Shell activated sintering of core-shell particles

Abstract

A sintered structure and method for forming it are disclosed. The method includes obtaining core-shell particles having a core material and a shell material, forming the particles into a powder compact, and annealing the powder compact at an annealing temperature. The shell material is a metal that diffuses faster than the core material at the annealing temperature and diffuses to the contacts between the core-shell particles during annealing to form sintered interfaces between the core-shell particles. The sintered structure can have discontinuous regions of shell material between the sintered interfaces. The core material can be a metal, semiconductor or ceramic. The core material can be copper and the shell material can be silver. The sintered interfaces can be almost purely shell material. The annealing temperature can be significantly lower than the temperature needed to form interfaces between particles of the core material without the shell material.

1 . A method for forming a sintered structure at an annealing temperature, the method comprising:
 obtaining core-shell particles having a core material and a shell material, the shell material being a metal material that diffuses faster than the core material at the annealing temperature;   forming the core-shell particles into a powder compact in which the core-shell particles are in physical contact; and   annealing the powder compact at the annealing temperature to cause the faster diffusing shell material to diffuse to the contacts between the core-shell particles to form sintered interfaces between the core-shell particles that are in physical contact.   
     
     
         2 . The method of  claim 1 , wherein the core material is a metal material, the core material being a different metal material than the shell material. 
     
     
         3 . The method of  claim 2 , wherein the core material is copper. 
     
     
         4 . The method of  claim 3 , wherein the shell material is silver. 
     
     
         5 . The method of  claim 1 , wherein the shell material is silver. 
     
     
         6 . The method of  claim 1 , wherein the core material is a semiconductor material. 
     
     
         7 . The method of  claim 1 , wherein the core material is a ceramic material. 
     
     
         8 . The method of  claim 1 , wherein the core material and the shell material have limited mutual solubility at the annealing temperature. 
     
     
         9 . The method of  claim 1 , wherein the core material and the shell material do not form an intermediate phase material between the core and shell materials at the annealing temperature. 
     
     
         10 . The method of  claim 1 , wherein the annealing temperature is significantly lower than the temperature needed to form sintered interfaces between particles of the core material without the shell material. 
     
     
         11 . The method of  claim 1 , wherein the annealing step is performed in an annealing atmosphere that promotes diffusion of the shell material at the annealing temperature, the shell material not being prone to diffusion at the annealing temperature in a standard air atmosphere. 
     
     
         12 . The method of  claim 1 , wherein the sintered interfaces are almost purely composed of the shell material. 
     
     
         13 . The method of  claim 1 , further comprising performing the annealing step long enough to form discontinuous regions of the shell material in the sintered structure between the sintered interfaces. 
     
     
         14 . The method of  claim 1 , wherein the core-shell particles have an average diameter of approximately 470 nm. 
     
     
         15 . The method of  claim 1 , wherein the average thickness of the shell material on the core-shell particles is approximately 7 nm. 
     
     
         16 . The method of  claim 1 , wherein annealing step causes an increase in the density of the core-shell particles in the powder compact. 
     
     
         17 . A sintered structure comprising:
 a sintered core-shell compact comprised of a plurality of core-shell particles sintered at an annealing temperature, each of the plurality of core-shell particles having a core material and a shell material, the shell material being a metal material that diffuses faster than the core material at the annealing temperature.   wherein the sintered core-shell compact includes a plurality of sintered interfaces between the core-shell particles that are in physical contact.   
     
     
         18 . The sintered structure of  claim 17 , wherein the core material is copper and the shell material is silver. 
     
     
         19 . The sintered structure of  claim 17 , wherein the core material is a semiconductor material. 
     
     
         20 . The sintered structure of  claim 17 , wherein the core material is a ceramic material. 
     
     
         21 . The sintered structure of  claim 17 , wherein the core material and the shell material have limited mutual solubility at the annealing temperature. 
     
     
         22 . The sintered structure of  claim 17 , wherein the sintered core-shell compact does not include an intermediate phase material formed between the core and shell materials. 
     
     
         23 . The sintered structure of  claim 17 , wherein the sintered interfaces are almost purely composed of the shell material. 
     
     
         24 . The sintered structure of  claim 17 , wherein the sintered core-shell compact includes discontinuous regions of the shell material on the sintered core-shell particles between the sintered interfaces.