Methods of forming a dense coating on particles

Abstract

Methods of forming a coating are presented. For example, a method for forming a coating on particles may include mixing an initial powder with a pressing medium, the initial powder comprising a plurality of core particles having an initial shell coating thereon; isostatic pressing the initial powder within the pressing medium to densify the initial shell coating on the plurality of core particles to form a pressed powder, the pressed powder comprising a densified shell coating on the plurality of core particles; and thereafter, removing the pressing medium from the pressed powder.

We claim: 
     
         1 . A method of forming a coating on particles, the method comprising:
 mixing an initial powder with a pressing medium, wherein the initial powder comprises a plurality of core particles having an initial shell coating thereon;   isostatic pressing the initial powder within the pressing medium to densify the initial shell coating on the plurality of core particles to form a pressed powder, wherein the pressed powder comprises a densified shell coating on the plurality of core particles; and   thereafter, removing the pressing medium from the pressed powder.   
     
     
         2 . The method of  claim 1 , further comprising:
 forming the initial shell coating on the plurality of core particles to form the initial coated powder.   
     
     
         3 . The method of  claim 2 , wherein the initial shell coating comprises a plurality of initial shell particles, and wherein an average diameter of the plurality of core particles is at least two times (2×) larger than an average diameter of the plurality of initial shell particles. 
     
     
         4 . The method of  claim 2 , wherein the plurality of initial shell particles is mixed with the plurality of core particles to form the initial shell coating on the plurality of core particles. 
     
     
         5 . The method of  claim 2 , wherein the initial shell coating is formed from a shell slurry composition applied onto the plurality of core particles. 
     
     
         6 . The method of  claim 1 , wherein the pressing medium is chemically inert with respect to the plurality of core particles and the initial shell coating. 
     
     
         7 . The method of  claim 1 , wherein the pressing medium is substantially free from water. 
     
     
         8 . The method of  claim 1 , wherein the pressing medium comprises an organic polymeric material. 
     
     
         9 . The method of  claim 1 , wherein the initial shell coating of the initial powder has an initial average density, and wherein the densified shell coating of the pressed powder has a pressed average density that is greater than the initial average density. 
     
     
         10 . The method of  claim 1 , wherein the initial shell coating of the initial powder has an initial chemical composition, and wherein the densified shell coating of the pressed powder has a pressed chemical composition that is the same as the initial chemical composition. 
     
     
         11 . The method of  claim 1 , wherein isostatic pressing is performed at a pressing temperature that ranges from 20° C. to 200° C. 
     
     
         12 . The method of  claim 1 , wherein removing the pressing medium comprises heating the pressing medium containing the pressed powder to an evaporation temperature at an evaporation pressure such that the pressing medium evaporates from the pressed powder. 
     
     
         13 . The method of  claim 1 , wherein removing the pressing medium comprises dissolving the pressing medium with a solvent to remove the pressing medium from the pressed powder. 
     
     
         14 . The method of  claim 1 , wherein the plurality of core particles of the initial powder has an initial average diameter that is substantially the same as a pressed average diameter of the plurality of core particles of the pressed powder. 
     
     
         15 . The method of  claim 1 , wherein a morphology of the plurality of core particles of the initial powder is substantially the same as a morphology of the plurality of core particles of the pressed powder. 
     
     
         16 . The method of  claim 1 , wherein the plurality of core particles of the initial powder comprises a magnetic material. 
     
     
         17 . A method of forming an article from a pressed powder, the method comprising:
 forming a pressed powder, wherein forming the pressed powder comprises:
 coating a plurality of core particles with an initial shell coating to form an initial powder, 
 mixing the initial powder with a pressing medium, 
 isostatic pressing the initial powder within the pressing medium to densify the initial shell coating on the plurality of core particles to form a pressed powder, wherein the pressed powder comprises a densified shell coating on the plurality of core particles, and 
 thereafter, removing the pressing medium from the pressed powder; 
   forming the pressed powder into a green pressed powder article; and   densifying the green pressed powder article to form the article.   
     
     
         18 . The method of  claim 17 , wherein the initial shell coating of the initial powder has an initial average density and an initial chemical composition, wherein the densified shell coating of the pressed powder has a pressed average density that is greater than the initial average density, and wherein the densified shell coating of the pressed powder has a pressed chemical composition that is the same as the initial chemical composition. 
     
     
         19 . The method of  claim 17 , wherein isostatic pressing is performed at a pressing temperature and a pressing pressure that avoids evaporation of the pressing medium during the isostatic pressing. 
     
     
         20 . The method of  claim 17 , wherein the article is an iron-ferrite soft magnetic composite (SMC) component.