Manufacture of carbon/carbon composites by hot pressing

Abstract

A mixture of carbon-containing fibers, such as mesophase or isotropic pitch fibers, and a suitable matrix material, such as a milled pitch, is compressed while resistively heating the mixture to form a carbonized composite material having a density of about 1.5 g/cm 3 , or higher. The composite material is formed in under ten minutes. This is a significantly shorter time than for conventional processes, which typically take several days and achieve a lower density material. Consequently, carbon/carbon composite materials having final densities of about 1.6-1.8 g/cm 3 , or higher are readily achieved with one or two infiltration cycles using a pitch or other carbonaceous material to fill voids in the composite and rebaking.

1 .- 21 . (Canceled)  
     
     
         22 . An apparatus for forming a compressed composite material comprising: 
 a vessel which defines a cavity for receiving composite material to be treated;    a means for applying pressure which applies a pressure of at least 35 kg/cm 2  to the material in the cavity;    a source of electric current which applies a current to the material, the current flowing through the material to resistively heat the material;    a temperature detector which detects the temperature of the material; and    a control system which controls the pressure applying means and source of electrical current such that the mixture is sequentially heated at a first temperature and pressed at a first pressure for a first period of time, and heated at a second temperature higher than the first temperature and at a second pressure higher than the first pressure for a second period of time.    
     
     
         23 . (Canceled)  
     
     
         24 . The apparatus of  claim 22 , wherein the means for applying pressure comprises a first piston positioned to engage the material within the vessel.  
     
     
         25 . The apparatus of  claim 24 , wherein the means for applying pressure comprises a second piston positioned opposite the first piston.  
     
     
         26 . The apparatus of  claim 22 , wherein the source of electric current operative engages the material through the means for applying pressure.  
     
     
         27 . The apparatus of  claim 22 , further comprising insulation positioned around the vessel.  
     
     
         28 . The apparatus of  claim 22 , further comprising a pressure sensor operatively attached to the pressure applying means and the control system to indicate the presence of the first pressure and the second pressure within the vessel.  
     
     
         29 . The apparatus of  claim 28 , wherein the pressure sensor is a displacement sensor relaying the displacement of the pressure applying means to the control system.  
     
     
         30 . An apparatus for forming a compressed composite material comprising: 
 a holding area shaped to receive the material;    a first pressure element positioned to engage the material to apply pressure to the material in a first direction; and    a source of electric current operatively engaging the first pressure element to apply a current to the material through the first pressure element to resistively heat the material.    
     
     
         31 . The apparatus of  claim 30 , further including a second pressure element positioned to engage the material to apply pressure to the material in a second direction.  
     
     
         32 . The apparatus of  claim 31 , wherein the first pressure element is positioned opposite the second pressure element.  
     
     
         33 . The apparatus of  claim 31 , wherein the source of electric current operatively engages the second pressure element to apply a current to the material through the second pressure element to resistively heat the material.  
     
     
         34 . The apparatus of  claim 30 , further comprising a control system operatively connected to the holding area, the first pressure element, and the source of electric current to regulate the pressure and the electrical current in the material.  
     
     
         35 . The apparatus of  claim 34 , wherein the control system controls the source of electric current and the first pressure element to sequentially heat the material at a first temperature and press the material to a first pressure for a first period of time and heat the material at a second temperature higher than the first temperature and press the material at a second pressure higher than the first pressure for a second period of time.  
     
     
         36 . The apparatus of  claim 34 , further comprising a temperature monitoring device operatively connected to the material and the control system to relay the temperature of the material to the control system.  
     
     
         37 . The apparatus of  claim 34 , further comprising a pressure monitoring device operatively connected to the material and the control system to relay the pressure of the material to the control system.  
     
     
         38 . The apparatus of  claim 30 , wherein the holding area includes sides and each side is substantially shaped as a parallelogram.  
     
     
         39 . An apparatus for forming a compressed composite material comprising: 
 a holding area shaped to receive the material;    a first pressure element positioned to engage the material to apply pressure to the material in a first direction;    a second pressure element positioned opposite the first pressure element to engage the material to apply pressure to the material in a second direction;    a source of electric current operatively engaging the first and second pressure elements to apply a current to the material through the first and second pressure elements to heat the material; and    a control system operatively connected to the first pressure element, the second pressure element, and the source of electric current to regulate the pressure and electrical current in the material.    
     
     
         40 . The apparatus of  claim 39 , wherein the control system controls the source of electric current and the first and second pressure elements to sequentially heat the material at a first temperature and press the material to a first pressure for a first period of time and heat the material at a second temperature higher than the first temperature and press the material at a second pressure higher than the first pressure for a second period of time.  
     
     
         41 . The apparatus of  claim 40 , further comprising: 
 a temperature monitoring device operatively connected to the material and the control system to relay the temperature of the material to the control system; and    a pressure monitoring device operatively connected to the material and the control system to relay the pressure of the material to the control system.    
     
     
         42 . The apparatus of  claim 41 , further including insulation positioned around the holding area.