Dry conversion of high purity ultrafine silicon powder to densified pellet form for silicon melting applications

Abstract

A method for making bulk silicon material consisting of silicon pellets for making silicon ingots from an agglomerate-free source of high purity, ultra fine silicon powder includes feeding a controlled amount of silicon powder into a pellet die and dry compacting the powder at ambient temperature with pressure to produce a pellet that has a density of about 50-85% of the theoretical density of elemental silicon, a weight within a range of about 1.0 gram to about 3.0 grams, a diameter in the range of 10 mm to 20 mm and preferably of about 14 mm, and a height in the range of 5 mm to 15 mm and preferably of about 10 mm.

1 . A method for making a silicon pellet comprising:
 providing a source of high purity silicon powder having a median particle size within a range of up to about 100 micrometers and a range of particle size of not greater than about 1000 micrometers;   feeding a controlled amount of said powder from said source into a pellet die;   compacting with pressure said controlled amount of said powder in said die thereby forming a dry pellet of high purity silicon; and   discharging said pellet from said die.   
     
     
         2 . The method for making a silicon pellet according to  claim 1 , said compacting being done at about ambient temperature. 
     
     
         3 . The method for making a silicon pellet according to  claim 1 , said powder being free of intentional additives and binders. 
     
     
         4 . The method for making a silicon pellet according to  claim 1 , said powder comprising an organic binder, and said compacting with pressure comprising adding sufficient heat whereby said binder is evaporated. 
     
     
         5 . The method for making a silicon pellet according to  claim 1 , wherein said step of dry compressing comprises applying a force greater than or equal to about approximately 10,000 Newton's to said powder.