U.S. patent application number 16/001766 was filed with the patent office on 2019-03-21 for low-density interconnected ionic material foams and methods of manufacture.
This patent application is currently assigned to THE REGENTS OF THE UNIVERSITY OF CALIFORNIA. The applicant listed for this patent is LAWERENCE LIVERMORE NATIONAL SECURITY, LLC, NATIONAL TECHNOLOGY & ENGINEERING SOLUTIONS OF SANDIA, LLC, THE REGENTS OF THE UNIVERSITY OF CALIFORNIA. Invention is credited to Edward C. Burks, Jeffrey D. Colvin, Thomas E. Felter, Dustin A. Gilbert, Sergei O. Kucheyev, Kai Liu.
Application Number | 20190085478 16/001766 |
Document ID | / |
Family ID | 65719916 |
Filed Date | 2019-03-21 |
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United States Patent
Application |
20190085478 |
Kind Code |
A1 |
Burks; Edward C. ; et
al. |
March 21, 2019 |
LOW-DENSITY INTERCONNECTED IONIC MATERIAL FOAMS AND METHODS OF
MANUFACTURE
Abstract
Ultralow density ionic material foams, with density approaching
0.1% of the bulk density, and synthesis methods using
interconnected metallic nanowires are provided. Nanowires of
various sizes and metals are dispersed into a freezable liquid
through a suitable fluid exchange. Surface treatments ensure that
nanowires remain sufficiently metallic and physically separated.
Wire-liquid solutions can be dropped directly into liquid nitrogen
in the form of droplets or placed into molds of various shapes. A
freeze drying technique is employed to turn the resulting ice-wire
mixture into a freestanding, low-density foam composed of
interlocked nanowires. Sintering or oxidation and reduction
treatment of the foam material at elevated temperatures is used to
connect the nanowires into an interconnected metallic foam. Metals
of the metal foams are then processed into ionic materials
including oxides, nitrides, chlorides, hydrides, fluorides, iodides
and carbides.
Inventors: |
Burks; Edward C.; (Davis,
CA) ; Gilbert; Dustin A.; (Germantown, MD) ;
Liu; Kai; (Davis, CA) ; Kucheyev; Sergei O.;
(Oakland, CA) ; Felter; Thomas E.; (Livermore,
CA) ; Colvin; Jeffrey D.; (Pleasanton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE REGENTS OF THE UNIVERSITY OF CALIFORNIA
LAWERENCE LIVERMORE NATIONAL SECURITY, LLC
NATIONAL TECHNOLOGY & ENGINEERING SOLUTIONS OF SANDIA,
LLC |
Oakland
Livemore
Albuquerque |
CA
CA
NM |
US
US
US |
|
|
Assignee: |
THE REGENTS OF THE UNIVERSITY OF
CALIFORNIA
Oakland
CA
LAWERENCE LIVERMORE NATIONAL SECURITY, LLC
Livermore
CA
NATIONAL TECHNOLOGY & ENGINEERING SOLUTIONS OF SANDIA,
LLC
Albuquerque
NM
|
Family ID: |
65719916 |
Appl. No.: |
16/001766 |
Filed: |
June 6, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15956993 |
Apr 19, 2018 |
|
|
|
16001766 |
|
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|
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PCT/US2016/064218 |
Nov 30, 2016 |
|
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15956993 |
|
|
|
|
62261211 |
Nov 30, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 2998/10 20130101;
C25D 1/20 20130101; B22F 3/1143 20130101; B22F 2202/06 20130101;
C25D 1/04 20130101; B22F 1/0025 20130101; B22F 3/1121 20130101;
C25D 1/006 20130101; C25D 3/46 20130101; C25D 3/12 20130101; B22F
9/14 20130101; C25D 3/50 20130101; B22F 2998/10 20130101; C25D
11/045 20130101; C25D 11/20 20130101; B22F 1/0022 20130101; B22F
3/11 20130101 |
International
Class: |
C25D 1/04 20060101
C25D001/04; C25D 1/00 20060101 C25D001/00; C25D 1/20 20060101
C25D001/20; B22F 3/11 20060101 B22F003/11 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0003] This invention was made with Government support under
BRCALL08-Per3-C-2-0006, awarded by the Defense Threat Reduction
Agency; under DMR-1008791, awarded by the National Science
Foundation; and under Contract DE-AC04-94AL85000 between Sandia
Corporation and the U.S. Department of Energy. The Government has
certain rights in the invention.
Claims
1. A method for fabricating low density and ultralow density
nanostructured ionic material foams, the method comprising: (a)
forming a liquid dispersion of metal nanowires in a freezable
fluid; (b) freezing the liquid dispersion to form an ice-nanowire
structure; (c) sublimating the ice-nanowire structure to expose a
free standing nanowire foam structure; (d) binding the nanowire
foam structure at points of contact to form an interconnected metal
foam monolith; and (e) converting the metals of the metal foam
monolith into an ionic material selected from the group of
materials consisting of a nitride, an oxide, a chloride, a hydride,
a fluoride, an iodide and a carbide to produce an ionic material
foam.
2. The method of claim 1, further comprising: treating nanowire
surfaces with an acid to remove oxide contaminants; and dispersing
treated nanowires in a freezable liquid.
3. The method of claim 1, further comprising: treating nanowire
surfaces with a surfactant to separate nanowires from each other;
and dispersing treated nanowires in a freezable liquid.
4. The method of claim 1, wherein said metal nanowires are formed
from a metal selected from the group of metals consisting of Al,
Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag,
Sn, Sb, La, Nd, Sm, Dy, Pt, Au, Pb, and Bi, and alloys based on one
or more of these metals.
5. The method of claim 1, wherein said metal nanowires have an
aspect ratio of length vs. diameter within the range of 2 to
1,000,000.
6. The method of claim 1, wherein said dispersion contains wires
diluted in volume by a factor of 2 to 10,000.
7. The method of claim 1, further comprising: depositing the liquid
dispersion in one or more molds; and freezing the liquid dispersion
in the molds.
8. The method of claim 1, wherein said binding of points of contact
of the ice-nanowire structure is performed by sintering.
9. The method of claim 1, wherein said binding of points of contact
of the ice-nanowire structure is performed by one or more oxidation
and reduction cycle(s) performed at elevated temperatures.
10. A method for fabricating low density and ultralow density
nanostructured ionic material foams, the method comprising: (a)
preparing a nanoporous membrane template; (b) applying an electrode
to one side of the nanoporous membrane template: (c) forming
nanowires within the nanoporous membrane template by
electrodeposition; (d) releasing the formed nanowires from the
membrane template; (e) forming a liquid dispersion of metal
nanowires in a freezable fluid; (f) freezing the liquid dispersion
to form an ice-nanowire structure; (g) sublimating the ice-nanowire
structure to expose an interlocked nanowire structure; (h) binding
the interlocked nanowire structure at points of contact between
nanowires to form an interconnected metal foam; and (i) converting
the metals of the interconnected metal foam into an ionic material
selected from the group of materials consisting of a nitride, an
oxide, a chloride, a hydride, a fluoride, an iodide and a carbide
to produce an ionic material foam.
11. The method of claim 10, wherein said releasing of formed
nanowires comprises: etching the membrane template to remove the
electrode; disintegrating the membrane template to release
nanowires; dispersing the released nanowires in a freezable fluid;
and agitating released nanowires to separate and randomize
nanowires in the freezable fluid.
12. The method of claim 10, wherein said nanoporous membrane
template comprises an anodized aluminum oxide (AAO) membrane, a
polycarbonate membrane, a porous mica membrane or a nanochannel
glass membrane.
13. The method of claim 10, further comprising: treating nanowire
surfaces with an acid to remove oxide contaminants; and dispersing
treated nanowires in a freezable liquid.
14. The method of claim 10, further comprising: treating nanowire
surfaces with a surfactant to separate nanowires from each other;
and dispersing treated nanowires in a freezable liquid.
15. The method of claim 10, further comprising: depositing the
liquid dispersion in one or more molds; and freezing the liquid
dispersion in the molds.
16. The method of claim 10, wherein said metal nanowires are formed
from a metal selected from the group of metals consisting of Al,
Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag,
Sn, Sb, La, Nd, Sm, Dy, Pt, Au, Pb, and Bi, and alloys based on one
or more of these metals.
17. The method of claim 10, wherein said metal nanowires have an
aspect ratio within the range of 2 to 1,000,000.
18. The method of claim 10, wherein said liquid dispersion contains
wires diluted in volume by a factor of 2 to 10,000.
19. The method of claim 10, wherein said binding of points of
contact of the interlocked nanowire structure is performed by
sintering.
20. The method of claim 10, wherein said binding of points of
contact of the interlocked nanowire structure is performed by one
or more oxidation and reduction cycle(s) performed at elevated
temperatures.
21. An ionic material foam structure having a bulk density and
comprising: (a) an interconnected nanoscale ionic material network
structure of an ionic material selected from the group of materials
consisting of a nitride, an oxide, a chloride, a hydride, a
fluoride, an iodide and a carbide to produce an ionic material
foam; (b) wherein the network structure has a density of about 0.1%
of the bulk density.
22. The ionic material foam structure of claim 21, wherein the
network structure has a density from about 20 g/cm.sup.3 to about 1
mg/cm.sup.3.
23. The ionic material foam structure of claim 21, wherein said
ionic material network structure is formed from one or more metals
selected from the group of metals consisting of consisting of Al,
Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag,
Sn, Sb, La, Nd, Sm, Dy, Pt, Au, Pb, and Bi, and alloys based on one
or more of these metals.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 15/956,993 filed on Apr. 19, 2018,
incorporated herein by reference in its entirety, which is a 35
U.S.C. .sctn. 111(a) continuation of PCT international application
number PCT/US2016/064218 filed on Nov. 30, 2016, incorporated
herein by reference in its entirety, which claims priority to, and
the benefit of, U.S. provisional patent application Ser. No.
62/261,211 filed on Nov. 30, 2015, incorporated herein by reference
in its entirety. Priority is claimed to each of the foregoing
applications.
[0002] The above-referenced PCT international application was
published as PCT International Publication No. WO 2017/095925 on
Jun. 8, 2017, which publication is incorporated herein by reference
in its entirety.
INCORPORATION-BY-REFERENCE OF COMPUTER PROGRAM APPENDIX
[0004] Not Applicable
BACKGROUND
1. Technical Field
[0005] The technology of this disclosure pertains generally to
nanoscale structure fabrication methods, and more particularly to
an ultralow-density, nanostructured, monolithic pure ionic material
foams and fabrication methods.
2. Background Discussion
[0006] Nanoporous metal foams have a host of fascinating
electrical, magnetic, mechanical, optical, thermal and chemical
properties due to their extremely high surface areas, nanoscale
constricted geometries, and high porosity. They have critical
potential applications in such fields as high energy density laser
targets, lightweight materials, coatings, photovoltaics, heat
exchangers and regenerators, trapping and targeted drug delivery,
etc.
[0007] Although a number of methods for preparing pure metal
nanoparticles exist, there are relatively few synthetic processes
for producing bulk, monolithic forms of nanostructured metals that
have been developed. Conventional methodologies for fabricating
monolithic metallic nanoporous materials or foams have limited
practical applications and are difficult to adapt to large scale
production because of their complicated procedures and use of
expensive materials.
[0008] One approach to fabricating nanoporous metal foams is by the
selective dealloying of a binary alloy which involves selectively
etching a less-noble metal from a bimetallic alloy. The metallic
alloy starting material contains two or more elements, one of which
is readily susceptible to selective chemical or electrochemical
etching that preferentially removes the element. The dealloying
process involves the removal of a substantial portion of the
starting material to create porosity. For example, aluminum based
alloys are often used with conventional chemical dealloying
approaches because aluminum can be removed from the alloy with
either a strong acid or a strong base.
[0009] Although selective dealloying approaches have been effective
for fabricating some nanoporous metallic structures, the
diffusion-controlled processes of electrochemical or acid etching
limit the practical dimensions of the structure that can be
formed.
[0010] In addition, the dealloying process also requires a starting
alloy with a percolating network of pores or the formation of a
network of pores to complete the etching process throughout the
structure. Immersion times in the acid or base are typically 2 to 5
days and times increase with the size of the starting
structure.
[0011] In some settings, full removal of the etched metal is
necessary for the functionality of the final monolith structure.
For example, residues of the selected etched metal of the starting
alloy can greatly affect the catalytic properties of the nanoporous
foam. This further limits the size and morphology of the starting
structure and final metal foam.
[0012] Additionally, many metals are readily oxidized in air at
room temperature resulting in the formation of oxides. Oxides may
form on the surfaces of the metal structure that may interfere with
the functionality of the final foam.
[0013] Another approach to the production of nanoporous metal
monoliths involves certain forms of combustion synthesis such as
the thermal decomposition of transition-metal complexes containing
high nitrogen energetic ligands. For example, nanostructured metal
monolithic foams can be formed with a self-propagating combustion
synthesis process utilizing metal complexes of the energetic
high-nitrogen ligand, bistetrazole amine (BTA) that are ignited in
inert environments. Generally, the BTA metal complexes are prepared
by the reaction of monohydrated bi(tetrazolato)amine or ammonium
bi(tetrazolo)amine and a selected metal salt. The product is
collected and dried as a fine powder.
[0014] This thermal decomposition process results in the formation
of a bulk material with nanoscale features in a matter of seconds.
However, the microstructural features of the resulting metal foams
can vary significantly depending on the composition and processing
conditions.
[0015] Other approaches have used sacrificial templates of carbon
or organic aerogels such as polysaccharide templates. However,
these approaches are usually better suited for use with metal
oxides.
[0016] Therefore, there is a need for fabrication methods for
producing mechanically stable, ultralow-density, nanostructured,
monolithic, metal foams, that are facile, inexpensive,
environmentally benign, and amenable to scale-up processing. The
present technology satisfies these needs and is generally an
improvement in the art.
BRIEF SUMMARY
[0017] The present technology provides methods for fabricating low
cost, ultralow density pure metal foams, with tunable densities
between 50% and 0.05% by volume of the bulk density, using
interconnected metallic nanowires. The metal foams are then
converted into ionic materials. The highly porous foam structures
have scalable and macroscopic overall sizes, in the range of
several millimeters or more. Such materials will provide an
unprecedented platform for exploration of lightweight materials,
coatings, photovoltaics, thermoelectrics, heat exchangers, hydrogen
storage and catalysts, and could have transformative impacts in
advanced materials and energy research.
[0018] The fabrication methods begin with the selection of the type
of metal nanowires that are preferably made from pure metals such
as Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh,
Pd, Ag, Sn, Sb, La, Nd, Sm, Dy, Pt, Au, Pb, and Bi, and alloys
based on one or more of these metals. Combinations of compatible
metal nanowires can also be formed in some embodiments. The term
nanowire is used in a general sense for a nanoscale element and is
intended to include a variety of structures such as nanotubes,
nanorods, nanowires and nanoribbons etc., that are either solid or
hollow.
[0019] In one embodiment, the nanowires are formed with a template
and electrodeposition. The characteristics of the nanowires are
determined by the configuration of the template. The
electrodeposition process allows the synthesis of a wide variety of
metallic nanowires as the building blocks for the foams. This is
easily scalable for mass production and is cost-effective, which
are highly advantageous features particularly compared to current
lithography approaches in the art. While templated
electrodeposition is preferred, the nanowires can be made with a
number of techniques including electrodeposition, electroless
deposition, atomic layer deposition, and solution based formation
schemes etc.
[0020] The selected metal nanowires are dispersed in a fluid that
is suitable for lyophilization such as deionized water. The
concentration or density of the nanowires within the freezable
fluid can be controlled to tune the density of the final foam. The
dispersion may be prepared with the density of nanoscale metal
wires tuned to a given application over a continuous range from
approximately 0.05% to approximately 50% by volume.
[0021] The outer surfaces of some metal nanowires may oxidize or
have otherwise reacted with the environment during formation or in
storage. Such contamination can be removed before the foam
formation. For example, nanowires may be placed into a solution of
an acid such an L-ascorbic acid to treat the wire surfaces and
remove oxides and other contaminants before being placed in the
lyophilization fluid.
[0022] The tuned dispersion of treated nanowires is then used to
fill shaped molds for freezing. The molds can be essentially any
shape and size. In another embodiment, the dispersion is dropped or
injected directly into a cryogenic liquid such as liquid nitrogen
to form spheres, cylinders, discs, cubes, rectangular prisms,
sheets, or other forms.
[0023] The frozen molded forms are then placed into a vacuum
chamber for lyophilization. The frozen liquid sublimates under
controlled conditions leaving a structure of interlocked
nanowires.
[0024] This structure of loosely interlocked nanowires is processed
further to bond the points of contact between the nanowires to form
the final foam without significant increase in density. The
technology utilizes a sintering step, the oxidation and reduction
or sintering of the nanowires to transform the foam from an
interlocked structure (where the nanowires are touching) into an
interconnected structure (where the nanowires are further bonded).
This greatly improves the strength of the material, allowing the
formation of low and ultralow density metal foams at 0.05% of the
bulk density (e.g., 5 mg/cm.sup.3 Copper foams), which are useful
for a far wider range of applications than previously possible.
[0025] Base metal foams may also be converted into other ionic
materials through simple processing such as by sintering or
exposure to air to form metal oxides, for example. In addition to
oxides, metal foams can be processed into nitrides, chlorides,
hydrides, fluorides, and iodides after foam formation.
[0026] According to one aspect of the technology, interconnected
pure metallic foams with a wide range of tunable densities and
characteristics is provided. Aspects of the final metal foam can be
tuned by the selection of the length and the cross-sectional
dimensions of the nanowire elements as well as the selection of the
concentration or density of the nanowires in the nanowire
dispersion.
[0027] Another aspect of the technology is to provide nanowire
surface treatments using L-ascorbic acid to help ensure that the
nanowires remain sufficiently metallic, which facilitates the
subsequent bonding processes during sintering.
[0028] An aspect of the technology is to provide a method for the
creation of three dimensional, low and ultralow density foam
structures through electrodeposition and a freeze-drying
process.
[0029] A further aspect of the technology is the creation of
interconnected pure metallic foams that have low density (down to
0.05% of its bulk density) and are still mechanically stable.
[0030] Another aspect of the technology is to provide a pure metal
foam that is particularly suited for producing x-ray emissions from
laser illumination. For example, metallic foam structures with
densities from about 20 g/cm.sup.3 to about 1 mg/cm.sup.3 are
particularly useful as targets for high energy density lasers to
generate bright x-rays.
[0031] Further aspects of the technology described herein will be
brought out in the following portions of the specification, wherein
the detailed description is for the purpose of fully disclosing
preferred embodiments of the technology without placing limitations
thereon.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0032] The technology described herein will be more fully
understood by reference to the following drawings which are for
illustrative purposes only:
[0033] FIG. 1 is a schematic flow diagram of a method of
fabricating low density interconnected pure metal foams for
conversion to ionic material foams according to one embodiment of
the technology.
[0034] FIG. 2 is a schematic flow diagram of an alternative
embodiment of the method of fabrication of pure metal foams of
interconnected nanowires and related ionic material foams according
to the technology.
[0035] FIG. 3 is an indentation curve with loading and unloading
portions for a 9 mg/cm.sup.3 strengthened Cu cylindrical foam that
was 2 mm in height and diameter. By measuring the initial slope of
the unloading curve, the modulus of the material can be
extracted.
[0036] FIG. 4 is a relative modulus vs. relative density plot for
various low density materials as compared to the foams of the
present technology.
DETAILED DESCRIPTION
[0037] Referring more specifically to the drawings, for
illustrative purposes, embodiments of systems and methods for
producing low-density interconnected metal foams and ionic material
foams are generally shown. Several embodiments of the technology
are described generally in FIG. 1 through FIG. 4 to illustrate the
fabrication system and methods. It will be appreciated that the
methods may vary as to the specific steps and sequence and the
systems and apparatus may vary as to structural details without
departing from the basic concepts as disclosed herein. The method
steps are merely exemplary of the order that these steps may occur.
The steps may occur in any order that is desired, such that it
still performs the goals of the claimed technology.
[0038] Turning now to FIG. 1, a flow diagram of one embodiment of a
method 10 for fabricating low density metal foams with controllable
characteristics is shown. The metals of the produced metal foams
can be processed further into ionic materials. In the step at block
20, the fabrication process generally begins with the preparation
of a dispersion of metal nanowires in a freezable liquid.
[0039] A variety of fluids can be used to prepare the dispersion at
block 20 of FIG. 1. The fluid that is used is preferably one that
does not react with the type of metal forming the metal nanowires
that have been selected for the foam. The preferred fluid will also
freeze and subsequently sublimate under controlled conditions and
otherwise be suitable for lyophilization processes. Preferred
fluids also will exert limited stresses on the dispersed wires upon
freezing. Deionized water is particularly preferred but other
solvents or pure substances that have a triple point may also be
suitable freezable fluids for wire dispersions, for example, liquid
CO.sub.2, iodine, arsenic, naphthalene and ammonium chloride.
[0040] The metal nanowires that are provided at block 20 are
preferably made from pure metals or metal alloys. Suitable metals
for metal nanowire foams generally include Al, Ti, V, Cr, Fe, Co,
Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Nd, Sm,
Dy, Pt, Au, Pb, and Bi, and alloys based on one or more of these
metals.
[0041] As used herein, the term "nanowire" generally refers to
nanoscale structures that have at least one cross-sectional
dimension that is less than about 1 .mu.m, (i.e. in the nanoscale
range), and preferably about 500 nm or less, and more preferably,
about 200 nm or less. Such nanoscale structures will typically have
an aspect ratio of the length to the smallest cross-sectional
dimension of greater than about 1, preferably, greater than about
10, and in many cases, greater than about 100. However, in some
embodiments, the nanoscale structures are nanorods with length and
diameter dimensions that produce aspect ratios of between about 2
and about 10. Accordingly, both the length and the cross-sectional
dimensions of the nanowire element are variable.
[0042] The cross-section of the nanowire element may also have any
arbitrary shape, including circular, square, rectangular, tubular,
or elliptical, and may have a regular or an irregular shape. The
nanoscale wire element may be solid or hollow. The term nanowire is
intended to include a variety of structure such as nanotubes,
nanorods, nanowires and nanoribbons etc.
[0043] The dispersion that is prepared at block 20 also has a
nanowire density that can be selected. Wire density refers to
number of nanowires per unit volume (e.g. .mu.m.sup.3). The wire
density of the final foam is determined, in part, by the
concentration of nanowires in the nanowire dispersion volume that
is initially prepared.
[0044] The dispersion may be prepared with essentially any density
of nanoscale wires. However, the preferred volume ratio of the
fluid in the dispersion vs. the nanowire volume, for example,
ranges from 1 to 10,000.
[0045] Therefore, some important aspects of the final metal foam
can be tuned by the selection of the length and the cross-sectional
dimensions of the nanowire elements as well as the selection of the
concentration or density of the nanowires in the dispersion that is
provided at block 20 of the method of FIG. 1.
[0046] The surfaces of the nanowires in the dispersion that is
provided may be treated to ensure that the nanowires remain
sufficiently metallic at block 30. This process is used to reduce
any oxides that may be present in on the surfaces of the nanowires.
Wires are then moved back into deionized water through fluid
exchanges immediately prior to freezing at block 40 of FIG. 1.
[0047] For example, the nanowires may be placed into a solution of
an acid such an L-ascorbic acid to treat the wire surfaces at block
30. For copper nanowires, the wires may be moved into 100 g/L
L-ascorbic acid, for example, where they are soaked for 48 hours in
order to reduce any oxide in the copper to ensure the wires are
pure copper during the foam formation process and to strengthen the
van der Waals attractions between the wires during the foam
formation step.
[0048] However, this L-ascorbic acid treatment may not be necessary
for silver, palladium, gold or platinum wires since they do not
readily oxidize.
[0049] Instead, the nanowire surface treatment at block 30 may be
the immersion of the nanowires into a volume of 0.25 g/10 mL
polyvinyl-pyrrolidone (PVP) surfactant to separate the wires. The
treated wires are then moved back to water through a fluid exchange
process. Alternative chemicals for such surface treatment may
include oxalic acid for oxide removal and surfactants are
Cetrimonium bromide (CTAB), Sodium dodecyl sulfate (SDS), and
polyvinyl alcohol (PVA) for nanowire separation.
[0050] Lyophilization techniques may be employed at block 40 and
block 50 to turn the resulting ice-wire structure into a
freestanding, low-density foam composed of interlocked nanowires.
In order to create a nanowire structure from the resulting
wire-water solution at block 30, the wires must undergo a
freeze-drying process to avoid collapse from the surface tension of
the water. Once the wire-water solution has been created, the
density of the final foam structure can be adjusted by changing the
water to wire ratio.
[0051] In one embodiment, the dispersion of treated nanowires and
freezable fluid may be placed into various shaped molds and frozen
at block 40 of the method of FIG. 1. To make foams of selected
shapes, thin copper molds (for high thermal conductivity) may be
used to freeze nanowire solutions into the shapes of the molds.
[0052] To create spherical ice-wire structures and foams,
wire-water solutions can also be dropped directly into liquid
nitrogen or other cryogenic liquid in the form of droplets and then
frozen as spheres at block 40. Pipettes of varying diameters can be
used to adjust the diameters of the spherical ice-wire
structures.
[0053] Lyophilization techniques that are employed at block 50
normally work by reducing the surrounding pressure of wire-liquid
material frozen at block 40, for example in a vacuum, to allow the
frozen water in the material to sublimate (i.e. move directly from
the solid phase to the gas phase).
[0054] Commercial lyophilization devices generally use a four-step
process:
[0055] 1) pretreatment; 2) freezing; 3) primary drying; and 4)
secondary drying. In the freezing step, the material is cooled to a
temperature that is below the lowest temperature where the solid
phase and liquid phase can coexist, called the triple point. This
cooling ensures that the material will sublimate rather than melt
during the drying steps.
[0056] In the primary drying phase, the pressure is lowered and the
material may be heated to an optimal point where the frozen
material sublimates efficiently. Typically, approximately 95% of
the water sublimates away in the primary drying phase.
[0057] During the secondary drying phase, the pressure may be
lowered further and the material temperature may also be increased
to facilitate desorption of remaining water molecules from the
material.
[0058] The freeze-drying steps of block 50 of FIG. 1 leave a
free-standing structure of interlocked nanowires. This interlocked
structure is processed further at block 60 of FIG. 1. The process
changes the structure from a loosely interlocked lattice of wires
into a single interconnected pure-metal foam without a substantial
increase in density. At block 60, the ice-wire structure preferably
undergoes several oxidation-reduction cycles to physically coalesce
the wires together at the intersections to form the final foam. The
final metal foams produced at block 60 may be used as a substrate
for further processing into ionic materials.
[0059] Referring now to FIG. 2, a flow diagram of an alternative
embodiment of a method 70 for fabricating low density metal foams
with controllable characteristics is shown. The method 70 described
in FIG. 2 begins with the formation of a nanoporous membrane
template at block 80. This membrane template has pores or channels
with controllable dimensions that provide a template for the
creation of nanowires. Nanowires can be grown by electrodeposition
into nanoporous templates of various sizes and types. The preferred
template materials include anodized aluminum oxide (AAO) membranes,
polycarbonate membranes, porous mica membranes or nanochannel glass
templates, to lengths of between approximately 1 .mu.m to 100 .mu.m
and diameters from approximately 10 nm to 1,000 nm.
[0060] At block 90, a working electrode is coated onto one side of
the starting membrane that was fabricated or provided at block 80.
For example, a metal layer may be coated onto one side of the
membrane by a variety of procedures such as by magnetron sputtering
to cover the template pores and to be used as a working electrode
during electrodeposition.
[0061] Nanowires are then formed by electrodeposition in the
membrane at block 100. One preferred electrodeposition process is
carried out in a three-electrode cell with electrolytes tailored to
the particular metal that is to be deposited in the pores and
channels of the template.
[0062] After electrodeposition at block 100, the working electrode
on the membrane template deposited at block 90 is removed at block
110. The working electrode may be removed by conventional etching
procedures at block 110 that will dissolve the electrode.
[0063] The nanowires are then released from the membrane template
by disintegration of the template at block 120. The nanowires can
be separated from template material by both chemical and mechanical
methods such as by etching and sonication.
[0064] At block 130 of FIG. 2, the released nanowires may be
optionally agitated to separate and randomize the nanowires. It was
found that during this template removal process the wires tended to
clump together (long axes parallel to one another) due to van der
Waals attractions between the wires. To disrupt this clumping, the
containers could be shaken aggressively by hand or sonicated.
[0065] The surfaces of the nanowires are then treated at block 140
to eliminate the presence of any oxides or other materials that may
appear on the surface of the nanowires during the fabrication
steps. One surface treatment is with a mild acid such as ascorbic
acid that will remove oxides formed on the surface. The nanowire
surface treatments at block 140 may also be in the form of exposure
to a surfactant.
[0066] The treated nanowires are then washed and dispersed in a
suitable fluid for freeze drying (lyophilization) at block 150.
Washing removes the unused surface treatments and other
contaminants. The washing and dispersion step at block 150 can also
include concentrating or diluting the nanowires to a desired
density, which will influence the characteristics of the final foam
that is produced.
[0067] At block 160 of the method of FIG. 2, the prepared
dispersion of treated nanowires is then frozen. Optionally, the
dispersion can be placed in shaped molds to produce foams with a
selected shape. Spherical shaped foams can also be produced by
placing drops of nanowire-fluid mixture into a cryogenic liquid
such as liquid nitrogen.
[0068] Lyophilization of the frozen wire-fluid mixture at block 160
will produce an interlocked nanowire structure at block 170. This
Lyophilization procedure can also be performed in commercially
available freeze-drying machines.
[0069] The interlocked wire structure that remains after the
removal of the frozen fluid at block 170 is processed further to
form an interconnected pure-metal foam at block 180 of the method
of FIG. 2. The points of contact between nanowires of the
interlocked nanowire structure are preferably sintered by heating
the interlocked nanowire structure without melting the wires to the
point of liquefaction or by exposing the structure to several
oxidation-reduction cycles.
[0070] The dimensions and physical characteristics of the metal
foams that are formed at block 180 can be controlled through the
formation steps and the selection of the metal nanoparticles. The
produced metal foams can then be used as a substrate for conversion
of the metals into ionic materials at block 190 of FIG. 2.
[0071] Further processing of the metals of the pristine metal foams
at block 190 can convert the metals into ionic materials such as
oxides, nitrides, chlorides, hydrides, fluorides, iodides and
carbides and other materials through established techniques. For
example, transition-metal nitrides may be synthesized by heating
nanoscale metal foams under flowing N.sub.2(g) or NH.sub.3(g),
typically in temperatures ranging from about 650.degree. C. to
about 800.degree. C. Similarly, metal oxide foams can be produced
by heating the foams under flowing oxygen. Metal oxide foams can
also be starting substrates for the production of other ionic
materials. Wet processing and other known processing schemes may be
used at block 190 to convert the metal foams to ionic materials.
The nanoscale ionic material foams with selected dimensions,
porosity and reactivity can be used in a wide variety of
settings.
[0072] The technology described herein may be better understood
with reference to the accompanying examples, which are intended for
purposes of illustration only and should not be construed as in any
sense limiting the scope of the technology described herein as
defined in the claims appended hereto.
EXAMPLE 1
[0073] In order to demonstrate the operational principles of the
fabrication methods, several metal foams were prepared using the
fabrication method shown schematically in FIG. 2. In this example,
pure metal nanowire foams of Cu, Pd, Co and Ag were fabricated with
a wide range of tunable densities.
[0074] Nanowires were grown by electrodeposition into nanoporous
templates of various sizes and types, including anodized aluminum
oxide (AAO) membranes and polycarbonate membranes, to lengths of
between 5 .mu.m and 40 .mu.m and diameters from about 50 nm to 200
nm.
[0075] Magnetron sputtering was used to coat thick conductive
layers (200 nm to 500 nm) on the backsides of the membranes for use
as working electrodes. For copper and cobalt nanowires, a 500 nm
thick copper layer was coated onto the backside of the membrane to
cover the template pores and to be used as a working electrode
during electrodeposition. For silver, palladium, gold and platinum
nanowires, a 500 nm gold working electrode was used instead.
[0076] These coated membranes were then placed into an
electrodeposition cell where metals were deposited
potentiostatically into the pores to grow nanowires. The
electrodeposition of wires was carried out in a three-electrode
cell with suitable electrolytes. In all cases, a platinum counter
electrode was used along with an Ag.sup.+/AgCI reference
electrode.
[0077] Potential was pulsed to help ensure uniform deposition (for
example, from 0 mV to -200 mV at one second intervals for copper
deposition). The deposition current was monitored and growth was
halted when an increase in current corresponding to the onset of
over-deposition was detected. Deposition potential was pulsed and
electrolytes containing large amounts of metal ions were used to
ensure deposition uniformity. For copper nanowires, the deposition
was carried out with an electrolyte composed of 238 g/L copper
sulfate and 21 g/L sulfuric acid. For silver nanowires the
electrolyte was composed of 15.6 g/L silver sulfate and 224 g/L
potassium thiocyanate. For palladium nanowires the deposition
electrolyte was composed of 5 g/L PdCl2 and 10 g/L HCI. Finally,
for cobalt nanowires the electrolyte was composed of 50 g/L cobalt
sulfate and 40 g/L boric acid.
[0078] Following deposition, the working electrodes of the
templates were removed by floating the wire-filled AAO (working
electrode side down) in an etchant solution. For a copper working
electrode, 7.9M nitric acid was used for 15 seconds. For a gold
working electrode, a solution containing 10 mL of water, 4 grams of
potassium iodide and 2 grams of iodine was used.
[0079] The wire-filled membrane was then thoroughly rinsed in
deionized water. The template was then immersed in 6M NaOH and
sonicated for 15 minutes to dissolve the AAO template and remove
the nanowires. It was found that during this template removal
process the wires tend to clump together (long axes parallel to one
another) due to van der Waals attractions between the nanowires. To
prevent this clumping it was necessary to aggressively shake by
hand the NaOH-nanowire solution periodically (e.g., at 5 minutes,
10 minutes and directly at the end of the sonication).
[0080] Following this process, multiple fluid exchanges were used
to move the nanowires into deionized water. Average wire diameter
of 150 nm and an average length was 20 .mu.m were found using
SEM.
[0081] For copper nanowires, the same exchange process was then
used to transfer the wires into 100 g/L L-ascorbic acid where they
were soaked for 48 hours in order to reduce any oxide in the copper
to ensure the wires are pure copper to strengthen van der Waals
attractions between the wires during the foam formation step. Wires
are transferred back into deionized water through fluid exchanges
immediately prior to foam formation. The Co, Ag and Pd wires were
instead immersed in 250 g/L PVP to separate the wires, which were
then transferred back to water through the fluid exchange
process.
[0082] In order to create a nanowire foam from the resulting
wire-water solution, the wires must undergo a freeze-drying process
to avoid collapse from the surface tension of the water. Once the
wire-water solution has been created, the density of the final foam
can be adjusted by changing the wire-water ratio. Densities from
200 mg/cm.sup.3 to 8 mg/cm.sup.3 were achieved using this process.
To create spherical foams, droplets of this solution were placed
directly into liquid nitrogen and frozen as spheres. Pipettes of
varying diameters were used to adjust the diameters of foams from 2
mm to 5 mm. Ice-wire spheres were then moved into small baskets
composed of a single loop of thin (127 .mu.m diameter) wire to
support the structure during freeze-drying. This wire was always
made of the same material as the foam. To make foams of other
shapes, thin copper molds (for high thermal conductivity) were used
to freeze nanowire solutions into the shapes of the rectangular and
cylindrical molds. Frozen foams were placed in rough vacuum
(.about.10 mTorr) in order to sublimate out the ice from the
sample, leaving a free-standing nanowire structures of interlocked
nanowires.
[0083] An additional process was used to strengthen the metal
nanowire foams. Spherical and cylindrical foams were transported
into a tube furnace and underwent oxidation-reduction cycles to
physically coalesce wires together at intersections, changing the
structure from a loosely interlocked lattice of wires into a single
interconnected pure-metal foam without a significant increase in
density. For copper nanowires, the foams were placed first in air
at 300.degree. C. for 20 minutes in order to oxidize them
completely. Next they were reduced back to pure copper by putting
them in a forming gas (5% hydrogen in nitrogen) for 20 minutes at
300.degree. C. Oxygen kinetics and copper atom mobility during
these processes allow the foams to form into interconnected
pure-metal structures.
EXAMPLE 2
[0084] Nanoindentation experiments were carried out on the foams
produced with the methods shown in Example 1 to quantify the
enhanced strength of the interconnected Cu nanowire foams. In order
to perform nanoindentation measurements, cylindrical Cu foams with
a 2 mm height and diameter were fabricated and strengthened using
the oxidation/reduction process. The final foams ranged in
densities from 8 mg/cm.sup.3 to 70 mg/cm.sup.3. The indenter tip
was a 2 mm ruby sphere and measurements were conducted at room
temperature and ambient laboratory humidity. The loading and
unloading rate was kept constant at 100 .mu.m/m. A sample
loading/unloading curve is shown in FIG. 3.
[0085] Loading/unloading curves were derived for a 9 mg/cm.sup.3
strengthened Cu cylindrical foam with 2 mm in height and diameter.
By measuring the initial slope of the unloading curve it was
possible to extract the modulus of the subject material. The
elastic modulus of each sample was extracted from the initial slope
of the unloading curve using the Oliver-Pharr multi-point unloading
method. For a spherical indenter tip contacting a flat surface the
Elastic Modulus, E.sup.r can be calculated as:
E r = S .pi. 2 A ( h contact ) ##EQU00001##
where S is the unloading stiffness of the sample,
dP dh , ##EQU00002##
taken here as the slope of the first 15% of the unloading curve of
each sample; A(h.sub.contact) is the area of contact between the
indenter tip and the sample at the depth of penetration below the
plane of contact:
A(h.sub.contact)=2 .pi.Rh.sup.contact-.pi.(h.sub.contact).sup.2
and h.sub.contact was calculated as:
h contact = h - 3 4 P S ##EQU00003##
where P is the load on the sample and h is the depth of
penetration.
[0086] FIG. 4 is a relative modulus vs. relative density plot for
various low density materials. The graph of FIG. 4 includes the
results of the Cu measurements as well as results from previous
measurements of low and ultralow density materials.
[0087] Plotted here are the relative density (defined as the final
density of the material normalized by the bulk density of the
material from which they are constructed) and the relative modulus
(the elastic modulus of the sample normalized by the bulk modulus
of its constituent material) of such samples.
[0088] The results shown as open circles in FIG. 4 represent
interlocked copper wire foams from previous results in the art for
comparison. At 9 mg/cm.sup.3, for example, the prior work shows a
modulus of about 5 Pa. At the same density, the interconnected
foams structure made from the same material produced by the current
methods was found to have a modulus of 1200 Pa, an improvement in
elastic modulus of three orders of magnitude at the same
density.
[0089] Also depicted in FIG. 4 are several other low and ultralow
density materials whose modulus has been measured through
nanoindentation for comparison. Using the methods of the present
technology it was possible to create a pure metallic foam whose
relative modulus is comparable to strong materials such as C and Si
aerogels at the same relative densities. Note that at similar
relative densities Ni microlattices have a much greater relative
modulus than the interconnected Cu foams, but require an elaborate
nanolithography process. The nanowire foams produced by the methods
described herein can be fabricated over large areas and volumes
much more easily and cost-effectively as the methods rely only on
electrodeposition and the samples are fabricated inside of
macroscopic molds.
Example 3
[0090] One potential use of ultralow density metal foams is for use
as high energy density laser targets due to their ability to be
heated volumetrically that allows targets composed of high-Z
elements to uniformly reach the extreme temperatures that are
required for X-ray emission. Gas targets, oxides, metal-doped
aerogels and metal-lined cavities have been employed previously for
reaching the necessary effective density. However, the pure metal
targets allow higher X-ray conversion efficiencies if the targets
can be fabricated at densities low enough to allow volumetric
heating while still maintaining mechanical stability.
[0091] To demonstrate the functionality of pure metal foam targets
produced by the methods, spherical Cu targets (2 mm and 4 mm
diameters) and cylindrical Ag targets (4 mm diameter and length)
were produced to be used as targets for testing at the OMEGA and
the National Ignition Facility (NIF) laser facilities. The enhanced
mechanical strength was critical to the use of such metal foams for
use as x-ray emission materials.
[0092] At the OMEGA facility each of 40 beams delivered 475 J of
351 nm laser light to the spherical foam sample. Of these beams, 20
beams were incident on each hemisphere of the spherical Cu targets
and were focused 600 .mu.m inside the sample.
[0093] In the OMEGA demonstration, the volumetric heating of the Cu
foams allowed for substantially higher K-shell energy conversion
efficiency than the solid copper reference, reaching a maximum of
2.59% for the Cu foam with a 22 mg/cm.sup.3 density.
[0094] At the NIF facility all 192 beams were used, delivering a
total of 500 kJ of energy to the sample with 351 nm laser light,
and 96 beams were focused 550 .mu.m inside each hemisphere.
Spherical samples were mounted on the end of small sticks with a
support ring also made of AWG 36 copper (99.9%).
[0095] In the NIF demonstration, time-resolved X-ray emission data
for energy integrated in the Cu K-shell was obtained from three
different foam density samples. The results obtained from Cu foams
with densities of 10 mg/cm.sup.3 to 18 mg/cm.sup.3 showed
increasing conversion efficiency as the density was increased.
[0096] Accordingly, the pure Cu metal foams with density around 20
mg/cm.sup.3 and below have been successfully shot at OMEGA and NIF
facilities, where the laser energy has allowed the foams to be
heated volumetrically and to produce high X-ray conversion
efficiencies. This opens up an uncharted territory to explore
high-Z plasma physics.
[0097] In summary, ultralow density Cu, Ag, Co and Pd pure metal
foams have been fabricated using nanowire starting material (made
by electrodeposition or other methods) and a freeze-drying process.
The densities of the foams can be tuned from as low as 8
mg/cm.sup.3, or 0.09% of the bulk density, to as high as 200
mg/cm.sup.3 and beyond.
[0098] Furthermore, it was shown that the Cu nanowire foams can be
greatly strengthened through an oxidation and reduction process by
transforming a loosely interlocked structure into a truly
interconnected nanowire monolith. The elastic modulus of such foams
was found to increase by three orders of magnitude compared to that
of an interlocked structure. Such mechanically stable pure metal
foams open up a wide range of applications, including high energy
density laser targets.
[0099] Embodiments of the present technology may be described
herein with reference to flowchart illustrations of methods and
systems according to embodiments of the technology, and/or
procedures, algorithms, steps, operations, formulae, or other
computational depictions, which may also be implemented as computer
program products. In this regard, each block or step of a
flowchart, and combinations of blocks (and/or steps) in a
flowchart, as well as any procedure, algorithm, step, operation,
formula, or computational depiction can be implemented by various
means, such as hardware, firmware, and/or software including one or
more computer program instructions embodied in computer-readable
program code.
[0100] Accordingly, blocks of the flowcharts, and procedures,
algorithms, steps, operations, formulae, or computational
depictions described herein support combinations of means for
performing the specified function(s), combinations of steps for
performing the specified function(s), and computer program
instructions, such as embodied in computer-readable program code
logic means, for performing the specified function(s). It will also
be understood that each block of the flowchart illustrations, as
well as any procedures, algorithms, steps, operations, formulae, or
computational depictions and combinations thereof described herein,
can be implemented by special purpose hardware-based computer
systems which perform the specified function(s) or step(s), or
combinations of special purpose hardware and computer-readable
program code.
[0101] From the description herein, it will be appreciated that
that the present disclosure encompasses multiple embodiments which
include, but are not limited to, the following:
[0102] 1. A method for fabricating low density and ultralow density
nanostructured ionic material foams, the method comprising: (a)
forming a liquid dispersion of metal nanowires in a freezable
fluid; (b) freezing the liquid dispersion to form an ice-nanowire
structure; (c) sublimating the ice-nanowire structure to expose a
free standing nanowire foam structure; (d) binding the nanowire
foam structure at points of contact to form an interconnected metal
foam monolith; and (e) converting the metals of the metal foam
monolith into an ionic material selected from the group of
materials consisting of a nitride, an oxide, a chloride, a hydride,
a fluoride, an iodide and a carbide to produce an ionic material
foam.
[0103] 2. The method of any preceding or following embodiment,
further comprising: treating nanowire surfaces with an acid to
remove oxide contaminants; and dispersing treated nanowires in a
freezable liquid.
[0104] 3. The method of any preceding or following embodiment,
further comprising: treating nanowire surfaces with a surfactant to
separate nanowires from each other; and dispersing treated
nanowires in a freezable liquid.
[0105] 4. The method of any preceding or following embodiment,
wherein the metal nanowires are formed from a metal selected from
the group of metals consisting of Al, Ti, V, Cr, Fe, Co, Ni, Cu,
Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Nd, Sm, Dy, Pt,
Au, Pb, and Bi, and alloys based on one or more of these
metals.
[0106] 5. The method of any preceding or following embodiment,
wherein the metal nanowires have an aspect ratio of length vs.
diameter within the range of 2 to 1,000,000.
[0107] 6. The method of any preceding or following embodiment,
wherein the dispersion contains wires diluted in volume by a factor
of 2 to 10,000.
[0108] 7. The method of any preceding or following embodiment,
further comprising: depositing the liquid dispersion in one or more
molds; and freezing the liquid dispersion in the molds.
[0109] 8. The method of any preceding or following embodiment,
wherein the binding of points of contact of the ice-nanowire
structure is performed by sintering.
[0110] 9. The method of any preceding or following embodiment,
wherein the binding of points of contact of the ice-nanowire
structure is performed by one or more oxidation and reduction
cycle(s) performed at elevated temperatures.
[0111] 10. A method for fabricating low density and ultralow
density nanostructured ionic material foams, the method
comprising:(a) preparing a nanoporous membrane template; (b)
applying an electrode to one side of the nanoporous membrane
template: (c) forming nanowires within the nanoporous membrane
template by electrodeposition;(d) releasing the formed nanowires
from the membrane template; (e) forming a liquid dispersion of
metal nanowires in a freezable fluid; (f) freezing the liquid
dispersion to form an ice-nanowire structure; (g) sublimating the
ice-nanowire structure to expose an interlocked nanowire structure;
(h) binding the interlocked nanowire structure at points of contact
between nanowires to form an interconnected metal foam; and (i)
converting the metals of the interconnected metal foam into an
ionic material selected from the group of materials consisting of a
nitride, an oxide, a chloride, a hydride, a fluoride, an iodide and
a carbide to produce an ionic material foam.
[0112] 11. The method of any preceding or following embodiment,
wherein the releasing of formed nanowires comprises: etching the
membrane template to remove the electrode; disintegrating the
membrane template to release nanowires; dispersing the released
nanowires in a freezable fluid; and agitating released nanowires to
separate and randomize nanowires in the freezable fluid.
[0113] 12. The method of any preceding or following embodiment,
wherein the nanoporous membrane template comprises an anodized
aluminum oxide (AAO) membrane, a polycarbonate membrane, a porous
mica membrane or a nanochannel glass membrane.
[0114] 13. The method of any preceding or following embodiment,
further comprising: treating nanowire surfaces with an acid to
remove oxide contaminants; and dispersing treated nanowires in a
freezable liquid.
[0115] 14. The method of any preceding or following embodiment,
further comprising: treating nanowire surfaces with a surfactant to
separate nanowires from each other; and dispersing treated
nanowires in a freezable liquid.
[0116] 15. The method of any preceding or following embodiment,
further comprising: depositing the liquid dispersion in one or more
molds; and freezing the liquid dispersion in the molds.
[0117] 16. The method of any preceding or following embodiment,
wherein the metal nanowires are formed from a metal selected from
the group of metals consisting of Al, Ti, V, Cr, Fe, Co, Ni, Cu,
Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Nd, Sm, Dy, Pt,
Au, Pb, and Bi, and alloys based on one or more of these
metals.
[0118] 17. The method of any preceding or following embodiment,
wherein the metal nanowires have an aspect ratio within the range
of 2 to 1,000,000.
[0119] 18. The method of any preceding or following embodiment,
wherein the dispersion wherein the dispersion contains wires
diluted in volume by a factor of 2 to 10,000.
[0120] 19. The method of any preceding or following embodiment,
wherein the binding of points of contact of the ice-nanowire
structure is performed by sintering.
[0121] 20. The method of any preceding or following embodiment,
wherein the binding of points of contact of the ice-nanowire
structure is performed by one or more oxidation and reduction
cycle(s) performed at elevated temperatures.
[0122] 21. An ionic material foam structure having a bulk density
and comprising: (a) an interconnected nanoscale ionic material
network structure of an ionic material selected from the group of
materials consisting of a nitride, an oxide, a chloride, a hydride,
a fluoride, an iodide and a carbide to produce an ionic material
foam; (b) wherein the network structure has a density of about
0.1.degree. A of the bulk density.
[0123] 22. The ionic material foam structure of any preceding or
following embodiment, wherein the network structure has a density
from about 20 g/cm.sup.3 to about 1 mg/cm.sup.3.
[0124] 23. The ionic material foam structure of any preceding or
following embodiment, wherein the metal nanowire network is formed
from one or more metals selected from the group of metals
consisting of Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo,
Ru, Rh, Pd, Ag, Sn, Sb, La, Nd, Sm, Dy, Pt, Au, Pb, and Bi, and
alloys based on one or more of these metals.
[0125] As used herein, the singular terms "a," "an," and "the" may
include plural referents unless the context clearly dictates
otherwise. Reference to an object in the singular is not intended
to mean "one and only one" unless explicitly so stated, but rather
"one or more."
[0126] As used herein, the term "set" refers to a collection of one
or more objects. Thus, for example, a set of objects can include a
single object or multiple objects.
[0127] As used herein, the terms "substantially" and "about" are
used to describe and account for small variations. When used in
conjunction with an event or circumstance, the terms can refer to
instances in which the event or circumstance occurs precisely as
well as instances in which the event or circumstance occurs to a
close approximation. When used in conjunction with a numerical
value, the terms can refer to a range of variation of less than or
equal to .+-.10% of that numerical value, such as less than or
equal to .+-.5%, less than or equal to .+-.4%, less than or equal
to .+-.3%, less than or equal to .+-.2%, less than or equal to
.+-.1%, less than or equal to .+-.0.5%, less than or equal to
.+-.0.1%, or less than or equal to .+-.0.05%. For example,
"substantially" aligned can refer to a range of angular variation
of less than or equal to .+-.10.degree., such as less than or equal
to .+-.5.degree., less than or equal to .+-.4.degree., less than or
equal to .+-.3.degree., less than or equal to .+-.2.degree., less
than or equal to .+-.1.degree., less than or equal to
.+-.0.5.degree., less than or equal to .+-.0.1.degree., or less
than or equal to .+-.0.05.degree..
[0128] Additionally, amounts, ratios, and other numerical values
may sometimes be presented herein in a range format. It is to be
understood that such range format is used for convenience and
brevity and should be understood flexibly to include numerical
values explicitly specified as limits of a range, but also to
include all individual numerical values or sub-ranges encompassed
within that range as if each numerical value and sub-range is
explicitly specified. For example, a ratio in the range of about 1
to about 200 should be understood to include the explicitly recited
limits of about 1 and about 200, but also to include individual
ratios such as about 2, about 3, and about 4, and sub-ranges such
as about 10 to about 50, about 20 to about 100, and so forth.
[0129] Although the description herein contains many details, these
should not be construed as limiting the scope of the disclosure but
as merely providing illustrations of some of the presently
preferred embodiments. Therefore, it will be appreciated that the
scope of the disclosure fully encompasses other embodiments which
may become obvious to those skilled in the art.
[0130] All structural and functional equivalents to the elements of
the disclosed embodiments that are known to those of ordinary skill
in the art are expressly incorporated herein by reference and are
intended to be encompassed by the present claims. Furthermore, no
element, component, or method step in the present disclosure is
intended to be dedicated to the public regardless of whether the
element, component, or method step is explicitly recited in the
claims. No claim element herein is to be construed as a "means plus
function" element unless the element is expressly recited using the
phrase "means for". No claim element herein is to be construed as a
"step plus function" element unless the element is expressly
recited using the phrase "step for".
* * * * *