Nanotube-containing composite bodies, and methods for making same

Abstract

A composite material featuring comminuted or otherwise well dispersed and separated nanotubes reinforcing a matrix featuring metal, ceramic and/or polymer. In a preferred embodiment, the nanotubes feature elemental carbon, and the composites can be produced using a molten silicon metal infiltration technique, which may be pressurized or not, for example, a siliconizing or a reaction-bonding process. In this preferred embodiment, carbon nanotubes may be prevented from chemically reacting with the silicon infiltrant by an interfacial coating disposed between the carbon nanotubes and the infiltrant. A reaction-bonded composite body containing even a small percentage of carbon nanotubes possessed a significant increase in electrical conductivity as compared to a reaction-bonded composite not containing such nanotubes, reflecting the high electrical conductivity of the nanotubes. When the nanotubes are well dispersed throughout the preform, mechanical property enhancements start to become noticeable, such as fracture toughness enhancement.

1 . A method for making a composite body containing nanotubes, comprising: 
 (a) providing a plurality of nanotubes;    (b) comminuting said nanotubes;    (c) organizing said comminuted nanotubes into a porous mass;    (d) infiltrating a molten infiltrant from a source into said porous mass; and    (e) solidifying said molten infiltrant.    
     
     
         2 . The method of  claim 1 , further comprising: 
 (f) supplying at least one carbon-containing liquid to said plurality of nanotubes, to substantially coat the external surfaces of the nanotubes;    (g) removing volatiles from said carbon-containing liquid; and    (h) wherein the molten infiltrant comprises silicon metal.    
     
     
         3 . A method of making a carbon nanotube-containing composite body, comprising: 
 (a) mixing a plurality of nanotubes with at least one filler material to disperse said nanotubes throughout said filler material;    (b) supplying at least one carbon-containing liquid to said dispersion of nanotubes and filler material, and stirring sufficiently to substantially coat at least all of the external surfaces of the at least one filler material and the nanotubes, thereby forming an admixture;    (c) organizing said admixture as a porous mass to be infiltrated;    (d) heating at least said carbon-containing liquid to remove volatile constituents, thereby leaving behind as a residue substantially pure elemental carbon;    (e) contacting a molten infiltrant comprising silicon to said porous mass;    (f) infiltrating said porous mass to a desired extent with said molten infiltrant to form an infiltrated mass; and    (g) cooling said infiltrated mass to form a composite body.    
     
     
         4 . The method of  claim 1 , further comprising arranging said porous mass into a desired bulk shape.  
     
     
         5 . The method of  claim 1 , wherein prior to infiltrating with molten infiltrant, said porous mass is green machined.  
     
     
         6 . The method of  claim 1 , wherein said porous mass further comprises at least one filler material.  
     
     
         7 . The method of  claim 1 , wherein said nanotube comprises elemental carbon.  
     
     
         8 . The method of  claim 2 , wherein said molten infiltrant comprises at least one metal other than silicon.  
     
     
         9 . The method of  claim 8 , wherein said at least one metal comprises aluminum.  
     
     
         10 . The method of  claim 1 , wherein said nanotubes make up about 1% to about 15% by volume of said porous mass.  
     
     
         11 . The method of  claim 2 , wherein said mixture of nanotubes and carbon-containing liquid is shaped or rendered in the form of a prepreg.  
     
     
         12 . The method of  claim 6 , wherein said at least one other filler material comprising a plurality of finely divided bodies that are infiltrated into said preform by means of a carrier fluid.  
     
     
         13 . The method of  claim 6 , wherein said at least one filler material comprises at least one substance selected from the group consisting of silicon carbide and boron carbide.  
     
     
         14 . The method of  claim 3 , wherein said at least one filler material comprises at least one substance selected from the group consisting of silicon nitride, aluminum oxide and titanium diboride.  
     
     
         15 . The method of  claim 1 , wherein said infiltrating occurs via capillarity.  
     
     
         16 . The method of  claim 1 , wherein said infiltrating occurs with the assistance of an externally applied force.  
     
     
         17 . A composite body made according to the method of  claim 1 .  
     
     
         18 . A composite body, comprising: 
 (a) a reinforcement component comprising a plurality of nanotubes, wherein at least a weight majority of said nanotubes are not in the form of a tangled mass of nanotubes; and    (b) a matrix component comprising at least one of elemental silicon and silicon carbide.    
     
     
         19 . The composite body of  claim 18 , further comprising at least one coating that substantially shields or isolates said nanotubes from said matrix.  
     
     
         20 . The composite body of  claim 18 , further comprising at least one zone of carbon disposed between said nanotubes and said matrix.  
     
     
         21 . The composite body of  claim 18 , comprising from about 1% to about 90% by volume of said nanotubes, about 1% to about 90% of said elemental silicon, about 10% to about 90% of said silicon carbide, and about 0.1% to about 90% of boron carbide.  
     
     
         22 . The composite body of  claim 18 , wherein said at least one coating comprises silicon carbide.  
     
     
         23 . The composite body of  claim 18 , wherein said carbon nanotubes make up about 0.1% to about 35% by volume of said composite body.  
     
     
         24 . The composite body of  claim 18 , wherein said nanotubes have a diameter that is less than about 500 nanometers.  
     
     
         25 . The composite body of  claim 18 , wherein said nanotubes have a diameter in the range of about 10 to 100 nanometers.  
     
     
         26 . The composite body of  claim 18 , wherein said reinforcement component further comprises at least one other filler material.  
     
     
         27 . The composite body of  claim 26 , wherein said at least one other filler material comprises at least one of carbon fibers, silicon carbide and boron carbide.  
     
     
         28 . The composite body of  claim 26 , wherein said at least one other filler material comprises a morphology selected from the group consisting of particulate, fiber, platelets and flakes.  
     
     
         29 . The composite body of  claim 26 , wherein said reinforcement component makes up at least about 10 vol % and no more than about 90 vol % of said composite body.  
     
     
         30 . The composite body of  claim 18 , wherein said nanotubes comprises elemental carbon.  
     
     
         31 . The composite body of  claim 18 , wherein said nanotubes comprise silicon carbide.  
     
     
         32 . A composite body, comprising: 
 (a) a reinforcement component comprising a plurality of nanotubes, wherein at least a weight majority of said nanotubes are not in the form of a tangled mass of nanotubes; and    (b) a matrix component comprising elemental aluminum.    
     
     
         33 . The composite body of  claim 32 , wherein said matrix further comprises at least one of elemental silicon and silicon carbide.  
     
     
         34 . A method for making a composite body comprising silicon carbide nanotubes, comprising: 
 (a) providing at least one carbon nanotube;    (b) comminuting said at least one carbon nanotube to form a plurality of carbon nanotubes;    (c) organizing said comminuted carbon nanotubes into a porous mass;    (d) contacting a source of molten infiltrant comprising silicon to said porous mass;    (e) infiltrating molten infiltrant into said porous mass;    (f) reacting at least a portion of said silicon with at least a portion of said nanotubes to form silicon carbide nanotubes; and    (g) solidifying said molten infiltrant.