Carbon foam with improved graphitizability
A carbon foam material with improved graphitizability is formed by including a graphitization promoting additive into the carbon foam. The graphitization promoting additive greatly improves the graphitic structure of the carbon foam resulting in a carbon foam with much greater thermal and electrical conductivities. This inventive foam may be created by introducing the graphitization promoting additive during the catalysis of a phenol-aldehyde mixture to a form phenolic resin or during the conversion of the phenolic resin to a phenolic foam. Alternatively, the graphitization promoting additive can be fixed onto a preformed carbon foam.
1 . A method for preparing a graphitizable carbon foam, comprising:
a) catalyzing a phenol-aldehyde mixture to form a phenolic resin in the presence of a graphitization promoting additive,
b) producing a phenolic foam from the phenolic resin,
c) carbonizing the phenolic foam to create a carbon foam having a carbon lattice,
d) heating the carbon foam to a temperature sufficient to incorporate the graphitization promoting additive into the carbon lattice.
2 . The method of claim 1 wherein the graphitization promoting additive functions as a catalyst.
3 . The method of claim 1 wherein excess catalyst is neutralized by the graphitization promoting additive.
4 . The method of claim 1 wherein the graphitization promoting additive is reactively inert.
5 . The method of claim 1 wherein the graphitization promoting additive comprises a metal carbide, a metal oxide, iron, nickel, boron, and combinations thereof.
6 . The method of claim 5 wherein the graphitization promoting additive comprises boric acid.
7 . The method of claim 5 wherein the graphitization promoting additive comprises boron and is introduced in a solid state.
8 . The method of claim 7 wherein the solid-state boron is selected from the group consisting of boron powder, boron carbide, boric oxide, and combinations thereof.
9 . The method of claim 1 wherein the graphitization promoting additive is a polymer additive.
10 . The method of claim 9 wherein the polymer additive is selected from the group consisting of polyvinyl chloride, polyacenaphthylene, polyvinyl alcohol, polyamide, and combinations thereof.
11 . The method of claim 1 wherein the graphitization promoting additive comprises boron and the concentration of boron in the phenolic foam is from about 0.1% to about 1% by weight.
12 . The method of claim 1 wherein the graphitization promoting additive comprises boron and the concentration of boron in the carbon foam is from about 0.2% to about 2% by weight.
13 . The method of claim 1 wherein step d) comprises heating the carbon foam material to a temperature of from about 2000° C. to about 2600° C.
14 . A carbon foam comprising a graphitization promoting additive incorporated into the carbon foam's lattice structure, wherein the carbon foam has a density from about 0.03 g/cm 3 to about 0.6 g/cm 3 and a compressive strength of at least about 2000 psi.
15 . The foam of claim 14 that has a porosity of between 50% and about 95%.
16 . The foam of claim 14 wherein the cells of the carbon foam have, on average, an aspect ratio of between about 1.0 and about 1.5.
17 . The foam of claim 14 wherein at least about 95% of the cell volume of the cells has a diameter of between about 25 and about 95 microns.
18 . The foam of claim 14 wherein the carbon foam has a graphitization promoting additive content of from about 0.2% to about 2% by weight.
19 . The foam of claim 14 , wherein the graphitization promoting additive comprises boron.
20 . The foam of claim 19 wherein the concentration of boron in the carbon foam is from about 0.2% to about 2% by weight.