U.S. patent application number 17/668329 was filed with the patent office on 2022-05-26 for additively manufactured metal energetic ligand precursors and combustion synthesis for hierarchical structure nanoporous metal foams.
This patent application is currently assigned to Triad National Security, LLC. The applicant listed for this patent is Triad National Security, LLC. Invention is credited to Alexander H. Mueller, Andrew Schmalzer, Bryce Tappan.
Application Number | 20220161322 17/668329 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-26 |
United States Patent
Application |
20220161322 |
Kind Code |
A1 |
Tappan; Bryce ; et
al. |
May 26, 2022 |
ADDITIVELY MANUFACTURED METAL ENERGETIC LIGAND PRECURSORS AND
COMBUSTION SYNTHESIS FOR HIERARCHICAL STRUCTURE NANOPOROUS METAL
FOAMS
Abstract
Processes for tailoring the macroscopic shape, metallic
composition, mechanical properties, and pore structure of
nanoporous metal foams prepared through combustion synthesis via
direct write 3D printing of metal energetic ligand precursor inks
made with water and an organic thickening agent are disclosed. Such
processes enable production of never before obtainable metal
structures with hierarchical porosity, tailorable from the
millimeter size regime to the nanometer size regime. Structures
produced by these processes have numerous applications including,
but not limited to, catalysts, heat exchangers, low density
structural materials, biomedical implants, hydrogen storage medium,
fuel cells, and batteries.
Inventors: |
Tappan; Bryce; (Santa Fe,
NM) ; Schmalzer; Andrew; (Los Alamos, NM) ;
Mueller; Alexander H.; (Santa Fe, NM) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Triad National Security, LLC |
Los Alamos |
NM |
US |
|
|
Assignee: |
Triad National Security,
LLC
Los Alamos
NM
|
Appl. No.: |
17/668329 |
Filed: |
February 9, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16381074 |
Apr 11, 2019 |
11278960 |
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17668329 |
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62656510 |
Apr 12, 2018 |
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International
Class: |
B22F 3/11 20060101
B22F003/11; C09D 11/52 20060101 C09D011/52; C22C 1/08 20060101
C22C001/08; B22F 10/60 20060101 B22F010/60; B22F 10/00 20060101
B22F010/00; H05K 1/09 20060101 H05K001/09 |
Goverment Interests
STATEMENT OF FEDERAL RIGHTS
[0002] The United States government has rights in this invention
pursuant to Contract No. 89233218CNA000001 between the United
States Department of Energy and Triad National Security, LLC for
the operation of Los Alamos National Laboratory.
Claims
1. A method for producing nanoporous metal foam, comprising: direct
write three-dimensional (3D) printing a metal energetic ligand
precursor ink by extruding the metal energetic ligand precursor ink
into a printed structure and allowing the printed structure to dry,
producing the nanoporous metal foam, wherein the printed structure
exhibits porosity at a macrostructural scale, the nanoporous metal
foam is a composite metal foam that comprises a higher catalytic
activity metal and a matrix metal that has lower catalytic activity
than the higher activity catalytic metal and/or a matrix metal that
has higher compressive strength than the higher catalytic activity
metal, the higher catalytic activity metal comprises Pt, Pd, Re, or
any combination thereof, and the matrix metal comprises Cu, Ni, or
any combination thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Nonprovisional
patent application Ser. No. 16/381,074 filed Apr. 11, 2019, which
claims the benefit of U.S. Provisional Patent Application No.
62/656,510 filed Apr. 12, 2018. The subject matter of these
earlier-filed applications is hereby incorporated by reference in
its entirety.
FIELD
[0003] The present invention generally relates to metal foams, and
more particularly, to processes for tailoring the macroscopic
shape, metallic composition, mechanical properties, and pore
structure of nanoporous metal foams prepared through combustion
synthesis via direct write three-dimensional (3D) printing of metal
energetic ligand precursor inks made with water and/or one or more
organic thickening agents.
BACKGROUND
[0004] Nanoporous metal foams (NMFs) are a class of advanced porous
architectures that combine metallic compositions with
macroporosity, mesoporosity, and sub-micron microporosity typical
of sol-gel-derived pore networks. NMFs thus present a nexus of
chemistry, nanostructure, and macrostructure. See image 100 of FIG.
1. The elemental composition can be variable and allows for
applications in structural materials, hydrogen storage, heat
transfer, catalysts, etc. The fine structure dictates catalytic
activity, surface area/kinetics, etc. The macrostructure allows for
the engineering, design, and control of flow paths and pressure
drop. Development of processes for controlling porosity over
nano-length, micro-length, and macro-length scales and strategies
for controlling monolithicity will be important for maximizing the
potential of NMFs for technological applications. Chemical
reactions 200 for producing [Fe(BTA).sub.3][NH.sub.4].sub.3 and
Cu(BTA)(NH3).sub.2 are shown in FIG. 2.
[0005] However, while a handful of metals, such as gold, can be
readily rendered into nanoporous foams through dealloying
techniques, the porosity and morphology of such foams is limited in
scope, and this dealloying does not extend well to most transition
and main-group metals. Combustion synthesis to produce metal foams
using metal bistetrazoleamine (mBTA) complexes, for example, is a
straightforward process for preparing aerogel-like densities and
open-celled pore networks of a wide variety of metals. However, one
primary disadvantage of the combustion synthesis approach to date
has been the difficulty in producing the foam material in relevant
form factors, thus limiting applications where macroscopic forms
and shape control are desired. Accordingly, an improved process for
producing metal foams may be beneficial.
SUMMARY
[0006] Certain embodiments of the present invention may provide
solutions to the problems and needs in the art that have not yet
been fully identified, appreciated, or solved by conventional metal
foam synthesis techniques. For example, some embodiments of the
present invention pertain to processes for tailoring the
macroscopic shape, metallic composition, mechanical properties, and
pore structure of nanoporous metal foams prepared through
combustion synthesis via direct write 3D printing of metal
energetic ligand precursor inks made with water and/or an organic
thickening agent.
[0007] In an embodiment, a method for producing nanoporous metal
foam includes direct write 3D printing a metal energetic ligand
precursor ink by extruding the metal energetic ligand precursor ink
into a printed structure and allowing the printed structure to dry,
producing the nanoporous metal foam. The printed structure exhibits
porosity at a macrostructural scale.
[0008] In another embodiment, an additive manufacturing process for
producing hierarchically structured nanoporous metal foam includes
extruding a slurry including one or more metal energetic ligand
precursors into a structure with a prescribed pattern and density.
The process also includes heating the structure in an inert
atmosphere such that the one or more metal energetic ligand
precursors of the structure undergo self-sustaining combustion
synthesis that transforms the one or more energetic metal ligand
precursors into a foaming gas, leaving behind a zero-valence state
metal. The process further includes heat treating the structure to
strengthen the structure and produce a post-processed structure. In
some embodiments, only the post-processing is performed at a
temperature higher than room temperature.
[0009] In yet another embodiment, a process includes 3D printing a
metal energetic ligand precursor ink by extruding the metal
energetic ligand precursor ink into a structure and allowing the
printed structure to dry, producing a nanoporous metal foam. The
metal energetic ligand precursor ink is a slurry that includes one
or more metal energetic ligands, as well as water, at least one
binder, or both. The one or more metal energetic ligand precursors
include mBTA, metal cyanimide, metal dicyanamide, metal
5-aminotetrozole, or any combination thereof. The process also
includes heating the structure in an inert atmosphere such that the
one or more metal energetic ligand precursors of the structure
undergo self-sustaining combustion synthesis. The process further
includes heat treating the structure to strengthen the structure
and produce a post-processed structure. The metal energetic ligand
precursor ink comprises a slurry of the one or more metal energetic
ligand precursors, water, and at least one binder, or the metal
energetic ligand precursor ink comprises a slurry of the one or
more metal energetic ligand precursors and at least one binder.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] In order that the advantages of certain embodiments of the
invention will be readily understood, a more particular description
of the invention briefly described above will be rendered by
reference to specific embodiments that are illustrated in the
appended drawings. While it should be understood that these
drawings depict only typical embodiments of the invention and are
not therefore to be considered to be limiting of its scope, the
invention will be described and explained with additional
specificity and detail through the use of the accompanying
drawings, in which:
[0011] FIG. 1 illustrates the nexus of chemistry, nanostructure,
and macrostructure presented by MNFs.
[0012] FIG. 2 illustrates chemical reactions for producing
[Fe(BTA).sub.3][NH.sub.4].sub.3 and Cu(BTA)(NH.sub.3).sub.2.
[0013] FIG. 3A is a magnified view of a simple cubic patterned
macrostructure, according to an embodiment of the present
invention.
[0014] FIG. 3B is a magnified view of a face centered tetragonal
patterned macrostructure, according to an embodiment of the present
invention.
[0015] FIG. 4 is a flowchart illustrating a process for generating
additively manufactured HS-NMFs, according to an embodiment of the
present invention.
[0016] FIG. 5A is a photograph illustrating a 3D printer extruding
a water-based slurry of mBTA precursors, according to an embodiment
of the present invention.
[0017] FIG. 5B is a photograph illustrating the printed mBTA
precursors undergoing a self-sustaining combustion synthesis via
input from a CO.sub.2 laser, according to an embodiment of the
present invention.
[0018] FIG. 5C is a photograph illustrating zero-valence state
metal structures before (left) and after (right) heat treatment,
according to an embodiment of the present invention.
[0019] FIG. 5D is a micrograph illustrating a post-processed
structure at a 300 .mu.m scanning electron microscope (SEM) scale,
according to an embodiment of the present invention.
[0020] FIG. 5E is a micrograph illustrating a post-processed
structure at a 20 .mu.m SEM scale, according to an embodiment of
the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0021] Some embodiments of the present invention pertain to
processes for tailoring the macroscopic shape, metallic
composition, mechanical properties, and pore structure of
nanoporous metal foams prepared through combustion synthesis via
direct write 3D printing of metal energetic ligand precursor inks
made with water and/or an organic thickening agent. The energetic
ligands may include, but are not limited to, BTA, cyanimide,
dicyanamide, 5-aminotetrozole, any other suitable energetic ligand,
or any combination thereof without deviating from the scope of the
invention. The energetic ligands are prepared with a metal (e.g.,
[Fe(BTA).sub.3][NH.sub.4].sub.3, Cu(BTA)(NH.sub.3).sub.2, silver
cyanimide, etc.), which constitutes the metal(s) in the NMF.
[0022] These combined technologies from Los Alamos National
Laboratory (LANL) enable production of never before obtainable
metal structures with hierarchical porosity, tailorable from the
millimeter size regime to the nanometer size regime. Such
hierarchical structures could prove to be revolutionary flow
catalysts. Additionally, the conductive metal substrate may be
utilized for electro-catalyst structures. These structures have
numerous applications including, but not limited to, catalysts,
heat exchangers, low density structural materials, biomedical
implants, hydrogen storage medium, fuel cells, and batteries.
[0023] Combustion conditions, incorporation of binders into
pre-combustion structures, and post-synthesis annealing on pore
size statistics and molar surface areas are discussed. Compressive
strength and modulus as a function of these conditions are
characterized and analyzed via micro- and nano-computed tomography
(CT). Hierarchical structures of NMFs are produced with various
macrostructures (e.g., grids in simple cubic and face centered
cubic patterns) with foam structures consisting of microporosity
and nanoporosity. Potential for using NMFs with enhanced mechanical
properties and form factors is discussed herein in an effort to
show how additive manufacturing and combustion synthesis can
produce unique and difficult to obtain hierarchical porous
architectures.
[0024] Hierarchical nanoporous and microporous metals with blended
constituents cannot be made with conventional 3D printing
processes. Accordingly, some embodiments employ a novel process for
manipulating the macroscopic form factors of metal foams, while
retaining the nanostructure and high surface area (e.g., 10 to 260
m.sup.2g.sup.-1) intrinsic to the combustion synthesis process of
mBTA, metal cyanimide, metal dicyanamide, metal 5-aminotetrozole,
etc., to produce hierarchically structured nanoporous metal foams
(HS-NMFs). In contrast to current technology for metal 3D printing
that requires expensive laser melting of powder beds or filaments,
the processing of some embodiments is conducted at room temperature
with a lower profile process (e.g., a lightly modified conventional
3D printer), where only the post-processing is done at a higher
temperature. This is a key and ground-breaking aspect of some
embodiments because it allows the user to print metallic structures
at room temperature, as well as to be able to incorporate small
stochastic pore size (e.g., less than 1 .mu.m) and large controlled
pore size (e.g., greater than 250 .mu.m) into the same structure.
Neither of these features have been previously demonstrated.
[0025] With this new capability, methods for tailoring the
macroscopic shape, mechanical properties, and pore structure of
NMFs prepared through combustion synthesis are provided via 3D
printing of metal energetic ligand precursor inks made with water
and an organic rheology modifier. One of the distinct advantages of
the process for making metallic foams of some embodiments is that
in the course of making the printable formulation, multiple metal
energetic ligand precursors can be combined in the same ink,
allowing for composite metallic foams. This will allow the
deposition of higher catalytic activity metals (e.g., Pt, Pd, Re,
etc.) in an efficient but disperse format throughout a lower
catalytic activity and/or higher compressive strength matrix (e.g.,
Cu or Ni).
[0026] Additionally, 3D printed structured metals have the ability
to withstand high elastic strain by distributing applied stresses
throughout the linkages that make up the macrostructure, which
could improve the lifetime of these materials under hydrodynamic
stresses that occur in flow cells. This inexpensive, rapid, and
novel capability would be of interest to fuel cell, carbon capture,
reactive metal, hydrogen storage, and heterogeneous catalysis
programs. On the federal side, the U.S. Department of Defense (DoD)
and the Department of Energy (DOE) Office of Energy Efficiency and
Renewable Energy (EERE) have various programs that this novel
capability would benefit.
[0027] The strategy for producing HS-NMFs in some embodiments is
centered around the concatenation of an additive manufacturing (AM)
process to the front end of the combustion synthesis technique
already established for generating NMFs. Through AM, various
macrostructures (e.g., grids in cubic and face centered tetragonal
patterns;
[0028] see magnified images 300, 310 of FIGS. 3A and 3B,
respectively) can be designed using a new mBTA feedstock that
retains the structural framework consisting of microporous and
nanoporous foam generated after combustion synthesis.
[0029] Generally speaking, the process of some embodiments includes
pressing or printing an energetic organometallic complex into the
desired architecture. The structure is then ignited by contacting
it with a hot wire or laser, for example. This causes the complex
to combust, releasing metal centers, heat, and combustion gases
(mostly H.sub.2/N.sub.2 in some embodiments). The metal centers
reduce to a zero-valency agglomerate of nanoparticles, and the
H.sub.2/N.sub.2 blows the foam in a manner somewhat analogous to a
Fourth of July carbon snake, but with metal.
[0030] Pressed pellets of Fe(BTA) may be used, which are the lowest
density metal foams yet discovered (0.011 g/cm.sup.3). Fe(BTA) also
has a high surface area (270 m.sup.2g.sup.-1). This surface area is
comparable to ultra-high surface area aerogels.
[0031] FIG. 4 is a flowchart illustrating a process 400 for
generating additively manufactured HS-NMFs, according to an
embodiment of the present invention. The process begins with
extruding a water-based slurry "ink" including at least one metal
energetic ligand precursor (see image 500 of FIG. 5A) into a
structure with a prescribed pattern and density at 410. See also
images 300, 310 of FIGS. 3A and 3B. In some embodiments, multiple
inks having different chemical structures and/or metals may be
used. For instance, an mBTA ink using copper and an mBTA ink using
titanium may be combined.
[0032] A suitable binder, such as methyl cellulose, may be used to
gel the water in the slurry to cause it to hold its shape as the
slurry is extruded. Methyl cellulose, for example, serves as binder
once the water dries. However, other cellulose and non-cellulose
binders may be used without deviating from the scope of the
invention. Such cellulose and non-cellulose binders may include,
but are not limited to, ethyl cellulose, butyl cellulose,
hydroxypropyl methyl cellulose, hydroxypropyl methyl cellulose,
hydroxypropyl cellulose, hydroxyethyl cellulose,
carboxymethylcellulose, methylethylcellulose, ethyl hydroxyethyl
cellulose, hydroxypropyl methyl cellulose, and/or other
polysaccharides, such as xanthan gum. In some embodiments, multiple
cellulose binders, multiple non-cellulose binders, or at least one
cellulose binder and at least one non-cellulose binder may be used.
Furthermore, organic solvents may be used in place of water in some
embodiments, and a suitable organic-soluble binder combination may
be used. Combinations that provide high viscosity with a low binder
content are preferable in some embodiments. Examples include, but
are not limited to, acetone, methyl acetate, ethyl acetate, and
butyl acetate, with cellulose esters such as cellulose nitrate,
cellulose acetate, and cellulose acetatebutyrate. Organic solvents
can be useful when the metal energetic ligand precursor(s) exhibit
high water solubility, particularly, but not exclusively, when
m=Fe, Co, Ni, or V.
[0033] The metal energetic ligand precursor(s) may be
[Fe(BTA).sub.3][NH.sub.4].sub.3, Cu(BTA)(NH.sub.3).sub.2, metal
cyanimide, metal dicyanamide, metal 5-aminotetrozole, and/or any
other suitable metal energetic ligand precursor without deviating
from the scope of the invention. Also, any metal may be used. Any
combination or ratio of suitable metal energetic ligand precursors
can be incorporated into a powder precursor fraction of a single
formulation in some embodiments without deviating from the scope of
the invention. However, copper is relatively inexpensive and easy
to work with, so Cu(BTA)(NH.sub.3).sub.2, for instance, is suitable
and cost-effective for many applications. Cu(BTA) also provides
structure-controlled macroporosity with stochastic
nanoporosity.
[0034] The 3D printer may be a direct ink write (DIW) printer in
some embodiments with a suitable nozzle size (e.g., 400 .mu.m). A
complex rheology may be employed to retain metal energetic ligand
precursor shape while drying. Yield stress behavior may allow for
the spanning of large gaps to increase the porosity.
[0035] The printed structure is allowed to dry at 420. In some
embodiments, this is the last step and the nanoporous metal foam is
produced via reactions within the ink. However, in other
embodiments, the process continues. The metal energetic ligand
precursor(s) of the printed structure undergo a self-sustaining
combustion synthesis via input from a CO.sub.2 laser (see image 510
of FIG. 5B) in a high-pressure inert atmosphere at 420 that
transforms the ligand(s) into a foaming gas. In image 510, the
transformation progressively occurs from the upper left to the
lower right. This leaves behind a zero-valence state metal. See the
left metal structure in image 520 of FIG. 5C. The zero-valence
state metal undergoes further heat treatment at 430 to strengthen
the remaining structure. See the right metal structure in image 520
of FIG. 5C. Both reactive and inert atmospheres can be used in both
combustion and post-processing in some embodiments to provide
reducing environments or oxidizing environments. Post-processing
can also be performed in a reduced pressure environment in some
embodiments.
[0036] The post-processed structure retains both the macroscale and
nanoscale features that make these materials unique. Micrograph 530
of FIG. 5D shows the post-processed structure at the 300 .mu.m
scanning electron microscope (SEM) scale and micrograph 540 of FIG.
5E shows the post-processed structure at the 20 .mu.m SEM scale. As
can be seen, both structure and porosity are achieved.
[0037] Synthesis conditions, such as the annealing under various
gaseous environments, flow rates, and temperature profiles, will
affect the pore structure and molar surface area. By using
Brunauer--Emmett--Teller (BET) analysis, the right balance of
compressive strength to pore size/surface area for a given
application can be discovered, while limiting sample shrinkage and
warpage. By tuning the synthesis conditions, the catalytic
properties of the nanofoams can be tuned as a promising catalyst
for nanotube and graphene synthesis, generating composite
nanostructures with tailored electrical and mechanical properties.
Other targeted reactions include the gas-phase, enhanced dry
reforming of methane with CO.sub.2, a reaction that could be a net
negative carbon sink with solar or nuclear energy input.
[0038] Mechanical response in compression can be determined using
dynamic micro-CT and nano-CT to show how the macrostructure can
improve these catalytic materials under load. By studying the
relationship between post-processing conditions and structure, the
printed materials can be tuned to have surface areas that optimize
catalytic activity. Energy-dispersive x-ray spectroscopy (EDS)
mapping of the as-processed samples can help to determine the
dispersion of various metallic components throughout the HS-NMF
matrix. Modifying the mechanical response of metal foams with
similar densities via AM is also possible. Producing NMFs with
enhanced mechanical properties and form factors via additive
manufacturing and combustion synthesis can yield unique and
conventionally difficult to obtain hierarchical porous
architectures.
[0039] Metal nanofoams can be produced for numerous metals, or
combinations of metals. Once the desired metal is selected and the
metal energetic ligand precursor(s) are produced, a slurry can be
formulated and 3D printed using the DIW process. The process
employed in some embodiments represents the first time that
nanoscale to macroscale feature size has been accomplished.
[0040] It will be readily understood that the components of various
embodiments of the present invention, as generally described and
illustrated in the figures herein, may be arranged and designed in
a wide variety of different configurations. Thus, the detailed
description of the embodiments of the present invention, as
represented in the attached figures, is not intended to limit the
scope of the invention as claimed, but is merely representative of
selected embodiments of the invention.
[0041] The features, structures, or characteristics of the
invention described throughout this specification may be combined
in any suitable manner in one or more embodiments. For example,
reference throughout this specification to "certain embodiments,"
"some embodiments," or similar language means that a particular
feature, structure, or characteristic described in connection with
the embodiment is included in at least one embodiment of the
present invention. Thus, appearances of the phrases "in certain
embodiments," "in some embodiment," "in other embodiments," or
similar language throughout this specification do not necessarily
all refer to the same group of embodiments and the described
features, structures, or characteristics may be combined in any
suitable manner in one or more embodiments.
[0042] It should be noted that reference throughout this
specification to features, advantages, or similar language does not
imply that all of the features and advantages that may be realized
with the present invention should be or are in any single
embodiment of the invention. Rather, language referring to the
features and advantages is understood to mean that a specific
feature, advantage, or characteristic described in connection with
an embodiment is included in at least one embodiment of the present
invention. Thus, discussion of the features and advantages, and
similar language, throughout this specification may, but do not
necessarily, refer to the same embodiment.
[0043] Furthermore, the described features, advantages, and
characteristics of the invention may be combined in any suitable
manner in one or more embodiments. One skilled in the relevant art
will recognize that the invention can be practiced without one or
more of the specific features or advantages of a particular
embodiment. In other instances, additional features and advantages
may be recognized in certain embodiments that may not be present in
all embodiments of the invention.
[0044] One having ordinary skill in the art will readily understand
that the invention as discussed above may be practiced with steps
in a different order, and/or with hardware elements in
configurations which are different than those which are disclosed.
Therefore, although the invention has been described based upon
these preferred embodiments, it would be apparent to those of skill
in the art that certain modifications, variations, and alternative
constructions would be apparent, while remaining within the spirit
and scope of the invention. In order to determine the metes and
bounds of the invention, therefore, reference should be made to the
appended claims.
* * * * *