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US 6,576,168 B2Granted
Process for making carbon foam induced by process depressurization
AssigneePoco Graphite, Inc.
InventorsLeland A. Hardcastle, Rex G. Sheppard, David F. Dingus
Life of this patent
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Abstract
A process for producing molded pitch based foam is shown which provides a more uniform density gradient throughout the ultimate product. The process utilizes a pressure drop during processing in order to induce foaming. By inducing foaming through process depressurization, additional viscosity manipulation can be achieved as well as improved density gradient characteristics in the ultimate product.
Claims21
A method of producing carbon foam, comprising the steps of:
- introducing a solid pitch to an appropriate level in a mold which is placed within a reaction vessel, the initially solid pitch, once melted to a liquid, having a characteristic boiling or foaming point at a given pressure and for a given temperature;
- purging air from the reaction vessel;
- pressurizing the reaction vessel between a preselected high initial pressure and a final process pressure, the preselected high initial pressure serving to increase the temperature at which the pitch would normally boil in the reaction vessel after being liquified by heating;
- wherein the pitch has a given solidification point with continued heating after being heated to liquid and wherein the pitch is heated to liquid within the reaction vessel to a selected temperature which is below the solidification point and above the boiling point of the pitch at the final process pressure but below the boiling point of the pitch at the preselected high initial pressure;
- holding the liquid pitch at the selected temperature for a predetermined period of time to increase the viscosity of the liquid pitch;
- depressurizing the pitch from the high initial pressure to the final process pressure while maintaining the process temperature above the typical boiling or foaming temperature at the final pressure, whereby boiling and foaming of the pitch begins;
- heating the foamed pitch to a temperature that solidifies the foamed pitch;
- cooling the solidified foamed pitch to room temperature while allowing natural depressurization during cooling to thereby produce a carbon foam.
5 more elements
A method of producing carbon foam, comprising the steps of:
- selecting an appropriate mold shape;
- introducing an initially solid pitch to an appropriate level in the mold, the initially solid pitch, once melted to a liquid, having a characteristic boiling or foaming point at a given pressure and for a given temperature;
- desiccating the pitch to assist in removing any residual moisture;
- placing the mold within a hot isostatic press and purging air from the press and from the mold;
- pressurizing the hot isostatic press between a preselected high initial pressure and a final process pressure, the preselected high initial pressure serving to increase the temperature at which the pitch would normally boil in the hot isostatic press after being liquified by heating;
- wherein the pitch has a given solidification point with continued heating after being heated to liquid and wherein the pitch is heated to liquid within the hot isostatic press to a selected temperature which is below the solidification point and above the boiling point of the pitch at the final process pressure but below the boiling point of the pitch at the preselected high initial pressure;
- holding the liquid pitch at the selected temperature for a predetermined time to increase the viscosity of the liquid pitch;
- depressurizing the pitch from the high initial pressure to the final process pressure while maintaining the process temperature above the typical boiling or foaming temperature at the final pressure, whereby boiling and foaming of the pitch begins;
- heating the foamed pitch to a temperature that solidifies the foamed pitch;
- cooling the solidified foamed pitch to room temperature while allowing natural depressurization during cooling to thereby produce a carbon foam;
- depressurizing the carbon foam to atmospheric pressure;
- and
- removing the carbon foam from the hot isostatic press and from the mold.
10 more elements
Dependencies are inferred from the claim text.