U.S. patent application number 14/259271 was filed with the patent office on 2014-12-04 for double jet process for producing nanosilver dispersions.
This patent application is currently assigned to E I DU PONT DE NEMOURS AND COMPANY. The applicant listed for this patent is CLARKSON UNIVERSITY, E I DU PONT DE NEMOURS AND COMPANY. Invention is credited to DANIEL V. GOIA, ROBERTO IRIZARRY-RIVERA, LU LU.
Application Number | 20140352497 14/259271 |
Document ID | / |
Family ID | 51983634 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140352497 |
Kind Code |
A1 |
IRIZARRY-RIVERA; ROBERTO ;
et al. |
December 4, 2014 |
DOUBLE JET PROCESS FOR PRODUCING NANOSILVER DISPERSIONS
Abstract
This invention provides a double jet process to produce silver
nanoparticles, the process comprising providing a double-jet system
to form a reaction mixture in a reactor containing the reactor
solution by adding a basic aqueous silver ammonia complex solution
and a basic reducing solution to the reactor solution at the same
controlled rate with a targeted pH profile for the reactor solution
from acidic to basic determined by the addition rate and the
initial pH of the reactor solution. Use of this process results in
a dispersion comprised of silver nanoparticles that have a specific
size and de-agglomeration level that is determined by the process
conditions.
Inventors: |
IRIZARRY-RIVERA; ROBERTO;
(RALEIGH, NC) ; GOIA; DANIEL V.; (POTSDAM, NY)
; LU; LU; (POTSDAM, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
E I DU PONT DE NEMOURS AND COMPANY
CLARKSON UNIVERSITY |
WILMINGTON
POTSDAM |
DE
NY |
US
US |
|
|
Assignee: |
E I DU PONT DE NEMOURS AND
COMPANY
WILMINGTON
DE
CLARKSON UNIVERSITY
POTSDAM
NY
|
Family ID: |
51983634 |
Appl. No.: |
14/259271 |
Filed: |
April 23, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61830808 |
Jun 4, 2013 |
|
|
|
Current U.S.
Class: |
75/370 |
Current CPC
Class: |
B22F 2301/255 20130101;
B22F 1/0014 20130101; B22F 9/24 20130101; B22F 1/0022 20130101 |
Class at
Publication: |
75/370 |
International
Class: |
B22F 9/24 20060101
B22F009/24 |
Claims
1. A process for preparing silver nanoparticles, said process
comprising the steps of: (a) preparing a basic aqueous silver
ammonia complex solution comprising a water soluble silver salt and
ammonia in deionized water; (b) preparing a basic reducing solution
comprising hydrazine monohydrate in deionized water; (c) preparing
an acidic reactor solution with a pH in the range of 3.0 to 5.0,
said reactor solution comprising: (i) one or more dispersing
agents, one of which is gum arabic hydrated in deionized water; and
(ii) nitric acid; (d) maintaining the basic aqueous silver ammonia
complex solution and the basic reducing solution at the same
temperature T.sub.M, wherein T.sub.M is in the range of 10.degree.
C. to 90.degree. C.; (e) providing a double-jet system to form a
reaction mixture in a reactor containing the reactor solution by
adding the basic aqueous silver ammonia complex solution and the
basic reducing solution to the reactor solution at the same
controlled rate with a targeted pH profile for the reactor solution
from acidic to basic determined by the addition rate and the
initial pH of the reactor solution; and (f) maintaining the
reaction mixture in the reactor at constant temperature in the
range of 10.degree. C. to 90.degree. C. to produce the silver
nanoparticles.
2. The process of claim 1 further comprising the steps of: (h)
separating the silver nanoparticles from the reaction mixture; (i)
washing the silver nanoparticles with deionized water; and (j)
transferring the silver nanoparticles to a nonaqueous solution
3. The process of claim 1, wherein said water soluble silver salt
is silver nitrate.
4. The process of claim 1, wherein said one or more additional
dispersing agents are selected from the group consisting of
benzotriazole, salts of polynaphthalene sulfonate formaldehyde
condensate, poloxamer block copolymer, ethoxylated phenols,
polyethylene glycol with molecular weight ranges from 200 to 8000,
and mixtures thereof.
5. The process of claim 1, wherein the molar ratio of ammonia to
silver is greater than 2.
Description
FIELD OF THE INVENTION
[0001] The invention is directed to a double jet process for
producing silver powders comprising silver nanoparticles with
spherical morphology. The silver powders produced are particularly
useful in electronic applications.
BACKGROUND OF THE INVENTION
[0002] Silver powder is used in the electronics industry for the
manufacture of conductor thick film pastes. The thick film pastes
are screen printed onto substrates forming conductive circuit
patterns. These circuits are then dried and fired to volatilize the
liquid organic vehicle and sinter the silver particles. Printed
circuit technology is requiring denser and more precise electronic
circuits. To meet these requirements, the conductive lines have
become narrower in width with smaller distances between lines.
Several printing technologies have been developed to achieve these
requirements, e.g., ink-jets and other jetting technologies. The
silver powder particles necessary for these new printing
technologies are nanoparticles (less than 100 nm), uniform in size,
and well dispersed.
[0003] Many processes currently used to manufacture metal powders
can be applied to the production of silver nanoparticles. Silver
nanoparticles used in electronic applications are generally
manufactured using chemical precipitation processes. Silver
nanoparticles are produced by chemical reduction in which an
aqueous solution of a soluble salt of silver is reacted with an
appropriate reducing agent under conditions such that silver powder
is precipitated.
[0004] There is a need for a process to efficiently produce well
dispersed silver nanoparticles particles, with capability to
control the particle size.
SUMMARY OF THE INVENTION
[0005] This invention provides a process for preparing a silver
dispersion comprising silver nanoparticles, wherein the silver
nanoparticles have a specific size that is determined by the
process conditions and the use of one or more dispersing agents in
the process.
[0006] One embodiment provides a process for preparing silver
nanoparticles, said process comprising the steps of:
[0007] (a) preparing a basic aqueous silver ammonia complex
solution comprising a water soluble silver salt and ammonia in
deionized water;
[0008] (b) preparing a basic reducing solution comprising hydrazine
monohydrate in deionized water;
[0009] (c) preparing an acidic reactor solution with a pH in the
range of 3.0 to 5.0, said reactor solution comprising: [0010] (i)
one or more dispersing agents, one of which is gum arabic hydrated
in deionized water; and [0011] (ii) nitric acid;
[0012] (d) maintaining the basic aqueous silver ammonia complex
solution and the basic reducing solution at the same temperature
T.sub.M, wherein T.sub.M is in the range of 10.degree. C. to
90.degree. C.;
[0013] (e) providing a double-jet system to form a reaction mixture
in a reactor containing the reactor solution by adding the basic
aqueous silver ammonia complex solution and the basic reducing
solution to the reactor solution at the same controlled rate with a
targeted pH profile for the reactor solution from acidic to basic
determined by the addition rate and the initial pH of the reactor
solution; and
[0014] (f) maintaining the reaction mixture in the reactor at
constant temperature in the range of 10.degree. C. to 90.degree. C.
to produce the silver nanoparticles.
[0015] In another embodiment the process further comprises the
steps of:
[0016] (g) separating the silver nanoparticles from the reaction
mixture;
[0017] (h) washing the silver nanoparticles with deionized water;
and
[0018] (i) transferring the silver nanoparticles to a nonaqueous
solution
DETAILED DESCRIPTION OF INVENTION
[0019] This invention provides a double jet process to efficiently
produce silver nanoparticles. Use of this process results in a
dispersion comprised of silver nanoparticles that have a specific
size and de-agglomeration level that is determined by the process
conditions and the use of one or more particle dispersing agents.
These silver particles are highly uniform and highly
dispersible.
[0020] The basic silver-ammonia complex aqueous solution is
prepared by adding a water soluble silver salt to deionized water.
In one embodiment the soluble salt is silver nitrate. Ammonia is
added to make the silver-ammonia complex. The molar ratio of
ammonia to silver is greater than 2. Small amounts of nitric acid
(1%-5%) can be added to this solution to increase the stability of
the silver complex.
[0021] The basic reducing solution is also an aqueous solution and
is prepared by adding hydrazine monohydrate to deionized water.
[0022] The acidic reactor solution is prepared by dissolving gum
arabic in deionized water and letting the gum arabic hydrate in the
water for a period of one to 24 hours. The gum arabic acts as a
dispersing agent. Nitric acid and one or more additional dispersing
agents are then added to the mixture. The nitric acid serves to
control the initial pH of the solution. The dispersing agent serves
to prevent aggregation and coat the particle.
[0023] The process is typically run such that the initial pH of the
reactor solution and the addition rate of the basic solutions are
utilized to control the size of the silver nanoparticles. This pH
is adjusted by adding sufficient nitric acid to the reactor
solution. The pH of the reactor solution is in the range of 3.0 to
5.0, preferably 3.5 to 4.5.
[0024] In addition, an additional dispersing agent selected from
benzotriazole, salts of polynaphthalene sulfonate formaldehyde
condensate such as Daxad.TM. 19 (manufactured by Hampshire Chemical
Corp., division of Dow Chemical Co.), Pluronic.TM., poloxamer block
copolymer (manufactured by BASF Corp.), ethoxylated phenols such as
Gafac.TM., (manufactured by GAF Corp.), polyethylene glycol with
molecular weight ranges from 200 to 8000, and mixtures of these
surfactants can be added to the reactor solution. The amount of
this surface modifying dispersing agent ranges from 0.001 g per
gram of silver to greater than 0.2 grams per gram of silver. The
preferred range to make finely divided particles is from 0.04 to
0.20 grams per gram of silver.
[0025] In typical processes the silver precipitation is carried at
high pH. The instant process starts at low pH by using a double jet
process. In this process the basic reducing solution and the basic
silver ammonia complex are outside the reactor initially and then
added slowly into the reactor. The initial pH of the reactor is in
the range of 3.5 to 4.5. At this starting pH range, hydrazine
hydrate is not capable of reducing silver ions at an observable
rate. During the addition of the two basic solutions, the pH is
increased and the reaction does proceed when the pH is raised to
greater than about 8.0. By adjusting the starting pH, the
concentration of silver ions present in the system when the
threshold pH needed for reduction is attained can be varied, and
thus the size of the particles controlled.
[0026] When an additional surface modifying dispersing agent is
added to the precipitations, the surface of the resulting silver is
further modified as the surface. By changing the type of additional
dispersing agent and its functional groups the cleanliness of the
surface of the particles and the sintering behavior are
modified.
[0027] The particle size d.sub.50 for the silver nanoparticles is
from 10 to 90 nm. The SEM size of the particles can also be
determined directly from field emission scanning electron
microscope (FESEM) images. The ratio of d.sub.50 to SEM size is in
the range of 1-2.
[0028] In one process embodiment the silver particles are
spherical. In one such embodiment the combination of dispersing
agents is the gum arabic and polyethylene glycol.
EXAMPLES
[0029] The following examples and discussion are offered to further
illustrate, but not limit the process of this invention. Note that
particle size distribution numbers (d.sub.10, d.sub.50, d.sub.90)
were measured using a LM-10 Particle Size Analyzer from Nanosight
UK. The d.sub.10, d.sub.50 and d.sub.90 represent the 10th
percentile, the median or 50th percentile and the 90th percentile
of the particle size distribution, respectively, as measured by
following the Brownian motion of the nanoparticles. That is, the
d.sub.50 d.sub.90) is a value on the distribution such that 50%
(10%, 90%) of the particles have a volume of this value or less.
The particle size d.sub.50 for the silver nanoparticles is from 10
to 90 nm. An average particle size, the SEM size of the particles,
can be determined directly from field emission scanning electron
microscope (FESEM) images.
Example 1
[0030] The basic silver-ammonia complex solution was prepared by
dissolving 63 g of silver nitrate in 200 g of deionized water. Then
75 ml of a 30% ammonia solution was added to form the complex
(ammonia to silver molar ratio must be larger than 2). This
solution was kept at 25.degree. C. while continuously stirring. The
basic reducing solution was prepared by adding and dissolving 9.5
ml of hydrazine monohydrate to 200 nil of deionized water in a
separate container from the silver-ammonia complex solution. This
solution was kept at 25.degree. C. while continuously stirring. The
reactor solution was prepared by adding and dissolving 12 g of
arabic gum to 1600 g of deionized water. This solution was kept at
25.degree. C. while continuously stirring for 16 hours. Then 2.5 ml
of nitric acid solution (1 N) was added followed by the addition of
0.5 g of polyethylene glycol (mw 8000).
[0031] After the three solutions were prepared, the silver-ammonia
complex solution and the reducing solution were added to the
reactor solution at equal addition rates for a total addition time
of 30 minute to make the reaction mixture. The reaction mixture is
continuously stirred during the addition. After the addition was
completed, the reaction mixture was stirred for 30 minutes. To
separate the nanoparticles, the gum arabic in the reaction mixture
was hydrolyzed by adjusting the pH of the reaction mixture to 12.5
using sodium hydroxide and the temperature was increased to
85.degree. C. for 4 hours. The reaction mixture was decanted and
the silver nanoparticle slurry was washed using decantation
followed by dialysis until a conductivity of the wash water was
less than or equal to 8 microsiemans.
[0032] The nanoparticle silver dispersion consisted of silver
particles with an average size of 25 nm as obtained from the field
emission scanning electron microscope image. Sizes were also
measured by Brownian motion. The d.sub.10, d.sub.50, and d.sub.90
were 12 nm, 21 nm and 40 nm, respectively.
Example 2
[0033] The conditions used were essentially the same as used in
Example 1 with the exception that the polyethylene glycol was not
added to the reactor solution.
[0034] The nanoparticle silver dispersion consisted of silver
particles with an average size of 24 nm as obtained from the field
emission scanning electron microscope image. Sizes were also
measured by Brownian motion. The d.sub.10, d.sub.50, and d.sub.90
were 13 nm, 22 nm and 52 nm, respectively.
Example 3
[0035] The conditions used were essentially the same as used in
Example 1 with the exception that the reactor solution contains 5
ml (1N) of nitric acid.
[0036] The nanoparticle silver dispersion consisted of silver
particles with an average size of 18 nm as obtained from the field
emission scanning electron microscope image.
Comparative Experiment A
[0037] The conditions used were essentially the same as used in
Example 1 with the exception that the pH of the reactor solution is
adjusted to 10 by adding hydrazine hydrate as base. The reduction
of silver complex in this case is almost instantaneous with the
precipitation of the metal occurring in the first 1-2 seconds. The
resulting particles are spherical, polycrystalline and have an
average diameter of about 350 nm as obtained from the field
emission scanning electron microscope image.
* * * * *