U.S. patent application number 10/451232 was filed with the patent office on 2004-11-11 for method for manufacturing nano-scaled copper powder by wet reduction process.
Invention is credited to Jeong, Byong-Soek, Jeong, In-Bum, Kim, Yoon-Hyun, Kim, Young-Sic, Lee, Byoung-Yoon, Lee, Moon-Soo.
Application Number | 20040221685 10/451232 |
Document ID | / |
Family ID | 32226205 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040221685 |
Kind Code |
A1 |
Jeong, In-Bum ; et
al. |
November 11, 2004 |
Method for manufacturing nano-scaled copper powder by wet reduction
process
Abstract
The present invention relates to a method for manufacturing a
nano-scaled copper powder by a wet reduction process, comprising
adding appropriate amounts of sodium hydroxide (NaOH) and hydrazine
(N.sub.2H.sub.4) to an aqueous copper chloride (CuCl.sub.2)
solution to finally obtain a copper powder having a particle size
of 100 nm (0.1 nm) grade via an intermediate product such as a
copper complex.
Inventors: |
Jeong, In-Bum; (Kyunggi-do,
KR) ; Kim, Young-Sic; (Seoul, KR) ; Lee,
Byoung-Yoon; (Incheon, KR) ; Kim, Yoon-Hyun;
(Kyunggi-do, KR) ; Jeong, Byong-Soek; (Inchoen,
JP) ; Lee, Moon-Soo; (Kyunggi-do, JP) |
Correspondence
Address: |
Cooper & Dunham
1185 Avenue of the Americas
New York
NY
10036
US
|
Family ID: |
32226205 |
Appl. No.: |
10/451232 |
Filed: |
June 18, 2003 |
PCT Filed: |
May 9, 2003 |
PCT NO: |
PCT/KR03/00918 |
Current U.S.
Class: |
75/373 |
Current CPC
Class: |
B22F 1/054 20220101;
B82Y 30/00 20130101; B22F 9/24 20130101; B22F 1/0018 20130101 |
Class at
Publication: |
075/373 |
International
Class: |
B22F 009/24 |
Claims
1. A method for manufacturing a nano-scaled copper powder by a wet
reduction process, comprising the steps of: adding sodium hydroxide
(NaOH) to an aqueous copper chloride (CuCl.sub.2) solution to give
an aqueous solution containing copper oxide and copper hydroxide;
reducing the copper oxide and the copper hydroxide to obtain a
nano-scaled copper powder as a precipitate by adding hydrazine
(N.sub.2H.sub.4) to the aqueous solution; and filtering and drying
the precipitated nano-scaled copper powder.
2. The method as set forth in claim 1, wherein the sodium hydroxide
(NaOH) is added in an amount of 2 to 33 moles per mole of the
copper chloride (CuCl.sub.2) when the aqueous copper chloride
(CuCl.sub.2) solution is kept within a temperature of 30 to
80.degree. C., and the hydrazine (N.sub.2H.sub.4) is added in an
amount of 0.5 to 12 moles per mole of the copper chloride when the
aqueous solution containing the copper oxide and the copper
hydroxide is kept within a temperature of 40 to 80.degree. C.
3. The method as set forth in claim 1, wherein in the step of
producing the copper oxide and the copper hydroxide, before the
addition of NaOH, silver nitrate (AgNO.sub.3) is added to the
aqueous copper chloride (CuCl.sub.2) solution in an amount of
1/1,000 to 1/10,000 moles per mole of the copper chloride.
4. A method for manufacturing a nano-scaled copper powder by a wet
reduction process, comprising the steps of: adding hydrazine
(N.sub.2H.sub.4) to an aqueous copper chloride (CuCl.sub.2)
solution to give an aqueous solution containing a copper complex
(Cu(N.sub.2H.sub.4).sub.mCl.sub.n); adding sodium hydroxide (NaOH)
to the aqueous copper complex solution to obtain a nano-scaled
copper powder; and filtering and drying the nano-scaled copper
powder.
5. The method as set forth in claim 4, wherein the hydrazine
(N.sub.2H.sub.4) is added in an amount of 0.5 to 12 moles per mole
of the copper chloride (CuCl.sub.2) when the aqueous copper
chloride (CuCl.sub.2) solution is kept within a temperature of 20
to 70.degree. C., and the sodium hydroxide (NaOH) is added in an
amount of 2 to 33 moles per mole of the copper chloride when the
aqueous solution containing the copper complex is kept within a
temperature of 40 to 80.degree. C.
6. The method as set forth in claim 4, wherein in the step of
producing the copper complex (Cu(N.sub.2H.sub.4).sub.mCl.sub.n),
before the addition of hydrazine, silver nitrate (AgNO.sub.3) is
added to the aqueous copper chloride (CuCl.sub.2) solution in an
amount of 1/1,000 to 1/10,000 moles per mole of the copper
chloride.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for manufacturing
a nano-scaled copper powder by a wet reduction process, and more
particularly to a method for manufacturing a nano-scaled copper
powder by a wet reduction process, comprising adding appropriate
amounts of hydrazine (N.sub.2H.sub.4) and alkaline hydroxide to an
aqueous copper salt(CuX, X.dbd.Cl.sub.2, Br.sub.2, SO.sub.4,
(NO.sub.3).sub.2 . . . ) solution to finally obtain copper powders
having 100 nm.about.1 .mu.m graded particle size via chelate.
BACKGROUND ART
[0002] Copper (Cu) powder is employed in an electrically conductive
paste material for multilayer passive devices, for example, a
multilayer ceramic chip capacitor (MLCC). Recently, in order to
produce the conductive material for inner electrode, a copper
powder with a submicron scaled particle size ranging from 0.8
.mu.m.about.1 .mu.m has been used.
[0003] In this regard, development of a nano-scaled copper powder
with good dispersibility may be considered. It is anticipated that
such nano-scaled copper powder be applied to any miniaturized
passive devices for which development is in progress in the
pertinent art.
[0004] Meanwhile, in the fields of PDPs (Plasma Display Panels),
FEDs (Field Emission Displays), automobile back light and the like
using glass as a substrate, a metal conductive paste material is
required to be sintered at a low temperature of 550.degree. C.
Various application industries also tend to lower the sintering
temperature.
[0005] The use of a nano-scaled (100 nm) metal powder can keep pace
with the trend of lowering the sintering temperature of a metal
conductive paste material. Therefore, it is anticipated that the
conductive paste material can be used for forming electrodes that
have up till now been exclusively carried out by a plating method,
due to a higher sintering temperature.
[0006] Many different methods have been involved in the synthesis
of a copper powder used in the conductive paste as described above,
such as a gas phase method and a liquid phase method.
[0007] Conventional methods for manufacturing metal powders have
various problems such as a low yield due to wide particle size
distribution, large particle size, low sphericity, and difficulty
in controlling a degree of oxidation. In order to overcome these
problems, a wet method such as a liquid phase reduction method and
a thermal decomposition method, as well as a gas phase method such
as gas evaporation method and the like, have been developed.
[0008] Methods generally used for manufacturing metal powders are
summarized, as follows.
[0009] With respect to a gas atomization method, a high-pressure
inert gas is atomized to a molten metal flowing through a nozzle to
obtain a metal powder. Although this method is suitable for mass
production, it is difficult to prepare a nano-scaled powder,
thereby powder yield being considerably lowered. Therefore, the gas
atomization method is restrictively used.
[0010] With respect to a thermal decomposition method, a metal
compound that has a weak binding force between metal and anion is
thermally decomposed using a gas reducing agent and milled to
obtain a metal powder. This method provides a fine metal powder.
However, because the metal powder may be burned during a heat
treatment the burned powder is required to be milled and
classified. Therefore, this method has a lower yield than a liquid
phase reduction method when used in preparing a metal powder for
forming a thick film conductive paste material.
[0011] In a gas evaporation method, an evaporation material is
evaporated by heating its source under an inert gas such as He and
Ar or an active gas such as CH.sub.4 and NH.sub.4, and the
evaporated gas is reduced and condensed in the seducing gas such as
H.sub.2 obtain a fine metal powder. This method is advantageous in
preparing a metal powder having its particle size of 5
nm.about.several .mu.m. However, productivity is very low and thus
the metal powder is very expensive.
[0012] A liquid phase reduction method is an exemplary chemical
method for manufacturing a metal powder. This method can more
easily control the shape of the powder and can prepare an ultrafine
powder having a particle size of a submicron unit, compared with
the aforementioned methods. The complete procedure of preparing a
metal powder by reducing an initial precipitate is carried out in a
liquid phase.
[0013] In detail, a metal powder can be prepared by a procedure
comprising a initial intermediate forming, producing an
intermediate product and adding a reducing agent. The reducing
agent comprises formalin, hydrazine, an organic compound and the
like.
[0014] Advantageously, the liquid phase reduction method provides
easy control of the powder shape, high sphericity, and narrow
particle size distribution. Furthermore, it is possible to prepare
an ultrafine powder having a submicron-scaled particle size that is
excellent in the surface property of the powder. Therefore, a
powder that is high in tap density, one of the most important
characteristics for a conductive paste material can be prepared.
Despite these advantages, optimization of concentration,
temperature, pH, and reaction rate is a prerequisite to prepare a
metal powder.
[0015] A conventional wet method, such as the liquid phase
reduction method, for preparing a copper powder controls the
particle size of the powder through a multi-step reaction, as shown
in FIG. 1.
[0016] In detail, in a first step, copper oxide (CuO) is
precipitated by adding sodium hydroxide (NaOH) to an aqueous copper
sulfate (CuSO.sub.4) solution, and then filtered.
[0017] In a second step, a stable Cu.sub.2O solution is obtained by
reacting the obtained CuO with glucose (C.sub.6H.sub.12O.sub.6), a
representative aldohexose (a monosaccharide having 6 carbons and an
aldehyde group).
[0018] In a third step, when the color of the resulting solution
changed into a dark red due to the production of Cu.sub.2O, glycine
(NH.sub.2--CH.sub.2--COOH), a kind of amino acid, and arabic gum
are added to the Cu.sub.2O solution and uniformly dispersed. Then,
hydrazine (N.sub.2H.sub.4) as a reducing agent is added to the
mixture to thereby reduce Cu.sub.2O, to obtain a copper powder as a
precipitate.
[0019] The glycine and arabic gum as the third additives are added
to control the size and surface shape of the final copper
powder.
[0020] By obtaining the copper oxide (CuO) as a precipitate, by
adding sodium hydroxide (NaOH) to an aqueous copper sulfate
(CuSO.sub.4) solution, the effect of impurities that are left in
the solution on the product can be minimized.
[0021] As described above, in the conventional wet method for
preparing a copper powder, copper sulfate (CuSO.sub.4) is used as a
copper source. As a result, an anionic effect is reduced, whereby
the particles of the copper powder become agglomerated.
[0022] It is difficult adjust the input condition by addition of
the glycine and Arabic gum as an organic additive to control the
size and surface shape of the copper powder, whereby a high degree
of reproducibility cannot be afforded.
[0023] The particle size of the copper powder is different
depending on the addition condition of the additives and thus it is
difficult to control the particle size.
[0024] The process is complicated due to many variables such as
additives, reaction agents (NaOH, N.sub.2H.sub.4), together with
its quantity and method of addition and a solution temperature and
requires a longer preparation time.
[0025] Relatively coarse copper powder, having a particle size of
0.5 to 4 .mu.m grade, is obtained and the particle size
distribution of the powder is not uniform.
[0026] In particular, because Cu.sub.2O is a chemically stable
intermediate product, the growth rate of the copper powder is slow.
Therefore, it is difficult to maintain the sphericity of the powder
surface.
[0027] For the forgoing reasons, it is difficult to prepare an
ultrafine copper powder having a particle size of 0.1 .mu.m (100
nm) grade using the conventional wet method.
DISCLOSURE OF THE INVENTION
[0028] Therefore, the present invention has been made in view of
the above problems, and it is an object of the present invention to
provide a method for manufacturing an ultrafine copper powder
having particle size of 100 nm grade.about.1 .mu.m grade by a wet
reduction process, comprising the steps of adding sodium hydroxide
(NaOH) to an aqueous copper chloride (CuCl.sub.2) solution with
high anionic effect, and reducing the resulting copper oxide
(Cu.sub.xO) by the addition of hydrazine (N.sub.2H.sub.4). The
method is a relatively simple process and also affords a high
degree of reproducibility. Furthermore, copper powder having
particle size of 100 nm grade.about.1 .mu.m grade can be prepared
which has good surface quality, narrow particle size distribution,
and good powder sphericity.
[0029] In accordance with one aspect of the present invention, the
above and other objects can be accomplished by the provision of a
method for manufacturing a nano-scaled copper powder by a wet
reduction process, comprising the steps of adding sodium hydroxide
(NaOH) to an aqueous copper chloride (CuCl.sub.2) solution to give
an aqueous solution containing copper oxide and copper
hydroxide;
[0030] reducing the copper oxide and the copper hydroxide to obtain
a nano-scaled copper powder as a precipitate by adding hydrazine
(N.sub.2H.sub.4) to the aqueous solution; and filtering and drying
the precipitated nano-scaled copper powder.
[0031] Preferably, the sodium hydroxide (NaOH) is added in an
amount of 2 to 33 moles per mole of the copper chloride
(CuCl.sub.2) when the aqueous copper chloride (CuCl.sub.2) solution
is kept within a temperature of 30 to 80.degree. C., and the
hydrazine (N.sub.2H.sub.4) is added in an amount of 0.5 to 12 moles
per mole of the copper chloride when the aqueous solution
containing the copper oxide and the copper hydroxide is kept within
a temperature of 40 to 80.degree. C.
[0032] Preferably, in the step of producing the copper oxide and
the copper hydroxide, before the addition of NaOH, silver nitrate
(AgNO.sub.3) is added to the aqueous copper chloride (CuCl.sub.2)
solution in an amount of 1/1,000 to 1/10,000 moles per mole of the
copper chloride.
[0033] In accordance with another aspect of the present invention,
there is provided a method for manufacturing a nano-scaled copper
powder by a wet reduction process, comprising the steps of adding
hydrazine (N.sub.2H.sub.4) to an aqueous copper chloride
(CuCl.sub.2) solution to give an aqueous solution containing a
copper complex (Cu(N.sub.2H.sub.4).sub.mCl.sub.n); adding sodium
hydroxide (NaOH) to the aqueous copper complex solution to obtain a
nano-scaled copper powder; and filtering and drying the nano-scaled
copper powder.
[0034] Preferably, the hydrazine (N.sub.2H.sub.4) is added in an
amount of 0.5 to 12 moles per mole of the copper chloride
(CuCl.sub.2) when the aqueous copper chloride (CuCl.sub.2) solution
is kept within a temperature of 20 to 70.degree. C., and the sodium
hydroxide (NaOH) is added in an amount of 2 to 33 moles per mole of
the copper chloride when the aqueous solution containing the copper
complex is kept within a temperature of 40 to 80.degree. C.
[0035] Preferably, in the step of producing the copper complex
(Cu(N.sub.2H.sub.4).sub.mCl.sub.n), before the addition of
hydrazine, silver nitrate (AgNO.sub.3) is added to the aqueous
copper chloride (CuCl.sub.2) solution in an amount of 1/1,000 to
1/10,000 moles per mole of the copper chloride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0037] FIG. 1 is a schematic flow diagram showing the conventional
wet method for preparing a copper powder;
[0038] FIG. 2 is a schematic flow diagram showing the wet reduction
method for preparing a nano-scaled copper powder according to the
first embodiment of the present invention;
[0039] FIG. 3 is a schematic flow diagram showing the wet reduction
method for preparing a nano-scaled copper powder according to the
second embodiment of the present invention;
[0040] FIG. 4 is a Scanning Electron Microscopy (SEM) photograph of
the nano-scaled copper powder prepared according to the first
embodiment of the present invention;
[0041] FIG. 5 is a SEM photograph of the nano-scaled copper powder
prepared according to the second embodiment of the present
invention;
[0042] FIG. 6 is a SEM photograph of the nano-scaled copper powder
prepared by adding a trace amount of silver nitrate for use with
the first embodiment of the present invention; and
[0043] FIG. 7 is a SEM photograph of the nano-scaled copper powder
prepared by adding a trace amount of silver nitrate for use with
the second embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0044] Hereinafter, the present invention will be described in more
detail.
[0045] According to the present invention, copper chloride
(CuCl.sub.2) is used as a copper salt for preparing a copper
powder, instead of copper sulfate (CuSO.sub.4) in a conventional
wet method.
[0046] Copper chloride (CuCl.sub.2) has an anionic group that is
higher in terms of electronegativity, relative to copper sulfate
(CuSO.sub.4), whereby the chlorine ion has a higher anionic effect
than the sulfate ion in a solution. Therefore, agglomeration of the
copper powder is more effectively prevented, thereby causing a much
finer powder to be produced. Furthermore, copper chloride acts to
effectively control the shape of the powder surface.
[0047] For the forgoing reasons, according to the present
invention, a nano-scaled copper powder is prepared by adding sodium
hydroxide (NaOH) to an aqueous copper chloride solution
(CuCl.sub.2) to give copper oxide (CuO) and copper hydroxide
(Cu(OH).sub.2) as intermediate products, reducing the intermediate
products using hydrazine (N.sub.2H.sub.4), followed by filtered and
dried.
[0048] In detail, the first step of adding sodium hydroxide (NaOH)
to an aqueous copper chloride solution (CuCl.sub.2) to give an
aqueous solution containing copper oxide (CuO, CU.sub.2O) and
copper hydroxide (Cu(OH).sub.2) as intermediate products is shown
as the following Scheme 1: 1
[0049] In the above reaction, NaOH is added to produce copper oxide
and copper hydroxide. The amount of the added NaOH ranges from 2 to
33 moles per mole of CuCl.sub.2. If the amount of NaOH exceeds 33
moles, the obtained aqueous solution is changed into a strong basic
solution. Therefore, a reduction reaction does not completely occur
in the subsequent step of adding N.sub.2H.sub.4. Furthermore, such
addition is uneconomical and a large amount of ions are left in the
aqueous solution, resulting in an increase of impurities.
[0050] On the other hand, if the amount of NaOH is less than 2
moles, the desired intermediate product, copper oxide (Cu.sub.xO)
is not obtained. As a result, subsequent reaction cannot be
accomplished.
[0051] It is preferable to limit the temperature of the aqueous
CuCl.sub.2 solution to a range of 30 to 80.degree. C. upon the
addition of NaOH. If the temperature of the aqueous CuCl.sub.2
solution is less than 30.degree. C., it is difficult to prepare the
intermediate products. On the other hand, if the temperature of the
aqueous CuCl.sub.2 solution exceeds 80.degree. C., the intermediate
products are quickly prepared, thus causing severe agglomeration.
At the same time, because the reduction reaction is carried out at
too high a temperature, 100.degree. C. or more, the thermal
stability of the intermediate products is lowered.
[0052] The second step of reducing the copper oxide (CuO) and
copper hydroxide (Cu(OH).sub.2) to obtain a copper powder as a
precipitate using hydrazine (N.sub.2H.sub.4) is shown as the
following Scheme 2: 2
[0053] In the above reaction, the amount of the added
N.sub.2H.sub.4 ranges from 0.5 to 12 moles per mole of CuCl.sub.2.
If the amount of N.sub.2H.sub.4 is less than 0.5 moles, the
reduction reaction may be incomplete. On the other hand, if it
exceeds 12 moles, although the reaction rate is increased, the
product is severely agglomerated and the surface quality of the
copper powder is lowered.
[0054] It is preferable to add hydrazine to an aqueous solution
containing the copper oxide (CuO) and copper hydroxide
(Cu(OH).sub.2) when the temperature of the aqueous solution is kept
within a range of 40 to 80.degree. C. If the temperature is less
than 40.degree. C., the reduction reaction is not easily carried
out, resulting in an incomplete reduction reaction. On the other
hand, if it exceeds 80.degree. C., the reduction reaction is easily
carried out but it is carried out at too high a temperature,
thereby causing agglomeration of the product.
[0055] The precipitated copper powder is filtered to eliminate NaCl
salt and then dried under a non-oxidizing atmosphere, to thereby
finally produce a nano-scaled copper powder.
[0056] Meanwhile, before the addition of sodium hydroxide (NaOH) to
the aqueous copper chloride (CuCl.sub.2) solution, silver nitrate
(AgNO.sub.3) may be added in a trace amount of 1/1,000 to 1/10,000
moles per mole of the copper chloride. Because silver is reduced
faster than copper, the addition of silver nitrate enables an
increase in the reduction rate of the copper.
[0057] That is, silver acts as a catalyst to promote the nucleation
of copper, thereby increasing the reduction rate of copper. As a
result, the total reduction rate of copper is increased.
[0058] In the presence of silver nitrate (AgNO.sub.3), the first
step is carried out as the following Scheme 3: 3
[0059] Hydrazine is added to the aqueous solution obtained
according to Scheme 3 to thereby give a copper powder, as the
following Scheme 4: 4
[0060] In the above reaction, the obtained copper powder is
filtered to eliminate NaCl salt and a nitrate ion (NO.sub.3.sup.-)
and then dried under a non-oxidizing atmosphere to thereby finally
produce a nano-scaled copper powder.
[0061] Meanwhile according to the present invention, a nano-scaled
copper powder can also be prepared, even though the addition
sequence of NaOH and hydrazine (N.sub.2H.sub.4) is changed.
[0062] This is feasible because CuCl.sub.2 reacts with hydrazine
(N.sub.2H.sub.4) to form a copper complex
(Cu(N.sub.2H.sub.4).sub.mCl.sub- .n).
[0063] In detail, hydrazine (N.sub.2H.sub.4) is added to an aqueous
copper chloride (CuCl.sub.2) solution in an amount of 1 to 12 moles
per mole of the copper chloride at a temperature of 20 to
70.degree. C. to produce a copper complex
(Cu(N.sub.2H.sub.4).sub.mCl.sub.n) as an intermediate product. This
reaction can be simplified as the following Scheme 5: 5
[0064] In the above reaction, if the temperature of the aqueous
copper chloride solution is less than 20.degree. C., the desired
intermediate product is not obtained. Rather, an undesirable
intermediate product may be obtained or such an undesirable
reaction may occur. On the other hand, if it exceeds 70.degree. C.,
the desired intermediate product is obtained and at the same time,
a partial reduction reaction thereof may occur.
[0065] If the amount of the added hydrazine (N.sub.2H.sub.4) is
less than 1 mole, the desired intermediate product is not obtained;
while, if it exceeds 12 moles a large amount of ions are left in
the aqueous copper chloride solution, thereby increasing
impurities. Furthermore, a partial reduction reaction may
occur.
[0066] Then, sodium hydroxide (NaOH) is added to an aqueous
solution containing the copper complex in an amount of 2 to 33
moles per mole of the copper chloride (CuCl.sub.2) at a temperature
of 40 to 80.degree. C. to separate a nano-scaled copper powder from
the copper complex. This reaction is shown as the following Scheme
6: 6
[0067] In the above reaction, if the temperature of the aqueous
solution containing the copper complex is less than 40.degree. C.,
a reduction reaction is not easily carried out and even then has a
slow reaction rate. On the other hand, if the temperature exceeds
80.degree. C., the reduction reaction is increased but the copper
powder is easily agglomerated due to a too high temperature.
[0068] If the amount of the added sodium hydroxide NaOH) is less
than 2 moles, the reduction reaction is not easily carried out. On
the other hand, if it exceeds 33 moles, the reduction reaction is
increased but a large amount of ions are left in the aqueous
solution, thereby increasing impurities. Furthermore, excess NaOH
is wasteful from an economical point of view.
[0069] Then, the obtained nano-scaled copper powder is filtered and
dried, to thereby finally give an ultrafine copper powder having a
particle size of 100 nm grade.
[0070] Meanwhile, in the step of producing the copper complex
(Cu(N.sub.2H.sub.4).sub.mCl.sub.n), before the addition of
hydrazine (N.sub.2H.sub.4), silver nitrate (AgNO.sub.3) is added to
the aqueous copper chloride (CuCl.sub.2) solution in an amount of
1/1,000 to 1/10,000 moles per mole of the copper chloride in order
to promote the reduction reaction rate of copper compiex. This
reaction is summarized as the following Scheme 7: 7
[0071] Subsequent to producing the copper complex
(Cu(N.sub.2H.sub.4).sub.- mCl.sub.n) by the addition of a trace
amount of silver nitrate and hydrazine, sodium hydroxide (NaOH) is
added to separate a copper powder from the aqueous solution
containing the copper complex (Cu(N.sub.2H.sub.4).sub.mCl.sub.n).
This reaction is summarized as the following Scheme 8: 8
[0072] The copper powder obtained is filtered and dried under a
non-oxidizing atmosphere to thereby finally produce a nano-scaled
copper powder.
[0073] The present invention will hereinafter be described more
specifically by non-limiting preferred examples.
EXAMPLE 1
[0074] According to a conventional wet method, first, a sodium
hydroxide (NaOH) with varying concentrations was added to 100 ml of
an aqueous copper sulfate (CuSO.sub.4) solution to produce an
aqueous solution containing copper oxide (Cu.sub.xO) as a
precipitate. Then, the copper oxide was filtered and recovered.
[0075] Distilled water and glucose (C.sub.6H.sub.12O.sub.6) were
added to the obtained copper oxide and agitated until the color of
the solution changed into dark red. As a result, an aqueous
solution containing a stable Cu.sub.2O was obtained.
[0076] Then, glycine (NH.sub.2--CH.sub.2--COOH) and arabic gum were
added to the aqueous solution containing Cu.sub.2O and then
dispersed uniformly.
[0077] Then, Cu.sub.2O was reduced to a copper powder as a
precipitate by mixing hydrazine (N.sub.2H.sub.4), as a reducing
agent, into the dispersion and then dried.
[0078] The result of the conventional wet method is given in Table
1.
1TABLE 1 Sample No. CuSO.sub.4:NaOH:N.sub.2H.sub.4:- Glycine
Average particle size (.mu.m) 11 1:3:3:0.1 0.4 12 1:3:4:0.25 0.5 13
1:2:7:0.30 1 Numbers in respective components denote M ratios based
on 2M CuSO.sub.4 Glucose and arabic gum as additives were added in
an amount of 0.1M. respectively, based on 2M CuSO.sub.4.
[0079] As shown in Table 1, the average particle size of each
copper powder (samples 11 to 13) prepared by the conventional wet
method varied, depending on the amounts of added reaction agents
and additives. Specifically, the particle size distribution ranged
from about 0.4 to 1 .mu.m.
EXAMPLE 2
[0080] According to the present invention, first, 1 00 ml of 2M
aqueous CuCl.sub.2 solution was heated to a temperature of 30 to
80.degree. C. and vigorously agitated at that temperature.
[0081] Sodium hydroxide (NaOH) was at a time added to the aqueous
copper chloride solution at the above temperature.
[0082] Because the particle size of the final product, copper
powder, depends on the concentration of the sodium hydroxide; the
amount of the sodium hydroxide can be adjusted according to the
desired particle size.
[0083] After the addition of sodium hydroxide (NaOH), hydrazine
(N.sub.2H.sub.4) was added to the resulting aqueous solution at a
temperature of 40 to 80.degree. C., to obtain a copper powder. In
this case, hydrazine (N.sub.2H.sub.4) was added at a time.
[0084] The copper powder obtained according to the above procedure
was washed with secondary distilled water and filtered. The
filtered copper powder was dried at an appropriate temperature
under a non-oxidizing atmosphere to thereby finally obtain a
nano-scaled copper powder.
[0085] That is, the conventional wet method for preparing a copper
powder comprises various processes such as filtering, recovering
and addition of distilled water. However, the wet reduction method
according to the present invention is carried out in one reaction
vessel and the process for recovering a copper powder is carried
out only once.
[0086] The particle size distribution of the copper powder obtained
according to the present invention is given in Table 2.
2TABLE 2 Particle size distribution of copper powder according to
the concentration of NaOH Particle size distribution Av- Sam- erage
ple D10 D50 D90 size Section No. CuCl.sub.2 NaOH N.sub.2H.sub.4
(.mu.m) (.mu.m) (.mu.m) (.mu.m) Com- 21 1 1 12 0.05 0.10 0.14 0.10
parative sample Inventive 22 1 2 12 0.05 0.10 0.16 0.10 samples 23
1 4 12 0.06 0.13 0.22 0.14 24 1 8 12 0.09 0.15 0.25 0.17 25 1 16 12
0.12 0.38 0.50 0.36 26 1 33 12 0.20 0.50 0.70 0.45 Com- 27 1 35 12
0.29 0.70 0.87 0.63 parative sample Numbers in NaOH and
N.sub.2H.sub.4 denote molar ratio based on 2M CuCl.sub.2.
[0087] As shown in Table 2, in case of samples 22 to 26, NaOH was
added with varying concentrations of 2 to 33 moles per mole of the
copper chloride (CuCl.sub.2).
[0088] It can be seen that when the concentration of hydrazine
(N.sub.2H.sub.4) is constant, as the [NaOH]/[CuCl.sub.2] ratio
increases, the particle size distribution of the copper powder
increases.
[0089] This is because the ratio of the obtained copper oxides,
Cu.sub.2O and CuO, varies according to the concentration of sodium
hydroxide (NaOH).
[0090] As the amount of sodium hydroxide (NaOH) increases, a stable
intermediate product, Cu.sub.2O, is produced in a large amount. As
a result, a reduction reaction is not easily carried out.
[0091] Due to differences in the degree of reduction, the particle
size distribution of the obtained copper powder becomes less
uniform as the concentration of NaOH increases.
[0092] In case of sample 21, in spite of good characteristics of
the copper powder, reaction rate was slow and thus productivity was
lowered. Sample 27 had a fast reaction rate but the average
particle size distribution of the copper powder exceeded 0.5 .mu.m.
Therefore, samples 21 and 27 are not preferable to prepare a
nano-scaled copper powder.
[0093] In particular, if the amount of added hydrazine
(N.sub.2H.sub.4) exceeds 12 moles per mole of the copper chloride,
a reaction rate is increased but the copper powder is easily
agglomerated. As a result, the surface quality of the copper powder
is lowered. Therefore, it is preferable to limit the amount of
hydrazine to up to 12 moles.
[0094] As shown in Table 3, copper powder having a particle size of
100 nm or less grade was easily obtained when the molar ratio
between CuCl.sub.2 and NaOH was 1:2. In addition, the physical
properties of the copper powder, such as particle size distribution
and particle shape, were excellent.
[0095] Table 3 shows chemical components of the copper powder
obtained according to Example 2 under the condition of
CuCl.sub.2:NaOH:N.sub.2H.su- b.4=1:2:12.
3TABLE 3 Chemical components Inspection Data (%) Method Na 0.0020
A.A.S. Ni No detection Pb 0.0040 Fe 0.0028 Mn No detection Mg
0.0009 C 0.140 KS D 1801-98 S 0.007 KS D 1673-97 K 0.004 (Korea
Environment & Merchandise Testing Institute) Cl 0.0001 I.C.
analysis (Korea Testing & Research Institute for the Chemical
Industry)
EXAMPLE 3
[0096] First, 100 ml of 2M aqueous CuCl.sub.2 solution was heated
to a temperature of 20 to 70.degree. C. and vigorously agitated at
that temperature.
[0097] Hydrazine (N.sub.2H.sub.4) was mixed into the resulting
aqueous copper chloride solution at the above temperature in an
amount of 1 to 12 moles per mole of the copper chloride and
vigorously agitated for about 5 minutes.
[0098] Subsequently, when the aqueous solution containing hydrazine
was kept at a temperature of 40 to 80.degree. C., sodium hydroxide
(NaOH) was added thereto.
[0099] The sodium hydroxide (NaOH) was added with varying
concentrations of 2 to 33 moles per mole of the copper chloride
(CuCl.sub.2).
[0100] Then, the copper powder obtained according to the above
procedure was washed with secondary distilled water and filtered.
The filtered copper powder was dried to obtain a nano-scaled copper
powder.
[0101] The particle size distribution of the finally obtained
copper powder is given in Table 4.
4TABLE 4 Particle size distribution of copper powder according to
the concentration of NaOH Particle size distribution Av- Sam- erage
ple D10 D50 D90 size Section No. CuCl.sub.2 N.sub.2H.sub.4 NaOH
(.mu.m) (.mu.m) (.mu.m) (.mu.m) Inventive 31 1 12 2 0.06 0.10 0.20
0.10 samples 32 1 12 4 0.08 0.13 0.21 0.13 33 1 12 8 0.20 0.31 0.40
0.31 34 1 12 16 0.21 0.51 0.75 0.51 Numbers in N.sub.2H.sub.4 and
NaOH denote molar ratio based on 2M CuCl.sub.2
[0102] Table 4 shows the particle size distribution according to
the amount of NaOH per mole of the copper chloride (CuCl.sub.2). As
shown in Table 4, as the amount of NaOH increased, the particle
size of the obtained powder increased and a wide particle size
distribution was obtained.
[0103] As shown in Table 4, when the amount of added NaOH was 2 to
4 moles per mole of CuCl.sub.2, a copper powder having a particle
size of 100 nm grade was obtained. Furthermore, dispersibility and
shape of the powder surface were excellent.
[0104] Although the intermediate product of the present example was
different than that of Example 2, the final result was almost
similar. It can be seen from the forgoing that the method of
Example 3 is suitable for preparing a copper powder having a
particle size of 100 nm grade, similar to Example 2.
EXAMPLE 4
[0105] According to Example 4, a trace amount of silver nitrate
(AgNO.sub.3) is further added to the aqueous copper chloride
solution in Examples 2 and 3. Because silver is reduced faster than
copper, the addition of silver nitrate enables the promotion of a
heterogeneous nucleation of copper, thereby increasing the
reduction rate of copper.
[0106] That is, a trace amount of silver nitrate was added to the
aqueous copper chloride solution in Example 2. Then, sodium
hydroxide and hydrazine were added in sequence to obtain a copper
powder.
[0107] A trace amount of silver nitrate was added to the aqueous
copper chloride solution in Example 3. Then, hydrazine and sodium
hydroxide were added in sequence to obtain a copper powder.
[0108] The copper powder according to Example 4 was compared with
those according to Examples 2 and 3 in terms of the particle size
distribution of a copper powder. The results are given in Table
5.
5TABLE 5 Particle size distribution of copper powder according to
presence or absence of AgNO.sub.3 Particle size distribution Sample
D10 D50 D90 Average No CuCl.sub.2 NaOH N.sub.2H.sub.4 AgNO.sub.3
(.mu.m) (.mu.m) (.mu.m) size (.mu.m) Remarks 22 1 2 12 X 0.05 0.10
0.16 0.10 NaOH N.sub.2H.sub.4 31 1 2 12 X 0.06 0.10 0.20 0.10
N.sub.2H.sub.4 NaOH 41 1 2 12 0.006 0.05 0.12 0.20 0.11 NaOH
N.sub.2H.sub.4 42 1 2 12 0.007 0.05 0.11 0.22 0.11 N.sub.2H.sub.4
NaOH Numbers in components denote molar ratios based on 2M
CuCl.sub.2.
[0109] Table 5 shows a particle size distribution according to the
presence or absence of the optional additive, AgNO.sub.3 under the
condition of CuCl.sub.2:NaOH:N.sub.2H.sub.4=1:2:12.
[0110] In sample 41, NaOH and N.sub.2H.sub.4 were in sequence added
to an aqueous (CuCl.sub.2+AgNO.sub.3) solution, and in sample 42,
N.sub.2H.sub.4 and NaOH were added in sequence to an aqueous
(CuCl.sub.2+AgNO.sub.3) solution, for the purpose of obtaining a
copper powder.
[0111] In the same conditions, the use of AgNO.sub.3 resulted in
small average particle size and small particle size deviation.
Furthermore, AgNO.sub.3 acted to increase the reaction rate.
Samples 41 and 42 exhibited almost same characteristics of copper
powders as corresponding sample 22 of Example 2 and sample 31 of
Example 3.
[0112] As shown in FIGS. 6 and 7, the copper powders prepared using
AgNO.sub.3 exhibited smaller average particle size and smaller
particle size deviation than those in corresponding Examples 2 and
3.
[0113] The copper powders prepared according to the conventional
wet method (samples 11 to 13) had relatively coarse average
particle size of 0.4 to 1 .mu.m. On the other hand, the copper
powders prepared according to the present invention had ultrafine
average particle size of 100 nm grade.about.1 .mu.m grade.
[0114] Industrial Applicability
[0115] As apparent from the above description, the present
invention provides two mechanisms for preparing an ultrafine copper
powder having a particle size of (100 nm grade.about.1 .mu.m
grade). The two mechanisms are very suitable for preparing an
ultrafine copper powder having a particle size of 100 nm grade.
[0116] The nano-scaled copper powder prepared according to the
present invention is excellent in particle size distribution and
dispersibility. The particle size of the copper powder varies
according to the amount of sodium hydroxide (NaOH), thereby making
it possible to control the particle size and distribution thereof.
At the same time, due to heterogeneous nucleation of copper by the
addition of the optional additive, silver nitrate (AgNO.sub.3), the
reduction reaction rate of copper increases and the particle size
of the copper powder becomes finer.
[0117] Accordingly, the method according to the present invention
is a relatively simple process and also affords a high degree of
reproducibility. In addition, copper powder having a particle size
of 100 nm can be prepared which has a good surface quality, narrow
particle size distribution, and good powder sphericity.
[0118] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *