U.S. patent application number 10/384586 was filed with the patent office on 2003-09-18 for microwave plasma chemical synthesis of ultrafine powders.
This patent application is currently assigned to Materials Modification, Inc.. Invention is credited to Kalyanaraman, Raja, Sethuram, Krupashankara M..
Application Number | 20030172772 10/384586 |
Document ID | / |
Family ID | 21852978 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030172772 |
Kind Code |
A1 |
Sethuram, Krupashankara M. ;
et al. |
September 18, 2003 |
Microwave plasma chemical synthesis of ultrafine powders
Abstract
The present invention relates to the production of ultrafine
powders using a microwave plasma apparatus and chemical synthesis
technique. Microwaves generated by a magnetron (1) are passed
through waveguides (2) before they arrive at the head of a
plasmatron (3). These high energy microwaves ionize a plasma gas,
thus releasing large amounts of energy. The energy thus released is
utilized to initiate and sustain chemical reactions between the
desired elements being pumped in a spiral pattern into the
plasmatron (3). The reaction products are quenched rapidly in a
reactor column (4) into ultrafine powders.
Inventors: |
Sethuram, Krupashankara M.;
(Falls Church, VA) ; Kalyanaraman, Raja; (Fairfax,
VA) |
Correspondence
Address: |
Dinesh Agarwal, Esquire
LAW OFFICE - DINESH AGARWAL, P.C.
Suite 330
5350 Shawnee Road
Alexandria
VA
22312
US
|
Assignee: |
Materials Modification,
Inc.
|
Family ID: |
21852978 |
Appl. No.: |
10/384586 |
Filed: |
March 11, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10384586 |
Mar 11, 2003 |
|
|
|
10114993 |
Apr 4, 2002 |
|
|
|
10114993 |
Apr 4, 2002 |
|
|
|
09262848 |
Mar 5, 1999 |
|
|
|
6409851 |
|
|
|
|
09262848 |
Mar 5, 1999 |
|
|
|
PCT/US97/20917 |
Nov 4, 1997 |
|
|
|
60030188 |
Nov 4, 1996 |
|
|
|
Current U.S.
Class: |
75/10.19 ;
148/565; 75/255 |
Current CPC
Class: |
B01J 2219/00094
20130101; C01P 2004/62 20130101; B01J 2219/0894 20130101; B01J
2219/0883 20130101; H05B 6/806 20130101; C01B 21/06 20130101; H01J
37/3244 20130101; H05H 1/46 20130101; C01P 2004/50 20130101; H01J
2237/339 20130101; B01J 19/126 20130101; B22F 3/105 20130101; B82Y
30/00 20130101; C01B 13/28 20130101; C01B 21/0724 20130101; B22F
1/054 20220101; B01J 2219/1269 20130101; C01P 2004/51 20130101;
B01J 2219/1227 20130101; C01G 23/07 20130101; H05H 1/463 20210501;
H05B 6/70 20130101; B22F 9/305 20130101; C01B 32/90 20170801; C01P
2004/64 20130101; B22F 2999/00 20130101; H01J 37/32192 20130101;
B22F 2999/00 20130101; B22F 1/054 20220101; B22F 9/305 20130101;
B22F 2202/13 20130101; B22F 2999/00 20130101; B22F 1/054 20220101;
B22F 2202/13 20130101; B22F 9/305 20130101 |
Class at
Publication: |
75/10.19 ;
148/565; 75/255 |
International
Class: |
C22B 004/08; C22B
009/22 |
Claims
What is claimed is:
1. An apparatus for the microwave synthesis of materials,
comprising: microwave generator; a waveguide through which a
microwave generated by said microwave generator passes into a
plasma zone in which a plasma heats reactants to form reaction
products; a plasma gas inlet offset at an angle so that plasma gas
passing through the inlet enters the plasma zone in a spiral-shaped
pattern; and a reaction products collector downstream from said
plasma zone for collecting the reaction products.
2. The apparatus of claim 1, wherein said plasma zone comprises a
microwave damper at a side of the plasma zone away from the
waveguide for damping microwaves that have passed through the
plasma zone to thereby reduce the power of a reflected microwave by
at least 60%.
3. The apparatus of claim 2, wherein the microwave damper is a
water cooled glass tube.
4. The apparatus of claim 2, wherein the microwave damper is a
water cooled metal tube.
5. The apparatus of claim 2, wherein the microwave damper is a
water cooled rectangular tube.
6. The apparatus of claim 1, comprising a column located between
the plasma zone and the reaction products collector for cooling the
reaction products leaving the plasma zone.
7. The apparatus of claim 6, wherein the column is 8-12" long.
8. The apparatus of claim 1, comprising a plurality of plasma gas
inlets.
9. The apparatus of claim 1, wherein the plasma gas inlet is offset
at an angle between 5-30.degree..
10. The apparatus of claim 1, wherein the plasma gas inlet is
offset at 15.degree..
11. An apparatus for the microwave synthesis of materials,
comprising: a microwave generator; a waveguide through which a
microwave generated by said microwave generator passes into a
plasma zone in which a plasma heats reactants to form reaction
products; a microwave damper at a side of the plasma zone away from
the waveguide for damping microwaves that have passed through the
plasma zone to thereby reduce the power of a reflected microwave by
at least 60%; and a reaction products collector downstream from
said plasma zone for collecting the reaction products.
12. A method for the microwave synthesis of materials, said method
comprising: introducing a plasma gas into a microwave applicator;
introducing at least one reactant into the microwave applicator;
generating a microwave in a microwave generator; directing the
microwave into the microwave applicator containing the plasma gas
to create a heated plasma in a plasma zone; absorbing the microwave
to reduce the microwave reflection off of a surface of the
microwave applicator by at least 60%; and causing a reaction in the
plasma zone thereby converting the at least one reactant into a
reaction product.
13. The method of claim 12, further comprising: introducing the
plasma gas into the microwave applicator in a spiral shaped
pattern.
14. The method of claim 12, further comprising: introducing the
plasma gas into the microwave applicator at an oblique angle to
thereby produce a spiral shaped pattern.
15. The method of claim 12, wherein at least one reactant is a
powder material.
16. The method of claim 13, wherein at least one reactant is
chemical vapor.
17. An aggregate of powders consisting essentially of particles
having an average particle size less than 1 micron, and a particle
size distribution of less than 50 nm.
18. The aggregate of powders of claim 17, wherein the particles are
metal particles.
19. The aggregate of powders of claim 17, wherein the particles are
ceramic particles.
20. The aggregate of powders of claim 19, wherein the ceramic
particles are selected from the group consisting of oxides,
carbides and nitrides.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to the field of microwave synthesis
of materials, particularly, ultrafine powders having an average
particle size <500 nm.
[0003] 2. Description of the Related Art
[0004] Ultrafine metallic and ceramic powders have unique
properties, and have the potential to contribute to significant
advances in the, field of electronics, solid lubricants,
capacitors, batteries, sensors, thermal management substrates, and
additives for the cosmetic and pharmaceutical industries. Ultrafine
powders also find applications in optical coatings, slurries used
for polishing, and in magnetic storage devices. Parts produced out
of ultrafine particles/powders demonstrate improved mechanical,
optical, and thermal properties. Conventionally, ultrafine powders
have been produced by a variety of techniques including mechanical
milling, flame pyrolysis, sol-gel, laser ablation, vapor
deposition, and evaporation-condensation techniques.
[0005] Low power (1-2.5 kW) microwave generated plasmas have been
used in many deposition, etching, and substrate processing
operations. Low power microwave systems operate at plasma
temperatures of less than 700.degree. C., deposition and etching
chamber are traditionally made out of brass and bronze or even
copper, with quartz tube lining in some cases. These chambers or
applicators can withstand 700.degree. C. without much cooling
requirements.
[0006] The application of microwaves to synthesize metallic and
ceramic powders offers unique benefits, especially in producing
particles of submicron size with controlled compositions and
phases.
SUMMARY OF THE INVENTION
[0007] The present invention includes an apparatus and method for
producing materials, preferably ultrafine powders, using microwave
plasma chemical synthesis. The principle components of a microwave
machine in accordance with the invention are: (1) a microwave
generator, such as a magnetron, and (2) a microwave applicator. A
magnetron produces microwaves by the interaction of electrons
traveling in electric and magnetic fields (often referred to as
"crossed fields"). This interaction coupled with high DC voltage
between the cathode and the anode results, in microwaves.
Microwaves thus generated are then passed through waveguides before
they arrive at the head of the applicator.
[0008] Microwave applicators are devices that are designed to heat
a material by exposing it to a microwave field in a controlled
environment. In the present invention, the applicator is referred
to as "plasmatron," wherein the high energy microwave electrons
ionize and dissociate the injected gas thus releasing large amounts
of energy. The energy thus released is utilized to initiate a
chemical reaction between the desired reactants. The interaction
between the chemical species results in ultrafine powders with the
desired chemical and physical characteristics. Due to rapid
quenching that takes place in the reactor column the powder sizes
are very fine. By controlling the diameter and length of the
column, it is therefore possible to control the particle size. This
apparatus can produce ultrafine powders of pure metals, such as
iron, cobalt, nickel, tungsten, and rhenium; metal oxides, such as
iron oxide; metal nitrides, such as titanium nitride; metal
carbides; and many other ceramics, such as aluminum nitride,
titanium dioxide, and aluminum dioxide. The apparatus also enables
the continuous production of ultrafine particles/powders of pure
metals, metal oxides, metal carbides, and metal nitrides,
particularly tungsten, molybdenum, iron, cobalt, nickel, aluminum,
titanium dioxide, and aluminum nitride, in contrast to the batch
processes of the prior art.
[0009] Additional features and advantages of the invention will be
set forth in the description which follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The objectives and other advantages of the invention
will be realized and attained by the process and apparatus,
particularly pointed out in the written description and claims
hereof, as well as the appended drawings.
[0010] To achieve these and other advantages, and in accordance
with the purpose of the invention as embodied and broadly
described, the invention includes an apparatus for the microwave
synthesis of materials. The apparatus includes a microwave
generator, waveguides through which microwaves generated by the
microwave generator passes into a plasma zone in which a plasma
heats the reactants to form reaction products, a plasma gas inlet
offset at an angle so that plasma gas passing through the inlet
enters the plasma zone in a spiral-shaped pattern, and a reaction
products collector downstream from the plasma zone for collecting
the reaction products.
[0011] In another aspect, the invention includes an apparatus for
the microwave synthesis of materials. The apparatus includes a
microwave generator, waveguides through which microwaves generated
by the microwave generator passes into a plasma zone in which a
plasma heats reactants to form reaction products, a microwave
damper at a side of the plasma zone away from the waveguide for
damping microwaves that have passed through the plasma zone to
thereby reduce the power of a reflected microwave by at least 60%,
and a reaction products collector downstream from the plasma zone
for collecting the reaction products.
[0012] In yet another aspect, the invention includes a method for
the microwave synthesis of materials. The method includes
introducing a plasma gas into a microwave applicator, introducing
at least one reactant into the microwave applicator, generating a
microwave in a microwave generator, directing the microwave into
the microwave applicator containing the plasma gas to create a
heated plasma in a plasma zone, absorbing the microwave to reduce
the microwave reflection off of a surface of the microwave
applicator by at least 60%, and causing a reaction in the plasma
zone thereby converting at least one reactant into a reaction
product.
[0013] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
[0014] The accompanying drawings are included to provide a further
understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate one/several
embodiment(s) of the invention and, together with the description,
serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and, together with the description, serve to explain
the objects, advantages, and principles of the invention.
[0016] In the drawings:
[0017] FIG. 1 is a schematic of a microwave plasma chemical
synthesis apparatus according to an embodiment of the
invention;
[0018] FIG. 2(a) is a schematic of a powder feeding device which
may be used with the invention; and
[0019] FIG. 2(b) is a schematic of a chemical vapor feeding device
which may be used in another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The device that generates the microwave is illustrated in
FIG. 1 and is called a "magnetron." The primary factors that
determine the choice of a particular magnetron are the power and
frequency of the microwave required for initiating and sustaining
the plasma chemical reaction. For example, continuously variable
magnetron input power between 1-6 kW is generated at frequency of
2425-2475 MHZ. The power of the microwave dictates the production
rate of the metallic and ceramic powders. The microwave generated
by the magnetron can operate in either transverse electromagnetic
(TEM), transverse electric (TE), or transverse magnetic (TM) modes.
The TE or TM wave is generated in a waveguide, which is typically a
hollow conducting pipe having either a rectangular or circular
cross-section.
[0021] The present invention preferably uses a rectangular
waveguide and the microwaves preferably operate in the TE mode
(TE01) where 0 or 1 are the field distributions for this mode of
propagation, which are generated by the rectangular waveguides.
[0022] The microwaves thus propagated are directed towards the
applicator, referred to as the "plasmatron," where they ionize the
plasma-forming gas, resulting in a "plasma" zone.
[0023] A microwave damper, preferably a water-cooled glass tube, a
water-cooled rectangular aluminum tube, or other water filled
damping system, is positioned after the plasmatron and opposite to
the rectangular waveguide. This. damper absorbs microwaves to
prevent their reflection back into the magnetron. Reflected
microwaves can propagate back through the plasma zone and into the
magnetron where they cancel out incident microwaves. This condition
drastically reduces the efficiency of the deposition apparatus and
inhibits the plasma temperature that can be attained. For example,
if the incident, or forward power of the microwave is 6 kW, and the
reflected power is 4 kW, the effective power, that is, the power of
the microwave that creates the plasma is only 2 kW. Prior art
devices either completely lack any capability of eliminating
reflected microwaves or use a metallic plate which must continually
be repositioned due to the dynamic nature and unpredictability of
the plasma contained within the plasma zone.
[0024] If the metallic plate is not precisely placed, the reflected
waves become out of phase with the incident waves, canceling them
out. Thus, positioning the plate becomes an inevitable step in
preparing the microwave system for production. Moreover, the
operator's freedom of dynamically modifying the parameters of the
system is severely restricted by the need to continually adjust the
plates to find the optimal position within the apparatus.
[0025] In contrast, the damper of the present apparatus diminishes
the strength of the reflected wave, thereby reducing the adverse
effect of the reflected wave regardless of its phase. This gives
the operator a faster equipment preparation time, and provides him
the freedom of continually adjusting the operating characteristics
of the apparatus. The microwave damper of this invention reduces
the power of the reflected microwave by 60-100%, preferably by an
amount greater than 80-85%.
[0026] Various types of gases can be used depending on the desired
powder and powder characteristics. Candidate plasma gases include
hydrogen, oxygen, helium, argon, nitrogen, methane, or a
combination of the above. Ionization of the gas results in the
release of large amounts of energy, which will instantly vaporize
the chemicals being injected into the plasmatron thereby initiating
the desired chemical reaction. The temperature in the plasmatron is
typically between 500-1100.degree. C. The plasma-forming gas
carries the reaction products into the reactor column where they
are rapidly quenched using, for example, a double-walled,
water-cooled stainless steel column with quartz lining. The gas may
be introduced through an axial, radial, or angled inlet.
Preferably, the plasma gas is introduced into the plasmatron using
a spiral gas flow pattern which confines the plasma to the central
region of the plasmatron thereby preventing it from damaging the
plasmatron walls or reaction column material. Specifically, the
spiral pattern creates a cyclone-like pattern with a central low
pressure section which controls the dimensions of the plasma.
Therefore, higher energies and higher temperatures may be used to
produce smaller, better quality, and more uniform powders than
otherwise would be attainable with a lower power system.
[0027] The spiral gas flow pattern may be produced by introducing
the plasma gas into the reaction zone at an oblique angle. One
manner of doing so is by offsetting the inlet port at an angle
between 0-90.degree., preferably angled at 15.degree.. The gas may
be introduced through a single inlet port or through multiple
(e.g., four) inlet ports circumferentially arranged about the
reaction zone. It is also possible to introduce the reactants
obliquely into the reaction zone either before or after being
entrained in the plasma gas.
[0028] The quenching rate, reactor column diameter, and the length
influence the powder size and distribution. The quenching rate
depends on the cooling water temperature, which may vary from
20.degree. C. to -5.degree. C.; the lower the temperature, the
finer the particle size. The reactor column diameter preferably
varies from 2-6" depending on the particle size distribution
required. The reaction column length preferably varies from 8-12"
and is a function of the temperature drop desired before the
ultrafine particles enter the filter bag. The filter bag is
designed to withstand temperatures in the range of 300-600.degree.
C. The construction of the rest of the apparatus and the raw
material feeding device varies with the desired end product as is
evident from the examples.
[0029] A particularly useful advantage of this invention is the
ability to generate ultrafine powders with a powder particle size
smaller than 10-500 nm, preferably smaller than 100 nm but having a
substantially uniform particle size distribution. A relatively
narrow particle size distribution is advantageous because of the
influence the particle size has on powder densification
characteristics and the final material properties. A uniform size
distribution that may be maintained and controlled enables the end
product manufacturer to better predict and control the properties
of the final product.
[0030] Existing processes result in relatively wide and
unpredictable particle size distributions. In some cases, the
distribution may be bimodal or asymmetrical.
[0031] This invention, however, enables a particle size
distribution 50 nm or less (as measured, for example, by a Laser
Scattering Particle Size Analyzer). Moreover, the parameters can be
varied to produce varying size distributions, e.g, from 50 nm or
less to 100 nm or more, across the entire range of average particle
sizes (e.g., from less than 10 nm to greater than 1 micron). The
distribution may also be controlled to be more symmetrical about
the mean than prior art processes, and can approximate a normal
distribution if so desired.
[0032] FIG. 1 is a schematic of a device according to the
invention. A microwave generator 1, which may include a magnetron
is used to generate microwaves. A continuously variable input power
of greater than 1 kW, preferably greater than 3-6 kW, and more
preferably greater than 5-6 kW, may be generated at a frequency of
2425-2475 MHZ. The microwaves thus generated are carried through
rectangular waveguides 2 to the plasmatron 3.
[0033] The plasmatron is a microwave applicator wherein the
microwaves ionize the gas which can be injected both radially and
axially through an injector port 6. The plasmatron also includes a
feed port for attaching a raw material dosing device 5. The
chemical interaction of the reactants in the form of starting
powders or vapors takes place in the plasmatron. The powders formed
are instantaneously quenched in a reaction column 4. The rapid
dissociation of the reactants followed by quenching results in the
production of the ultrafine powders. The reaction column preferably
used in the invention is longer than conventional reaction columns
thereby enabling the user to produce ultrafine particles not
capable of being produced in the prior art devices. Specifically,
the longer reaction column in combination with higher temperatures,
gives the reaction an opportunity to continue as a residual
reaction which may cause the reactants and products to melt,
evaporate, and recondense thereby enabling a size heretofore
unattainable.
[0034] After formation, the powders passing through the reaction
column are still hot. The heat associated with the ultrafine
powders is removed using a heat exchanger 7. The powders pass
through the heat exchanger into a powder collector 8. The powder
collector is preferably a stainless steel container including a
filter bag which retains the powders while the gases are removed
through an exhaust located downstream from the powder
collector.
[0035] FIG. 2(a) is a schematic of a powder feeding device which
may be connected to the feed port located in the plasmatron. This
device preferably includes a motor located near the powder zone 9,
which rotates a blade to continuously create an aerosol, which is
also a driving force for the powders to be fed into the injection
port. The powders may be carried to the powder zone through a
piston support 10 which is driven by a motor 11.
[0036] FIG. 2(b) is a schematic of a chemical vapor feeding device
which may be used with the invention. Liquid precursors such as
metal carbonyls are injected into the plasmatron from, for example,
a double-walled stainless steel container 13, which may be
continuously heated by water pipes (14, 15). Vapors of the liquid
precursors are then fed into the plasmatron 3 through electrically
heated hose 12 in order to prevent any condensation. The ultrafine
powders formed are quenched in the reactor column 4, and
subsequently collected in the stainless steel container which
houses a filter bag to retain the fine powders and allow the gases
to-pass through the exhaust.
EXAMPLE 1
[0037] Ultrafine powders of pure tungsten powders were produced
using a tungsten carbonyl, specifically tungsten hexacarbonyl, as
the raw material and nitrogen as the carrier gas and also as the
plasma gas. The plasma gas flow rate was 2-2.2 m.sup.3/min and that
of the carrier gas was 0.3-0.4 m.sup.3/min. The plasma temperature
was 600-650.degree. C., the powder feed rate was 25-30 gm/hr and
the quenching water flow rate was 2.4-2.5 liter/min at 20.degree.
C. The reactor column diameter was 48 mm and its length was 1041 .
The microwave forward power was 4.5 kW, the reflected power was 1.2
kW, and the operating frequency was 2400 MHZ. The particles so
produced had a particle size of less than 50 nm.
EXAMPLE 2
[0038] Ultrafine powders of molybdenum were produced using
molybdenum carbonyl, specifically molybdenum hexacarbonyl, as the
raw material and nitrogen as the carrier gas and also the plasma
gas. The plasma gas flow rate was 2.5-3.0 m.sup.3/min and that of
the carrier gas was 0.4-0.6 m.sup.3/min. The plasma temperature was
1000-1200.degree. C., the powder feed rate was 20-25 gm/hr, and the
quenching water flow rate was 1.5-1.8 liter/min at 20.degree. C.
The reactor column diameter was 48 mm and its length was 10". The
microwave forward power was 3.5 kW, the reflected power was 0.6 kW,
and the operating frequency was 2400 MHZ. The produced powders had
a particle size less than 50 nm.
EXAMPLE 3
[0039] Ultrafine powders of aluminum nitride (AIN) with a particle
size less than 60 nm, were produced using aluminum powder and
ammonia as the carrier gas and a combination of argon (30%) and
nitrogen (70%) as the plasma gas. The plasma gas flow rate was
3.5-4.0 m.sup.3/min and that of the carrier gas was 1.2-1.5
m.sup.3/min. The plasma temperature was 1100-1200.degree. C., the
powder feed rate was 25-30 gm/hr, and the quenching water flow rate
was 2.0-2.2 liter/min at 20.degree. C. The reactor column diameter
was 48 mm and its length was 10". The microwave forward power was
3.5 kW, the reflected power was 0.7 kW, and the operating frequency
was 2450 MHZ.
EXAMPLE 4
[0040] Ultrafine powders of cobalt with a particle size less than
40 nm were produced when cobalt carbonyl, specifically cobalt
octacarbonyl, were fed into the plasmatron with argon as the plasma
gas. The plasma gas flow rate was 2.5-2.6 m.sup.3/min and that of
the carrier gas was 0.3-0.5 m.sup.3/min. The plasma temperature was
900-950.degree. C., the powder feed rate was 50-60 gm/hr, and the
quenching water flow rate was 1.8-2.0 liter/min at 20.degree.C. The
reactor column diameter was 48 mm and its length was 10". The
microwave forward power was 3.5 kW, the reflected power was 0.9 kW,
and t he operating frequency was 2400 MHZ.
EXAMPLE 5
[0041] Ultrafine powders of rhenium were produced with an average
particle size of 70 nm using rhenium carbonyl, specifically rhenium
hexacarbonyl as the rate material precursor. Argon was used as the
plasma gas. The plasma gas flow rate was 2-2.2 m.sup.3/min and that
of the carrier gas was 0.3-0.4 m.sup.3/min. The plasma temperature
was 1200.degree. C., the powder feed rate was 25-30 gm/hr, and the
quenching water flow rate was 2.4-2.5 liter/min at 20.degree. C.
The reactor column diameter was 48 mm and its length was 10". The
microwave forward power was 4.5 kW, the reflected power was 0.6 kW,
and the operating frequency was 2450 MHZ.
EXAMPLE 6
[0042] Ultrafine powders of iron with a particle size less than 20
nm were produced when vapors of iron pentacarbonyl were fed into
the plasmatron with argon as the plasma gas. The plasma gas flow
rate was 3-3.4 m.sup.3/min and that of the carrier gas was 0.3-0.4
m.sup.3/min. The plasma temperature was 900-950.degree. C., the
powder feed rate was 50-60 gm/hr, and the quenching water flow rate
was 2.0-2.5 liter/min at 20.degree. C. The reactor column diameter
was 48 mm and its length was 10". The microwave forward power was 4
kW, the reflected power was 0.7 kW, and the operating frequency was
2450 MHZ.
EXAMPLE 7
[0043] Ultrafine powders of titanium dioxide with a particle size
less than 40 nm were produced when vapors of titanium tetrachloride
dissolved in water were injected into an oxygen plasma. The plasma
gas flow rate was 2-2.2 m.sup.3/min and that of the carrier gas was
0.3-0.4 m.sup.3/min. The plasma temperature was 600-650.degree. C.,
the powder feed rate was 25-30 gm/hr, and the quenching water flow
rate was 2.4-2.5 liter/min at 20.degree. C. The reactor column
diameter was 48 mm and its length was 10". The microwave forward
power was 4.5 kW, the reflected power as 1.2 kW, and the operating
frequency was 2400 MHZ.
EXAMPLE 8
[0044] Ultrafine powders of nickel with a particle size less than
40 nm were produced when vapors of nickel pentacarbonyl were fed
into the plasmatron with argon as the plasma gas. The plasma gas
flow rate was 2-2.2 m.sup.3/min and that of the carrier gas was
0.3-0.4 m.sup.3/min. The plasma temperature was 600-650.degree. C.,
the powder feed rate was 25-30 gm/hr, and the quenching water flow
rate was 2.4-2.5 liter/min at 20.degree. C. The reactor column
diameter was 48 mm and its length was 10". The microwave forward
power was 4.5 kW, the reflected power was 1.2 kW, and the operating
frequency was 2400 MHZ.
[0045] It will be apparent to those skilled in the art that various
modifications and variations can be made in the disclosed process
and product without departing from the scope or spirit of the
invention. Other embodiments of the invention will be apparent to
those skilled in the art from consideration of the specification
and practice of the invention disclosed herein. It is intended that
the specification and examples be considered as exemplary only,
with a true scope and spirit of the invention being indicated by
the following claims.
* * * * *