U.S. patent application number 11/664640 was filed with the patent office on 2008-05-08 for method of production of high purity silver particles.
This patent application is currently assigned to TOKUSEN U.S.A., INC. Invention is credited to Insoo Kim, Sang Ho Kim, Young Jin Kim, Chang Gun Lee, Charles E. Smith.
Application Number | 20080105085 11/664640 |
Document ID | / |
Family ID | 36319502 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080105085 |
Kind Code |
A1 |
Kim; Insoo ; et al. |
May 8, 2008 |
Method Of Production Of High Purity Silver Particles
Abstract
A method for synthesizing high purity silver particles and
colloids without requiring the addition of either surfactants or
reducing agents thereto, or requiring only a minimal amount
thereof. The synthesizing process comprises: (i) a silver oxalate
synthesizing process; (ii) a process of dispersing silver oxalate
into an appropriate carrier; and {iii) a process of heating said
silver oxalate dispersed into said carrier at a temperature of at
least 100.degree. C. Silver particles and colloids of various form
factor and size may be synthesized depending upon the reaction
conditions, the carrier, and the type of surfactant.
Inventors: |
Kim; Insoo; (Busan, KR)
; Lee; Chang Gun; (Gyoungsangnam Do, KR) ; Kim;
Sang Ho; (Busan, KR) ; Smith; Charles E.;
(Conway, AR) ; Kim; Young Jin; (Conway,
AR) |
Correspondence
Address: |
WRIGHT, LINDSEY & JENNINGS LLP
200 WEST CAPITOL AVENUE, SUITE 2300
LITTLE ROCK
AR
72201-3699
US
|
Assignee: |
TOKUSEN U.S.A., INC
|
Family ID: |
36319502 |
Appl. No.: |
11/664640 |
Filed: |
October 13, 2005 |
PCT Filed: |
October 13, 2005 |
PCT NO: |
PCT/US05/36727 |
371 Date: |
April 4, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60618876 |
Oct 14, 2004 |
|
|
|
Current U.S.
Class: |
75/370 ;
75/343 |
Current CPC
Class: |
B22F 2998/10 20130101;
B22F 2999/00 20130101; B22F 9/30 20130101; B22F 2202/01 20130101;
B22F 9/30 20130101; B22F 1/0003 20130101; B22F 9/30 20130101; B22F
2999/00 20130101; B22F 2998/10 20130101 |
Class at
Publication: |
75/370 ;
75/343 |
International
Class: |
B22F 9/00 20060101
B22F009/00 |
Claims
1. A method for production of silver particles, comprising the
steps of: (a) dispersing solid silver oxalate particles in a
carrier; and (b) heating said dispersed silver oxalate to a
temperature of at least 100.degree. C. under a pressure that is
greater than atmospheric pressure to decompose said silver oxalate
into silver particles.
2. The method of claim 1, further comprising the step before step
(a) of producing said silver oxalate by mixing a first solution of
a silver compound and a second solution of an oxalate compound to
form silver oxalate.
3. The method of claims 1 or 2, further comprising the step of
adding a surfactant to said dispersed silver oxalate before the
heating of step (b).
4. The method of claim 3 wherein said surfactant is selected from
the group consisting of anionic surfactants, cationic surfactants,
amphoteric surfactants, nonionic surfactants, fluorochemical
surfactants, polymerizable surfactants, and any combination of the
preceding surfactants.
5. The method of claim 2, further comprising the step of adding a
surfactant to said first solution before said mixing step.
6. The method of claim 5 wherein said surfactant is selected from
the group consisting of anionic surfactants, cationic surfactants,
amphoteric surfactants, nonionic surfactants, fluOrochemical
surfactants, polymerizable surfactants, and any combination of the
preceeding surfactants.
7. The method of claim 2 further comprising the step of adding a
surfactant to said second solution before said mixing step.
8. The method of claim 7 wherein said surfactant is selected from
the group consisting of anionic surfactants, cationic surfactants,
amphoteric surfactants, nonionic surfactants, fluorochemical
surfactants, polymerizable surfactants, and any combination of the
preceeding surfactants.
9. The method of claims 1 or 2, wherein the dispersing of step (a)
comprises adding silver oxalate to said carrier and subjecting the
mixture of silver oxalate and carrier to ultrasonic treatment.
10. The method of claims 1 or 2, wherein said carrier is selected
from the group consisting of water, methyl alcohol, ethyl alcohol,
propyl alcohol, and a mixture of any of the preceding.
11. The method of claim 2, wherein said silver compound is
AgNO.sub.3.
12. The method of claim 2, wherein said oxalate compound is
selected from the group consisting of sodium oxalate and oxalic
acid.
13. The method of claim 2, further comprising the step following
the production of silver oxalate of washing said silver oxalate
with water to remove impurities.
14. The method of claim 4, wherein said surfactant is selected from
the group consisting of PVP (polyvinyl pyrrolidone) and
gelatin.
15. The method of claim 6, wherein said surfactant is selected from
the group consisting of PVP (polyvinyl pyrrolidone) and
gelatin.
16. The method of claim 8, wherein said surfactant is selected from
the group consisting of PVP (polyvinyl pyrrolidone) and
gelatin.
17. The method of claim 3, wherein said surfactant is no greater
than 80% by weight of the silver in step (b).
18. The method of claim 5, wherein said surfactant is no greater
than 80% by weight of the silver in step (b).
19. The method of claim 7, wherein said surfactant is no greater
than 80% by weight of the silver in step (b).
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/618,876, filed Oct. 14, 2004 and entitled
"Method for Production of Fine Silver Particles," which is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a method of forming silver
particles by dispersing silver oxalate into an appropriate carrier
and then applying heat at a temperature of 100.degree. C. or higher
to decompose the silver oxalate.
BACKGROUND ART
[0003] A number of methods have been developed to synthesize silver
particles including, but not limited to, chemical reduction,
photochemical, sonochemical and gas evaporation methods. Of these
methods, the chemical reduction method is widely used due to the
ease of production. However, silver powder produced using the
chemical reduction method can be contaminated by the reducing
agent, the surfactant and impurity ions used during the reaction
process, which can serve as a limiting factor in the field of
electronics requiring high conductivity or in the field of bacteria
resistance requiring high purity.
[0004] In order to resolve these problems, it is desirable to have
a method of producing high purity silver powder and silver colloids
that does not require either surfactants or reducing agents, or
only a minimal amount of a surfactant.
DISCLOSURE OF THE INVENTION
[0005] The object of the present invention is to synthesize high
purity silver particles and colloids in a process that does not
require either surfactants or reducing agents, or only a minimal
amount of a surfactant. In the present invention, this object is
achieved by dispersing silver oxalates into an appropriate carrier
and then thermally decomposing the silver oxalates at a temperature
of 100.degree. C. or higher to synthesize high purity silver
particles and colloids.
[0006] The process of synthesizing silver particles and colloids by
the method of the present invention comprises: (i) a silver oxalate
synthesizing process; (ii) a process of dispersing silver oxalates
into an appropriate carrier, for example, water, alcohol or the
like, including a combination of more than one carrier; and (iii) a
process of heating said silver oxalates dispersed into said carrier
at a temperature of 100.degree. C. or higher under a pressure
greater than atmospheric pressure.
[0007] These and other features, objects and advantages of the
present invention will become better understood from a
consideration of the following detailed description of the
preferred embodiments and appended claims in conjunction with the
drawings as described following.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a microphotograph of silver particles obtained
under the conditions described in Example 1.
[0009] FIG. 2 is a microphotograph of silver particles obtained
under the conditions described in Example 2.
[0010] FIG. 3 is a microphotograph of silver particles obtained
under the conditions described in Example 3.
[0011] FIG. 4 is a microphotograph of silver particles obtained
under the conditions described in Example 4.
[0012] FIG. 5 is a microphotograph of silver particles obtained
under the conditions described in Example 5.
[0013] FIG. 6 is a microphotograph of silver particles obtained
under the conditions described in Example 6.
BEST MODE FOR CARRYING OUT THE INVENTION
[0014] With reference to FIGS. 1-6, the preferred embodiments of
the present invention may be described as follows.
[0015] In the present invention, a method for the production of
silver particles and colloids comprises three processes as follows:
(i) a silver oxalate (Ag.sub.2C.sub.2o.sub.4) synthesizing process;
(ii) a process of dispersing silver oxalate into an appropriate
carrier, for example, water, alcohol or the like, including a
combination of more than one carrier; and (iii) a process of
heating said silver oxalate dispersed into said carrier at a
temperature of 100.degree. C. or higher under a pressure greater
than atmospheric pressure to form silver particle or colloids from
the decomposition of the silver oxalate.
[0016] A first solution of a water soluble silver compound and a
second solution of an oxalate compound are mixed together to
precipitate silver oxalates. The silver compound may be AgNO.sub.3.
The oxalate compound may be sodium oxalate or oxalic acid. The
present invention is not, however, limited to these specific
compounds but may include any two solutions of compounds that form
silver oxalates upon mixing. After water cleaning processes,
preferably two or more rounds of water cleaning processes, are
performed to remove impure ions from the precipitated silver
oxalate, the silver oxalate is used as the starting material for
synthesizing silver powder or colloids.
[0017] The synthesized silver oxalate is dispersed into an
appropriate carrier. The silver oxalate is not dissolved to any
substantial extent in the carrier, but is dispersed as solid
particles by using ultrasonic treatment. The appropriate carrier
may include all types of carriers which can disperse silver oxalate
to effectively deliver heat. The carrier is selected to have
properties that allow it to behave similarly to a surfactant so as
to prevent agglomeration of the silver particles formed from the
thermal decomposition of the silver oxalate. For example, alcohols
consist of alkyl and hydroxyl groups. Generally, alkyl groups have
hydrophobic properties and hydroxyl groups have hydrophilic
properties. Organic materials having both hydrophobic and
hydrophilic properties can play a role as a surfactant. However,
organic materials having higher carbon numbers tend to be
dominantly hydrophobic and may therefore tend to lose the ability
to act as a surfactant in the process of the present invention.
Generally, organic materials having higher numbers of carbon atoms
have superior surfactant properties. However, in the present
invention, organic materials with a higher number of carbon atoms
is observed to agglomerate silver particles. Furthermore, organic
materials with a higher number of carbon atoms do not mix well with
water. Therefore, the present invention is limited to methyl, ethyl
and propyl alcohols, which have a low number of carbon atoms. Water
is also effective in the practice of the present invention. The
appropriate carrier may therefore consist of ethyl alcohol, methyl
alcohol, propyl alcohol, water or a combination of more than one of
the preceding.
[0018] The carriers selected for the practice of the present
invention all have low boiling points: water (100.degree. C.),
methyl alcohol (64.65.degree. C.), ethyl alcohol (78.3.degree. C.),
and propyl alcohol (82.degree. C.). Accordingly, when the carrier
with the dispersed silver oxalate is heated in a container at or
above 100.degree. C., the pressure is always above atmospheric
pressure. Typical reaction pressures are about 1.86*10.sup.5
N/m.sup.2 when using water as the carrier and about 5.31*10.sup.5
N/m.sup.2 when using ethyl alcohol as the carrier. During thermal
decomposition of silver oxalate, the silver oxalate
(Ag.sub.2C.sub.2O.sub.4) decomposes into silver (Ag) and carbon
dioxide (CO.sub.2) according to the formula
Ag.sub.2C.sub.2O.sub.4=2Ag+2CO.sub.2. The carbon dioxide gas
evolved during the thermal decomposition of the silver oxalate and
the carrier vapor may be evacuated as necessary but pressure drops
of less than about 6.89*10.sup.4 N/m.sup.2 do not affect the
quality of the silver particles.
[0019] The dispersed silver oxalate in the carrier is placed into a
closed reactor to heat the dispersed silver oxalate and carrier up
to at least 100.degree. C. to synthesize silver powder or colloids
of various form factors.
[0020] This method may optionally use surfactants in order to
prevent coagulation or agglomeration of the silver particles.
Surfactants may be added to the water soluble silver or oxalate
solutions used to produce silver oxalate, or may be added after the
silver oxalate is produced by mixing the two solutions. Surfactants
used in this method may include anionic surfactants, cationic
surfactants, amphoteric surfactants, nonionic surfactants,
fluorochemical surfactants, and polymerizable surfactants, or
combinations of the preceding, which may be added to aid in forming
silver particles and to break down silver plates or prevent silver
plates from coagulation. Surfactants suitable for use in the
present invention include PVP (polyvinyl pyrrolidone) and
gelatine.
[0021] Irrespective of the amount of surfactant added, silver
particles or colloids can be obtained by the method of the present
invention, however, it is desirable to limit the amount of
surfactant to no more than 80% of the weight of the silver. For
example, if 10 grams of silver is placed into the reactor, the
weight of the surfactant, such as PVP or gelatin, should be no more
than 8 grams.
EXAMPLE 1
[0022] After 2.8 grams of silver oxalate was placed into 300 cc of
distilled water, ten minutes of ultrasonic treatment was performed
to disperse the particles. The dispersed silver oxalate was reacted
for 15 minutes at 130.degree. C. to obtain a solution containing
silver particles as shown in FIG. 1.
EXAMPLE 2
[0023] After 28 grams of silver oxalate was placed into 1000 cc of
ethyl alcohol, ten minutes of ultrasonic treatment was performed to
disperse the particles. The dispersed silver oxalate was reacted
for 15 minutes at 134.degree. C. to obtain silver powder as shown
in FIG. 2.
EXAMPLE 3
[0024] After 70 mg of silver oxalate was placed into 1000 cc of
ethyl alcohol, ten minutes of ultrasonic treatment was performed to
disperse the particles. The dispersed particles were reacted for 25
minutes at 135.degree. C. to obtain nano-sized silver particles as
shown in FIG. 3.
EXAMPLE 4
[0025] After 4.2 grams of silver oxalate was placed into a mixed
solution of water (vol. 50%) and ethyl alcohol (vol. 50%), the
solution was reacted for 15 minutes at 130.degree. C. to synthesize
0.5 .mu.m silver particles as shown in FIG. 4.
EXAMPLE 5
[0026] 30 wt % of PVP (polyvinyl pyrrolidone) was placed into 4.2
grams of silver oxalate in 1 Liter of water and ultrasonic
treatment was performed to disperse the particles thereof. The
dispersed particles were reacted for 20 minutes at 135.degree. C.
to synthesize silver particles of 0.5 .mu.m or smaller in size as
shown in FIG. 5.
EXAMPLE 6
[0027] 10 grams of gelatin was placed into 28 grams of silver
oxalate in 1 Liter of water and ultrasonic treatment was performed
to disperse the particles thereof. The dispersed particles were
reacted for 15 minutes at 135.degree. C. to synthesize silver
particles of 50 nm or smaller in size as shown in FIG. 6.
INDUSTRIAL APPLICABILITY
[0028] Due to its inherent characteristics of high conductivity and
bacteria resistance, silver particles are widely used in the
electronics industry as well as in other industries requiring
bacteria resistance.
[0029] The present invention has been described with reference to
certain preferred and alternative embodiments that are intended to
be exemplary only and not limiting to the full scope of the present
invention as set forth in the appended claims.
* * * * *