Process for manufacturing high density boron carbide

Abstract

A process for manufacturing high density boron carbide by pressureless sintering, enabling to create sintered products of complex shapes and high strength. The process comprises mixing raw boron carbide powder with carbon precursor, such as a polysaccharide, compacting the mixture to create an object of the desired shape, and finally carbonizing and sintering the object at higher temperatures.

1 . A process for manufacturing boron carbide objects comprising the steps of:
 (a) pre-washing a raw boron carbide powder with an organic solvent, said pre-washing including mixing for about 24 hours, followed by drying of the washed boron carbide;   (b) mixing the washed boron carbide powder with a carbon precursor;   (c) drying the mixture;   (d) granulating the dried mixture;   (e) compacting the granulated dried mixture to form a shaped object by applying a pressure thereto;   (f) carbonizing the shaped body in an inert atmosphere, by dwelling at a high temperature for a predetermined period of time; and   (g) sintering the carbonized shaped body at a temperature between about 2290° C. and about 2350° C. in an inert atmosphere for a time period of not less than about 30 min.   
     
     
         2 . The process of  claim 1 , wherein the boron carbide powder has a particle size D 50  less than or equal to 5.8 μm and D 90  less than or equal to 10 μm. 
     
     
         3 . The process of  claim 1 , wherein the organic solvent is selected from the group consisting of isopropyl alcohol, ethyl alcohol, methyl alcohol, acetone, and a combination thereof. 
     
     
         4 . The process of  claim 1 , wherein the carbon precursor which is mixed with the boron carbide powder includes a phenolic resin. 
     
     
         5 . The process of  claim 1 , wherein the carbon precursor which is mixed with the boron carbide powder includes an aqueous solution of a polysaccharide or a mixture of two or more saccharides. 
     
     
         6 . The process according to  claim 5 , wherein the polysaccharide is maltodextrin. 
     
     
         7 . The process according to  claim 5 , wherein the drying is carried out by spray drying. 
     
     
         8 . The process of  claim 1 , wherein the pressure is applied uniaxially. 
     
     
         9 . The process of  claim 1 , wherein the pressure is applied isostatically. 
     
     
         10 . The process of  claim 1 , wherein the compaction is carried out with heating. 
     
     
         11 . The process of  claim 10 , wherein the compaction is carried out at a temperature of between about 130° C. and about 170° C. 
     
     
         12 . The process of  claim 1 , wherein compaction is carried out until the density of the compacted shaped body reaches between about 1.36 to about 1.60 g/cc. 
     
     
         13 . The process of  claim 1 , wherein the carbonization step is carried out in a nitrogen atmosphere. 
     
     
         14 . The process of  claim 1 , wherein the carbonization step is carried out in an argon atmosphere. 
     
     
         15 . The process of  claim 1 , wherein the carbonization step is carried out at a controlled heating rate, which is between about 25° C./hr to about 100° C./hr. 
     
     
         16 . The process of  claim 1 , wherein the carbonization step is at a temperature greater than 500° C. 
     
     
         17 . The process of  claim 16 , wherein the carbonization step is at a temperature between about 550° C. to about 1050° C. 
     
     
         18 . The process of  claim 1 , wherein the sintering is carried out in an argon atmosphere. 
     
     
         19 . The process of  claim 1 , wherein the sintering is carried out for a time period of about 120 minutes. 
     
     
         20 . The process of  claim 1 , wherein the sintering is performed while the shaped body is constrained between shaped graphite dies having essentially a geometry to match a desired final geometry of said shaped body. 
     
     
         21 . The process of  claim 20 , wherein the graphite dies have a non-flat, multi-curved shape. 
     
     
         22 . The process of  claim 1 , wherein the boron carbide object, after sintering, has a density greater than or equal to about 2.42 g/cc, corresponding to about 96% or greater of the theoretical density (TD). 
     
     
         23 . A shaped, high-density boron carbide object made by a process for manufacturing boron carbide objects comprising the steps of:
 (a) pre-washing a raw boron carbide powder with an organic solvent, said pre-washing including mixing for about 24 hours, followed by drying of the washed boron carbide;   (b) mixing the washed boron carbide powder with a carbon precursor;   (c) drying the mixture;   (d) granulating the dried mixture;   (e) compacting the granulated dried mixture to form a shaped object by applying a pressure thereto;   (f) carbonizing the shaped body in an inert atmosphere, by dwelling at a high temperature for a predetermined period of time; and   (g) sintering the carbonized shaped body at a temperature between about 2290° C. and about 2350° C. in an inert atmosphere for a time period of not less than about 30 min.   
     
     
         24 . The shaped, high-density boron carbide object of  claim 23 , wherein the shaped, high-density boron carbide object, after sintering, has a density greater than or equal to about 2.42 g/cc, corresponding to about 96% or greater of the theoretical density (TD).