Spherical silver powder and method for producing same

Abstract

A spherical silver powder has a good dispersibility and is capable of obtaining a good degree of sintering even if used for forming a paste to be fired at a low temperature of 600° C. or less to form a conductor. An aqueous solution containing a reducing agent is added to a water reaction system containing silver ions, to deposit silver particles by reduction, to produce a spherical silver powder wherein a ratio (Dx/BET) of a crystallite diameter Dx (nm) to a BET specific surface area (m 2 /g) is in the range of from 5 to 200 and which has a crystallite diameter of not greater than 40 nm, a mean particle size of not greater than 5 μm, a tap density of not less than 2 g/cm 3 , and a BET specific surface area of not greater than 5 m 2 /g.

1 . A spherical silver powder wherein a ratio (Dx/BET) of a crystallite diameter Dx (nm) to a BET specific surface area (m 2 /g) is in the range of from 5 to 200.  
     
     
         2 . A spherical silver powder as set forth in  claim 1 , which has a crystallite diameter of not greater than 40 nm, and a mean particle size of not greater than 5 μm.  
     
     
         3 . A spherical silver powder as set forth in  claim 1 , which has a tap density of not less than 2 g/cm 3 , and a BET specific surface area of not greater than 5 m 2 /g.  
     
     
         4 . A spherical silver powder as set forth in  claim 2 , which has a tap density of not less than 2 g/cm 3 , and a BET specific surface area of not greater than 5 m 2 /g.  
     
     
         5 . A method for producing a spherical silver powder as set forth in  claim 1 , wherein an aqueous solution containing a reducing agent is added to a water reaction system containing silver ions, to deposit silver particles by reduction to produce the spherical silver powder.  
     
     
         6 . A method for producing a spherical silver powder as set forth in  claim 5 , wherein a dispersing agent is added to a slurry-like reaction system before or after said silver particles are deposited.  
     
     
         7 . A method for producing a spherical silver powder as set forth in  claim 6 , wherein said dispersing agent is at least one selected from the group consisting of fatty acids, fatty acid salts, surface active agents, organic metals, chelating agents and protective colloids.  
     
     
         8 . A method for producing a spherical silver powder as set forth in  claim 5 , wherein said reducing agent contained in said aqueous solution containing the reducing agent is at least one selected from the group consisting of ascorbic acid, alkanol amine, hydroquinone, hydrazine and formalin.  
     
     
         9 . A method for producing a spherical silver powder as set forth in  claim 5 , wherein said aqueous solution containing the reducing agent is added at a rate of not lower than 1 equivalent/min with respect to the content of silver in said water reaction system containing silver ions.  
     
     
         10 . A method for producing a spherical silver powder as set forth in  claim 5 , wherein a surface of said spherical silver powder is smoothed by a surface smoothing process which mechanically causes particles to collide with each other.  
     
     
         11 . A method for producing a spherical silver powder as set forth in  claim 10 , wherein silver agglomerates are removed by a classification after said surface smoothing process.