Microcellular carbon foam and method

A microcellular carbon foam of a density in the range of about 30-1000 mg/cm.sup.2 and open porosity provided by well interconnected strut morphology produced by a method comprising the steps of:

• a) dissolving polyacrylonitrile in a heated solution consisting essentially of at least one alkali metal halide and a solvent for the dissolution of the polyacrylonitrile in the heated solution and the phase inversion of the dissolved polyacrylonitrile to a liquid gel upon sufficient cooling of the heated solution, said solvent being selected from the group consisting of propylene carbonate, tetramethylene sulfone, gamma-butyrolactone, and mixtures thereof, said heated solution of a solvent and at least one alkali metal halide containing the polyacrylonitrile consisting essentially of about 0.75 to about 30 wt. % polyacrylonitrile, about 68 to about 97 wt. % solvent, and a sufficient concentration of at least one alkali metal halide to promote solubilization and the unraveling of molecules of polyacrylonitrile in solution and maintain these molecules in extended positions to promote a firm gel, an interconnected strut formation and an expanded d(002) X-ray turbostatic spacing during the formation of the gel by phase inversion;
• b) placing the heated solution including the dissolved polyacrylonitrile in containment means provided with one of a nucleating promoting means and a relatively smooth surface;
• c) sufficiently cooling the heated solution in the containment means to form a liquid gel of the polyacrylonitrile by phase inversion;
• d) removing the solvent and substantially all of the dissolved alkali metal halide from the gel to provide a porous foam consisting essentially of polyacrylonitrile;
• e) removing the residual solvent under vacuum;
• f) cross linking the dry polyacrylonitrile foam at an elevated temperature;
• g) curing the porous foam at an elevated temperature in an oxygen containing environment;
• and
• h) heating the porous foam in an inert atmosphere to a temperature sufficient to carbonize the polyacrylonitrile forming the porous foam to provide the microcellular carbon foam, said temperature being of less than about 1200.degree. C. through a series of sequential heating stages at preselected heating rates with a soak period of a selected duration after selected heating stages.

A microcellular graphite foam of a density in the range of about 30-1000 mg/cm.sup.2 and open porosity provided by well interconnected strut morphology produced by a method comprising the steps of:

• a) dissolving polyacrylonitrile in a heated solution consisting essentially of at least one alkali metal halide and a solvent for the dissolution of the polyacrylonitrile in the heated solution and the phase inversion of the dissolved polyacrylonitrile to a liquid gel upon sufficient cooling of the heated solution, said solvent being selected from the group consisting of propylene carbonate, tetramethylene sulfone, gamma-butyrolactone, and mixtures thereof, said heated solution of a solvent and at least one alkali metal halide containing the polyacrylonitrile consisting essentially of about 0.75 to about 30 wt. % polyacrylonitrile, about 68 to about 97 wt. % solvent, and a sufficient concentration of at least one alkali metal halide to promote solubilization and the unraveling of molecules of polyacrylonitrile in solution and maintain these molecules in extended positions to promote a firm gel, an interconnected strut formation and an expanded d(002) X-ray turbostatic spacing during the formation of the gel by phase inversion;
• b) placing the heated solution including the dissolved polyacrylonitrile in containment means provided with one of a nucleating promoting means and a relatively smooth surface;
• c) sufficiently cooling the heated solution in the containment means to form a liquid gel of the polyacrylonitrile by phase inversion;
• d) removing the solvent and substantially all of the dissolved alkali metal halide from the gel to provide a porous foam consisting essentially of polyacrylonitrile;
• e) removing the residual solvent under vacuum;
• f) cross linking the dry polyacrylonitrile foam at an elevated temperature;
• g) curing the porous foam at an elevated temperature in an oxygen containing environment;
• h) heating the porous foam in an inert atmosphere to a temperature sufficient to carbonize the polyacrylonitrile forming the porous foam to provide the microcellular carbon foam, said temperature being of less than about 1200.degree. C. through a series of sequential heating stages at preselected heating rates with a soak period of a selected duration after selected heating stages;
• and
• i) heating the carbonized microcellular foam in an inert atmosphere to a temperature in the range of about 2400.degree. to about 3000.degree. C. for converting the carbon foam to a foam containing a graphite phase.