Copper powder and process for producing copper powder

Abstract

A copper powder is provided that has an average particle diameter in the range of from not less than 0.1 μm to less than 1.5 μm, that has a narrow particle size distribution width whose value A defined by Equation ( 1 ) below in terms of X25, X50 and X75 defined below is not greater than 1.2, and that forms a pseudo-fused sintered product when held at a temperature of 800° C. under an atmosphere of inert gas at one atmosphere pressure: A =( X 75− X 25 )/ X 50   ( 1 ), where X25, X50 and X75 are values of particle diameter X corresponding to Q% =25%, 50% and 75% on a cumulative particle-size curve plotted in an orthogonal coordinate system whose abcissa represents particle diameter X (μm) and ordinate represents Q% (ratio of particles present of a diameter not greater than the corresponding value of X; expressed in units of vol % of particles). The copper powder is produced by conducting wet reduction of cuprous oxide into metallic copper powder in the presence of ammonia or an ammonium salt. When used to form the terminal electrodes of multi-layer capacitor, it enables the electrodes to form into solid sintered bodies with few pores by sintering at a low temperature.

What is claimed is:  
     
         1 . In a process for producing copper powder comprising a step of reacting an aqueous solution of a copper salt and an alkali to precipitate copper hydroxide, thereby obtaining a suspension containing copper hydroxide, a primary- reduction step conducted in the suspension to reduce the copper hydroxide obtained to cuprous oxide, a secondary-reduction step conducted in the suspension to reduce the cuprous oxide obtained to metallic copper and a step of separating the metallic copper from the suspension; the improvement characterizing in that the suspension before or in the course of the secondary-reduction step is contacted with ammonia or an ammoniate.  
     
     
         2 . A process according to    claim 1   , wherein the copper powder has an average particle diameter of not greater than 1.2 μm and is non-agglomerative.  
     
     
         3 . A process according to    claim 1   , wherein the ammonia or ammoniate is contained in the suspension in an amount of 0.01-0.1 mole as ammonia per mole of copper in the system.  
     
     
         4 . A copper powder that has an average particle diameter in the range of from not less than 0.1 μm to less than 1.5 μm, that has a narrow particle size distribution width whose value A defined by Equation (1) below in terms of X25, X50 and X75 defined below is not greater than 1.2, and that forms a pseudo-fused sintered product when held at a temperature of 800° C. under an atmosphere of inert gas at one atmosphere pressure:  
         A =(X75−X25)/X50  (1),  
       where X25, X50 and X75 are values of particle diameter X corresponding to Q%=25%, 50% and 75% on a cumulative particle-size curve plotted in an orthogonal coordinate system whose abscissa represents particle diameter X (μm) and ordinate represents Q% (ratio of particles present of a diameter not greater than the corresponding value of X; expressed in units of vol % of particles).  
     
     
         5 . A copper powder according to    claim 4    whose average particle diameter is in the range of 0.3-1.2 μm and whose value A is not greater than 1.0.  
     
     
         6 . A copper powder according to    claim 4    or    5    utilized in forming a terminal electrode of a multi-layer ceramic capacitor by sintering the powder under heating an electrical conductive past containing the powder.