U.S. patent application number 10/981074 was filed with the patent office on 2006-05-04 for aqueous-based method for producing ultra-fine silver powders.
Invention is credited to Daniel Andreescu, Christopher Eastman, Dan V. Goia.
Application Number | 20060090598 10/981074 |
Document ID | / |
Family ID | 36260303 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060090598 |
Kind Code |
A1 |
Goia; Dan V. ; et
al. |
May 4, 2006 |
Aqueous-based method for producing ultra-fine silver powders
Abstract
The present invention provides a method for forming compositions
having a plurality of ultra-fine metallic particles, and the
metallic composition produced therewith. Also provided is a
substrate coated with the plurality of ultra-fine metallic
particles obtained in accordance with the method of the present
invention.
Inventors: |
Goia; Dan V.; (Potsdam,
NY) ; Andreescu; Daniel; (Potsdam, NY) ;
Eastman; Christopher; (Adams, NY) |
Correspondence
Address: |
Leslie Gladstone Restaino;Brown Raysman Millstein Felder & Steiner LLP
163 Madison Avenue
P.O. Box 1989
Morristown
NJ
07962-1989
US
|
Family ID: |
36260303 |
Appl. No.: |
10/981074 |
Filed: |
November 3, 2004 |
Current U.S.
Class: |
75/371 |
Current CPC
Class: |
B22F 2998/00 20130101;
B22F 2998/00 20130101; C23C 30/00 20130101; C23C 24/00 20130101;
B22F 2998/00 20130101; B22F 1/0018 20130101; B22F 1/0022 20130101;
B22F 9/24 20130101; B82Y 30/00 20130101; B22F 1/0022 20130101 |
Class at
Publication: |
075/371 |
International
Class: |
B22F 9/24 20060101
B22F009/24 |
Claims
1. A metallic composition comprising a plurality of ultra-fine
silver particles obtained in accordance with a process comprising:
(a) obtaining a reducing solution comprising a reducing agent and a
stabilizing agent; (b) obtaining a silver-ammonia solution
comprising a silver-ammonia complex; (c) forming a reaction mixture
comprising the reducing solution and the silver-ammonia solution;
(d) maintaining the reaction mixture under a suitable condition for
a time sufficient to reduce the silver-ammonia complex to silver
particles; and optionally, (e) isolating the silver particles.
2. The metallic composition of claim 1, wherein the silver-ammonia
complex is obtained by reacting a solution comprising a silver ion
with one of ammonium hydroxide and ammonia.
3. The metallic composition of claim 1, wherein the reducing agent
is a saccharide.
4. The metallic composition of claim 3, wherein the saccharide is
an aldose.
5. The metallic composition of claim 4, wherein the aldose is
glucose.
6. The metallic composition of claim 1, wherein the stabilizing
agent is a water-soluble resin.
7. The metallic composition of claim 6, wherein the water-soluble
resin is a naturally occurring water-soluble resin.
8. The metallic composition of claim 1, wherein the stabilizing
agent is one of a gum arabic and a salt of naphthalene
sulphonic-formaldehyde co-polymers.
9. The metallic composition of claim 1, wherein the stabilizing
agent is removed during the isolation of the silver particles.
10. The metallic composition of claim 9, wherein the stabilizing
agent is removed through hydrolysis.
11. The metallic composition of claim 1, wherein the plurality of
ultra-fine silver particles has an average size of less than about
100 nm.
12. The metallic composition of claim 1, wherein the plurality of
ultra-fine silver particles has a tight size distribution.
13. The metallic composition of claim 12, wherein the plurality of
ultra-fine silver particles has a tight size distribution when at
least about 80% of the plurality of ultra-fine silver particles has
a diameter within a range of N.+-.15% N, wherein N is the average
diameter of the plurality of ultra-fine silver particles.
14. The metallic composition of claim 1, wherein the plurality of
ultra-fine silver particles has a high degree of crystallinity.
15. The metallic composition of claim 14, wherein at least about
80% of the plurality of ultra-fine silver particles is highly
crystalline.
16. The metallic composition of claim 14, wherein about 99% of the
plurality of ultra-fine silver particles is highly crystalline.
17. The metallic composition of claim 1, wherein the plurality of
ultra-fine silver particles has a low degree of agglomeration.
18. The metallic composition of claim 17, wherein the degree of
agglomeration is measured with an I.sub.agg value and wherein the
I.sub.aggl of the plurality of ultra-fine silver particles is less
than about 1.2.
19. The metallic composition of claim 1, wherein at least about 80%
of the plurality of ultra-fine silver particles is not irreversibly
aggregated.
20. The metallic composition of claim 1, wherein the plurality of
ultra-fine silver particles when re-dispersed into a liquid forms
dispersion which is stable for at least one week.
21. The metallic composition of claim 20, wherein the liquid is
water.
22. The metallic composition of claim 21, wherein the dispersion is
stable for 12 weeks.
23. A method for forming a plurality of ultra-fine silver particles
comprising: (a) obtaining a reducing solution comprising a reducing
agent and a stabilizing agent; (b) obtaining a silver-ammonia
solution comprising a silver-ammonia complex; (c) forming a
reaction mixture comprising the reducing solution and the
silver-ammonia solution; (d) maintaining the reaction mixture under
a suitable condition for a time effective to reduce the
silver-ammonia complex to silver particles; and optionally, (e)
isolating the silver particles.
24. The method of claim 23, wherein the silver-ammonia complex is
obtained by reacting a solution comprising a silver ion with one of
ammonium hydroxide and ammonia.
25. The method of claim 23, wherein the reducing agent is a
saccharide.
26. The method of claim 25, wherein the saccharide is an
aldose.
27. The method of claim 26, wherein the aldose is glucose.
28. The method of claim 23, wherein the stabilizing agent is a
water-soluble resin.
29. The method of claim 28, wherein the water-soluble resin is a
naturally occurring water-soluble resin.
30. The method of claim 23, wherein the stabilizing agent is one of
a gum arabic and a salt of naphthalene sulphonic-formaldehyde
co-polymers.
31. The method of claim 23, wherein the stabilizing agent is
removed during the isolation of the silver particles.
32. The method of claim 23, wherein the stabilizing agent is
removed through hydrolysis.
33. The method of claim 23, wherein the plurality of ultra-fine
silver particles has an average size of less than about 100 nm.
34. The method of claim 23, wherein the plurality of ultra-fine
silver particles has a tight size distribution.
35. The method of claim 34, wherein the plurality of ultra-fine
silver particles has a tight size distribution when at least about
80% of the plurality of ultra-fine silver particles has a diameter
within a range of N.+-.15% N, wherein N is the average diameter of
the plurality of ultra-fine silver particles.
36. The method of claim 23, wherein the plurality of ultra-fine
silver particles has a high degree of crystallinity.
37. The method of claim 36, wherein at least about 80% of the
plurality of ultra-fine silver particles is highly crystalline.
38. The method of claim 36, wherein about 99% of the plurality of
ultra-fine silver particles is highly crystalline.
39. The method of claim 23, wherein the plurality of ultra-fine
silver particles has a low degree of agglomeration.
40. The method of claim 39, wherein the degree of agglomeration is
measured with an I.sub.agg value and wherein the I.sub.aggl of the
plurality of ultra-fine silver particles is less than about
1.2.
41. The method of claim 23, at least about 80% of the plurality of
ultra-fine silver particles is not irreversibly aggregated.
42. The method of claim 23, wherein the plurality of ultra-fine
silver particles when re-dispersed into a liquid forms dispersion
which is stable for at least one week.
43. The method of claim 42, wherein the liquid is water.
44. The method of claim 43, wherein the dispersion is stable for 12
weeks.
45. A substrate coated with a plurality of ultra-fine silver
particles obtained in accordance with the method of claim 23.
46. The substrate of claim 45, wherein the substrate is one of a
metallic substrate and a non-metallic substrate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation application of
U.S. nonprovisional application Ser. No. ______, filed Oct. 29,
2004, and is hereby incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates generally to ultra-fine
metallic compositions and methods of making thereof. The present
invention further relates to methods of coating various substrates
with the ultra-fine metallic compositions.
BACKGROUND OF THE INVENTION
[0003] Ultra-fine metallic particles have many unique physical and
chemical characteristics, which make them ideal materials for a
variety of applications, such as electronics, catalysis,
metallurgy, and decorations. Compared to the various
particle-producing techniques used in the art, the methods based on
the chemical precipitation in solutions provide several advantages,
e.g., low manufacturing cost and a very good control of the
mechanism of metal particles formation. Others in the art have
successfully prepared micron and submicron-size metallic powders of
Co, Cu, Ni, Pb, and Ag using chemical-based techniques, such as the
ones based on the reduction in alcohols or polyols. For example,
U.S. Pat. No. 4,539,041 discusses a method for producing
micrometer-size metallic particles by using polyols to convert
various metallic compounds into metal powders. Nonetheless, these
processes require complex equipment and the metallic powders
produced are generally more expensive because of the cost of the
organic solvents used. The present invention provides a process
capable of generating cost effectively highly dispersed crystalline
ultra-fine metallic particles in aqueous medium, which are highly
desirable in many practical applications, especially in
electronics.
SUMMARY OF THE INVENTION
[0004] The present invention provides a method for forming
compositions having a plurality of ultra-fine metallic particles,
and the metallic composition produced therewith, where the
plurality of ultra-fine metallic particles is obtained in
accordance with a process including: [0005] (a) obtaining a
reducing solution comprising a reducing agent and a stabilizing
agent; [0006] (b) obtaining a metal-ammonia solution containing a
metal-ammonia complex; [0007] (c) forming a reaction mixture
containing the reducing solution and the metal-ammonia solution;
[0008] (d) maintaining the reaction mixture under a suitable
condition for a time effective to reduce the metal-ammonia complex
to metallic particles; and optionally, [0009] (e) isolating the
metallic particles. In one embodiment of the present invention, the
metal-ammonia complex is the complex of ammonia with a transition
metal or a noble metal, e.g., Cu, Pd, and Ag, formed by reacting a
solution comprising a metal salt with ammonium hydroxide or
ammonia. In another embodiment, the reducing agent is a saccharide,
such as D-glucose. In yet another embodiment, the stabilizing agent
is a water-soluble resin (e.g., a natural occurring, synthetic, or
semi-synthetic water-soluble resin) or gum arabic. The gum arabic
may be removed during the isolation of the metallic particles
through hydrolysis. The plurality of ultra-fine metallic particles
may have at least one desirable feature, such as tight size
distribution, low degree of agglomeration, high degree of
crystallinity, ability to re-disperse fully into a liquid (e.g. an
aqueous solution) to form stable dispersions.
[0010] In another aspect, the present invention provides a
substrate coated with the plurality of ultra-fine metallic
particles obtained in accordance with the method disclosed
herein.
[0011] Additional aspects of the present invention will be apparent
in view of the description that follows.
BRIEF DESCRIPTION OF THE FIGURES
[0012] FIG. 1 depicts an experimental set-up used in the synthesis
of ultra-fine silver particles.
[0013] FIG. 2 shows the FE-SEM images of ultra-fine silver
particles produced using the method of the present invention. (a)
198.7 g AgNO.sub.3 and flow rate at 8 ml/min; (b) 382 g AgNO.sub.3
and flow rate at 8 ml/min; and (c) 382 g AgNO.sub.3 and flow rate
at 30 ml/min. Images were acquired using a FE-SEM at two
magnifications (25,000 and 100,000).
[0014] FIG. 3 illustrates the particle size distribution (PSD) of
silver particles as number (%) (a) and volume (%) (b), obtained
from 382 g AgNO.sub.3 at a flow rate of the metallic precursor
solution of 30 ml/min.
[0015] FIG. 4 shows the X-ray diffraction patterns of silver
particles shown in FIG. 2 a.
DETAILED DESCRIPTION OF THE INVENTION
[0016] As used herein and in the appended claims, the singular
forms "a," "an," and "the" include plural references unless the
content clearly dictates otherwise. Thus, for example, reference to
"a particle" includes a plurality of such particles and equivalents
thereof known to those skilled in the art, and reference to "the
reducing agent" is a reference to one or more reducing agent and
equivalents thereof known to those skilled in the art, and so
forth. All publications, patent applications, patents, and other
references mentioned herein are incorporated by reference in their
entirety.
[0017] The present invention generally provides a simple and more
cost effective chemical based method for producing highly dispersed
ultra-fine metallic powders than those known in the art. The
present invention also provides ultra-fine metallic particles
having at least one desirable feature, such as tight size
distribution, low degree of agglomeration, high degree of
crystallinity, ability to re-disperse fully into a liquid (e.g. an
aqueous solution) to form stable dispersions.
[0018] In at least one embodiment of the invention, the present
invention provides a method or system beneficially produces
metallic powders, and also metallic powders produced therewith,
that include a plurality of ultra-fine metallic particles obtained
by (a) obtaining a reducing solution containing a reducing agent
and a stabilizing agent; (b) obtaining an aqueous solution
containing a metal-ammonia complex; (c) forming a reaction mixture
containing the reducing solution and the aqueous solution of step
(b); (d) maintaining the reaction mixture under a suitable
condition (e.g. pH) for a time effective to reduce the
metal-ammonia complex to metallic particles; and optionally, (e)
isolating the metallic particles.
[0019] The process of the present invention may be used to
manufacture ultra-fine particles of various metals, such as Ag, Au,
Co, Cr, Cu, Fe, Ir, Mo, Ni, Nb, Os, Pd, Pt, Re, Rh, Ru, Sn, Ta, Ti,
V, and W, and alloys or composites containing these metals. The
metal-ammonia complex may be mixed with a reducing composition or
agent, which converts the metal ions to ultra-fine metal particles
under various reaction conditions.
[0020] The metal-ammonia complex used in the process of the present
invention may be the complex of ammonium with a variety of metals,
including, without limitation, transitional metals and noble
metals, such as, Ag, Au, Co, Cr, Cu, Fe, In, Ir, Mn, Mo, Ni, Nb,
Os, Pd, Pt, Re, Rh, Ru, Sn, Ta, Ti, V, W, Zn, and the combinations
thereof. In one embodiment, the metal-ammonia complex may be
obtained by reacting a solution containing a metal salt with
ammonium hydroxide or ammonia. For example, 198.7 g AgNO.sub.3 is
dissolved in 234 ml DI water in a 2 L glass beaker. After the
silver nitrate is completely dissolved, 195 ml ammonium hydroxide
is added into the silver nitrate solution under stirring. 291 ml DI
water is then added and the overall volume of the silver ammonia
solution is 720 ml. This solution may be covered with plastic wrap
(to avoid the ammonia evaporation) and protected with aluminum foil
(to prevent the exposure to light).
[0021] The term "reducing composition" or "reducing agent," as used
herein and in the appended claims, generally includes any reducing
substance, and a combination thereof, which is capable of reducing
metal ions to metallic particles, such as, without limitation,
alcohol, aldehydes, aldose, monohydroxylic alcohols, polyhydroxylic
alcohols (polyols), hydrazine hydrate, and reducing saccharides
(including, e.g., monosaccharides, oligosaccharides, and
polysaccarides). Examples of reducing saccharides include, but not
limited to, glyceraldehydes, erythrose, threose, ribose, arabinose,
xylose, lyxose, allose, altrose, glucose, dextrose, mannose,
gulose, idose, galactose, talose, lactose, maltose, isomaltose,
cellobiose, and starch. The nature of the reducing species and
their composition in the process of the present invention may be
commanded by the particular reaction/metallic element.
[0022] The term "stabilizing composition" or "stabilizing agent,"
as used herein and in the appended claims, generally includes any
stabilizing substance, such as, without limitation, water soluble
resins (including, e.g., naturally occurring, synthetic, and
semi-synthetic water soluble resins), gum arabic, polymers,
polysaccharides, glycoproteins, nucleic acids, various salts of
naphthalene sulphonic-formaldehyde co-polymers, and a combination
thereof, which is capable of dispersing and stabilizing the newly
formed ultra-fine metallic particles in the reaction mixture and
thus preventing undesirable aggregation of these particles such
that the size of the resulting metallic particles is less than
about 10 .mu.m, preferably, less than about 1 .mu.m, and more
preferably, less than about 100 nm. As used herein and in the
appended claims, the term "ultra-fine particles" generally includes
particles having diameters of less than about 10 .mu.m, preferably,
less than about 1,000 nm, and more preferably, less than about 500
nm, and even more preferably, less than about 100 nm. The
ultra-fine metallic particles may be the metallic particles of
various metals, including, without limitation, transitional metals
and noble metals, such as, Ag, Au, Co, Cr, Cu, Fe, In, Ir, Mn, Mo,
Ni, Nb, Os, Pd, Pt, Re, Rh, Ru, Sn, Ta, Ti, V, W, Zn, and the
combinations thereof.
[0023] The stabilizing composition used in the process of the
present invention may be commanded by the particular reaction.
Examples of suitable stabilizing agents include, without
limitation, gum arabic, cellulose derivatives (e.g., carboxymethyl
cellulose, carboxyethyl cellulose, methyl cellulose, etc.) and
modified products thereof, polyvinyl alcohol and derivatives
thereof, polyvinyl pyrrolidone, polyacrylamide and copolymers
thereof, acrylic acid copolymers, vinylmethyl ether-maleic
anhydride copolymers, vinyl acetate-maleic anhydride copolymers,
various salts of naphthalene sulphonic-formaldehyde co-polymers,
styrene-maleic anhydride copolymers, calcined dextrin,
acid-decomposed dextrin, acid-decomposed etherified dextrin,
agarose, and salmon sperm DNA. In one embodiment of the present
invention, the stabilizing agent may be gum arabic. In another
embodiment of the present invention, the stabilizing agent is a
salt of naphthalene sulphonic-formaldehyde co-polymer.
[0024] The stabilizing agent, such as gum arabic, may be removed
after the reaction. A number of protocols for removing the
stabilizing agent are known in the art, such as, acid, alkaline,
and/or enzymatic hydrolysis. In one embodiment, gum arabic may be
removed from the reaction mixture after the reaction through
alkaline hydrolysis. For example, the hydrolysis may be performed
for extended time at high temperature (e.g. between 70.degree. and
100.degree. C., or between 80.degree. and 90.degree. C., or between
82.degree. and 88.degree. C.) and high pH (e.g. pH 11.5). It is
generally desirable to maintain the pH of the mixture during the
hydrolysis at between 9 and 14, or between 10 and 12, or between
10.5 and 11.5. The duration of the hydrolysis may be commanded by a
number of facts, such as, the amount of stabilizing agent (e.g. gum
arabic) used. In one embodiment, the hydrolysis of the gum may
generally be performed for about 0.2 to 10 hours, or about 1 to 5
hours, or about 2 to 3 hours.
[0025] The resulting ultra-fine metal particles may be obtained
following standard protocols known in the art, such as by
precipitation, filtration, and centrifugation. The particles may
further be washed, such as by using methanol or ethanol, and dried,
such as by air, N.sub.2, or vacuum.
[0026] The ultra-fine metallic particles may also have at least one
desirable feature, such as, tight size distribution, low degree of
agglomeration, high degree of crystallinity, ability to re-disperse
fully into a liquid (e.g. an aqueous solution) to form stable
dispersion, or a combination thereof.
[0027] Unlike other metallic powders appearing in the art, in one
embodiment, the system of the present invention produces metallic
powders that include ultra-fine metallic particles, particularly,
isometric ultra-fine metallic particles, that have a tight size
distribution. The breadth of the size distribution, as used herein,
generally refers to the degree of variation in the diameter of the
ultra-fine metallic particles in a metallic composition. Tight,
used in this context, indicates a relatively small variation in the
size of the ultra-fine particles. In one embodiment, the ultra-fine
metallic particles are deemed to have a tight size distribution
when the diameters of at least about 80%, preferably, at least
about 85%, and more preferably, at least about 95%, of the
ultra-fine metallic particles of the present invention are within
the range of N.+-.15% N, where N is the average diameters of the
ultra-fine metallic particles. The diameters of the ultra-fine
metallic particles may be measured by a number of techniques, such
as, by an electron microscope, particularly, a scanning electron
microscope (e.g. field emission scanning electron microscope).
[0028] The metallic powders produced with the system of the present
invention may also include ultra-fine metallic particles that have
a low degree of agglomeration, as illustrated in FIG. 3. The degree
of agglomeration may be expressed using the index of agglomeration
I.sub.aggl, which is the ratio between the average size
distribution of the ultra-fine metallic particles ("PSD50%") and
the average diameter of the particles. The average particle size
distribution may be determined by any methods known in the art,
including, but not limited to, dynamic light scattering (DLS),
laser diffraction, and sedimentation methods, while the average
particle size may be determined by averaging the diameter of the
individual ultra-fine metallic particles obtained by, e.g.,
electron microscopy. An I.sub.aggl value of 1.0 indicates
completely lack of agglomeration, while an increase in I.sub.aggl
value indicates an increase in the degree of aggregation. In one
embodiment, the powders of ultra-fine metallic particles of the
present invention have an I.sub.aggl value of 1.2 or less.
[0029] The metallic powders produced in accordance with the present
invention may also include ultra-fine metallic particles that have
a high degree of crystallinity. The term "degree of crystallinity,"
as used herein and in the appended claims, generally refers to the
ratio between the size of the crystallites in the metallic powder
and the diameter of the metallic particles. The size of the
constituent crystallites may be deduced from XRD measurements using
the Sherrer's equation, while the particle size may be determined
by electron microscopy. A larger ratio of the size of the
crystallites in comparison to the diameter of the metallic
particles indicates an increased degree of crystallinity and a
lower internal grain boundary surface. In one embodiment, the
ultra-fine metallic particles have a high degree of crystallinity
if at least about 80%, preferably, at least about 85%, more
preferably, at least about 90-95%, and even more preferably, about
100% of the ultra-fine metallic particles of the present invention
are highly crystalline. The high degree of crystallinity is
reflected by the visible splitting of the peaks corresponding to
the (220), (311), and (222) reflections in the XRD spectrum (see
FIG. 4).
[0030] The ultra-fine metallic particles produced in accordance
with the present invention may form a free flowing dry powder in
which the majority of the individual particles may not be strongly
attached to each other and may be readily re-dispersed in a liquid
of choice.
[0031] In another embodiment of the present invention, the
ultra-fine metallic particles forms stable dispersion when
re-dispersed into a liquid, such as water, or an aqueous solution,
where the majority of the individual particles may move
substantially freely in the liquid in which they are dispersed. In
one embodiment, the particle dispersion is stable for at least one
week. In another embodiment, the particle dispersion is stable for
12 weeks.
[0032] The present invention further provides a substrate coated
with a plurality of ultra-fine metallic particles, where the
plurality of ultra-fine metallic particles have at least one
desired feature, such as, tight size distribution, a low degree of
agglomeration, a high degree of crystallinity, and oxidation
resistance. The term "substrate" as used herein includes, without
limitation, metallic subjects (e.g., metallic particles, flakes,
tubes, and sheets), plastic materials, ceramic subjects, fibers,
films, glasses, polymers, organic materials (e.g. resins),
inorganic materials (e.g., carbon nanotubes), and any other object
capable of being coated with the ultra-fine metallic particles
produced in accordance with the present invention. The ultra-fine
metallic particles may be the metallic particles of various metals,
preferably, Cu, Pd, and Ag.
EXAMPLES
[0033] The following examples illustrate the present invention,
which are set forth to aid in the understanding of the invention,
and should not be construed to limit in any way the scope of the
invention as defined in the claims which follow thereafter.
[0034] The ultra-fine silver, palladium and copper particles were
prepared by reducing the metallic ammonium complex with D-glucose
in the presence of gum arabic. The experimental set-up for these
experiments is illustrated in FIG. 1.
Example 1
Materials
[0035] Silver nitrate (AgNO.sub.3) was obtained from Ames Goldsmith
Corp. (Glens Falls, N.Y.). Gum arabic was obtained from Frutarom
Incorporated (North Bergen, N.J.). Ammonium hydroxide (NH.sub.4OH)
was purchased from Fischer Scientific Co. (Fair Lawn, N.J.).
Acetone, ethanol, and sodium hydroxide (NaOH) solution (10 N) were
supplied by Alfa Aesar (Ward Hill, Mass.). D-glucose was purchased
from Avocado Research Chemicals Ltd. (Shore Road, Heyshane,
Lancs.). Cupric nitrate hydrate [Cu(NO.sub.3).sub.2 21/2H.sub.2O]
was obtained from T.J. Baker Chemical Co. (Phillipsburg, N.J.),
while the palladium nitrate solution 9.0% was obtained from Umicore
(South Plainfield, N.J.).
Example 2
Preparation of Ultra-Fine Silver Particles
(A) Preparation of the Reducing Solution
[0036] 3 L deionised ("DI") water was heated to 55.degree. C. in a
8 L stainless steel beaker. When the temperature reaches 55.degree.
C., 62.5 g gum arabic was slowly added into the water and dissolved
by stirring the solution with a stirring propeller at low speed for
55 minutes. 36 g of D-glucose were then added to the solution. The
mixture was stirred at 1700 rpm for 5 minutes.
(B) Preparation of Silver Ammonium Complex Solution
[0037] 198.7 g AgNO.sub.3 were dissolved in 234 ml DI water in a 2
L glass beaker. After the silver nitrate was completely dissolved,
195 ml ammonium hydroxide was added under stirring, followed by the
addition of 291 ml DI water to reach a final volume of 720 ml.
(C) Preparation of Ultra-Fine Silver Particles
[0038] The reduction process was conducted by pumping the silver
ammonium solution into the reducing solution at a flow rate of 8
ml/min using a peristaltic pump. When the addition of the silver
complex solution is completed, the temperature was brought to
80.degree. C. The process was conducted under continued stirring
(1700 rpm).
(D) Hydrolysis of Gum Arabic
[0039] The excess of gum arabic was removed by increasing the pH of
the dispersion to 11.5 with 10.0 N sodium hydroxide at the
temperature of about 85.degree. C. The dispersion was maintained in
the condition for 2.5 hours.
(D) Processing the Silver Powder
[0040] When the hydrolysis of the gum was complete, the dispersion
was allowed to cool and the silver particles to settle. The
supernatant was then discarded and the silver particles were washed
with water through 3 successive decantations. During the last wash,
50% ethanol (in DI water) was added to the settled metallic deposit
instead of DI water. Two more washes with pure alcohol were
performed. The powder was then dried overnight on filter paper at
room temperature.
Example 3
Preparation of Ultra-Fine Palladium Particles
(A) Preparation of the Reducing Solution
[0041] A volume of 500 ml DI water was heated to 70.degree. C. in 2
L glass beaker. When the temperature reaches 70.degree. C., 10 g
gum arabic was slowly added into the water and dissolved by
stirring the solution. 100 g of D-glucose were then added to the
solution and the mixture was stirred at 1700 rpm for 5 minutes. The
pH of solution was adjusted at 10.5 with 10.0 N NaOH.
(B) Preparation of Palladium Ammonium Complex Solution
[0042] 80 ml ammonium hydroxide was added quickly under stirring to
50 ml Pd(NO.sub.3).sub.2 solution 9.0% in a 0.2 L glass beaker,
followed by the addition of 50 ml DI water (final volume: 180
ml).
(C) Preparation of Ultra-Fine Palladium Particles
[0043] The reducing reaction was conducted by pumping the palladium
ammonium solution to the reducing solution at a flow rate of 5
ml/min using a peristaltic pump. When the addition of the palladium
complex solution is completed, the temperature was brought to
80.degree. C. The process was conducted under continued stirring
(1700 rpm).
[0044] The hydrolysis of gum arabic and the processing of palladium
powder were carried out in a similar manner as in Example 2 (steps
D and E).
Example 4
Preparation of Ultra-Fine Copper Particles
(A) Preparation of the Reducing Solution
[0045] A volume of 500 ml DI water was heated to 70.degree. C. in 2
L glass beaker. When the temperature reaches 70.degree. C., 25 g
gum Arabic was slowly added into the water and dissolved by
stirring the solution with a stirring propeller at 1700 rpm for 55
minutes. 100 g of D-glucose were then added to the solution and the
mixture was stirred at 1700 rpm for 5 minutes. The pH of solution
was adjusted at 10.5 with 10.0 N NaOH.
(B) Preparation of Copper Ammonium Complex Solution
[0046] 18.2 g [Cu(NO.sub.3).sub.2 21/2H.sub.2O] were dissolved in
50 ml DI water in a 0.2 L glass beaker. After the cupric nitrate
was completely dissolved, 100 ml ammonium hydroxide was added
quickly under stirring, followed by the addition of 50 ml DI water
(overall volume: 200 ml).
(C) Preparation of Ultra-Fine Copper Particles
[0047] The reduction process was conducted by pumping the cupric
ammonium solution to the reducing solution at a flow rate of 5
ml/min using a peristaltic pump. When the addition of the cupric
complex solution is completed, the temperature was brought to
80.degree. C. The process was conducted under continued stirring
(1700 rpm). The remaining steps are similar to those of Example
2.
[0048] Discussed below are results obtained by the inventors in
connection with the experiments of Example 1-4:
[0049] The size of the silver particles obtained did not undergo a
substantial change when the process was scaled up by a factor of
two or when the flow rate of the silver ammonium complex solution
was raised to 30 ml/min from 8 ml/min, suggesting a minor impact of
both parameters on the size of the particles formed. For all
experiments the processing yield was >97%.
[0050] The experimental conditions and results of Example 2 are
summarized in Table I. TABLE-US-00001 TABLE I Bach size Reducing
solution Silver ammonium solution Flow rate Average Exp. Ag (g)
Water (L) Gum arabic (g) Glucose (g) Water (ml) AgN0.sub.3 (g)
NH.sub.4OH (ml) (ml/min) size (nm) 1 125 3 62.5 36 525 198.7 195 8
.about.70 2 245 4 120 69 775 382 390 8 .about.65 3 245 4 120 69 775
382 390 30 .about.65
[0051] While the foregoing invention has been described in some
detail for purposes of clarity and understanding, it will be
appreciated by one skilled in the art, from a reading of the
disclosure, that various changes in form and detail can be made
without departing from the true scope of the invention in the
appended claims.
* * * * *