U.S. patent application number 10/436772 was filed with the patent office on 2003-10-23 for composite metal oxide particles.
This patent application is currently assigned to NanoGram Corporation. Invention is credited to Bi, Xiangxin, Kumar, Sujeet, Reitz, Hariklia Dris.
Application Number | 20030198590 10/436772 |
Document ID | / |
Family ID | 22694449 |
Filed Date | 2003-10-23 |
United States Patent
Application |
20030198590 |
Kind Code |
A1 |
Kumar, Sujeet ; et
al. |
October 23, 2003 |
Composite metal oxide particles
Abstract
A powder of lithiated manganese oxide has an average particle
diameter preferably less than about 250 nm. The particles have a
high degree of uniformity and preferably a very narrow particle
size distribution. The lithiated manganese oxide can be produce by
the reaction of an aerosol where the aerosol comprises both a first
metal (lithium) precursor and a second metal (manganese) precursor.
Preferably, the reaction involves laser pyrolysis where the
reaction is driven by heat absorbed from an intense laser beam.
Inventors: |
Kumar, Sujeet; (Fremont,
CA) ; Reitz, Hariklia Dris; (Santa Clara, CA)
; Bi, Xiangxin; (San Ramon, CA) |
Correspondence
Address: |
Patterson, Thuente, Skaar & Christensen, P.A.
4800 IDS Center
80 South 8th Street
Minneapolis
MN
55402-2100
US
|
Assignee: |
NanoGram Corporation
|
Family ID: |
22694449 |
Appl. No.: |
10/436772 |
Filed: |
May 13, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10436772 |
May 13, 2003 |
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09188768 |
Nov 9, 1998 |
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6607706 |
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Current U.S.
Class: |
423/599 ;
423/594.8 |
Current CPC
Class: |
C01P 2004/51 20130101;
C01P 2004/64 20130101; C01G 45/02 20130101; C01P 2002/02 20130101;
Y02E 60/10 20130101; C01G 45/1221 20130101; C01G 45/1242 20130101;
C01P 2002/72 20130101; H01M 4/131 20130101; C01P 2006/40 20130101;
C01P 2004/04 20130101; C01P 2004/52 20130101; B82Y 30/00 20130101;
H01M 4/485 20130101; C01P 2002/77 20130101; C01P 2004/62 20130101;
C01P 2004/80 20130101; H01M 4/50 20130101; C01G 45/1292 20130101;
H01M 4/525 20130101 |
Class at
Publication: |
423/599 ;
423/594.8 |
International
Class: |
C01G 045/12 |
Claims
What is claimed is:
1. A method of producing composite metal oxide particles, the
method comprising reacting a reactant stream to form, within the
flow of the reactant stream, a powder of composite metal oxide
particles with an average diameter less than about 500 nanometers,
the reactant stream comprising a first metal compound precursor and
a second metal compound precursor, wherein the reaction is driven
by heat from a light beam and wherein the light beam intersects the
reactant stream at a reaction zone.
2. The method of claim 1 wherein the composite metal oxide
comprises lithiated manganese oxide.
3. The method of claim 1 wherein the composite metal oxide
comprises lithiated vanadium oxide.
4. The method of claim 1 wherein a metal precursor comprises a
compound selected from the group consisting of MnCl.sub.2 and
MnNO.sub.3.
5. The method of claim 1 wherein a metal precursor comprises a
compound selected from the group consisting of LiCl and
Li.sub.2NO.sub.3.
6. The method of claim 1 wherein a metal precursor comprises
VOCl.sub.2.
7. The method of claim 7 wherein the light beam is generated by an
infrared laser.
8. The method of claim 1 wherein the reaction is performed in a
reaction chamber, the chamber having a cross section along a
direction perpendicular to a reactant stream with a dimension along
a major axis greater than a factor of about two larger than a
dimension along a minor axis.
9. The method of claim 1 wherein the precursor comprises a third
metal precursor.
10. The method of claim 1 wherein the reactant stream comprises an
aerosol of the first metal precurosr and a vapor of the second
metal precursor.
11. The method of claim 1 wherein the reactant stream comprises an
aerosol.
12. The method of claim 11 wherein the aerosol is generated by a
mechanical atomization aerosol generator.
13. The method of claim 1 wherein the reaction stream further
comprises O.sub.2.
14. The method of claim 1 wherein the composite metal oxide
particles have an average diameter less than about 250 nm.
15. The method of claim 1 wherein the composite metal oxide
particles have an average diameter less than about 100 nm.
16. The method of claim 1 wherein the composite metal oxide
particles have essentially no particles with a diameter greater
than about 4 times the average diameter.
17. A method of producing composite metal oxide particles, the
method comprising reacting a reactant stream to form, within the
flow of the reactant stream, a powder of composite metal oxide
particles with an average diameter less than about 500 nanometers,
the reactant stream comprising a first metal compound precursor, a
second metal compound precursor and a third metal compound
percursor.
18. The method of claim 17 wherein the reaction is driven by heat
from a light beam and wherein the light beam intersects the
reactant stream at a reaction zone.
19. The method of claim 17 wherein the reactant stream comprises an
aerosol.
20. The method of claim 17 wherein the first metal precursor
comprises lithium, the second metal precursor comprises manganese.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to copending U.S. patent
application Ser. No. 09/188,768, now U.S. Pat. No. ______, to Kumar
et al., entitled "Composite Metal Oxide Particles," incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to composite metal oxide powders. More
particularly, the invention relates to highly uniform, nanoscale
composite metal oxide particles, such as lithiated manganese oxide,
produced by laser pyrolysis.
BACKGROUND OF THE INVENTION
[0003] Manganese can exist in various oxidation states.
Correspondingly, manganese oxides are known to exist with various
stoichiometries. In addition, manganese oxides with a particular
stoichiometry can have various crystalline lattices, or they can be
amorphous. Thus, manganese oxides exhibit an extraordinarily rich
phase diagram. Various crystalline forms of manganese oxide, as
well as other metal oxides, can accommodate lithium atoms and/or
ions into its lattice.
[0004] The ability of metal oxide, such as manganese oxide, to
intercalate lithium can be used advantageously for the production
of lithium and lithium ion batteries. In particular,
LixMn.sub.2O.sub.4, 0<x<2 can be used in the formation of
cathodes for secondary batteries, i.e., rechargeable batteries.
These are referred to as "rocking-chair" batteries by their ability
to reversibly vary x between certain values as the battery charges
or discharges. The lithiated manganese oxides can have a variety of
crystal structures. Because of the interest in lithiated manganese
oxides and other composite metal oxides, there is considerable
interest in developing better approaches for producing composite
metal oxides, such as lithiated manganese oxide.
SUMMARY OF THE INVENTION
[0005] In a first aspect, the invention pertains to a method of
producing a composite metal oxide particles, the method comprising
reacting an aerosol to form a powder of composite metal oxide
particles with an average diameter less than about one micron, the
aerosol comprising a first metal compound precursor and a second
metal compound precursor.
[0006] In a further aspect, the invention pertains to a method for
producing lithium metal oxide, the method comprising pyrolyzing a
reactant stream in a reaction chamber, the reactant stream
comprising a lithium precursor, a non-lithium metal precursor, an
oxidizing agent, and an infrared absorber, where the pyrolysis is
driven by heat absorbed from a light beam.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic, sectional view of an embodiment of a
laser pyrolysis apparatus taken through the middle of the laser
radiation path. The upper insert is a bottom view of the injection
nozzle, and the lower insert is a top view of the collection
nozzle.
[0008] FIG. 2 is schematic, side view of a reactant delivery
apparatus for the delivery of an aerosol reactant to the laser
pyrolysis apparatus of FIG. 1.
[0009] FIG. 3 is a schematic, perspective view of an elongated
reaction chamber for the performance of laser pyrolysis, where
components of the reaction chamber are shown as transparent to
reveal internal structure.
[0010] FIG. 4 is a perspective view of an embodiment of an
elongated reaction chamber for performing laser pyrolysis.
[0011] FIG. 5 is a sectional, side view of a reactant delivery
apparatus for the delivery of an aerosol reactant into the reaction
chamber of FIG. 4, where the section is taken through the center of
the reactant delivery apparatus.
[0012] FIG. 6 is a schematic, sectional view of an oven for heating
nanoparticles, in which the section is taken through the center of
the quartz tube.
[0013] FIG. 7 is an x-ray diffractogram of nanoparticles of
lithiated manganese oxide produced by laser pyrolysis of a reactant
stream with an aerosol.
[0014] FIG. 8 is an x-ray diffractogram of nanoparticles of
lithiated manganese oxide following heating in an oven.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Lithiated manganese oxide particles having diameters
substantially less than a micron have been produced directly by
laser pyrolysis. Laser pyrolysis with an aerosol based reactant
delivery provides for the direct production of lithium/manganese
composite materials. Lithiated manganese oxide nanoparticles
preferably are produced by laser pyrolysis with a relatively high
production rate. Heat processing of the composite materials results
in crystalline lithiated manganese oxide particles. The small size
of the particles results in a significantly increased surface area
for a given weight of material. The aerosol based approach
described herein can be used for the production of other composite
metal oxides, in particular other lithiated metal oxides such as
lithiated vanadium oxides.
[0016] Preferred collections of composite metal oxide particles
have an average diameter less than a micron and a very narrow
distribution of particle diameters. Furthermore, the collection of
composite metal oxides preferably are very uniform. In particular,
the distribution of particle diameters preferably does not have a
tail. In other words, there are effectively no particles with a
diameter significantly greater than the average diameter such that
the particle size distribution rapidly drops to zero.
[0017] To generate the desired nanoparticles, laser pyrolysis is
used either alone or in combination with additional processing.
Specifically, laser pyrolysis has been found to be an excellent
process for efficiently producing lithiated manganese oxide
nanoparticles with a narrow distribution of average particle
diameters. In addition, nanoscale lithiated manganese oxide
particles produced by laser pyrolysis can be subjected to heating
in an oxygen environment or an inert environment to alter the
crystal properties of the lithiated manganese oxide particles
without destroying the nanoparticle size.
[0018] A basic feature of successful application of laser pyrolysis
for the production of composite metal oxide (lithiated manganese
oxide) nanoparticles is production of a reactant stream containing
a first metal (e.g., lithium) precursor, a second metal (e.g.,
manganese) precursor, a radiation absorber and an oxygen source.
The second metal precursor involves a different metal than the
first metal precursor. In preferred embodiments, the first metal
(lithium) precursor and/or the second metal (manganese) precursor
are supplied as an aqueous solution or solutions that are formed in
an aerosol and injected into the pyrolysis chamber using an
ultrasonic nozzle. The novel injection system for the laser
pyrolysis instrument is described in greater detail below.
Additional metal precursors can be included to produce ternary and
higher metal particles.
[0019] The reactant stream is pyrolyzed by an intense laser beam.
The intense heat resulting from the absorption of the laser
radiation induces the oxidation of the first metal (lithium)
precursor, second metal (manganese) precursor, any additional metal
precursors in the oxidizing environment. The laser pyrolysis
provides for formation of phases of materials that are difficult to
form under thermodynamic equilibrium conditions. As the reactant
stream leaves the laser beam, the composite metal oxide particles
are rapidly quenched.
[0020] As noted above, lithium atoms and/or ions can intercalate
into various forms of manganese oxide. The result is lithiated
manganese oxide. As described herein, lithiated manganese oxide is
formed directly as a composite. The lithiated manganese oxide
nanoparticles can be incorporated into a film with a binder such as
a polymer. The film preferably incorporates additional electrically
conductive particles held by a binder along with the lithiated
manganese oxide particles. The film can be used as a cathode in a
lithium battery or a lithium ion battery.
[0021] A. Particle Production
[0022] Laser pyrolysis has been discovered to be a valuable tool
for the direct production of nanoscale lithiated manganese oxide
particles and composite metal oxides, generally. In addition, the
particles produced by laser pyrolysis are a convenient material for
further processing to expand the pathways for the production of
desirable composite metal oxide particles and to improve the
particle properties. Thus, using laser pyrolysis alone or in
combination with additional processes, a wide variety of composite
metal oxide particles can be produced.
[0023] The reaction conditions determine the qualities of the
particles produced by laser pyrolysis. The reaction conditions for
laser pyrolysis can be controlled relatively precisely in order to
produce particles with desired properties. The appropriate reaction
conditions to produce a certain type of particles generally depend
on the design of the particular apparatus. Specific conditions used
to produce lithiated manganese oxide particles in a particular
apparatus are described below in the Examples. Furthermore, some
general observations on the relationship between reaction
conditions and the resulting particles can be made.
[0024] Increasing the laser power results in increased reaction
temperatures in the reaction region as well as a faster quenching
rate. A rapid quenching rate tends to favor production of high
energy phases, which may not be obtained with processes near
thermal equilibrium. Similarly, increasing the chamber pressure
also tends to favor the production of higher energy structures.
Also, increasing the concentration of the reactant serving as the
oxygen source in the reactant stream favors the production of
particles with increased amounts of oxygen.
[0025] Reactant gas flow rate and velocity of the reactant gas
stream are inversely related to particle size so that increasing
the reactant gas flow rate or velocity tends to result in smaller
particle size. Also, the growth dynamics of the particles have a
significant influence on the size of the resulting particles. In
other words, different forms of a product compound have a tendency
to form different size particles from other phases under relatively
similar conditions. Laser power also influences particle size with
increased laser power favoring larger particle formation for lower
melting materials and smaller particle formation for higher melting
materials.
[0026] Laser pyrolysis has been performed generally with gas phase
reactants. The use of exclusively gas phase reactants is somewhat
limiting with respect to the types of precursor compounds that can
be used. Thus, techniques have been developed to introduce aerosols
containing reactant precursors into laser pyrolysis chambers. The
aerosol atomizers can be broadly classified as ultrasonic
atomizers, which use an ultrasonic transducer to form the aerosol,
or as mechanical atomizers, which use energy from one or more
flowing fluids (liquids, gases, or supercritical fluids) themselves
to form the aerosol.
[0027] Furthermore, as described herein, aerosol based approaches
can be used to produce metal composite particles by the
introduction of multiple metal compounds into a solution to be
delivered as an aerosol in the reaction chamber. Improved aerosol
delivery apparatuses for reactant systems are described further in
commonly assigned and simultaneously filed U.S. patent application
Ser. No. 09/188,670, now U.S. Pat. No. 6,193,936 to Gardner et al.,
entitled "Reactant Delivery Apparatuses," incorporated herein by
reference. If desired, selected metal precursors can be delivered
in the reaction chamber as an aerosol while others are delivered as
a vapor.
[0028] Using aerosol delivery apparatuses, solid precursor
compounds can be delivered by dissolving the compounds in a
solvent. Alternatively, powdered precursor compounds can be
dispersed in a liquid.backslash.solvent for aerosol delivery.
Liquid precursor compounds can be delivered as an aerosol from a
neat liquid, a liquid/gas mixture or a liquid solution, if desired.
Aerosol reactants can be used to obtain significant reactant
throughput. The solvent, if any, can be selected to achieve desired
properties of the solution. Suitable solvents include water,
methanol, ethanol and other organic solvents. The solvent should
have a desired level of purity such that the resulting particles
have a desired purity level.
[0029] If the aerosol precursors are formed with a solvent present,
the solvent is rapidly evaporated by the laser beam in the reaction
chamber such that a gas phase reaction can take place. Thus, the
fundamental features of the laser pyrolysis reaction is unchanged.
However, the reaction conditions are affected by the presence of
the aerosol. Below, examples are described for the production of
lithiated manganese oxide nanoparticles using aerosol precursors
using a particular laser pyrolysis reaction chamber. The parameters
associated with aerosol reactant delivery can be explored fully
based on the description below.
[0030] A number of suitable solid, manganese precursor compounds
can be delivered as an aerosol from solution. For example,
manganese chloride (MnCl.sub.2) is soluble in water and alcohols
and manganese nitrate (Mn(NO.sub.3).sub.2) is soluble in water and
certain organic solvents. Similarly, as substitutes for the
manganese precursors, suitable vanadium precursors include, for
example, VOCl.sub.2, which is soluble in absolute alcohol. Also,
suitable lithium precursors for aerosol delivery from solution
include, for example, lithium chloride (LiCl), which is somewhat
soluble in water, alcohol and some other organic solvents, and
lithium nitrate (LiNO.sub.3), which is somewhat soluble in water
and alcohol.
[0031] The compounds are dissolved in a solution preferably with a
concentration greater than about 0.5 molar. Generally, the greater
the concentration of precursor in the solution the greater the
throughput of reactant through the reaction chamber. As the
concentration increases, however, the solution can become more
viscous such that the aerosol has droplets with larger sizes than
desired. Thus, selection of solution concentration can involve a
balance of factors in the determination of a preferred solution
concentration. In the formation of composite particles, the
relative amounts of the metal precursors also influences the
relative amount of the metals in the resulting particles. Thus, the
relative amounts of different metal precursors is selected to yield
a desired product particle composition.
[0032] Preferred reactants serving as oxygen source include, for
example, O.sub.2, CO, CO.sub.2, O.sub.3 and mixtures thereof. The
reactant compound from the oxygen source should not react
significantly with the manganese or lithium precursor prior to
entering the reaction zone since this generally would result in the
formation of large particles.
[0033] Laser pyrolysis can be performed with a variety of optical
laser frequencies. Preferred lasers operate in the infrared portion
of the electromagnetic spectrum. CO.sub.2 lasers are particularly
preferred sources of laser light. Infrared absorbers for inclusion
in the molecular stream include, for example, C.sub.2H.sub.4,
NH.sub.3, SF.sub.6, SiH.sub.4 and O.sub.3. O.sub.3 can act as both
an infrared absorber and as an oxygen source. The radiation
absorber, such as the infrared absorber, absorbs energy from the
radiation beam and distributes the energy to the other reactants to
drive the pyrolysis.
[0034] Preferably, the energy absorbed from the radiation beam
increases the temperature at a tremendous rate, many times the rate
that heat generally would be produced even by strongly exothermic
reactions under controlled condition. While the process generally
involves nonequilibrium conditions, the temperature can be
described approximately based on the energy in the absorbing
region. The laser pyrolysis process is qualitatively different from
the process in a combustion reactor where an energy source
initiates a reaction, but the reaction is driven by energy given
off by an exothermic reaction.
[0035] An inert shielding gas can be used to reduce the amount of
reactant and product molecules contacting the reactant chamber
components. Appropriate shielding gases include, for example, Ar,
He and N.sub.2.
[0036] An appropriate laser pyrolysis apparatus generally includes
a reaction chamber isolated from the ambient environment. A
reactant inlet connected to a reactant supply system produces a
reactant stream through the reaction chamber. A laser beam path
intersects the reactant stream at a reaction zone. The
reactant/product stream continues after the reaction zone to an
outlet, where the reactant/product stream exits the reaction
chamber and passes into a collection system. Generally, the laser
is located external to the reaction chamber, and the laser beam
enters the reaction chamber through an appropriate window.
[0037] Referring to FIG. 1, a particular embodiment 100 of a
pyrolysis apparatus involves a reactant supply system 102, reaction
chamber 104, collection system 106, laser 108 and shielding gas
delivery system 110. Reactant supply system 102 is used to deliver
one or more reactants as an aerosol.
[0038] Referring to FIG. 2, reactant supply system 102 is used to
supply an aerosol to duct 132. Duct 132 connects with rectangular
channel 134, which forms part of an injection nozzle for directing
reactants into the reaction chamber. Reactant supply system 102
includes a delivery tube 152 that is connected to duct 132. Venturi
tube 154 connects to delivery tube 152 as a source of the aerosol.
Venturi tube 154 is connected to gas supply tube 156 and liquid
supply tube 158.
[0039] Gas supply tube 156 is connected to gas source 160. Gas
source 160 can include a plurality of gas containers that are
connected to deliver a selected gas mixture to gas supply tube 156.
The flow of gas from gas source 160 to gas supply tube 156 is
controlled by one or more valves 162. Liquid supply tube 158 is
connected to liquid supply 164. Delivery tube 152 also connects
with drain 166 that flows to reservoir 168.
[0040] In operation, gas flow through venturi tube 154 creates
suction that draws liquid into venturi tube 154 from liquid supply
tube 158. The gas liquid mixture in venturi tube 154 forms an
aerosol when venturi tube 154 opens into delivery tube 152. The
aerosol is drawn up into duct 132 by pressure within the system.
Any aerosol that condenses within delivery tube 152 is collected in
reservoir 168, which is part of the closed system. Suitable venturi
based aerosol generators for attachment to duct 132 include, for
example, model 3076 from the Particle Instrument Division, TSI
Inc., Saint Paul, Minn.
[0041] Referring to FIG. 1, shielding gas delivery system 110
includes inert gas source 190 connected to an inert gas duct 192.
Inert gas duct 192 flows into annular channel 194. A mass flow
controller 196 regulates the flow of inert gas into inert gas duct
192.
[0042] The reaction chamber 104 includes a main chamber 200.
Reactant supply system 102 connects to the main chamber 200 at
injection nozzle 202. The end of injection nozzle 202 has an
annular opening 204 for the passage of inert shielding gas, and a
rectangular slit 206 for the passage of reactants to form a
reactant stream in the reaction chamber. The end of injection
nozzle 202 can be seen in the lower insert of FIG. 1. Annular
opening 204 has, for example, a diameter of about 1.5 inches and a
width along the radial direction from about 1/8 in to about
{fraction (1/16)} in. The flow of shielding gas through annular
opening 204 helps to prevent the spread of the reactants and
product particles throughout reaction chamber 104.
[0043] Tubular sections 208, 210 are located on either side of
injection nozzle 202. Tubular sections 208, 210 include ZnSe
windows 212, 214, respectively. Windows 212, 214 are about 1 inch
in diameter. Windows 212, 214 are preferably cylindrical lenses
with a focal length equal to the distance between the center of the
chamber to the surface of the lens to focus the beam to a point
just below the center of the nozzle opening. Windows 212, 214
preferably have an antireflective coating. Appropriate ZnSe lenses
are available from Janos Technology, Townshend, Vt. Tubular
sections 208, 210 provide for the displacement of windows 212, 214
away from main chamber 200 such that windows 212, 214 are less
likely to be contaminated by reactants or products. Window 212, 214
are displaced, for example, about 3 cm from the edge of the main
chamber 200.
[0044] Windows 212, 214 are sealed with a rubber o-ring to tubular
sections 208, 210 to prevent the flow of ambient air into reaction
chamber 104. Tubular inlets 216, 218 provide for the flow of
shielding gas into tubular sections 208, 210 to reduce the
contamination of windows 212, 214. Tubular inlets 216, 218 are
connected to inert gas source 190 or to a separate inert gas
source. In either case, flow to inlets 216, 218 preferably is
controlled by a mass flow controller 220.
[0045] Laser 108 is aligned to generate a laser beam 222 that
enters window 212 and exits window 214. Windows 212, 214 define a
laser light path through main chamber 200 intersecting the flow of
reactants at reaction zone 224. After exiting window 214, laser
beam 222 strikes power meter 226, which also acts as a beam dump.
An appropriate power meter is available from Coherent Inc., Santa
Clara, Calif. Laser 108 can be replaced with an intense
conventional light source such as an arc lamp. A conventional light
source preferably produces considerable amount of infrared light.
Preferably, laser 108 is an infrared laser, especially a CW
CO.sub.2 laser such as an 1800 watt maximum power output laser
available from PRC Corp., Landing, N.J.
[0046] Reactants passing through slit 206 in injection nozzle 202
initiate a reactant stream. The reactant stream passes through
reaction zone 224, where reaction involving the lithium precursor
compound and the manganese precursor compound takes place. Heating
of the gases in reaction zone 224 is extremely rapid, roughly on
the order of 105 degree C./sec depending on the specific
conditions. The reaction is rapidly quenched upon leaving reaction
zone 224, and particles 228 are formed in the reactant/product
stream. The nonequilibrium nature of the process allows for the
production of nanoparticles with a highly uniform size distribution
and structural homogeneity.
[0047] The path of the reactant.backslash.product stream continues
to collection nozzle 230. Collection nozzle 230 is spaced about 2
cm from injection nozzle 202. The small spacing between injection
nozzle 202 and collection nozzle 230 helps reduce the contamination
of reaction chamber 104 with reactants and products. Collection
nozzle 230 has a circular opening 232. Circular opening 232 feeds
into collection system 106. The end of collection nozzle 230 can be
seen in the upper insert of FIG. 1.
[0048] The chamber pressure is monitored with a pressure gauge
attached to the main chamber. The preferred chamber pressure for
the production of the desired oxides generally ranges from about 80
Torr to about 500 Torr.
[0049] Reaction chamber 104 has two additional tubular sections not
shown. One of the additional tubular sections projects into the
plane of the sectional view in FIG. 2, and the second additional
tubular section projects out of the plane of the sectional view in
FIG. 2. When viewed from above, the four tubular sections are
distributed roughly, symmetrically around the center of the
chamber. These additional tubular sections have windows for
observing the inside of the chamber. In this configuration of the
apparatus, the two additional tubular sections are not used to
facilitate production of particles.
[0050] Collection system 106 includes a curved channel 270 leading
from collection nozzle 230. Because of the small size of the
particles, the product particles follow the flow of the gas around
curves. Collection system 106 includes a filter 272 within the gas
flow to collect the product particles. A variety of materials such
as Teflon, glass fibers and the like can be used for the filter as
long as the material is inert and has a fine enough mesh to trap
the particles. Preferred materials for the filter include, for
example, a glass fiber filter from ACE Glass Inc., Vineland, N.J.
and cylindrical polypropylene filters from Cole-Parmer Instrument
Co., Vernon Hills, Ill.
[0051] Pump 274 is used to maintain collection system 106 at a
selected pressure. A variety of different pumps can be used.
Appropriate pumps for use as pump 274 include, for example, Busch
Model B0024 pump from Busch, Inc., Va. Beach, Va. with a pumping
capacity of about 25 cubic feet per minute (cfm) and Leybold Model
SV300 pump from Leybold Vacuum Products, Export, Pa. with a pumping
capacity of about 195 cfm. It may be desirable to flow the exhaust
of the pump through a scrubber 276 to remove any remaining reactive
chemicals before venting into the atmosphere. The entire apparatus
100 can be placed in a fume hood for ventilation purposes and for
safety considerations. Generally, the laser remains outside of the
fume hood because of its large size.
[0052] The apparatus is controlled by a computer. Generally, the
computer controls the laser and monitors the pressure in the
reaction chamber. The computer can be used to control the flow of
reactants and/or the shielding gas. The pumping rate is controlled
by a valve 278 such as a manual needle valve or an automatic
throttle valve inserted between pump 274 and filter 272. As the
chamber pressure increases due to the accumulation of particles on
filter 272, valve 278 can be adjusted to maintain the pumping rate
and the corresponding chamber pressure.
[0053] The reaction can be continued until sufficient particles are
collected on filter 272 such that the pump can no longer maintain
the desired pressure in the reaction chamber 104 against the
resistance through filter 272. When the pressure in reaction
chamber 104 can no longer be maintained at the desired value, the
reaction is stopped, and the filter 272 is removed. With this
embodiment, about 1-300 grams of particles can be collected in a
single run before the chamber pressure can no longer be maintained.
A single run generally can last up to about 10 hours depending on
the type of particle being produced and the type of filter being
used.
[0054] The reaction conditions can be controlled relatively
precisely. The mass flow controllers are quite accurate. The laser
generally has about 0.5 percent power stability. With either a
manual control or a throttle valve, the chamber pressure can be
controlled to within about 1 percent.
[0055] The configuration of the reactant supply system 102 and the
collection system 106 can be reversed. In this alternative
configuration, the reactants are supplied from the top of the
reaction chamber, and the product particles are collected from the
bottom of the chamber. In this configuration, the collection system
may not include a curved section so that the collection filter is
mounted directly below the reaction chamber.
[0056] An alternative design of a laser pyrolysis apparatus has
been described. See, copending and commonly assigned U.S. patent
application Ser. No. 08/808,850, now U.S. Pat. No. 5,958,348,
entitled "Efficient Production of Particles by Chemical Reaction,"
incorporated herein by reference. This alternative design is
intended to facilitate production of commercial quantities of
particles by laser pyrolysis. The introduction of aerosol reactants
into this alternative apparatus design is described in copending
and simultaneously filed U.S. patent application Ser. No.
09/188,670, now U.S. Pat. No. 6,193,936 to Gardner et al., entitled
"Reactant Delivery Apparatuses," incorporated herein by reference.
The production of manganese oxide particles using this alternative
design of the reaction chamber with an aerosol delivery system is
described in commonly assigned and simultaneously filed U.S. patent
application Ser. No. 09/188,770, now U.S. Pat. No. 6,506,493 to
Kumar et al., entitled "Metal Oxide Particles," incorporated herein
by reference.
[0057] In general, the alternative apparatus includes a reaction
chamber designed to reduce contamination of the chamber walls, to
increase the production capacity and to make efficient use of
resources. To accomplish these objectives, an elongated reaction
chamber is used that provides for an increased throughput of
reactants and products without a corresponding increase in the dead
volume of the chamber. The dead volume of the chamber can become
contaminated with unreacted compounds and/or reaction products.
[0058] The design of the improved reaction chamber 300 is
schematically shown in FIG. 3. A reactant inlet 302 enters the main
chamber 304. Reactant inlet 302 conforms generally to the shape of
main chamber 304. Main chamber 304 includes an outlet 306 along the
reactant/product stream for removal of particulate products, any
unreacted gases and inert gases. Tubular sections 320, 322 extend
from the main chamber 304. Tubular sections 320, 322 hold windows
324, 326 to define a laser beam path 328 through the reaction
chamber 300. Tubular sections 320, 322 can include shielding gas
inlets 330, 332 for the introduction of shielding gas into tubular
sections 320, 322. Shielding gas can also be introduced through
shielding gas inlets around the reactant inlet to form a blanket of
shielding gas around the reactant stream.
[0059] Referring to FIG. 4, a specific embodiment of a laser
pyrolysis reaction system 350 with aerosol reactant delivery
includes reaction chamber 352, a particle collection system 354,
laser 356 and a reactant delivery apparatus. A variety of
embodiments of the reactant delivery apparatuses can be used to
provide aerosol reactants. One embodiment of a reactant delivery
apparatus 358 to delivery an aerosol is depicted in FIG. 5.
Additional embodiments of aerosol delivery apparatuses for use with
reactant chamber 252 are described in copending and simultaneously
filed U.S. patent application Ser. No. 09/188,670, now U.S. Pat.
No. 6,193,936 to Gardner et al., entitled "Reactant Delivery
Apparatuses," incorporated herein by reference. The reactant
delivery apparatus may or may not provide an aerosol that is
elongated along the elongated dimension of reaction chamber
352.
[0060] Reaction chamber 352 includes reactant inlet 364 at the
bottom of reaction chamber 352. In this embodiment, the reactants
are delivered from the bottom of the reaction chamber while the
products are collected from the top of the reaction chamber. The
configuration can be reversed with the reactants supplied from the
top and product collected from the bottom, if desired. Reactant
delivery apparatus 358 is connected to the reaction chamber at
reactant inlet 364.
[0061] For the performance of laser pyrolysis based reaction
synthesis, the aerosol generally is mixed with one or more
additional reactant gases, a laser absorbing gas if the reactants
do not sufficiently absorb the laser radiation, and, optionally, an
inert gas. The gases can be supplied from a pressurized cylinder or
other suitable container. In addition, multiple reactants can be
mixed in the liquid phase and delivered as the aerosol.
[0062] Reaction chamber 352 is elongated along one dimension
denoted in FIG. 4 by "w". A laser beam path 366 enters the reaction
chamber through a window 368 displaced along a tube 370 from the
main chamber 372 and traverses the elongated direction of the
reaction chamber. The laser beam passes through tube 374 and exits
window 376 and terminates at beam dump 378. In operation, the laser
beam intersects a reactant stream generated through reactant inlet
364.
[0063] The top of main chamber 372 opens into particle collection
system 354. Particle collection system 354 includes outlet duct 380
connected to the top of main chamber 372 to receive the flow from
main chamber 372. Outlet duct 380 carries the product particles out
of the plane of the reactant stream to a cylindrical filter within
compartment 382. Compartment 382 is connected to a pump through
port 384. The filter blocks flow from duct 380 to port 384 such
that particles within the flow are collected on the filter.
[0064] Referring to FIG. 5, reactant delivery apparatus 358
includes an aerosol generator 482 is supported by mount 484 and a
cap 486. Reactant delivery apparatus 358 is secured to reactant
inlet 364 to extend within main chamber 372 of FIG. 4. Mount 484 is
connected to a base plate 488. Base plate 488 is fastened to
reactant inlet 364 with bolts 490. An o-ring or the like, suitably
shaped, can be placed within hollow 492 to form a seal between base
plate 488 and reactant inlet 364.
[0065] As noted above, properties of the product particles can be
modified by further processing. In particular, lithiated manganese
oxide nanoscale particles can be heated in an oven in an oxidizing
environment or an inert environment to alter the oxygen content, to
change the crystal lattice, or to remove adsorbed compounds on the
particles to improve the quality of the particles.
[0066] The use of sufficiently mild conditions, i.e., temperatures
well below the melting point of the particles, results in
modification of the lithiated manganese oxide particles without
significantly sintering the particles into larger particles. The
processing of metal oxide nanoscale particles in an oven is
discussed further in copending and commonly assigned, U.S. patent
application Ser. No. 08/897,903, now U.S. Pat. No. 5,989,514, filed
Jul. 21, 1997, entitled "Processing of Vanadium Oxide Particles
With Heat," incorporated herein by reference.
[0067] A variety of apparatuses can be used to perform the heat
processing. An example of an apparatus 700 to perform this
processing is displayed in FIG. 6. Apparatus 700 includes a tube
702 into which the particles are placed. Tube 702 is connected to a
reactant gas source 704 and inert gas source 706. Reactant gas,
inert gas or a combination thereof are placed within tube 702 to
produce the desired atmosphere.
[0068] Preferably, the desired gases are flowed through tube 702.
Appropriate reactant gases to produce an oxidizing environment
include, for example, O.sub.2, O.sub.3, CO, CO.sub.2 and
combinations thereof. The reactant gas can be diluted with inert
gases such as Ar, He and N.sub.2. The gases in tube 702 can be
exclusively inert gases if an inert atmosphere is desired. The
reactant gases may not result in changes to the stoichiometry of
the particles being heated.
[0069] Tube 702 is located within oven or furnace 708. Oven 708
maintains the relevant portions of the tube at a relatively
constant temperature, although the temperature can be varied
systematically through the processing step, if desired. Temperature
in oven 708 generally is measured with a thermocouple 710. The
lithiated manganese oxide particles can be placed in tube 702
within a vial 712. Vial 712 prevents loss of the particles due to
gas flow. Vial 712 generally is oriented with the open end directed
toward the direction of the source of the gas flow.
[0070] The precise conditions including type of oxidizing gas (if
any), concentration of oxidizing gas, pressure or flow rate of gas,
temperature and processing time can be selected to produce the
desired type of product material. The temperatures generally are
mild, i.e., significantly below the melting point of the material.
The use of mild conditions avoids interparticle sintering resulting
in larger particle sizes. Some controlled sintering of the
particles can be performed in oven 708 at somewhat higher
temperatures to produce slightly larger, average particle
diameters.
[0071] For the processing of lithiated manganese oxide, for
example, the temperatures preferably range from about 50.degree. C.
to about 600.degree. C. and more preferably from about 50.degree.
C. to about 550.degree. C. The particles preferably are heated for
about 5 minutes to about 100 hours. Some empirical adjustment may
be required to produce the conditions appropriate for yielding a
desired material.
[0072] B. Particle Properties
[0073] A collection of particles of interest preferably has an
average diameter for the primary particles of less than about 250
nm, preferably from about 5 nm to about 100 nm, more preferably
from about 5 nm to about 50 nm. The primary particles usually have
a roughly spherical gross appearance. Upon closer examination,
crystalline lithiated manganese oxide particles generally have
facets corresponding to the underlying crystal lattice.
Nevertheless, the primary particles tend to exhibit growth that is
roughly equal in the three physical dimensions to give a gross
spherical appearance. Generally, 95 percent of the primary
particles, and preferably 99 percent, have ratios of the dimension
along the major axis to the dimension along the minor axis less
than about 2. Diameter measurements on particles with asymmetries
are based on an average of length measurements along the principle
axes of the particle.
[0074] Because of their small size, the primary particles tend to
form loose agglomerates due to van der Waals and other
electromagnetic forces between nearby particles. Nevertheless, the
nanometer scale of the primary particles is clearly observable in
transmission electron micrographs of the particles. The particles
generally have a surface area corresponding to particles on a
nanometer scale as observed in the micrographs. Furthermore, the
particles can manifest unique properties due to their small size
and large surface area per weight of material. For example,
TiO.sub.2 nanoparticles generally exhibit altered absorption
properties based on their small size, as described in copending and
commonly assigned U.S. patent application Ser. No. 08/962,515, now
U.S. Pat. No. 6,099,798, entitled "Ultraviolet Light Block and
Photocatalytic Materials," incorporated herein by reference.
[0075] Laser pyrolysis, as described above, generally results in
particles having a very narrow range of particle diameters. With
aerosol delivery, the distribution of particle diameters is
particularly sensitive to the reaction conditions. Nevertheless, if
the reaction conditions are properly controlled, a very narrow
distribution of particle diameters can be obtained with an aerosol
delivery system as described above. The primary particles
preferably have a high degree of uniformity in size. When mixed
phase materials are formed, it is sometimes observed that each
phase has a separate narrow size distribution such that the mixed
phase materials overall involves multiple overlapping narrow
distributions.
[0076] As determined from examination of transmission electron
micrographs, the primary particles of a single phase and possibly
multiple phases generally have a distribution in sizes such that at
least about 95 percent, and preferably 99 percent, of the primary
particles have a diameter greater than about 40 percent of the
average diameter and less than about 160 percent of the average
diameter. Preferably, the primary particles have a distribution of
diameters such that at least about 95 percent of the primary
particles have a diameter greater than about 60 percent of the
average diameter and less than about 140 percent of the average
diameter.
[0077] Furthermore, in preferred embodiments essentially no primary
particles have an average diameter greater than about 4 times the
average diameter and preferably 3 times the average diameter, and
more preferably 2 times the average diameter. In other words, the
particle size distribution effectively does not have a tail
indicative of a small number of particles with significantly larger
sizes. This is a result of the small reaction region and
corresponding rapid quench of the particles. An effective cut off
in the tail indicates that there are less than about 1 particle in
106 have a diameter greater than a particular cut off value above
the average diameter. The narrow size distributions, lack of a tail
in the distributions and the roughly spherical morphology can be
exploited in a variety of applications. Also, crystalline lithiated
manganese oxide particles produced by annealing (heating) particles
made by laser pyrolysis have a high degree of crystallinity.
[0078] Lithium manganese oxide is known to exist in a variety of
oxidation states and several crystalline phases corresponding to
the underlying crystal structure of the manganese oxide and the
degree of lithium intercalation. The phase diagram of lithiated
manganese oxide is extremely complex. The manganese oxygen ratio
can vary from 1:1 to 1:2. Also, the ratio of lithium to manganese,
i.e., the amount of lithium intercalated into the manganese oxide
lattice, can vary from 0 to 2:1. Also, for a given stoichiometry
such as LiMn.sub.2O.sub.4, the crystal structure can be a cubic
spinel or other crystal structures. Different portions of the vast
phase diagram can be explored by varying the processing
parameters.
EXAMPLES
Example 1
Laser Pyrolysis; Aerosol Metal Precursors
[0079] The synthesis of magnesium oxide/lithiated manganese oxide
particles described in this example was performed by laser
pyrolysis. The particles were produced using essentially the laser
pyrolysis apparatus of FIG. 1, described above, using the reactant
delivery apparatus of FIG. 2.
[0080] The manganese chloride (Alfa Aesar, Inc., Ward Hill, Mass.)
precursor and lithium chloride (Alfa Aesar, Inc.) precursor were
dissolved into deionized water. The aqueous solution had a
concentration of 4 molar LiCl and 4 molar MnCl.sub.2. The aqueous
solution with the two metal precursors was carried into the
reaction chamber as an aerosol. C.sub.2H.sub.4 gas was used as a
laser absorbing gas, and Argon was used as an inert gas. O.sub.2,
Ar and C.sub.2H.sub.4 were delivered into the gas supply tube of
the reactant supply system. The reactant mixture containing
MnCl.sub.2, LiCl, Ar, O.sub.2 and C.sub.2H.sub.4 was introduced
into the reactant nozzle for injection into the reaction chamber.
The reactant nozzle had an opening with dimensions of 5/8
in..times.{fraction (1/16)} in. Additional parameters of the laser
pyrolysis synthesis relating to the particles of Example 1 are
specified in Table 1.
1 TABLE 1 {PRIVATE} 1 Crystal Structure Amorphous Pressure (Torr)
450 Argon-Window (SCCM) 700 Argon-Shielding (SLM) 5.6 Ethylene
(SLM) 1.27 Argon (SLM) 1.46 Oxygen (SLM) 1.07 Laser Output (Watts)
590 Li Precursor 4 M Lithium Chloride Mn Precursor 4 M Manganese
Chloride Precursor Temperature .degree.C. Room Temperature sccm =
standard cubic centimeters per minute Argon-Win. = argon flow
through inlets 216, 218 Argon-Sld. = argon flow through annular
channel 142. Argon = Argon directly mixed with the aerosol
[0081] The production rate of manganese oxide/lithiated manganese
oxide particles was typically about 1 g/hr. To evaluate the atomic
arrangement, the samples were examined by x-ray diffraction using
the Cu(Ka) radiation line on a Siemens D500 x-ray diffractometer.
X-ray diffractograms for a sample produced under the conditions
specified in Table 1 is shown in FIG. 7. The x-ray diffractogram
shown in FIG. 7 indicates that the sample was amorphous. In
particular, a broad peak from about 27.degree. to about 35.degree.
corresponds to the amorphous lithiated manganese oxide. A sharp
peak at about 15.degree. is due to the presence of a trace amount
of manganese chloride contamination. A sharp peak at 53.degree. is
due to a trace amount of an unidentified contaminant.
Example 2
Heat Treatment
[0082] A sample of manganese oxide/lithiated manganese oxide
nanoparticles produced by laser pyrolysis according to the
conditions specified in the Example 1 were heated in an oven under
oxidizing conditions. The oven was essentially as described above
with respect to FIG. 6. Between about 100 and about 300 mg of
nanoparticles were placed in an open 1 cc vial within the quartz
tube projecting through the oven. Oxygen gas was flowed through a
1.0 inch diameter quartz tube at a flow rate of 308 cc/min. The
oven was heated to about 400.degree. C. The particles were heated
for about 16 hours.
[0083] The crystal structure of the resulting heat treated
particles were determined by x-ray diffraction. The x-ray
diffractogram for heated sample is shown in FIG. 8. The x-ray
diffractogram shown in FIG. 8 indicates that the collection of
particles involved mixed phase material with major components of
LiMn.sub.2O.sub.4 (about 60% by volume) and Mn.sub.3O.sub.4 (about
30% by volume) and a minor component of Mn.sub.2O.sub.3 (about 10%
by volume). The LiMn.sub.2O.sub.4 compound has a cubic spinel
crystal structure. It is possible that the sample included
additional amorphous phases of materials. In particular, based on
the amount of lithium introduced in the reactant stream, the sample
presumably contains additional lithium that is not identified in
the crystalline phases.
[0084] The embodiments described above are intended to be
illustrative and not limiting. Additional embodiments are within
the claims. Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *