnium and one mole
of aluminum; one mole of hafnium and two moles of boron; one mole
of nickel and one mole of aluminum; one mole of titanium and one
mole of aluminum; one mole of titanium and two moles of aluminum;
one mole of zirconium and one mole of aluminum; one mole of
zirconium and two moles of aluminum; one mole of molybdenum and two
moles of aluminum; one mole of aluminum and two moles of boron; one
mole of hafnium and two moles of boron; one mole of tantalum and
one mole of boron; one mole of titanium and two moles of boron; one
mole of zirconium and one mole of boron; or other intermetallic
compositions may also be used.
The fluoropolymer may be present in the reactive material at
approximately 15-90% by weight. Preferably, the fluoropolymer is
present at approximately 25-75% by weight. The metal filler may be
present at approximately 10-85% by weight.
The reactive material may be produced by mixing the fluoropolymer
and the metal filler, as known in the art. If the fluoropolymer is
soluble in ketones or esters, a particle size of the fluoropolymer
may not be critical to the operability of the present invention.
However, if the fluoropolymer is insoluble in ketones or esters,
the fluoropolymer may be commercially obtained in milled form or
may be processed to its milled form, as known in the art. The
insoluble fluoropolyner preferably has a small particle size, such
as an average particle size of approximately 1 micron. The
fluoropolymer may then be combined with the metal filler and
blended with a solvent to form a suspension of reactive material. A
twin-screw extruder may also be used to compound or mix the metal
filler with the fluoropolymer if solvents are undesirable. If the
fluoropolymer is soluble in ketones or esters, the reactive
material may be mixed by a solvent loss technique or a polymer
precipitation technique, which are described in more detail
below.
After the fluoropolymer and metal filler are mixed, the reactive
material may be processed by pressing or extrusion to manufacture
near-net-shape preforms. A reactive material comprising a
fluoropolymer that is insoluble in ketones or esters may be
directly pressed or extruded, as described below. A reactive
material comprising a soluble fluoropolymer may be processed by the
polymer precipitation or solvent loss techniques, followed by
pressing or extrusion. If the reactive material is processed by
pressing, the solution of reactive material is dried in an oven.
The dried reactive material is then loaded into a die that is
heated to approximately 165-180.degree. C. This temperature is
dependent on the melting point and the viscosity of the reactive
material. Higher temperatures will be required to process reactive
materials comprising fluoropolymers with higher melting points. The
reactive material is melted under pressure (approximately 1500 psi)
and under vacuum. This pressure is dependent on the rheology of the
reactive material. The die is cooled to below the melt temperature
of the die (approximately 80-100.degree. C.) for several minutes.
The pressing pressure is then increased to approximately 3000-4000
psi and the cooling of the die is continued to 50-60.degree. C. It
is essential that the die have a slow cooling rate to maximize
polymer crystallinity and mechanical properties. Once the reactive
material is adequately cooled, it is pressed from the die and
allowed to cool to ambient room temperature.
If the reactive material is processed by extrusion, the solution of
reactive material is dried in an oven. The dried reactive material
is then loaded into an extruder heated to approximately
165-180.degree. C. The reactive material is melted under pressure
(approximately 1500 psi) and under vacuum. The pressure required to
melt the reactive material is dependent on the fluoropolymer used
in the reactive material and the metal content in the reactive
material. The extrusion pressure is then increased to form an
extrudate, which is then cut into pieces and allowed to cool to
ambient room temperature.
It is also contemplated that these reactive materials may be used
to allow near-net-shape fabrication of components using injection
molding or extrusion, thereby reducing waste and machining
time.
The processed reactive materials formed by either of these methods
may be analyzed to determine the percentage of theoretical maximum
density ("% of TMD") for each reactive material. The % of TMD is
measured as known in the art. If the reactive material has a % of
TMD equal to approximately 100%, it indicates that no voids are
present in the reactive material. The desired % of TMD of the
reactive material may range between approximately 80-100%.
Preferably, the % of TMID of the reactive material is between
approximately 90-100% and, more preferably, between approximately
95-100%. The desired % of TMD may depend on the ultimate
application in which the reactive material may be used.
The reactive material having a sufficient % of TMD may be used in
reactive fragments 12 for fragmentary warheads 10 or liners 8 in
penetrating warheads 2. In a penetrating warhead 2, the reactive
material may be machined, pressed, or extruded into a desired shape
for use as the liner 8. In addition, the reactive material may be
placed into a mold to produce the desired shape of the liner 8. For
example, the reactive material is weighed into the desired
quantity. TEFLON.RTM. tape is placed on a top surface of a first
copper dish and a bottom surface of a second copper dish. The first
copper dish is heated in a 170.degree. C. oven. A TEFLON.RTM. brick
is placed over the first copper dish and the reactive material is
stacked into the middle of the first copper dish. The reactive
material is heated for about 45 minutes or until it becomes easily
pliable. The second copper dish is placed on top of the material
and lightly pressed down, making sure that the alignment of the
dish is flat. A TEFLON.RTM. donut is placed on top of the second
copper dish and two metal weights are placed on top of the
TEFLON.RTM. donut. The TEFLON.RTM. donut and metal weights are
arranged so that the weight is pressing straight down on the
reactive material to ensure that the reactive material will have a
uniform thickness. The set-up is left for 45 minutes in the oven
and then removed. The mold is removed from the TEFLON.RTM. brick
and cooled for 15 minutes. The two copper dishes are then pried
off, thereby releasing a liner formed from the reactive material in
the desired shape. The liner may be formed into a shape up to
several inches thick.
In a fragmentary warhead 10, which comprises fragments 12 of
reactive material, the reactive material may be processed into the
desired fragment shapes by extrusion or pressing. These reactive
fragments 12 may have a thickness up to several inches thick. The
dimensions of a liner 8 or reactive fragments 12 may vary,
depending on the application in which the reactive material is
being used. Therefore, each application may require optimization
testing.
The reactive material of the present invention may be deposited in
the warhead as known in the art. The reactive material may replace
the conventional liner 8, such as the copper liner, that is used in
penetrating warheads 2. In addition, it is also contemplated that
the reactive material may be used in addition to the copper liner.
For example, the reactive material may be deposited on top of the
copper liner. The reactive material may also be formed into
reactive fragments 12 for use in a fragmentary warhead 10. These
reactive fragments 12 may be secured in the warhead as known in the
art.
The reactive materials of the present invention significantly
reduce or eliminate the safety concerns associated with the
processing of high density, reactive metals and fluoropolymers.
These reactive materials can be processed at dramatically lower
temperatures and pressures in comparison to the temperatures and
pressures required to process PTFE reactive materials. These
reactive materials can also be processed more efficiently because
the sintering step necessary to process PTFE is eliminated. The
reactive materials also allow near-net-shape fabrication of
reactive material components using injection molding or extrusion,
thus reducing waste. In addition, waste is eliminated because the
reactive material can be readily recycled into new components.
Finally, processing of these reactive materials eliminates the use
of solvent in the process as they may be mixed or compounded in a
twin screw extruder.
EXAMPLE 1
Compositions of Ta/THV 220 and Hf/THV 220 Reactive Materials
The compositions of Ta/THV 220 and Hf/THV 220 reactive materials
are shown in Table 2.
TABLE-US-00002 TABLE 2 High Density Reactive Material Compositions
Theoretical Filler Fluoropolymer Maximum Metal Density Density Wt %
Wt % Vol % Vol % Density Filler Fluoropolymer (g/cm3) (g/cm3) Metal
Fluoropolymer Metal Fluoropolym- er (g/cm3) Tantalum THV 220 16.69
1.95 71.70 28.30 22.84 77.16 5.317 Tantalum THV 220 16.69 1.95
47.20 52.80 9.46 90.54 3.344 Hafnium THV 220 13.30 1.95 67.00 33.00
22.94 77.06 4.554 Hafnium THV 220 13.30 1.95 52.50 47.50 13.95
86.05 3.533
EXAMPLE 2
Mixing of Ta/THV 220 and Hf/THV 220 Reactive Materials
The Ta/THV 220 reactive materials were mixed using two techniques,
the solvent loss technique and the polymer precipitation technique,
to determine which technique provided the best mixing. Two small
10-gram mixes were made using both techniques. In the solvent loss
method, the THV 220 was dissolved in acetone. The tantalum was
mixed in with the THV 220 while stirring continuously to drive off
the acetone. Small chunks of homogeneous, tantalum-filled THV 220
material were produced, which were then dried in a forced-air oven.
The solvent loss technique resulted in a well mixed composition of
tantalum-filled THV 220. However, one disadvantage of this
technique is that solvent is required when the reactive material is
produced in batch mixes.
In the polymer precipitation technique, THV 220 was dissolved in
acetone and tantalum was mixed into the solution. A non-polar
solvent, such as hexane or heptane, was then added to change the
polarity of the solution, forcing the THV 220 to precipitate. One
advantage of this technique is its increased speed, which reduces
the time needed for mixing. In addition, this process works
extremely well with reactive materials that have less than 20
percent by volume of the fluoropolymer. However, the high-density
Ta/THV 220 and Hf/THV 220 reactive materials contained
approximately 70% by volume of THV 220, which resulted in large
sticky agglomerates that were hard to process.
Samples of the Ta/THV 220 reactive materials produced by the two
techniques were submitted for safety characterization testing.
Surprisingly, the safety characteristics of the reactive materials
varied with onset temperature sensitivity depending on how the
samples were processed. The polymer precipitation technique created
a reactive material that was more easily ignited, which may be
related to the presence of uncoated tantalum that is extremely
thermally unstable in an oxygen atmosphere. The safety
characteristics of the Ta/THV 220 reactive materials produced by
the solvent loss and polymer precipitation techniques are listed in
Table 3.
TABLE-US-00003 TABLE 3 Safety Data For Ta/THV 220 Reactive
Materials Comparing The Solvent Loss Technique To The Polymer
Precipitation Technique Thiokol ABL Sliding Thiokol Simulated Bulk
Impact Friction ESD Auto Ignition DSC Onset Thiokol Composition
(cm) (lbs@8 ft/s) (Joules) Onset Temp (.degree. F.) Temp (.degree.
C.) Safety Class 30.0% THV 220 >46 800 >8.0 Onset 500 F.
435.2 Green Line- 70.0% Tantalum Burned Safe to Solvent Loss
Process 30.0% THV 220 >46 800 >8.0 Onset 500 F. 360.7 Green
Line- 70.0% Tantalum Burned Safe to Polymer Precip. Process 30.0%
THV 220 ARC Step Heated to 350.degree. C., Ignited 70.0% Tantalum
Solvent Loss 30.0% THV 220 ARC: 5 gram sample isothermally aged at
250.degree. C., ignited after 6 hours 70.0% Tantalum Polymer
Precip.
Based on the safety data for the Ta/THV 220 reactive material and
the processing issues involved with the polymer precipitation
technique, the solvent loss technique was used to produce
subsequent Ta/THV 220 and Hf/THV 220 reactive materials. A total of
3.times.1000 -gram mixes were made with tantalum and hafnium,
respectively.
EXAMPLE 3
Additional Compositions of Reactive Materials Comprising
Fluoropolymers and Metal Fillers
Reactive materials comprising one of THV 220, THV X 310, THV 415,
THV 500, or HTEX 1510 as the fluoropolymer and one of tantalum,
hafnium, aluminum, magnesium, tungsten, titanium, or zirconium as
the metal filler are produced as described in Examples 1 and 2. For
each reactive material, the weight percentage of fluoropolymer and
metal filler is determined as known in the art.
EXAMPLE 4
Thermal Stability Testing on Ta/THV 220 And Hf/THV 220 Reactive
Materials
Thermal stability tests were performed on samples of the Ta/THV 220
and the Hf/THV 220 reactive materials. All samples were placed into
sealed one-inch diameter, spherical titanium bombs with a 11/4-inch
stem. Four runs were made on the Ta/THV 220 mixes as described
below: 1. Step heat run, 50-580.degree. C., 5.degree. C. steps, 70%
Ta/30% THV 220 Mix #4 (#909), 0.33 grams; 2. 250.degree. C./24 hour
isothermal age run, "isotracked" mode, Ta/THV 220 1791-64-1, 5.11
grams; 3. 200.degree. C./24 hour isothermal age run, "isofixed"
mode, 70% Ta/30% THV 220 Solvent Loss 1665-74-1, 1.52 grams; and 4.
200.degree. C./24 hour isothermal age run, "isofixed" mode, 70%
Ta/30% THV 220 Solvent Loss 1665-74-1, 5.27 grams.
In ARC isothermal aging, the difference between the "isotracked"
and "isofixed" modes was that during the "isotracked" mode, the
calorimeter walls tracked the bomb temperature during the entire
course of the run. In the "isofixed" mode, the calorimeter walls
remained at the isothermal age temperature until the sample
self-heated beyond the isothermal age temperature plus an
"isothermal window" (approximately 2.degree. C). When the
isothermal window was exceeded and the self-heat rate exceeded the
preset threshold (0.020.degree. C./minute for all tests reported)
the walls of the calorimeter began to track the bomb.
The "isofixed" algorithm was used for isothermal aging on the
original ARC. The disadvantage to the "isotracked" mode was that
the calorimeter was more likely to drift and even registered false
exotherms during a long isothermal age run. Long-term temperature
stability was better with the classic "isofixed" aging mode. Since
some positive temperature drift problems were experienced in the
"isotracked" mode, all remaining experiments were conducted in the
"isofixed" mode.
The results of the Ta/THV 220 step heat run on a 0.3267 gram sample
are shown in FIG. 2. No exotherms (self-heat rates in excess of
0.02.degree. C./minute) were observed up to roughly 310.degree. C.
For purposes of these experiments, exotherms were defined as
self-heat rates in excess of 0.02.degree. C./minute. However, it is
to be understood that this definition may vary, as known in the
art, depending on the safety protocol used. Upon heating to
310.degree. C., the sample exothermed and apparently exploded
during the wait period. However, 310.degree. C. is significantly
above the temperatures that will be used to process the Ta/THV 220
reactive materials. One would expect to detect the exotherm at
lower temperatures with larger samples, which better simulate a
true bulk thermal runaway, but unfortunately these could not be
allowed to autoignite because bomb rupture would occur.
The 250.degree. C./24 hour isothermal age run was performed on the
Ta/THV 220 reactive material (using a different sample than the
original run, possibly with different thermal stability
characteristics) on a 5.1143 gram sample. This sample size was
large enough to provide a good simulation of a bulk sample. Also,
isothermal aging did a better job than step heating of unmasking
initially slow autocatalytic reactions that can lead to a sudden
thermal runaway. FIG. 3 shows the temperature versus time behavior
of this sample, which autoignited after less than seven hours at
250.degree. C. This temperature is also significantly above the
temperatures that will be used to process the Ta/THV 220 reactive
materials.
Two additional isothermal age runs were conducted on a different
sample (a solvent loss process) at a lower temperature, 200.degree.
C., for 24 hours, using progressively larger samples (1.5191 grams,
then 5.267 grams). These results are shown in FIGS. 4 and 5. No
exotherms (self-heat rates in excess of 0.02.degree. C./minute)
were detected with either sample. The 1.5 gram sample showed a
slight temperature rise at the start of the run, which may have
been due to calorimeter drift. The second run using a 5.3 gram
sample did not show this behavior. This temperature is also above
the temperatures that will be used to process the Ta/THV 220
reactive materials.
For the Hf/THV 220, two runs were made: 1. step heat run,
50-580.degree. C., 5.degree. C. steps, 70% Hf/30% THV 220 1791-66-1
#1065, 0.31 gram sample; and 2. 200.degree. C./24 hour isothermal
age run, 70% HUf/30% THV 220 1791-66-1 #1065, 5.16 gram sample.
FIGS. 6 and 7 show the temperature/pressure v. time and self-heat
rate v. temperature curves respectively for a small (0.3109 gram)
sample of Hf/THV 220 reactive material. Starting at about
275.degree. C., there were several small exotherms with self-heat
rates near the exotherm threshold (0.020.degree. C./min) that were
not sustained. When the self-heat rate dropped below the exotherm
threshold, step heating resumed, which happened several times
between 275 and 355.degree. C. At 355.degree. C., a sustained
exotherm was finally observed. However, 355.degree. C. is
significantly above the temperatures that will be used to process
the Hf/THV 220 reactive materials. The lower temperature exothermic
behavior may have had a contribution from calorimeter drift. It is
also unclear what happened to the pressure trace on this run at
high temperatures.
Finally, a 200.degree. C./24 hour isothermal age experiment was
conducted on a 5.17 gram sample of material. As shown in FIG. 8, no
appreciable self-heating or exothermic behavior was observed at
this temperature.
The results of these stability tests on the Ta/THV 220 and Hf/THV
220 reactive materials indicated that no thermal hazard potential
exists for the proposed extrusion involving short-term exposure of
the Ta/THV 220 (solvent loss process) and Hf/THV 220 reactive
materials to temperatures of approximately 140.degree. C. In fact,
both reactive materials were thermally stable at temperatures of
approximately 200.degree. C.
EXAMPLE 5
Thermal Stability Testing on Additional Compositions of Reactive
Materials Comprising Fluoropolymers and Metal Fillers
Reactive materials produced according to Example 3 are evaluated
for thermal stability according to Example 4. Thermal stability
tests are performed as described in Example 4.
Reactive materials are obtained that have no thermal hazard
potential for the proposed extrusion involving short-term exposure
of these reactive materials to temperatures slightly greater than
the melt temperature of the specific fluoropolymers used in the
composition.
EXAMPLE 6
Processing of Ta/THV 220 and Hf/THV 220 Reactive Materials
The mixed Ta/THV 220 and Hf/THV 220 reactive materials were
processed by pressing or ram extrusion. The two methods were
evaluated to determine whether the method of processing affected
the reactive material. Initially, the reactive material was pressed
into right circular cylinders and evaluated and eliminated for
safety reasons due to the large amount of flashing produced when
small samples of inert THV 220 (NaCl/THV 220 and KCl/THV 220)
compositions were pressed. Pressing the Al/THV 220, Ta/THV 220 and
Hf/THV 200 reactive materials while they were being melted
potentially presented a safety hazard due to the flashing formed
around the pressing ram. Coupled with the fact that the tantalum
and hafnium metal fillers are extremely sensitive to electrostatic
discharge ("ESD"), ram extrusion was pursued as the processing
technique. By using extrusion, flashing is eliminated, exposure of
personnel to the reactive materials is minimized, and safety is
improved.
Ram extrusion was used to fabricate 1.1-inch diameter cylinders
because the extrusion produced reactive material with low void
content, thereby yielding high-density reactive material close to
the theoretical maximum density. With both the Ta/THV 220 and
Hf/THV 220 reactive materials, multiple extrusions were performed
with quantities restricted by volumetric limitations. On average,
each extrusion produced enough material to make six 1.1-inch
cylinders with very few voids. Unconsolidated reactive material was
loaded into the top of the extruder barrel and heated under vacuum
until it melted. Pressure was then applied to the ram, which forced
the soft reactive material through the die and formed a cylindrical
extrudate. As the extrudate grew in length, it eventually contacted
a conveyor, which applied backpressure. The backpressure caused the
extrudate to bulge near the die where the extrudate was still soft.
The resulting extrudates therefore had sections of varying
diameter.
Visual inspection of the extruded Hf/THV 220 reactive material
showed the presence of shiny specks randomly dispersed in the
material. This was compared to the extruded Ta/THV 220 reactive
material, where no specks were present. The shiny specs in the
Hf/THV 220 extrudates were believed to be uncoated particles of
Hf.
The processed Ta/THV 220 and Hf/THV 220 extrudates were evaluated
to determine the % of TMD for each sample.
EXAMPLE 7
Processing of Additional Compositions of Reactive Materials
Comprising Fluoropolymers and Metal Fillers
Reactive materials comprising the metal fillers and fluoropolymers
described in Example 3 are processed as described in Example 6.
The extrudates from these processed reactive materials are
evaluated to determine the % of TMD for each sample.
EXAMPLE 8
TMD Values of Ta/THV 220 Extrudates
The % of TMD values for the Ta/THV 220 extrudates were calculated
and are presented in Table 4.
TABLE-US-00004 TABLE 4 Ta/THV 220 TMD Data Testing Date Sample
Position Density (g/cc) % of TMD Jan. 21, 2002 Middle of Rod 5.256
98.86 Feb. 4, 2002 End of Delivered Rod 5.281 99.32 Feb. 4, 2002
Middle of Rod 5.254 98.81 Feb. 4, 2002 Middle of Rod 5.281 99.32
Feb. 4, 2002 End of Delivered Rod 5.275 99.21 Average 5.269
99.106
As shown in Table 4, these Ta/THV 220 extrudates had TMD values
ranging from 98.81-99.32%, with an average TMD value of 99.106%.
These TMD values are significantly higher than the average TMD
value for W/PTFE, which was determined to be approximately 96%
(data not shown). These TMD values are also higher than the TMD
values for Al/THV 220, which were determined to range from
approximately 97.9%-99.2% (data not shown).
EXAMPLE 9
TMD Values For Hf/THV 220 Extrudates
The % of TMD values for the Hf/THV 220 extrudates were calculated
and are presented in Table 5. When hafnium was used as the metal
filler, the extrudate density was not as close to the % of TMD as
the Ta/THV 220 extrudates. The lower % of TMD may be related to
changes in the reactive material's rheology or poor bonding of the
THV 220 to the surface of the hafnium powder. As previously
mentioned, the Hf/THV 220 extrudates comprised small shiny specks
that were believed to be uncoated Hf particles. The lower density
values of the Hf/THV 220 extrudate support this observation because
the uncoated Hf would result in microscopic voids in the material,
thereby reducing the % of TMD.
TABLE-US-00005 TABLE 5 Hf/THV 220 TMD Data Testing Date Sample
Position Density (g/cc) % of TMD Feb. 4, 2002 End of Delivered Rod
4.427 97.21 Feb. 4, 2002 End of Delivered Rod 4.440 97.49 Feb. 4,
2002 End of Delivered Rod 4.450 97.71 Feb. 4, 2002 End of Delivered
Rod 4.444 97.58 Average 4.440 97.50
The TMD values for the Hf/THV 220 reactive materials are slightly
lower than the TMD values for the Ta/THV 220 reactive materials.
However, the % of TMD for the Hf/THV 220 reactive materials are
higher than the average TMD value for W/PTFE, which was determined
to be approximately 96% (data not shown). These TMD values are also
comparable to the TMD values for Al/THV 220, which were determined
to range from approximately 97.9%-99.2% (data not shown).
EXAMPLE 10
TMD Values for Additional Compositions of Reactive Materials
Comprising Fluoropolymers and Metal Fillers
The % of TMD values for the reactive materials comprising the metal
fillers and fluoropolymers described in Example 3 are measured.
Reactive materials that have TMD values greater than the average
TMD value for W/PTFE are obtained. The average TMD value for W/PTFE
was determined to be approximately 96% (data not shown).
EXAMPLE 11
Penetration Ability of Ta/THV 220 and Hf/THV 220 Reactive
Materials
The Ta/THV 220 and Hf/THV 220 reactive materials exhibited improved
penetration into solid targets compared to the Ta/PTFE and W/PTFE
reactive materials (data not shown).
EXAMPLE 12
Penetration Ability of Additional Compositions of Reactive
Materials Comprising Fluoropolymers and Metal Fillers
Reactive materials comprising the metal fillers and fluoropolymers
described in Example 3 are obtained. These reactive materials have
improved penetration into solid targets compared to the Ta/PTFE and
W/PTFE reactive materials.
* * * * *
References