U.S. patent application number 10/358304 was filed with the patent office on 2004-02-12 for preparation of nanoparticles.
This patent application is currently assigned to NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND TECHNOLOGY. Invention is credited to Maeda, Hideaki, Miyazaki, Masaya, Nakamura, Hiroyuki.
Application Number | 20040025634 10/358304 |
Document ID | / |
Family ID | 27749860 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040025634 |
Kind Code |
A1 |
Nakamura, Hiroyuki ; et
al. |
February 12, 2004 |
Preparation of nanoparticles
Abstract
A method of preparing a nanoparticle having a particle size of 1
nm to 1 .mu.m, said method comprising continuously supplying a
solution containing a particle-forming precursor into a micro
channel having a diameter of 1 .mu.m to 1 mm, said micro channel
being disposed in a heating zone. The solution is heated rapidly up
to a reaction initiation temperature to cause a reaction in said
solution. The solution is rapidly cooled to prepare the
nanoparticle.
Inventors: |
Nakamura, Hiroyuki;
(Tosu-shi, JP) ; Maeda, Hideaki; (Tosu-shi,
JP) ; Miyazaki, Masaya; (Tosu-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
WASHINGTON
DC
20037
US
|
Assignee: |
NATIONAL INSTITUTE OF ADVANCED
INDUSTRIAL SCIENCE AND TECHNOLOGY
|
Family ID: |
27749860 |
Appl. No.: |
10/358304 |
Filed: |
February 5, 2003 |
Current U.S.
Class: |
75/335 |
Current CPC
Class: |
B22F 9/24 20130101; C01P
2004/64 20130101; B22F 2998/00 20130101; B01J 2219/00873 20130101;
B82Y 30/00 20130101; C01P 2004/62 20130101; C01B 13/34 20130101;
H01F 1/0045 20130101; B22F 2999/00 20130101; B01J 2219/00891
20130101; C01B 19/007 20130101; B01J 19/0093 20130101; C01P 2004/04
20130101; B01J 2219/00788 20130101; B01J 2219/00783 20130101; B22F
1/054 20220101; B22F 2999/00 20130101; B22F 9/24 20130101; B22F
2202/01 20130101; B22F 2998/00 20130101; B22F 1/0545 20220101; B22F
2998/00 20130101; B22F 1/0545 20220101 |
Class at
Publication: |
75/335 |
International
Class: |
B22F 009/24 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 5, 2002 |
JP |
2002-28790 |
Claims
What is claimed is:
1. A method of preparing a nanoparticle having a particle size of 1
nm to 1 .mu.m, said method comprising: continuously supplying a
solution containing a particle-forming precursor into a micro
channel having a diameter of 1 .mu.m to 1 mm, said micro channel
being disposed in a heating zone; heating said solution rapidly up
to a reaction initiation temperature to cause a reaction in said
solution; and rapidly cooling said solution to prepare the
nanoparticle.
2. The method of claim 1, wherein the heating temperature and the
residence time of said particle-forming precursor solution in said
heating zone are adjusted to control a particle size of the
nanoparticle.
3. The method of claim 1, wherein the reaction is performed while
agitating said particle-forming precursor solution.
4. The method of claim 3, wherein said particle-forming precursor
solution is agitated by means of ultrasound.
5. The method of claim 1, wherein said particle-forming precursor
solution includes a first solution and a second solution adapted to
form different phases, respectively, wherein said first and second
solutions are reacted with one another along an interface
therebetween.
6. The method of claim 1, wherein said particle-forming precursor
solution is injected with a fluid for segmenting said solution to
control the residence-time distribution of said solution.
7. The method of claim 1, wherein a concentration of the precursor
is 0.001-5% by mass.
8. The method of claim 1, wherein a concentration of the precursor
is 0.01-5% by mass.
9. The method of claim 1, wherein a solvent in the solution, is
selected from a group consisting of water, an organic solvent,
methyl alcohol, ethyl alcohol, acetone, dimethylformamide,
dimethylacetamide, dimethyl sulfoxide, octane, cyclohexane,
benzene, xylene, diethyl ether and acetic ether.
10. The method of claim 1, wherein the nanoparticle is made of a
material selected from a group consisting of gold, silver,
palladium, cobalt, nickel, a metalloid, silicon, germanium, a
metalloid oxide, zinc oxide, silicon oxide, germanium oxide, a
metal chalcogenide compound, cadmium selenide, cadmium sulfide,
zinc sulfide, an organic complex compound and an organic
pigment.
11. The method of claim 2, wherein the residence time in the micro
channel is controlled by adjusting a feeding rate of the
solution.
12. The method of claim 2, wherein the residence time in the micro
channel is controlled by adjusting a volume of the micro
channel.
13. The method of claim 6, wherein the fluid is selected from a
group consisting of nitrogen, argon, helium, air, oxygen, hydrogen,
ammonia, hexane, cyclohexane, toluene, water, methyl alcohol, ethyl
alcohol, dimethyl sulfoxide and dimethylformamide.
14. An apparatus for producing a nanoparticle, the apparatus
comprising: a micro channel with a diameter of 1 .mu.m to 1 mm,
with at least one source of input for a solution containing a
particle-forming precursor; a heating zone for heating the micro
channel, where the solution can be heated rapidly to a reaction
initiation temperature; and a collection vessel for collecting a
reaction product.
15. The apparatus of claim 14, wherein the micro channel is a
capillary tube.
16. The apparatus of claim 15, wherein the capillary tube is made
using a material selected from a group consisting of glass, metal,
alloy, a plastic, polyolefin, polyvinyl chloride, polyamide,
polyester and fluororesin.
17. The apparatus of claim 14, wherein the micro channel is
provided by a groove on a layer, said layer being on a heat
resistant substrate.
18. The apparatus of claim 17, wherein the layer is made of a
material selected from a group consisting of a metal oxide, silica,
alumina, titania, a heat-resistant plastic, and fluorinated
resin.
19. The apparatus of claim 17, wherein the heat-resistant substrate
is a metal or an alloy.
20. The apparatus of claim 14 wherein the heating zone is made of a
heat plate, an oil bath, an infrared heater or a high frequency
heater.
Description
FIELD OF THE INVENTION
[0001] This disclosure teaches techniques related to continuously
preparing product particles with particle size in the order of a
nanometer from a solution containing a particle-forming
precursor.
BACKGROUND
[0002] Nanoparticles are used in many applications, including, as
stable monochromatic fluorescence particles, magnetic particles,
etc. Current research also includes efforts aimed at utilizing
nanoparticles as building blocks of a wavelength-tunable
light-emitting diode, monoparticle semiconductor,
super-concentration magnetic storage medium and such other devices.
Because of remarkable technical advances in various related fields
in recent times, nanoparticles are being used in an increasingly
wide range of application. Therefore, the demand for nanoparticles
have increased rapidly.
[0003] Production of nanoparticles of metal such as gold, platinum
and nickel, and compound such as titanium oxide, zinc oxide,
cadmium selenide and zinc sulfide have been reported. Various
techniques of preparing nanoparticles, such as a homogeneous
precipitation method, a hydrothermal crystallization method and an
organometallic synthesis method are conventionally known.
[0004] In order to obtain a desirable reduced size of the
nanoparticle using a production process, in many cases, a number of
nuclei are required to be formed. This also means that the
concentration of a precursor, during the nucleus formation, needs
to be sharply increased. This process inevitably leads to
heterogeneity in the precursor concentration and increased
temperature in a reaction system. This heterogeneity has a great
affection on the particle size distribution of nanoparticles to be
obtained. This adverse affect will be significant as the production
facility is scaled up.
[0005] On the other hand, it is difficult to prepare nanoparticles
on a mass production basis. To overcome this problem, a continuous
preparation method has been conventionally attempted. However,
these attempts have not succeeded in providing an effective
technique.
[0006] Heretofore, to obtain nanoparticles with a desired particle
size range the following technique has been used. Adequate raw
materials are selected along with associated surfactants and other
additions. A reaction temperature and reaction time is adjusted to
control the rate of reaction of the raw materials or intermediate
products and the rate of formation of the end product.
[0007] However, even if the reaction could be actually completed in
a short period of time, the reaction rate is intentionally reduced
due to the difficulty of controlling the reaction temperature and
reaction time with a high degree of accuracy.
SUMMARY
[0008] The disclosed teachings are aimed at overcoming the
disadvantages in the conventional preparation methods of
nanoparticles, and continuously preparing nanoparticles with a
narrow particle size distribution while facilitating a highly
accurate control of the reaction temperature and reaction time.
[0009] The disclosed teachings provide a method of preparing
nanoparticles each having a particle size of 1 nm to 1 .mu.m,
preferably in the range of 1 to 20 nm, comprising continuously
supplying a solution containing a particle-forming precursor
(hereinafter referred to as "particle-forming precursor solution")
into a micro channel which has a diameter of 1 .mu.m to 1 mm and is
disposed in a heating zone, simultaneously heating the solution
rapidly up to a reaction initiation temperature to cause a reaction
in the solution, and then rapidly cooling the solution.
[0010] Another aspect of the disclosed teachings is a an apparatus
for producing a nanoparticle, the apparatus comprising a micro
channel with a diameter of 1 .mu.m to 1 mm, with at least one
source of input for a solution containing a nanoparticle-forming
precursor. A heating zone is provided for heating the micro
channel, where solution can be heated rapidly to a reaction
initiation temperature. A collection vessel is provided for
collecting a reaction product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic diagram showing one example of an
apparatus suitable for implementing a method of the present
invention;
[0012] FIG. 2 is a schematic diagram showing another example of an
apparatus suitable for implementing a method of the present
invention;
[0013] FIG. 3 is a transmission electron microscopic picture of
gold colloid nanoparticles obtained in Example 1; and
[0014] FIG. 4 is a transmission electron microscopic picture of
gold colloid nanoparticles obtained in Example 2.
DETAILED DESCRIPTION
[0015] With reference to the drawings, the disclosed techniques are
described in detail.
[0016] FIG. 1 schematically shows an example of an apparatus
embodying the disclosed techniques. This apparatus uses two
different kinds of particle-forming precursor solutions A and B.
The two kinds of particle-forming precursor solutions A and B are
simultaneously supplied to a micro channel such as a capillary tube
3 by their corresponding syringe pumps 1 and 2, and mixed together
in the micro channel. The resulting mixture is transferred to a
heating zone such as an oil bath 4, and rapidly heated up to a
reaction initiation temperature in the heating zone 4. After
reaction in the heating zone in the mixture, the reacted mixture is
discharged from the heating zone 4 to the atmosphere, and rapidly
cooled down. Finally, the reacted mixture is collected in a vessel
5. When the mixture passes through the heating zone 5, the product
is precipitated in the form of nanoparticles.
[0017] If the two particle-forming precursor solutions do not react
at room temperature but react only at a high temperature, these
precursor solutions may be mixed together in advance. In such a
case, the mixture is then supplied to the micro channel, and heated
in the heating zone to generate nanoparticles. This causes
turbulence and facilitates the mixing and the subsequent reaction
that results in the creation of nanoparticles.
[0018] The micro channel 3 should be designed to have a diameter in
the range of 1 .mu.m to 1 mm. The reduced diameter of the micro
channel reduces the ratio of the volume to surface area of the
precursor solutions (or the mixed precursor solution) passing
through the micro channel. Such a reduced ratio ensures that more
of the solution can sufficiently receive the heat from an outside
heating source or the heating zone in the quickest possible time.
The solution also can more quickly respond to the changes in
temperature of the outside heating source. This results in a rapid
and highly accurate temperature control of the solution. In
addition, the concentration of the solution can be controlled with
a high degree of accuracy by reducing the width of the micro
channel to provide a reduced diffusion length.
[0019] If the diameter of the micro channel is greater than 1 mm,
the effectiveness of the apparatus deteriorates. In such a case,
back mixing will occur at the front end due to turbulent flows.
This makes it difficult to maintain evenly, the residence time of
the solutions in the heating zone, thereby making it difficult to
provide a narrow size distribution of the nanoparticles that are
produced. If the diameter of the micro channel is less than 1
.mu.m, it becomes very difficult to handle the micro channel. This
also increases the pressure loss in the apparatus, deteriorating
the production efficiency.
[0020] The material of the capillary tube may include glass, metal,
alloy or plastic such as polyolefin, polyvinyl chloride, polyamide,
polyester or fluororesin.
[0021] While the example in FIG. 1 uses a capillary tube as the
micro channel, alternately the micro channel may be provided by
forming a layer and then cutting a groove having a width of 1 nm to
1 .mu.m on the surface of the layer. The layer could be made of,
for example, metal oxides such as silica, alumina or titania. It
could also be made of a heat-resistant plastic such as fluorinated
resin, on a heat-resistant substrate, for example, made of metal or
alloy,
[0022] Another example having such a structure is schematically
shown in FIG. 2. Specifically, a heat-resistant layer is formed on
a substrate 6, and a groove 3' serving as the micro channel is cut
on the substrate 6. The mixture of the particle-forming precursor
solutions A and B supplied to the groove 3' is heated as it passed
through the heating zone 4. The heating zone could be a heat plate.
The solutions react in the heating zone and the product mixture is
collected in the vessel 5.
[0023] While the examples in FIGS. 1 and 2 use two separate syringe
pumps as material feeders, the particle-forming precursor solutions
A and B may be supplied by using a single common feeder.
[0024] A heating device for the heating zone 4 may be composed of a
bath with a heating medium such as oil as described above. Any
other suitable conventional heating device such as a heat plate, an
infrared heater, and a high-frequency heater may also be used.
[0025] According to the disclosed technique, the particle-forming
precursor solution is preferably heated up to its reaction
initiation temperature at a high heating rate of 5.degree. C./sec
or more in the heating zone. Such a rapid heating allows heat
energy from outside to be transferred to the particle-forming
precursor solution approximately without time lay. Thus, the
reaction is formed in the solution very quickly to create a number
of nuclei and consequently grow a number of particles so as to form
nanoparticles having a small particle size. If the heating rate is
less than 5.degree. C./sec, the number of nuclei to be created will
be reduced. This causes the particles to gradually grow around the
respective nuclei at a lower speed. Thus, the particle size of the
particles to be formed will be increased, and desired nanoparticles
with a particle diameter 1 nm to 1 .mu.um become harder to be
obtained. Besides, in such a case, since the particle-forming
precursor solution is gradually heated from its outer region toward
its inner region, the reaction initiation timing and the particle
growth time will be varied in the respective regions of the
solution. Therefore, in such a case, the particle-size distribution
cannot be controlled within a desired narrow range.
[0026] It is technically difficult to increase the heating rate in
an unrestricted manner. Further, if an excessive number of nuclei
are created, it will be practically impossible to supply the
precursor at a concentration required for growing and forming
particles corresponding to the nuclei. From this point of view, the
heating rate is preferably set in a reasonable average range of
5.degree. C./sec to 10,000.degree. C./sec or more.
[0027] The nanoparticles formed in the heating zone in this way
should be rapidly cooled immediately after the reacted solution
exits the heating zone. The cooling rate is preferably set at
5.degree. C./sec or more. A cooling rate of less than
5.degree.C./sec will cause increased unevenness of the cooling, the
reaction termination timing and the particle growth time in the
respective regions of the reacted solution, resulting in
undesirably expanded particle-size distribution.
[0028] The cooling may be done by means of natural cooling,
air-cooling, oil-cooling or the like. Any conventional cooling
device may be used. Further, the particle-forming precursor
solution may be locally heated and cooled by a small-size heating
element or Peltier element disposed around the micro channel.
[0029] In the disclosed technique the reaction is not restricted to
any specific mode. Any suitable mode may be selected. According to
one mode, one or more reactants in the form of solution are heated
or mixed together to form a powdery solid. In another mode,
insoluble compound particles are precipitated from plural kinds
(e.g. two kinds) of soluble compounds. In yet another mode, one
kind of soluble compound is pyrolytically decomposed to form
powdery compound particles. Among these modes, one that provides a
higher reaction rate or having a particle precipitation-rate to be
significantly influenced by the reaction temperature or the
concentration of chemical species is particularly preferable.
[0030] Such a reaction may include a reaction in which a reducer is
reacted with a soluble metal compound solution to precipitate
various kinds of metal particles. It may also include: a reaction
in which carbonic acid is reacted with a calcium hydroxide solution
to precipitate calcium carbonate particles, a reaction in which a
sulfuric acid solution is reacted with a calcium chloride solution
to precipitate calcium sulfide particles, a reaction in which a
hydrogen sulfide solution is reacted with a cadmium chloride
solution to precipitate cadmium sulfide particles, a reaction in
which tetraalkoxysilane is thermally decomposed to precipitate
silicon oxide particles, and a reaction in which a water-soluble
selenium compound solution is reacted with a water-soluble cadmium
compound solution to precipitate cadmium selenide particles.
[0031] The materials forming the nanoparticles using such a
reaction may include: metal such as gold, silver, palladium, cobalt
or nickel; metalloids such as silicon or germanium; metal or
metalloid oxide such as zinc oxide, silicon oxide or germanium
oxide; metal chalcogenide compound such as cadmium selenide,
cadmium sulfide or zinc sulfide; and organic compounds such as
organic complex compound or organic pigment.
[0032] The solvent of the particle-forming precursor solution used
in the method of the present invention may be selected from: water;
water-miscible organic solvent such as methyl alcohol, ethyl
alcohol, acetone, dimethylformamide, dimethylacetamide or dimethyl
sulfoxide; and water-immiscible organic solvent such as octane,
cyclohexane, benzene, xylene, diethyl ether or acetic ether,
depending on the type of precursor and the mode of reaction to be
used.
[0033] In this case, an excessively high concentration of the
precursor in the particle-forming precursor solution will increase
the viscosity of the solution. This leads to a heterogeneous
reaction having an adverse affect on the smooth formation of
nanoparticles. If the precursor concentration is excessively low,
the reaction rate will be reduced, and more time will be required
for forming nanoparticles. Thus, the precursor concentration is
typically set in the range of 0.001 to 5% by mass, preferably in
the range of 0.01 to 1% by mass.
[0034] In the disclosed techniques, the particle size of
nanoparticles to be formed can be controlled by adjusting the
heating temperature and the residence time in the heating zone. In
this process, the reaction temperature may be controlled by using a
heating device having a temperature control function. The residence
time may be controlled by adjusting the feeding rate of the
particle-forming precursor solution or the volume of the micro
channel, and introducing a certain gas or liquid into the micro
channel to segment the solution. In this manner, the residence-time
distribution of the solution can be maintained to be uniform to
provide a narrow particle-size distribution. Such a residence
time-distribution depends on the flow rate distribution, which in
turn arises from the friction between the solution and the inner
wall of the micro channel.
[0035] In this case, the gas to be used may include: inert gas such
as nitrogen, argon or helium; oxidant gas such as air or oxygen;
and reductant gas such as hydrogen or ammonia. The liquid to be
used may include any suitable liquid which is not homogeneously
mixed with the particle-forming precursor solution. For example,
when the solution is a hydrophilic solution, the liquid may be a
hydrophobic solvent such as hexane, cyclohexane or toluene. When
the solution is a oleophilic solution, the liquid may be a
hydrophilic solvent such as water, methyl alcohol, ethyl alcohol,
dimethyl sulfoxide or dimethylformamide.
[0036] In the disclosed technique, the particle-forming precursor
solution may be agitated to provide homogeneous reaction and
reduced reaction time in the heating zone, as needed. This
agitation may be performed using a micro stirrer, a mixing tube or
an ultrasound device. The solution may also be agitated by mixing
magnetic particles or magnetic fluid with the particle-forming
precursor solution in advance, and applying a magnetic field
thereto from outside.
[0037] In the disclosed techniques, a pump is used to continuously
supply the particle-forming precursor solution to the heating zone.
The pump is not limited to a specific type, but any suitable
small-size pump may be selected. However, it is preferable to
select a pump having low pulsations, such as a syringe pump or a
non-pulsating pump.
[0038] In the disclosed techniques, when two kinds of
particle-forming precursor solutions are used and reacted with one
another in the heating zone, these solutions are preferably
selected as a combination capable of forming different phases.
These solutions are then made to react with one another along the
interface between the different phases in the heating zone to form
nanoparticles. In this case, the reaction can be homogeneously
caused to provide nanoparticles having a constant particle-size
distribution. The entire flow rate and reaction time can be readily
controlled by changing the respective flow rates of the phases.
[0039] According to the disclosed techniques, nanoparticles with a
particle size of greater than 1 .mu.m can also be prepared.
However, particles having an excessively increased size will
sediment under gravity. These sedimented particles clog the micro
channel and prevent the continuous operation of the apparatus.
Thus, it is desirable to select the reaction conditions such that
nanoparticles having a particle size in the range of 1 nm to 1
.mu.m, preferably in the range of 1 to 20 nm are produced.
[0040] The disclosed techniques are described in more detail in
conjunction with Examples, but not limited to these Examples.
[0041] Example 1
[0042] A micro reactor constructed as shown in FIG. 1 was prepared
by immersing approximately one-half of the intermediate portion of
a glass capillary tube having an inner diameter of 0.5 mm and a
length of 1 m, into an oil bath having a volume of 500 ml.
[0043] A 1 mM-chloroauric acid solution and a 2% by mass of citric
acid solution were fed from first and second syringe pumps,
respectively, at a feed speed of 0.05 ml/minute, and mixed together
before their introduction into the oil bath. Then, the mixture was
introduced into the oil bath heated at 200.degree. C. in advance,
and rapidly heated up to 100.degree. C. at a heating rate of
10.degree. C./sec to cause a reaction in the mixture. Then, the
reacted mixture was naturally cooled under ambient air, and
collected in a vessel. In this case, the residence time in the oil
bath was 10 minutes, and the cooling rate was 10.degree.
C./sec.
[0044] In this manner, gold colloid nanoparticles having an average
particle size of 15 nm could be continuously obtained. A
transmission electron microscopic picture of the obtained gold
colloid nanoparticles is shown in FIG. 3.
[0045] Example 2
[0046] Based on a micro reactor using a hot water bath as a
substitute for the oil bath of the micro reactor in Example 1,
chloroauric acid was deoxidized by tannic acid and citric acid.
[0047] More specifically, a 1 mM-chloroauric acid solution and a
solution containing 2% by mass of mixture consisting of tannic
acid, citric acid and potassium carbonate (mass ratio:5:7:4) were
fed from the first and second syringe pumps, respectively, at a
feed speed of 0.3 ml/minute, and mixed together. Then, the mixture
was rapidly heated up to 60.degree. C. in the hot water bath to
cause a reaction in the mixture while applying ultrasounds from
outside. Then, the reacted mixture was rapidly cooled under ambient
air. In this case, the heating rate was 10.degree. C./sec, the
residence time being 1 minute, and the cooling rate being
10.degree. C./sec.
[0048] In this manner, gold colloid nanoparticles having an average
particle size of 8 nm could be continuously obtained. A
transmission electron microscopic picture of the obtained gold
colloid nanoparticles is shown in FIG. 4.
[0049] Example 3
[0050] This example is based on a micro reactor having the same
structure as that in Example 1 except that a single syringe pump
was used as a substitute for the two syringe pumps. Further, the
capillary tube had an inner diameter of 1 mm and a length of 700
mm. Further, cadmium sulfide particles were prepared through a
homogeneous precipitation method.
[0051] More specifically, 50 mg/liter of cadmium sulfide, 60
mg/liter of thiourea, 500 mg/liter of sodium hexametaphosphate and
30 mg/liter of sodium hydroxide were dissolved in ion-exchange
water. Then, the mixture was fed from the syringe pump to the
capillary tube in the oil bath heated at 97.degree. C. in advance,
at a feed speed of 0.5 to 0.25 ml/minute to cause a reaction in the
mixture. Then, the reacted mixture was rapidly cooled under ambient
air.
[0052] In this case, both the heating rate and the cooling rate
were maintained at a constant value of 5.degree. C./sec, but only
the residence time was changed between 2 minutes, 5 minutes and 10
minutes. The average particle sizes of gold colloid nanoparticles
obtained in the respective conditions were judged from UV-VIS
absorption spectrums. The result is shown in Table 1.
1TABLE 1 Test No. No. 1 No. 2 No. 3 Residence Time 2 5 10 Average
Particle Size (nm) 3.0 3.6 4.0
[0053] As seen in Table 1, the particle size of nanoparticles to be
formed can be controlled by changing the residence time.
[0054] Example 4
[0055] This example is based on a micro reactor having a structure
as shown in FIG. 1, provided with a micro channel composed of a
capillary tube having an inner diameter of 0.2 mm and a length of
1.2 mn. A single syringe pump was used. A mixed solution containing
70 g/kg of cadmium stealate, 300 g/kg of trioctylphosphineoxide, 90
g/kg of trioctylphosphineselenide and 280 g/kg of trioctylphosphine
was fed at a feed speed of 0.1 to 0.01 ml/minute. The mixture was
passed through the oil bath maintained at 275.degree. C., and
rapidly heated therein to cause a reaction. Then, the reacted
mixture was rapidly cooled and then collected. The average particle
sizes of gold colloid nanopaiticles were measured and determined
from UV-VIS absorption spectrums.
[0056] In this case, the heating rate was maintained at
3000.degree. C./sec, and the cooling rate was maintained at
1000.degree. C./sec. The residence time was changed between 0.5
minutes, 5 minutes and 10 minutes. The result is shown in Table
2.
2 TABLE 2 Test No. No. 1 No. 2 No. 3 Residence Time 0.5 5.0 10.0
Average Particle Size (nm) 3.4 3.8 4.2
[0057] As seen in Table 2, the particle size of nanoparticles to be
formed can be controlled by changing the residence time.
[0058] Example 5
[0059] The residence time was maintained at 0.5 minutes, and the
reaction temperature was changed from 245.degree. C. to 320.degree.
C. Other conditions of the reaction were the same as those in
Example 4. The average particle sizes of obtained cadmium selenide
particles were determined. The result is shown in Table 3.
3 TABLE 3 Test No. No. 1 No. 2 No. 3 No. 4 Reaction Temperature
(.degree. C.) 245 260 275 320 Particle Size (nm) 2.4 2.8 3.4
4.0
[0060] As seen in Table 2, the particle size of nanoparticles to be
formed can be controlled by changing the reaction temperature.
[0061] As mentioned above, according to the present invention,
particles having a controlled particle size of nanometer order can
be continuously prepared by using a simple apparatus.
[0062] Other modifications and variations to the invention will be
apparent to those skilled in the art from the foregoing disclosure
and teachings. Thus, while only certain embodiments of the
invention have been specifically described herein, it will be
apparent that numerous modifications may be made thereto without
departing from the spirit and scope of the invention.
* * * * *