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.

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 agg  value and wherein the I 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 agg  value and wherein the I 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.