U.S. patent application number 10/172848 was filed with the patent office on 2003-12-18 for process for preparing nanostructured materials of controlled surface chemistry.
Invention is credited to Piepenbrink, Jonathan, Sarkas, Harry W..
Application Number | 20030231992 10/172848 |
Document ID | / |
Family ID | 29733187 |
Filed Date | 2003-12-18 |
United States Patent
Application |
20030231992 |
Kind Code |
A1 |
Sarkas, Harry W. ; et
al. |
December 18, 2003 |
PROCESS FOR PREPARING NANOSTRUCTURED MATERIALS OF CONTROLLED
SURFACE CHEMISTRY
Abstract
A process to prepare stoichiometric-nanostructured materials
comprising generating a plasma, forming an "active volume" through
introduction of an oxidizing gas into the plasma, before the plasma
is expanded into a field-free zone, either (1) in a region in close
proximity to a zone of charge carrier generation, or (2) in a
region of current conduction between field generating elements,
including the surface of the field generation elements, and
transferring energy from the plasma to a precursor material to form
in the "active volume" at least one stoichiometric-nanostructured
material and a vapor that may be condensed to form a
stoichiometric-nanostructured material. The surface chemistry of
the resulting nanostructured materials is substantially enhanced to
yield dispersion stable materials with large zeta-potentials.
Inventors: |
Sarkas, Harry W.;
(Plainfield, IL) ; Piepenbrink, Jonathan; (Crete,
IL) |
Correspondence
Address: |
WILDMAN, HARROLD, ALLEN & DIXON
225 WEST WACKER DRIVE
CHICAGO
IL
60606
US
|
Family ID: |
29733187 |
Appl. No.: |
10/172848 |
Filed: |
June 17, 2002 |
Current U.S.
Class: |
422/186.04 ;
204/164; 422/186.29 |
Current CPC
Class: |
B01J 19/129 20130101;
B01J 19/088 20130101; C01P 2006/90 20130101; C23C 4/123 20160101;
Y10S 977/811 20130101; C01P 2004/64 20130101; B01J 2219/0847
20130101; C01P 2006/22 20130101; B01J 2219/0894 20130101; C01P
2006/12 20130101; Y10S 977/847 20130101; B82Y 30/00 20130101; C23C
14/32 20130101; C23C 4/134 20160101; C23C 8/36 20130101; C23C
14/0021 20130101; B01J 2219/0886 20130101; Y10S 977/90 20130101;
B01J 19/126 20130101; C01F 7/02 20130101; C01B 13/145 20130101;
Y10S 977/844 20130101; B01J 2219/0809 20130101 |
Class at
Publication: |
422/186.04 ;
422/186.29; 204/164 |
International
Class: |
B01J 019/08 |
Claims
We claim:
1. A process to prepare stoichiometric-nanostructured materials
comprising: generating a plasma; forming an "active volume" through
introduction of an oxidizing gas into the plasma, before the plasma
is expanded into a field-free zone, either (1) in a region in close
proximity to a zone of charge carrier generation, or (2) in a
region of current conduction between field generating elements,
including the surface of the field generation elements; and
transferring energy from the plasma to a precursor material or
materials and forming in the "active volume" at least one of
stoichiometric-nanostructured materials and a vapor that may be
condensed to form a stoichiometric-nanostructured material.
2. The process of claim 1, wherein the step of generating comprises
utilizing a radio-frequency field to generate the plasma.
3. The process of claim 1, wherein the step of generating comprises
utilizing a microwave discharge to generate the plasma.
4. The process of claim 1, wherein the step of generating comprises
utilizing a free-burning electric arc to generate the plasma.
5. The process of claim 1, wherein the step of generating comprises
utilizing a transferred electric arc to generate the plasma.
6. The process of claim 1, wherein the step of generating comprises
utilizing a high-intensity laser to generate the plasma.
7. The process of claim 1, wherein the step of generating comprises
utilizing a capacitively coupled electro-thermal igniter to
generate the plasma.
8. The process of claim 1, wherein the step of generating comprises
utilizing a DC glow discharge to generate the plasma.
9. The process of claim 1, wherein the step of generating comprises
utilizing a DC cold cathode discharge to generate the plasma.
10. The process of claim 1, wherein the step of forming comprises
selecting the oxidizing gas from one of a gas containing oxygen
atoms or a gas mixture containing oxygen atoms.
11. The process of claim 1, wherein the step of forming comprises
selecting non-oxygen components of the oxidizing gas from a group
comprising He, Ne, Ar, Kr, Xe, N.sub.2, and H.sub.2, or mixtures
thereof.
12. The process of claim 1, wherein the step of forming comprises
selecting N.sub.2O as the oxidizing gas.
13. The process of claim 1, wherein the step of forming comprises
selecting O.sub.2 as the oxidizing gas.
14. The process of claim 1, wherein the step of forming comprises
selecting CO.sub.2 as the oxidizing gas.
15. The process of claim 1, wherein the step of forming comprises
introducing the oxidizing gas into a anodic column of a transferred
electric arc.
16. The process of claim 1, wherein the step of forming comprises
introducing the oxidizing gas into a cathodic column of a
transferred electric arc.
17. The process of claim 1, wherein the step of forming comprises
introducing the oxidizing gas into a anodic column of a
free-burning electric arc.
18. The process of claim 1, wherein the step of forming comprises
introducing the oxidizing gas into a cathodic column of a
free-burning electric arc.
19. The process of claim 1, wherein the step of forming comprises
introducing the oxidizing gas to the plasma by natural
convection.
20. The process of claim 1, wherein the step of forming comprises
introducing the oxidizing gas to the plasma by forced
convection.
21. The process of claim 1, wherein the step of forming comprises
allowing the oxidizing gas to atomize a liquid nanoparticle
precursor and introduce it into the "active volume".
22. The process of claim 1, wherein the step of forming comprises
allowing the oxidizing gas to fluidize and transport a solid
nanoparticle precursor into the "active volume".
23. The process of claim 1, further comprising: Injecting at least
one of a quench and dilution stream just beyond the "active
volume."The injection point beyond the "active volume" is from one
mean free path of a plasma species to a larger distance deemed to
be appropriate to quench the vapor and is generally determined by
process equipment configuration.
24. The process of claim 23, wherein the step of injecting
comprises creating a nanoparticle aerosol of controlled particle
size.
25. Stoichiometric-nanostructured materials produced through steps
comprising: generating a plasma; forming an "active volume" through
introduction of an oxidizing gas into the plasma, before the plasma
is expanded into a field free zone, in a region in close proximity
to either (1) a zone of charge carrier generation, or (2) a region
of current conduction between field generating elements, including
the surface of the field generating electrodes; and transferring
energy from the plasma to a precursor material or materials and
forming in the "active volume" at least one of
stoichiometric-nanostructured materials and a vapor that may be
condensed to form a stoichiometric-nanostructured material.
26. The stoichiometric-nanostructured materials of claim 25,
wherein the stoichiometric-nanostructured materials are metal
oxides.
27. The stoichiometric-nanostructured materials of claim 25,
wherein the stoichiometric-nanostructured materials are
substantially spherical nanocrystalline metal oxides.
28. The stoichiometric-nanostructured materials of claims 26 and
27, wherein the metal oxides are selected from a group comprising
aluminum oxide, zinc oxide, iron oxide, cerium oxide, chromium
oxide, antimony tin oxide, mixed rare earth oxides, and indium tin
oxide.
29. The stoichiometric-nanostructured materials of claim 25,
wherein the stoichiometric-nanostructured materials generally have
a size distribution and range in mean diameter from about 1 nm to
about 900 nm.
30. The stoichiometric-nanostructured materials of claim 29,
wherein the stoichiometric-nanostructured materials generally have
a size distribution and range in mean diameter from about 2 nm to
about 100 nm.
31. The stoichiometric-nanostructured materials of claim 30,
wherein the stoichiometric-nanostructured materials generally have
a size distribution and range in mean diameter from about 5 nm to
about 40 nm.
32. The stoichiometric-nanostructured materials of claim 25,
wherein the stoichiometric-nanostructured materials have a surface
chemistry having a high aqueous dispersion stability.
33. The stoichiometric-nanostructured materials of claim 25,
wherein the stoichiometric-nanostructured materials have a surface
chemistry having a low rate of hydrolysis.
34. The stoichiometric-nanostructured materials of claim 25,
wherein the stoichiometric-nanostructured materials have a surface
chemistry with the absolute value of the zeta potential greater
than 20 mV.
35. The stoichiometric-nanostructured materials of claim 34,
wherein the stoichiometric-nanostructured materials have a surface
chemistry with the absolute value of the zeta potential greater
than 30 mV.
36. The stoichiometric-nanostructured materials of claim 35,
wherein the stoichiometric-nanostructured materials have a surface
chemistry with the absolute value of the zeta potential greater
than 35 mV.
Description
THE FIELD OF THE INVENTION
[0001] The present invention is concerned generally with making
nanostructured materials using plasma technologies. More
particularly, the invention is concerned with a method of making a
variety of stoichiometric-nanostructured materials by forming a
unique "active volume" in a plasma through the introduction of an
oxidizing gas. The surface chemistry of the resulting
nanostructured material is substantially enhanced to yield
dispersion stable materials with large zeta-potentials.
BACKGROUND OF THE INVENTION
[0002] Methods of plasma formation are previously known in the art
and may be selected from a group of comprising radio-frequency
fields, microwave discharges, free-burning electric arcs,
transferred electric arcs, high-intensity lasers, capacitively
coupled electro-thermal igniters, DC glow discharges, and DC cold
cathode discharges.
[0003] Methods for transferring energy to a precursor material by
exposing a precursor material to the energy of a plasma are
previously known in the art. Precursor material may be introduced
into a plasma at any point. For example, a plasma may be created by
a high intensity electric arc and a precursor may be introduced at
any point of the arc column. In U.S. Pat. No. 3,209,193, the
precursor material is introduced into the arc column of a
free-burning plasma at the anode and U.S. Pat. No. 3,900,762
describes a working embodiment of the volumetric introduction of
precursor into a plasma arc.
[0004] The precursor material may also be a consumable electrode.
For example, in U.S. Pat. Nos. 5,460,701 and 5,514,349, a
transferred electric arc between a cathode and a consumable anode
is used to generate precursors in an elongated ionized arc that
extends beyond the conduction columns.
[0005] Prior art teaches that materials formed by plasma techniques
may have unusual properties. But prior art does not teach the
synthesis of stoichiometric-nanostructured materials with
controlled surface chemistry.
[0006] Materials produced by the method of this patent have surface
chemistry characterized by a high aqueous dispersion stability, a
low rate of hydrolysis, and a large zeta-potential. Materials
produced by the method of this patent are
stoichiometricly-nanostructured by the "active volume". The "active
volume" is in a plasma and is created by introducing an oxidizing
gas into the plasma, before the plasma is expanded into a
field-free zone, either (1) in a region in close proximity to a
zone of charge carrier generation, or (2) in a region of current
conduction between field generating elements, including the surface
of the field generating elements. Energy is transferred from the
plasma to a precursor material and at least one of a
stoichiometric-nanostructured material and a vapor that may be
condensed to form a stoichiometric-nanostructured material are
formed in the "active volume". The "active volume" is the most
reactive part of the plasma and material synthesized in the "active
volume" are stoichiometric-nanostructures with unique surface
chemistry.
[0007] Stoichiometric-nanostructures or
stoichiometriclly-nanostructured materials are defined as materials
having controlled chemistry at the nanoscale. The chemistry of the
nanostructured material may be controlled to be of full or partial
stoichiometry, in the chemical sense, with respect to a
reactant.
[0008] Prior art does not teach the introduction of oxidizing gas
in a plasma to nanostructure materials to have unique surface
chemistry. Instead prior art teaches away from the use of oxidizing
gases in a plasma. For example U.S. Pat. No. 3,899,573 teaches the
use of a reducing gas in the plasma created by a free-burning arc.
The use of oxidizing plasma environments is conventionally
discouraged because the materials used to generate the plasma are
aggressively corroded. For example U.S. Pat. No. 4,642,207
discloses the use of an oxidizing plasma. But this process cannot
be practiced in a manufacturing environment because aggressive
corrosion rapidly renders process equipment inoperable. This is
often the case even under conditions where shielding gas flows are
used to protect specific process equipment as disclosed in prior
art. The present invention teaches that judicious formation of an
"active volume" enables the use of an oxidizing environment within
the conduction column of a variety of plasmas to synthesize
stoichiometric-nanostructured materials with unique surface
chemistry.
[0009] Prior art does not teach the importance of forming at least
one of stoichiometric-nanostructured material or vapor that may be
condensed to form stoichiometric-nanostructured material in the
"active volume" of a plasma. Instead prior art transfers energy
from a plasma to precursors and forms nanoparticles by injecting at
least one of a quench and a reaction gas:
[0010] after the plasma is expanded into a field-free zone;
and/or
[0011] down stream from either (1) a zone of charge carrier
generation, or (2) a region of current conduction between field
generating elements.
[0012] U.S. Pat. Nos. 5,460,701 and 5,514,349, use a transferred
electric arc between a cathode and a consumable anode to generate
an elongated ionized arc that extends beyond the conduction columns
and injects at least one of a quench and a reaction gas into the
elongated ionized arc. Other forms of the art introduce a reactive
gas down stream from the "active volume" and form materials during
thermal quench or gas phase nucleation. In all cases the art
teaches the formation of materials in less reactive plasmas.
[0013] Experiments in our laboratory indicate the "active volume"
must be carefully controlled, to form before the plasma is expanded
into a field-free zone, either (1) in a region in close proximity
to a zone of charge carrier generation, or (2) in a region of
current conduction between field generating elements, including the
surface of the field generating elements, to derive the benefits of
the reactive plasma and synthesize a
stoichiometricly-nanostructured material with unique surface
chemistry.
OBJECTS OF THE INVENTION
[0014] An object of the present invention is the development of a
process for producing stoichiometric-nanostructured materials. This
process comprises the steps of:
[0015] generating a plasma;
[0016] forming an "active volume" through introduction of an
oxidizing gas into the plasma, before the plasma is expanded into a
field-free zone, either (1) in a region in close proximity to a
zone of charge carrier generation, or (2) in a region of current
conduction between field generating elements, including the surface
of the field generating elements; and
[0017] transferring energy from the plasma to a precursor material
or materials and forming in the "active volume" at least one of
nanoparticles and a vapor that may be condensed to form a
nanoparticle.
[0018] A further object of the present invention is the production
of stoichiometric-nanostructured materials with unique surface
chemistry characterized by high aqueous dispersion stability, a low
rate of hydrolysis, and a large zeta-potential.
[0019] These and other objects of the invention will become more
apparent as the description thereof proceeds.
DESCRIPTION OF THE INVENTION
[0020] A free-burning electric arc is struck between anode and
cathode using methods taught in U.S. Pat. Nos. 3,900,762,
3,899,573, and 4,080,550. Plasma generation is not limited to
free-burning arcs, but may be selected from a group comprising
radio-frequency fields, microwave discharges, free-burning electric
arcs, transferred electric arcs, high-intensity lasers,
capacitively coupled electro-thermal igniters, DC glow discharges,
and DC cold cathode discharges.
[0021] Precursor materials are injected into the cathodic arc
column by forced convection. Prior art teaches the injection
velocity of the precursor materials, with respect to the cathodic
arc column, must be controlled to enable the precursors to cross
the arc column boundary to yield an efficient process. But
precursors may also be aspirated into the arc from the surrounding
atmosphere in the absence of forced convection. The object of this
invention is not limited by the method or efficiency by which
precursors are introduced into the plasma--only that the precursors
are introduced into the plasma and energy is transferred from the
plasma to the precursors. The form of the precursor does not limit
the object of this invention; precursors are selected from a group
comprising solids (powders, electrodes, etc.), liquids (atomized
fluids, etc.) and gases or vapors.
[0022] The "active volume" is created through introduction of an
oxidizing gas into the plasma, before the plasma is expanded into a
field-free zone, either (1) in a region in close proximity to a
zone of charge carrier generation, or (2) in a region of current
conduction between field generating elements, including the surface
of the field generation elements.
[0023] Energy is transferred from the plasma to a precursor
material or materials and at least one of a
stoichiometric-nanostructured material and a vapor that may be
condensed to form a stoichiometric-nanostructured material is
formed in the "active volume".
[0024] Injecting at least one of a quench and dilution stream just
beyond the "active volume" enables additional control of the size
of the stoichiometric-nanostructured material. The injection point
beyond the "active volume" may vary from one mean free path of a
plasma species (one collisional distance) to a larger distance
deemed to be appropriate to quench the vapor and is generally
determined by process equipment configuration.
[0025] The stoichiometric-nanostructured material may be collected
by methods known to those familiar with the art.
EXAMPLE 1
Cerium Oxide--"Active Volume"
[0026] Two experiments utilizing nanostructured cerium oxide,
synthesized with and without an "active volume" in the plasma, are
presented.
[0027] The plasma was generated using a free-burning electric arc.
The plasma gas was argon and the arc power was 62 kW.
[0028] The precursor material was particulate cerium oxide powder
having an average particle size greater than 2 microns and 99.95%
pure. The precursor was fluidized with a feed gas to create a
heterogeneous precursor feed that was injected into cathodic arc
column.
[0029] In Experiment 1 no "active volume" was created in the
plasma. In Experiment 2 an "active volume" was created in the
plasma by fluidizing the precursor with an oxidizing
gas--oxygen--to form a heterogeneous precursor feed. In all other
respects the two experiments were conducted under identical
conditions.
[0030] Experiment 1 uses an inert gas to fluidize the precursor and
is representative of prior teachings. In contrast, Experiment 2
creates an "active volume" in the plasma. Experiment 2 illustrates
the teachings of this invention.
[0031] Both experiments yield nanostructured materials of similar
particle sizes (approximately 95 nm) but have very different
surface chemistry. The zeta potential for Experiment 1 and
Experiment 2 material are 2.6 mV and 43.5 mV, respectively.
Experiment 1 material does not form stable aqueous dispersions
without the aid of dispersants.
[0032] The stoichiometicly-nanostructured material produced in
Experiment 2 has a very high zeta potential, exhibits high
dispersion stability without additives, and is hydrolytically
stable. The stoichiometicly-nanostructure material produced in
Experiment 2 has great value in polishing applications.
EXAMPLE 2
Cerium Oxide--"Active Volume" with Quench and Dilution
[0033] Two experiments utilizing nanostructured cerium oxide,
synthesized with and without an "active volume" in the plasma
followed by quenching and dilution, are presented.
[0034] The plasma was generated using a free-burning electric arc.
The plasma gas was argon and the arc power was 62 kW.
[0035] The precursor material was particulate cerium oxide powder
having an average particle size greater than 2 microns and 99.95%
pure. The precursor was fluidized with a feed gas to create a
heterogeneous precursor feed that was injected into cathodic arc
column.
[0036] In Experiment 3 no "active volume" was created in the
plasma. In Experiment 4 an "active volume" was created in the
plasma by fluidizing the precursor with an oxidizing
gas--oxygen--to form a heterogeneous precursor feed. A quench and
dilution stream comprised of an oxidizing gas--oxygen--was injected
just beyond the "active volume" in both experiments. In all other
respects the two experiments were conducted under identical
conditions.
[0037] Experiment 3 is representative of prior teaching and uses an
inert gas to fluidize the precursor and an oxidizing gas to quench
and dilute the product. In contrast, Experiment 4 creates an
"active volume" in the plasma and quenches and dilutes the product.
Experiment 4 illustrates the teachings of this invention.
[0038] Both experiments yield nanostructured materials of similar
particle sizes (approximately 30 nm) but have very different
surface chemistry. The zeta potential for Experiment 3 and
Experiment 4 material are 10.9 mV and 39.4 mV, respectively.
Experiment 3 material does not form stable aqueous dispersions
without the aid of dispersants. Thus, the injection of an oxidizing
gas just beyond the "active volume", as is shown in Experiment 3,
is not sufficient to produce stoichiometicly-nanostructure
materials with high zeta-potentials, hydrolytic stability, and the
ability to form stable aqueous dispersions without additives.
[0039] The stoichiometicly-nanostructure material produced in
Experiment 4 has a very high zeta potential, exhibits high
dispersion stability without additives, and is hydrolytically
stable. The stoichiometicly-nanostructure material produced in
Experiment 4 has great value in polishing applications.
EXAMPLE 3
Extension of Process to Materials other than Cerium Oxide
[0040] The methods taught in this patent may be extended to
materials other than cerium oxide. For example, stable aqueous
dispersions may be formed from the following materials listed with
their zeta-potentials.
1 Material Zeta-Potential Alumina 46.5 mV Antimony Tin Oxide 49.9
mV Indium Tin Oxide 37.9 mV
[0041] The preceding specific embodiments are illustrative of the
practice of the invention. It is to be understood, however, that
other expedients known to those skilled in the art, or disclosed
herein, may be employed without departing from the spirit of the
invention or the scope of the appended claims.
* * * * *