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.

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° 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° C./minute up to 200-220° 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° C./minute to 800° 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 agg  value and wherein the I 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° 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° 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.