Methods of producing composite powders

Abstract

An improved method for producing a uniform distribution of substances within a powder mixture is provided. By control of pH, a metal containing substance is precipitated on a powder and converted into a coating to form a relatively homogeneous powder mixture. The powder mixture may be pressed and sintered to form a composite powder.

What is claimed:  
     
         1 . A method of producing a coated powder comprising a metallic layer on an insoluble powder, the method comprising: 
 a. preparing a solution comprising a metal ion;    b combining an insoluble powder with the solution to form a slurry containing constituents;    c mixing the constituents of the slurry;    d. adjusting the pH of the slurry to convert the metal ion into a metallic intermediate that is capable of being precipitated onto the insoluble powder;    e. precipitating the metallic intermediate onto the insoluble powder to form a precipitate;    f. recovering the precipitate, said precipitate comprising said insoluble powder and said metallic intermediate; and    g. treating said precipitate to form a coated powder.    
     
     
         2 . A method according to  claim 1 , wherein in the metal ion comprises at least one ion selected from the group consisting of Co ions, Ni ions, Cu ions, Cr ions, V ions, W ions and Fe ions.  
     
     
         3 . A method according to  claim 2 , wherein the metal ion comprises Co ions.  
     
     
         4 . A method according to  claim 1 , wherein the solution is prepared by mixing a soluble salt of a metal and water.  
     
     
         5 . A method according to  claim 4 , wherein the soluble salt is a cobalt salt selected from the group consisting of cobalt chloride, cobalt sulfate, cobalt nitrate and cobalt acetate.  
     
     
         6 . A method according to  claim 1 , wherein the solution is prepared by dissolving a metal into an acid solution containing water.  
     
     
         7 . A method according to  claim 1 , wherein the insoluble powder comprises at least one substance selected from the group consisting of carbides, nitrides and carbonitrides.  
     
     
         8 . A method according to  claim 7 , wherein the carbide, nitride or carbonitride is a carbide, nitride or carbonitride of an element selected from the group consisting of W, Ti, Ta, Cr, V, Mo and Nb.  
     
     
         9 . A method according to  claim 1 , wherein the insoluble powder comprises at least one metal selected from the group consisting of Co, Ni, Cu, W, Fe, V, Cr, Mo, and Nb.  
     
     
         10 . A method according to  claim 1 , wherein the step of adjusting the pH is accomplished by the addition of acid.  
     
     
         11 . A method according to  claim 10 , wherein the acid is oxalic acid.  
     
     
         12 . A method according to  claim 1 , wherein the step of adjusting of the pH is accomplished by the addition of alkali.  
     
     
         13 . A method according to  claim 12 , wherein the alkali is selected from the group of consisting of NH 3 , KOH, NaOH and combinations thereof.  
     
     
         14 . A method according to  claim 1 , wherein the pH is adjusted in step (d) to a pH between about pH 8 and about pH 9.  
     
     
         15 . A method according to  claim 1 , wherein the step of precipitating is accomplished by heating the slurry.  
     
     
         16 . A method according to  claim 1 , wherein said metallic intermediate comprises a metal hydroxide.  
     
     
         17 . A method according to  claim 1 , wherein said metallic intermediate comprises a metal oxide.  
     
     
         18 . A method according to  claim 1 , wherein the step of recovering comprises washing, filtering and drying.  
     
     
         19 . A method according to  claim 1 , wherein the step of treating comprises reducing in an environment comprising predominantly hydrogen.  
     
     
         20 . A method according to  claim 1 , wherein the step of treating comprises reducing in an environment comprising predominantly nitrogen.  
     
     
         21 . A method according to  claim 1 , wherein the step of treating the precipitate occurs at a temperature sufficient to decompose the metallic intermediate into metallic form.  
     
     
         22 . A method according to  claim 1 , wherein the insoluble powder that is combined with the solution is an amount that yields a coated powder that contains the insoluble powder in an amount from about 70 wt. % to about 99 wt. %, based on the weight of the coated powder.  
     
     
         23 . A method for producing a composite powder which comprises producing a coated powder in accordance with the method of  claim 1  and pressing and sintering the coated powder to form a composite powder.  
     
     
         24 . A method for producing cobalt coated tungsten carbide comprising: 
 a. dissolving a cobalt salt in hydrochloric acid to form a solution;    b. adding tungsten carbide to the solution to form a slurry containing constituents;    c. mixing the constituents of the slurry;    d. adding ammonia to the slurry to adjust the pH and to form a cobalt intermediate;    e. precipitating the cobalt intermediate onto the surface of the tungsten carbide to form a precipitate;    f. washing, filtering and drying the precipitate to form a dried powder; and    g. heating the dried powder under a hydrogen atmosphere, to reduce the cobalt intermediate to cobalt metal so as to form a cobalt coated tungsten carbide.    
     
     
         25 . A method for producing a composite powder which comprises producing a coated powder in accordance with the method of  claim 24  and pressing and sintering the coated powder to form the composite powder.  
     
     
         26 . A method according to  claim 24 , wherein the tungsten carbide is present in an amount that yields said cobalt coated tungsten carbide having from about 90 wt. % to about 98 wt. % tungsten carbide, based on the weight of the cobalt coated tungsten carbide.