Method for making a pitch-based foam

Details Method for making a pitch-based foam Method for making a pitch-based foam

1998-07-10

2001-11-13

Hendrickson, Stuart L. (Department: 1754)

Chemistry of inorganic compounds

Carbon or compound thereof

Elemental carbon

C264S029100

Reexamination Certificate

active

06315974

ABSTRACT:

The present invention relates generally to the utilization of a solvated mesophase pitch to make a carbon foam, and in particular to the use of a solvated mesophase pitch to make a carbon foam which requires little or no oxidative stabilization prior to carbonization of the carbon foam.
Carbon-carbon composites are widely used for aircraft brake friction materials. Although carbon-carbon is attractive because it is lightweight and can operate at very high temperatures, the use of carbon-carbon raw material entails the use of an expensive material. Expensive carbon fiber is a significant component; sometimes up to 45 percent fiber is used in making the composite. Additionally, the manufacture of carbon-carbon is a time-consuming process. Long cycle times are undesirable in a modern manufacturing environment. U.S. Pat. No. 6,077,464 describes inventions for making an aircraft brake friction material by means of a carbon-carbon composite material made from densified carbon foam. U.S. Pat. No. 6,077,464 is incorporated by reference in its entirety herein. The manufacturing process disclosed therein may be generally described by the steps of utilizing a precursor material (thermoset or thermoplastic), foaming the precursor material, oxygen stabilization for foams produced from thermoplastics, carbonization, optional heat treatment, densification, and a subsequent heat treatment. As disclosed in the above paten, when a foam is made from a thermoplastic such as a mesophase pitch, it may be necessary to cross link the foam by oxidation before it can be heated to carbonization temperatures. Without this oxidation (stabilization) step, the pitch may melt when it is heated. The oxidative stabilization step can be a time-consuming process (up to 100 hours). The objective of the inventions disclosed herein is to reduce the time required for processing the carbon foam by eliminating or replacing, or shortening, the oxidative stabilization step.
The inventions disclosed herein utilize solvated mesophase pitches which offer the potential for foaming at low temperatures, followed by carbonization at high temperatures without the need for stabilization. By using a solvated mesophase pitch, a carbon foam preform can be produced by the methods described in U.S. Pat. No. 6,077,464 and herein. Removal of the “solvent” fraction of the mesophase ensures that the mesophase pitch has a higher softening point (greater than 350° C.) than the onset temperature of carbonization (300-500° C.). Thus, the mesophase carbonizes before it can soften, thereby eliminating the requirement for stabilization.


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