U.S. patent application number 10/978154 was filed with the patent office on 2006-05-04 for polyol-based method for producing ultra-fine metal powders.
Invention is credited to Daniel Andreescu, Brendan P. Farrell, Dan V. Goia.
Application Number | 20060090597 10/978154 |
Document ID | / |
Family ID | 36260302 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060090597 |
Kind Code |
A1 |
Goia; Dan V. ; et
al. |
May 4, 2006 |
Polyol-based method for producing ultra-fine metal powders
Abstract
The present invention provides a metallic composition, which
contains a plurality of ultra-fine metallic particles (e.g.,
ultra-fine copper, nickel, or silver particles) having at least one
desirable feature, such as, tight size distribution, low degree of
agglomeration, and high degree of crystallinity and oxidation
resistance. The present invention further provides a method for
forming the ultra-fine metallic particles. Also provided are a
substance or substrate coated with the ultra-fine metallic
particles and a method of coating a substance or substrate with the
ultra-fine metallic particles. Furthermore, the present invention
provides a method of controlling the size of ultra-fine metal
particles formed in a reducing reaction in a liquid. Also provided
is a method for producing ultra-fine metallic particles, which
utilizes a concentrated reaction system.
Inventors: |
Goia; Dan V.; (Potsdam,
NY) ; Andreescu; Daniel; (Potsdam, NY) ;
Farrell; Brendan P.; (Potsdam, 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: |
36260302 |
Appl. No.: |
10/978154 |
Filed: |
October 29, 2004 |
Current U.S.
Class: |
75/371 |
Current CPC
Class: |
Y10T 428/12014 20150115;
B22F 1/0011 20130101; B82Y 30/00 20130101; B22F 9/24 20130101; C23C
26/00 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
metallic particles, wherein the plurality of ultra-fine metallic
particles is resistant to oxidation.
2. The metallic composition of claim 1, wherein the plurality of
ultra-fine metallic particles undergoes minimal oxidation for 12
months in ambient environment, wherein oxidation is minimal when
the oxygen content of the ultra-fine metallic particles is less
than about 5-10% at the end of such period of time.
3. The metallic composition of claim 1, wherein the plurality of
ultra-fine metallic particles undergoes minimal oxidation when
exposed to a temperature up to 100.degree. C. for about 120 minutes
in air.
4. The metallic composition of claim 1, wherein the plurality of
ultra-fine metallic particles undergoes minimal oxidation when
heated in air at 20.degree. C./minute up to 200-220.degree. C.
5. The metallic composition of claim 1, wherein oxidation is
characterized by a weight gain in the plurality of metallic
particles and wherein the weight gain of the plurality of
ultra-fine metallic particles does not exceed about 80% of a
theoretical weight gain for the plurality of ultra-fine metallic
particles when the plurality of ultra-fine metallic particles are
heated in air at 20.degree. C./minute to 800.degree. C.
6. The metallic composition of claim 1, wherein the plurality of
ultra-fine metallic particles has a tight size distribution.
7. The metallic composition of claim 6, wherein the plurality of
ultra-fine metallic particles have a tight size distribution when
at least about 80% of the plurality of ultra-fine metallic
particles has a diameter within the range of N.+-.15% N, wherein N
is the average diameter of the plurality of ultra-fine metallic
particles.
8. The metallic composition of claim 1, wherein the plurality of
ultra-fine metallic particles has a high degree of
crystallinity.
9. The metallic composition of claim 8, wherein at least about
80-95% of the plurality of ultra-fine metallic particle is highly
crystalline.
10. The metallic composition of claim 1, wherein the plurality of
ultra-fine metallic particles has a low degree of
agglomeration.
11. The metallic composition of claim 9, 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 metallic particles is
less than about 1.2.
12. The metallic composition of claim 1, wherein the metallic
composition comprises ultra-fine particles of one of a transition
metal and a noble metal.
13. The metallic composition of claim 1, wherein the metallic
composition comprises ultra-fine particles a metal selected from
the group consisting of Cu, Ni, and Ag.
14. A metallic composition comprising a plurality of ultra-fine
metallic particles obtained in accordance with a process
comprising: (a) forming a reaction mixture comprising a precursor
of a metal, a branched dispersing agent, and an alcoholic agent;
(b) adjusting a temperature of the reaction mixture to a reaction
temperature suitable for reducing the precursor of the metal to
metallic particles; (c) maintaining the reaction mixture under the
reaction temperature for a time sufficient to reduce the precursor
of the metal to metallic particles; and optionally, (d) isolating
the metallic particles.
15. The metallic composition of claim 14, wherein the branched
dispersing agent is a branched polyol.
16. The metallic composition of claim 15, wherein the branched
polyol is pentaerythritol.
17. The metallic composition of claim 14, wherein the reaction
mixture further comprises at least one other dispersant selected
from the group consisting of a linear polyol dispersant and a salt
of polynaphtalene sulphonic/formaldehyde co-polymer.
18. The metallic composition of claim 14, wherein the alcoholic
agent is at least one polyol selected from the group consisting of
1,2-propylene glycol, 1,3-propylene glycol, and
diethyleneglycol.
19. The metallic composition of claim 14, wherein the alcoholic
agent is a mixture of 1,2-propylene glycol and
diethyleneglycol.
20. The metallic composition of claim 14, wherein the precursor of
a metal is at least one selected from the group consisting of a
salt of the metal, an oxide of the metal, a hydroxide of the metal,
an acid wherein the metal is part of an oxyanion, and a salt of the
acid.
21. The metallic composition of claim 20, wherein the precursor of
a metal is a metal carbonate.
22. The metallic composition of claim 20, wherein the precursor of
a metal is a mixture of a metal carbonate and at least one of a
metal acetate and a metal salycilate.
23. The metallic composition of claim 14, wherein the metal is one
of a transition metal and a noble metal.
24. The metallic composition of claim 14, wherein the metal is a
metal selected from the group consisting of Cu, Ni, and Ag.
25. The metallic composition of claim 14, wherein the reaction
temperature is a temperature above 85.degree. C.
26. The metallic composition of claim 14, wherein the process
further comprises adjusting pH of the reaction mixture.
27. The metallic composition of claim 26, wherein the pH of the
reaction mixture is adjusted by introducing a buffering agent into
the reaction mixture.
28. The metallic composition of claim 27, wherein the buffering
agent is triethanolamine.
29. The metallic composition of claim 14, wherein the reaction
mixture further comprises an agent which releases an organic
counter ion.
30. The metallic composition of claim 29, wherein the organic
counter ion is at least one of an acetate and a salycilate.
31. A method for forming a plurality of ultra-fine metallic
particles comprising: (a) forming a reaction mixture comprising a
precursor of a metal, a branched dispersing agent, and an alcoholic
agent; (b) adjusting a temperature of the reaction mixture to a
reaction temperature suitable for reducing the precursor of the
metal to metallic particles; (c) maintaining the reaction mixture
under the reaction temperature for a time sufficient to reduce the
precursor of the metal to metallic particles; and optionally, (d)
isolating the metallic particles.
32. The method of claim 31, wherein the branched dispersing agent
is a branched polyol.
33. The method of claim 32, wherein the branched polyol is
pentaerythritol.
34. The method of claim 31, wherein the reaction mixture further
comprises at least one other dispersant selected from the group
consisting of a linear polyol dispersant and a salt of
polynaphtalene sulphonic/formaldehyde co-polymer.
35. The method of claim 31, wherein the alcoholic agent is at least
one polyol selected from the group consisting of 1,2-propylene
glycol, 1,3-propylene glycol, and diethyleneglycol.
36. The method of claim 35, wherein the alcoholic agent is a
mixture of 1,2-propylene glycol and diethyleneglycol.
37. The method of claim 31, wherein the precursor of a metal is at
least one selected from the group consisting of a salt of the
metal, an oxide of the metal, a hydroxide of the metal, an acid
wherein the metal is part of an oxyanion, and a salt of the
acid.
38. The method of claim 37, wherein the precursor of a metal is a
metal carbonate.
39. The method of claim 37, wherein the precursor of a metal is a
mixture of a metal carbonate and at least one of a metal acetate
and a metal salycilate.
40. The method of claim 31, wherein the metal is one of a
transition metal and a noble metal.
41. The method of claim 31, wherein the metal is a metal selected
from the group consisting of Cu, Ni, and Ag.
42. The method of claim 31, wherein the reaction temperature is a
temperature above 85.degree. C.
43. The method of claim 31, further comprising adjusting pH of the
reaction mixture.
44. The method of claim 43, wherein the pH of the reaction mixture
is adjusted by introducing a buffering agent into the reaction
mixture.
45. The method of claim 44, wherein the buffering agent is
triethanolamine.
46. The metallic composition of claim 31, wherein the reaction
mixture further comprises an agent which releases an organic
counter ion.
47. The metallic composition of claim 46, wherein the organic
counter ion is at least one of an acetate and a salycilate.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to ultra-fine
metallic compositions and methods of making thereof. The present
invention further relates to methods of depositing ultra-fine
metallic compositions onto various substrates.
BACKGROUND OF THE INVENTION
[0002] 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 decorative. 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.
[0003] These procedures, however, are characterized by rather low
concentrations of metallic precursors and consume large quantities
of organic solvents per unit weight of metallic powder produced.
Furthermore, the metallic powders produced using these procedures
have a wide size distribution, a low degree of crystallinity, and
in the case of the base metals, a pronounced tendency to
oxidation.
SUMMARY OF THE INVENTION
[0004] The present invention provides a metallic composition, which
includes a plurality of ultra-fine metallic particles (e.g.,
ultra-fine copper, nickel, or silver particles) having at least one
desirable feature, such as tight size distribution, low degree of
agglomeration, and high degree of crystallinity and oxidation
resistance.
[0005] In one aspect, the present invention provides a method for
forming compositions having a plurality of ultra-fine metallic
particles (e.g., ultra-fine copper, nickel, or silver particles),
and the metallic composition produced therewith, where the
plurality of ultra-fine metallic particles may be obtained in
accordance with a process that includes the steps of: [0006] (a)
forming a reaction mixture containing a precursor of a metal, a
branched dispersing agent, and an alcoholic agent; [0007] (b)
adjusting the temperature of the reaction mixture to a temperature
suitable for reducing the metal precursor to the metallic state
("the reaction temperature"); [0008] (c) maintaining the reaction
mixture under the reaction temperature for a time sufficient to
reduce the precursor of the metal to metal particles; and
optionally, [0009] (d) isolating the metal particles. In one
embodiment, the branched dispersing agent may be a branched polyol,
e.g. pentaerythritol. In another embodiment, the reaction mixture
further may contain at least one other dispersing agent, such as
linear polyols (e.g., sorbitol and/or mannitol) and ammonium or
sodium salts of polynaphtalene sulphonic/formaldehyde co-polymers.
In yet another embodiment, the alcoholic agent may be 1,2-propylene
glycol, 1,3-propylene glycol, diethyleneglycol, or the combinations
thereof. In still another embodiment, the method of the present
invention may further include a step of adjusting the pH of the
reaction mixture (e.g., by introducing a buffering agent, such as,
triethanolamine).
[0010] In another aspect, the present invention provides a
substance or substrate coated with a plurality of ultra-fine
metallic particles (e.g., ultra-fine copper, nickel, or silver
particles) having at least one desirable feature, such as tight
size distribution, low degree of agglomeration, and high degree of
crystallinity and oxidation resistance.
[0011] Also provided is a method of coating a substance with a
plurality of ultra-fine metallic particles (e.g., copper, nickel,
or silver particles), and the coated substance produced therewith,
including the steps of: [0012] (a) forming a reaction mixture
containing the substance, a precursor of a metal, a branched
dispersing agent, and an alcoholic agent; [0013] (b) adjusting the
temperature of the reaction mixture to a temperature suitable for
reducing the precursor of the metal to metal particles ("the
reaction temperature"); [0014] (c) maintaining the reaction mixture
under the reaction temperature for a time sufficient to reduce the
precursor of the metal to metal particles and permit the resulting
metal particles to form a coating on the surface of the substance;
and optionally, [0015] (d) isolating the coated substance. In one
embodiment, the branched dispersing agent may be a branched polyol,
e.g. pentaerythritol. In another embodiment, the reaction mixture
may further contain at least one other dispersing agent, such as
linear polyols (e.g., sorbitol and/or mannitol) and ammonium or
sodium salts of polynaphtalene sulphonic/formaldehyde co-polymers.
In yet another embodiment, the alcoholic agent may be 1,2-propylene
glycol, 1,3-propylene glycol, diethyleneglycol, or the combinations
thereof. In still another embodiment, the method of the present
invention may further include a step of adjusting the pH of the
reaction mixture (e.g., by introducing a buffering agent, such as,
triethanolamine).
[0016] In yet another aspect, the present invention provides a
method of controlling the size of ultra-fine metal particles (e.g.,
copper, nickel, or silver particles) formed in a reducing reaction
in a liquid, where the method includes the step of adjusting the pH
of the liquid, e.g. by introducing a buffering agent into the
liquid, such as triethanolamine. In one embodiment, the ultra-fine
metal particles may be formed by reducing a precursor of the metal
in the liquid containing a polyol composition. In another
embodiment, the polyol composition may contain a branched
dispersing agent, such as a branched polyol (e.g.,
pentaerythritol). Further provided is a method for producing
ultra-fine metallic particles, which utilizes a concentrated
reaction system.
[0017] Additional aspects of the present invention will be apparent
in view of the description that follows.
BRIEF DESCRIPTION OF THE FIGURES
[0018] FIG. 1 includes images that depict the effects of buffering
agent TEA on the copper particles produced by the method in
accordance with one embodiment of the present invention, where the
reaction mixture includes 50% 1,2-PG, 50-x % DEG, and x % TEA and
(a) x=0; (b) x=1.5; (c) x=5; and (d) x=10. The images were acquired
using field emission scanning electron microscope.
[0019] FIG. 2 shows the effects of buffering agent TEA on the size
of the copper particles produced by the method according to one
embodiment of the present invention.
[0020] FIG. 3 illustrates the effects of various mixtures of
polyols on the size of the copper particles produced by the method
according to one embodiment of the present invention, where the
reaction mixture includes (a) 1,2-PG and TEA (90:10 v/v); (b)
1,2-PG, 1,3-PG, and TEA (50:40:10, v/v, respectively); and (c)
1,2-PG, DEG, and TEA (50:40:10, v/v, respectively). Images were
acquired using a scanning electron microscope at two magnifications
(5,000.times. and 10,000.times.).
[0021] FIG. 4 demonstrates the effects of changing the
concentration of the copper salt on the size of the copper
particles produced by the method according to one embodiment of the
present invention, where the reaction mixture includes: (a) 0.174
g/cm.sup.3 CuCO.sub.3; (b) 0.261 g/cm.sup.3 CuCO.sub.3; (c) 0.348
g/cm.sup.3 CuCO.sub.3; and (d) 0.400 g/cm.sup.3 CuCO.sub.3. Images
were acquired using a scanning electron microscope (5000.times.
magnification).
[0022] FIG. 5 contains the typical XRD pattern of highly
crystalline copper particles produced by the method according to
one embodiment of the present invention, displaying a pronounced
split of the (220), (311), and (222) reflections.
[0023] FIG. 6 shows the SEM images of nickel particles produced by
the method according to one embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] 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 reference
to "the polyol" is a reference to one or more polyols 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.
[0025] The present invention provides ultra-fine metallic particles
having at least one desirable feature, such as, a tight size
distribution, a high degree of crystallinity, oxidation resistance,
and a low degree of agglomeration, or a combination thereof. The
present invention also generally provides a more cost effective
chemical based method for producing metallic powders than those
known in the art. The present invention further generally provides
a method for producing metallic powders having ultra-fine metallic
particles of a particular size by reducing precursors of the metals
in an alcoholic agent at higher concentrations than those used in
the systems known in the art to produce particles with
substantially the same sizes. The concentrated method or system of
the present invention may therefore be used to reduce the cost of
making ultra-fine metallic particles in terms of energy, resources,
waste, etc.
[0026] In at least one embodiment of the invention, the present
method or system beneficially produces metallic powders that
include a plurality of ultra-fine metallic particles having at
least one desirable feature, e.g., a tight size distribution, a
high degree of crystallinity, oxidation resistance, and a low
degree of agglomeration, or a combination thereof. As used herein
and in the appended claims, the term "ultra-fine particles"
generally includes particles having diameters of about 1 nm-10
.mu.m, preferably, about 10-5,000 nm, and more preferably, 50-3,000
nm, and even more preferably, 100-1000 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. In one embodiment, the metallic powders include a metal
selected from the group consisting of Cu, Ni, and Ag.
[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. 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,
e.g. FIG. 5).
[0030] The metallic powders produced in accordance with the present
invention may also include ultra-fine metallic particles that are
resistant to oxidation. In one embodiment, the ultra-fine metallic
particles of the present invention undergo minimal or insubstantial
oxidation when exposed to the air in ambient environment for about
12 months or longer. Oxidation is generally minimal or
insubstantial if the ultra-fine metallic particles display an
increase of less than about 5-10% in their oxygen content as
measured by the LECO combustion method. In another embodiment, the
ultra-fine metallic particles of the present invention do not
undergo substantial oxidation when exposed to a temperature of up
to 100.degree. C. in ambient environment for about 120 minutes. In
still another embodiment, the overall weight gain of the ultra-fine
metallic particles is minimal or insubstantial when they are heated
in the air at 20.degree. C./minute up to about 200-220.degree. C.
and does not exceed about 80% of the theoretical weight gain when
the temperature reaches about 800.degree. C. For example, the
theoretical weight gain of 100 g Cu particles when treated under
the above condition is .about.26 g. The weight gain of 100 g
ultra-fine Cu particles of the present invention when treated under
the same condition does not exceed .about.21 g.
[0031] The present invention also provides methods for producing
metallic powders, and also metallic powders produced therewith,
that include a plurality of ultra-fine metallic particles that, in
one embodiment, are obtained by: (a) forming a reaction mixture
containing a precursor of a metal, a branched dispersing agent, and
an alcoholic agent; (b) adjusting the temperature of the reaction
mixture to a temperature suitable for reducing the precursor of the
metal to metal particles ("the reaction temperature"); (c)
maintaining the reaction mixture under the reaction temperature for
a time effective to reduce the precursor of the metal to metal
particles; and optionally, (d) isolating the metal particles. In
one embodiment, the method of the present invention further
includes a step of adjusting the pH of the reaction mixture (e.g.,
by introducing a buffering agent, such as, triethanolamine).
[0032] 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, In, Ir, Mo, Ni, Nb, Os, Pd, Pt, Re, Rh, Ru, Sn, Ta,
Ti, V, and W, and alloys or composites containing these metals. A
metal precursor is mixed with an alcoholic composition or agent,
which converts the metal precursor to ultra-fine metal particles
under various reaction conditions. The term "alcoholic composition"
or "alcoholic agent," as used herein and in the appended claims,
generally includes alcohols, such as, monohydroxylic and
polyhydroxylic alcohols (polyols).
[0033] The form of the metal precursor used in the reaction depends
upon the particular metal itself and the types of ultra-fine metal
particle products desired. Generally, the precursor may be any
metal-containing compound or complex that may be reduced into
elemental metal under the reaction conditions. The precursor needs
not to be completely soluble in the reaction mixture. Typical
precursors include, e.g., metal carbonates and hydrates thereof,
metal acetates and hydrates thereof, metal chlorides and hydrates
thereof, metal nitrates, metal oxides, metal oxalates, metal
hydroxides, and acids including the desired metal as part of an
oxyanion (e.g., tungstic acid) and salts of such acids (e.g.,
sodium tungstate and potassium hexachlorplatinate). In one
embodiment, metal carbonates, such as CuCO.sub.3, NiCO.sub.3,
CoCO.sub.3, Ag.sub.2CO.sub.3, may be used as the precursor for
producing ultra-fine metal particles of Cu, Ni, Co, and Ag,
respectively. The use of metal carbonates may be a critical element
in providing highly dispersed metallic particles at high metal ion
concentrations, as the carbonate counter ions may decompose and
leave the system. Consequently, the ionic strength of the reaction
system does not increase substantially during the reaction, which
promotes the stabilization of the metallic particle dispersion. In
another embodiment, a mixture of metal precursors, such as, metal
carbonates and metal acetates or metal salycilates may be used for
the production of ultra-fine metallic particles. The inventors have
also found that the presence of organic counter ions, such as
acetate and salycilate, may further enhance the stability of the
metallic particles at high concentrations of metal ions. In yet
another embodiment, agents which provide organic counter ions, such
as acetate ions or salycilate ions, may be administered into the
reaction system of the present invention.
[0034] The term "branched dispersing agent" as used herein and in
the appended claims includes any dispersing agents, which have at
least one side group that includes at least one carbon, such as, a
branched polyol. The term "branched polyol" as used herein and in
the appended claims includes any polyols, which have at least one
side group that includes at least one carbon. Branched polyols
suitable for the process of the present application includes,
without limitation, 2-C-methylerythritol, 2-C-methylthreitol, and
pentaerythritol ("PE"). Branched polyols may have a number of roles
in the reaction mixture, including functioning as a dispersant
and/or a reducing agent. The term "reducing agent" as used herein
and in the appended claims generally includes any agent which is
capable of reducing a precursor of a metal to elemental metals
and/or metal particles. The inventors of the present invention
discovered that, compared to the use of linear polyols, using
branched polyols, mixtures of branched and linear polyols, and
mixtures of branched polyols and ammonium or sodium salts of
polynaphtalene sulphonic/formaldehyde co-polymers in accordance
with the present invention, offers some unexpected advantages,
e.g., resulting in metallic particles with tighter size
distribution, lower degree of agglomeration, high degree of
crystallinity, and less susceptible to oxidation, etc. The term
"linear polyols" includes, without limitation, molecules containing
linear chains of 3 to 7 carbon atoms, where each carbon atom having
a hydroxyl group attached, such as, sorbitol and mannitol. In one
embodiment, the branched polyol may be PE. In another embodiment,
the sodium salts of polynaphtalene sulphonic/formaldehyde
co-polymers may be the Daxad dispersants, such as, Daxad 11G and
Daxad 19.
[0035] The polyol composition used in the process of the present
invention may be commanded by the particular reaction. A broad
range of polyols may be used in the process, such as the polyols
disclosed in U.S. Pat. Nos. 4,539,041 and 5,759,230, each of which
are hereby incorporated herein by reference. The polyols may be in
either liquid or solid form. In one embodiment, 1,2-propylene
glycol ("1,2-PG"), 1,3-propylene glycol ("1,3-PG"),
diethyleneglycol ("DEG"), or the combinations thereof, may be used
in the reaction mixture. In another embodiment, a mixture of 1,2-PG
and DEG may be used as the reducing polyol.
[0036] When forming the reaction mixture, the branched dispersing
agent (e.g. the branched polyol) and the alcoholic agent may be
either unheated or heated. Generally, the reaction temperature may
be maintained or adjusted to about 80-350.degree. C., or more
preferably, about 110-200.degree. C. For example, to produce
ultra-fine Cu particles, 1,2-PG, DEG, and PE may be mixed and
heated to bring the temperature of the mixture to about 70.degree.
C. The required amount of CuCO.sub.3 may then be added into the
polyol mixture at about 80-85.degree. C. after PE is fully
dissolved. The reaction mixture may further be heated to bring the
temperature of the mixture to an appropriate reaction temperature.
In the present example, the reaction temperature is about
180-185.degree. C.
[0037] 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.
[0038] The size and the uniformity of the ultra-fine metallic
particles may be affected by a variety of factors, such as the
types of metal precursor, branched polyol, alcoholic agent, and
dispersant used, the concentration of the metal ions, the reaction
temperature, and the pH of the reaction mixture. In one embodiment,
the pH of the reaction mixture may be adjusted to control the size
of the ultra-fine metallic particles produced at any given metal
precursor concentrations. The inventors discovered that pH changes
significantly affect the reduction reaction and the formation of
metallic particles. In a preferred embodiment, the pH of the
reaction mixture may be adjusted by adding a buffering agent. The
term "buffering agent" as used herein generally includes an agent
which, upon addition to the reaction mixture, reduces the change of
pH of the reaction mixture caused by the H.sup.+ produced during
the reaction or when an acid or base is added into the reaction
mixture. The buffering agent is added to the reaction mixture to
control, e.g., increase, decrease, or stabilize, the pH of the
reaction mixture in order to control the size of the particles
produced by the reaction system at a given concentration of a metal
precursor in the reaction mixture. In this respect, the pH of the
reaction mixture may be controlled to produce smaller particles
than would otherwise be possible at a particular concentration of
the metal precursor. Examples of buffering agents are
triethanolamine ("TEA"),
4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid ("HEPES"),
4-morpholinepropanesulfonic acid ("MOPS"),
tris(hydroxymethyl)aminomethane ("Tris"), and
N-[tris(hydroxymethyl)methyl]-2-aminoethanesulfonic acid ("TES").
In one embodiment, the buffering agent may be TEA.
[0039] The inventors discovered that the size of ultra-fine
metallic particles formed by the process of the present invention
may be significantly affected by the amount of buffering agent
added to the reaction mixture. For example, in a typical reaction
system with 1,2-PG (250 ml), DEG (250 ml), and CuCO.sub.3 (200 g),
the pH of the reaction mixture measured at room temperature in the
absence of PE decreases from about 8.6 at the beginning of the
process to about 4.85 at the end of the reaction and the average
size of the copper particles product is about 2.4 .mu.m. The
addition of 2% TEA (final concentration) raised the final pH to
about 6.20 and the size of the copper decreased to about 1.5 .mu.m.
When 5% and 10% of TEA (final concentration) was introduced into
the reaction mixture, the pH at the end of the reaction was about
7.70 and about 8.60, respectively, and the size of the copper
particles produced by the process was reduced to about 700 nm and
about 300 nm, respectively.
[0040] Moreover, controlling of the pH of the reaction mixture
during the reduction process offers additional unexpected benefits.
For example, it may dramatically reduce the cost of making
ultra-fine metallic particles by enabling the uses of a
concentrated reaction system. The polyol-based systems known in the
art are rather diluted systems, i.e. the concentrations of the
metal ions in these systems are kept low in order to form
ultra-fine metal particles in the sub-mircrometer scale, typically
lower than 5-10%. Therefore, the diluted systems will consume more
energy and materials (polyols, etc.) to produce a particular size
of ultra-fine metallic particles than using a concentrated system.
Furthermore, the concentrated system of the present invention
reduces the cost of processing the organic solvent waste. In the
polyol system of the present invention, the pH of the reaction
mixture may be controlled, e.g., by the addition of a buffering
agent, such as TEA. Thus, the reaction rate is not or significantly
less affected by the potential change in the pH as a result of the
presence of a large quantity of metal precursors in the system. For
example, Cu particles with a size of about 300 nanometer may be
produced by adding more than 200 g of CuCO.sub.3 into a reaction
mixture of 500 ml (250 ml 1,2-PG, 200 ml DEG, and 50 ml TEA)
following the process of the present invention, while Cu particles
with a much larger size (about 2.4 .mu.m) are formed when the same
amount of CuCO.sub.3 is added into a reaction mixture where the pH
is not controlled (250 ml 1,2-PG and 250 ml DEG).
[0041] The inventors also discovered that the types of polyol used
in the process affect the size and uniformity of the metallic
particles produced. For example, in a typical reaction, the
ultra-fine copper particles formed in reaction mixture of 1,2-PG as
the sole reducing polyol shown the widest particle size
distribution (100-700 nm). The uniformity of the copper particles
considerably improves when polyol mixtures, such as a mixture of
1,2-PG and 1,3-PG or a mixture of 1,2-PG and DEG, are used (see,
e.g., FIG. 3). Furthermore, comparing to the use of 1,3-PG, the use
of DEG resulted in somewhat larger copper particles (e.g., 300 nm
vs. 500 nm, respectively). The inventors further demonstrated that
the copper particles produced by the process, which utilized a
mixture of 1,2-PG and DEG, has the highest uniformity (i.e. the
tightest size distribution) (see, e.g., FIG. 3).
[0042] 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
desirable feature, such as, a 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, Ni, and Ag.
[0043] In one aspect, the present invention provides a method of
coating a substrate with a plurality of ultra-fine metallic
particles, and also coated substrates produced therewith, by: (a)
forming a reaction mixture containing the substrate, a precursor of
a metal, a branched dispersing agent (e.g., a branched polyol), and
an alcoholic agent; (b) adjusting the temperature of the reaction
mixture to a temperature suitable for reducing the precursor of the
metal to metal particles ("the reaction temperature"); (c)
maintaining the reaction mixture under the reaction temperature for
a time effective to reduce the precursor of the metal to metal
particles and permit the resulting metal particles to form a
coating on the surface of the substance; and optionally, (d)
isolating the coated substance. In one embodiment, the ultra-fine
metallic particles may be introduced to the surface of the
substrate in such a manner that they form a uniform and continuous
layer(s) the surface.
EXAMPLES
[0044] 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.
Example 1
Materials
[0045] The copper carbonate (CuCO.sub.3) was supplied by Shepherd
Chemical Co. 1,2-PG and DEG were obtained from Alfa Aesar (Ward
Hill, Mass.). 1,3-PG and PE were obtained from Avocado Research
Chemical Ltd., while TEA was purchased from Aldrich (Milwaukee,
Wis.).
Example 2
Copper Particles Synthesis
[0046] All experiments were carried out in a 1 L--4-necked round
flask equipped with a Dean Stark trap and a refluxing condenser.
The stirring was provided by a two inch Teflon--blade connected to
a variable speed mixer. The amount of cupric carbonate used in the
precipitation process was in general kept at 200 g (1.62 mol)
although smaller or larger amounts were occasionally used as well
(i.e., 87 g and 300 g). The CuCO.sub.3 was added into 500 cm.sup.3
polyols or polyols mixture containing 15 g PE (for 200 g
CuCO.sub.3). The dispersant agent (PE) was initially added in
polyols and heated at low power (10%) in the heating mantle to
bring the temperature to 70.degree. C. The required amounts of
CuCO.sub.3 were added into the flask at 80-85.degree. C. after the
PE was fully dissolved. The CuCO.sub.3/polyol mixture was stirred
at 500 RPM in all experiments. The mixture was then heated at 50%
setting of heating power until the temperature reaches
180-185.degree. C. The copper particles obtained were washed three
times with ethanol (3.times.400 mL) and were filtered using a
vacuum system and Whatmann #50 filter paper. The particles were
then dried overnight at 80.degree. C. in a regular oven.
Example 3
Particles Characterization
[0047] The morphology of copper particles was investigated by
scanning electron microscopy (SEM) using a JEOL--JSM 6300 scanning
microscope at 15 kV accelerating voltage and the magnification
between 2500 and 10000. Also, the copper powders were analyzed by
field emission scanning electron microscopy (FE-SEM) with 5 kV
accelerating voltage and the same range of magnification using a
JEOL JSM -7400F field emission scanning electron microscope.
[0048] Discussed below are results obtained by the inventors in
connection with the experiments of Example 1-3:
[0049] In order to evaluate the effect of pH in the formation of Cu
particles in polyols, variable amounts of triethanolamine (TEA)
were added into the dispersion of CuCO.sub.3 prior to the heating
as shown in Table 1. The reaction time in the presence of TEA
varied between 3 and 4 hours, the addition of more base tending to
speed up the reaction. The images of copper particles produced in
the manner described in the present invention, obtained by FE-SEM,
are illustrated in FIG. 1.
[0050] Almost all copper particles prepared by the reduction of
copper carbonate in polyols or mixtures of polyols in the presence
of TEA are isometric and very crystalline in shape. Their diameter
can be varied from several hundred nanometers (200-300 nm) to
several micrometers (2-3 .mu.m) by modifying the amount of TEA (pH)
added into the reaction mixture.
[0051] The experimental conditions and data including the size
range of the copper particles obtained at different pH values are
summarized in Table 1. In all experiments containing TEA, the
copper particles retained the original morphology obtained in the
absence of TEA (pH=4-5).
[0052] The particles sizes shown in Table 1 were obtained by
averaging the size of minimum 50 particles generated in each
experiment. TABLE-US-00001 TABLE 1 Experimental condition and
characteristics of the copper powder obtained in polyols mixtures
containing TEA Average Polyols (ml) TEA CuCO.sub.3 particle size
1,2-PG DEG ml (%) (g).sup.1 PE (g) pH.sup.2 (.mu.m) 500 0 0 0 200
15 n/a 2.2 250 250 0 0 200 15 4.85 2.5 250 240 10 2 200 15 6.20 1.2
250 225 25 5 200 15 7.70 0.7 250 200 50 10 200 15 8.62 0.3
.sup.1Lot# 1018121. .sup.2The pH of emulsions was measured at room
temperature at the end of the reaction.
[0053] The changes in the average diameter of copper particles size
produced as a function of the concentration of TEA are illustrated
in FIG. 2. The differences in average diameter of particles
obtained in similar experimental conditions between different lots
of CuCO.sub.3 are .about.10%.
[0054] In order to evaluate the influence of different polyol
composition in the preparation of copper particles, several
experiments were carried out using pure 1,2-PG and mixtures of
1,2-PG containing DEG and 1,3-PG respectively. In all these
experiments a 10% content of TEA and the same amounts of PE (7 g)
and CuCO.sub.3 (87 g) were used. FIG. 3 a, b, c shows the SEM
images at two magnifications (5000.times. and 10000.times.) of the
copper particles formed in a 1,2-PG:DEG:TEA=50:40:10 (v/v) mixture
and 1,2-PG:1,3-PG:TEA=50:40:10 (v/v), respectively. For comparison,
FIG. 3 includes also the SEM of copper particles obtained in
1,2-PG:TEA=90:10 (v/v).
[0055] For copper particles formed in 1,2-PG/TEA mixture the SEM
analysis shown the widest particle size distribution (100-700 nm).
The uniformity of the copper particles improves when polyol
mixtures were used. It appears that the nature of the second polyol
affects the size of the particles, the addition of DEG generating
larger particles (0.5 .mu.m) than in the case of 1,3-PG (0.3
.mu.m). Furthermore, the results of this set of experiments tend to
suggest that the addition of DEG leads to the most uniform copper
particles.
[0056] It has been shown in the inventors' earlier work that, when
the amount of the CuCO.sub.3 is changed, the size of the copper
particles decreases with the decrease in the concentration of the
Cu ions of the system. This trend causes an increase in the cost of
producing ultra-fine Cu particles with a decreased size. It is
expected that, in more concentrated systems, the pH of the reaction
mixture decreases more, causing a decrease in the reducing power of
the polyol and a slowdown in the reaction rate of the second stage
of the copper reduction (Cu.sup.+->Cu.sup.0). The inventors
demonstrated that the fine copper particles could be in fact
produced even in highly concentrated system providing that the pH
of the reaction mixture is controlled. In order to evaluate the
influence of CuCO.sub.3 concentration on the copper particles size,
a systematic study was carried out using 87 g (0.174 g/cm.sup.3);
130.5 g (0.261 g/cm.sup.3); 174 g (0.348 g/cm.sup.3); and 200 g
(0.40 g/cm.sup.3) CuCO.sub.3 in reduction process. For all
experiments a fixed amount of PE (7 g) and a fixed 1,2-PG:DEG:TEA
ratio (250:200:50, v/v) were used. The pH of the initial slurry did
not change with the amount of carbonate used and it decreased only
slightly during the reduction process. The SEM pictures at
5000.times. magnification of copper particles obtained at different
CuCO.sub.3 concentrations are illustrated in FIG. 4.
[0057] The average size copper particles was .about.0.5 .mu.m for
all the CuCO.sub.3 concentrations tested, the differences between
separate precipitations being less than .+-.20%. A somehow better
homogeneity was observed at the lowest concentration, probably
because of the higher dipersant:metal ratio.
[0058] These results further confirm the hypothesis that the rate
of the reduction with polyols is pH dependent and that by
controlling the pH during the reaction the size of the resulting Cu
particles can also be controlled. The discovery provided by the
present invention may have significant implications in the
production of ultra-fine Cu powders since it enables a
manufacturing method which may be easily scaled up to produce
ultra-fine Cu powder at very competitive prices.
[0059] Among the factors that may affect the size of copper
particles produced by the chemical reduction of copper carbonate in
polyols and/or polyols mixtures, one of the most influencing factor
is the pH of solution. The inventors demonstrated that this
parameter can be adjusted by adding TEA in controlled
concentrations. At high pH values (8.6-9.0), such as when 10% TEA
was added into the reaction mixture, smaller copper particles (size
range 0.2-0.5 .mu.m) are formed, while the sizes of copper
particles increase with the decreasing of pH. The size of the
copper particles is not substantially affected by the changes of pH
when the value of the pH of the reaction mixture is less than 5.75
or higher than 8.5.
[0060] The second factor that influences the copper particle size
is the composition of the polyol mixtures used in the precipitation
process. When the copper particles were synthesized in only one
polyol (e.g., 1,2-PG), a broad size distribution was obtained
(1.5-2.6 .mu.m). The uniformity of copper particles obtained in
polyol mixtures is somehow improved compared to the case when pure
1,2-PG is used, the narrowest distribution being obtained in
1,2-PG:DEG mixtures (2-2.8 .mu.m) (FIG. 3).
[0061] The third factor that influences the size of copper
particles is the CuCO.sub.3 concentration. When the pH of the
system is not controlled, the diameters of the Cu particles varies
significantly with the concentrations of the Cu precursor. However,
when the pH is controlled by adding a buffering agent (i.e., TEA),
the size of the copper particles was relatively stable for a wide
range of CuCO.sub.3 (0.174-0.40 g/cm.sup.3). An approximately 10%
increasing in average diameter of copper particles obtained was
observed in experiments using a higher CuCO3 concentration (0.40
g/cm.sup.3) (FIG. 4).
Example 4
Preparation of Ultra-Fine Nickel Particles
[0062] Nickel carbonate (NiCO.sub.3) was supplied by Shepherd
Chemical Co., 1,2-PG and DEG were obtained from Alfa Aesar (Ward
Hill, Mass.). 1,3-PG and PE were obtained from Avocado Research
Chemical Ltd., and the Palladium Chloride solution (PdCl.sub.2) was
obtained from OMG (South Plainfield, N.J.).
[0063] All experiments were carried out in a 1 L-4-necked flask
equipped with a refluxing condenser preceded by a dean stark trap
and 7'' extension. The stirring was provided by a two inch
Teflon--blade connected to a variable speed mixer. The amount of
nickel carbonate used in the precipitation process was in general
kept at 140 g (1.18 mol). NiCO.sub.3 was added into a 500 ml polyol
mixture, composed of 50% PG and 50% DEG and 7 g PE. The dispersing
agent, PE, was added in the polyol and heated at 75% power in the
heating mantel to bring the temperature up to 70.degree. C. The
required amount of NiCO.sub.3 was then added into the flask at
80-85.degree. C., after the PE was fully dissolved. The
NiCO.sub.3/polyol mixture was stirred at 500 RPM in all
experiments. The mixture was continually heated at 75% power until
the suspension reached the end point. The nickel particles shown in
FIG. 6 were washed three times with ethanol (3.times.400 ml) and
were filtered with a vacuum system using Whatman #50 filter paper.
The particles were then dried overnight at 100.degree. C. in a
regular oven.
Example 5
Preparation of Ultra-Fine Silver Particles
[0064] All experiments were carried out in a 1 L-4-necked flask
equipped with a refluxing condenser preceded by a dean stark trap
and 7'' extension. The stirring was provided by a two inch
Teflon--blade connected to a variable speed mixer. The amount of
silver carbonate used in the precipitation process was in general
kept at 100 g. Ag.sub.2CO.sub.3 was added into a 500 ml polyol
mixture, composed of 50% PG and 50% DEG and 7 g PE. The dispersing
agent was initially added in the polyol and mixed until completely
dissolved. The required amount of Ag.sub.2CO.sub.3 was then added
into the flask, after the PE was fully dissolved. The
carbonate/polyol mixture was stirred at 500 RPM in all experiments.
The mixture was continually heated until the suspension reached the
end point.
[0065] 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.
* * * * *