Conventional carbonization employs a thermal pyrolysis process that is slow and energy and space intensive. This microwave-assisted plasma (MAP) carbonization approach is based upon a discovery that microwave energy likely could be used to rapidly convert previously oxidized polyacrylonitrile, or PAN, precursor fibers into finished carbon fibers while potentially reducing energy usage substantially. Early in the project, researchers determined that the best approach involved using a combination of single-frequency microwaves and plasma to carbonize and graphitize oxidized PAN fibers. Using the modeling along with materials and processing data experiments, the team essentially optimized the original MAP process for accomplishing both low- and high-temperature carbonization processes (in conventional thermal processing, these tow processes typically are performed in discrete steps in totally separate furnaces) for up to five tows to about 60 in./min. The team has demonstrated the process' capability to operate for extended periods of time. It is believed a key inherent advantage of the MAP process is the ability to stop and start rapidly, although its greatest efficiencies stem from continuous operations.
Current hardware can fully carbonize up to five tows continuously at a residence time significantly shorter than for conventional furnaces while achieving comparable properties.
The MAP process is truly unique in that both low- and high-temperature carbonization can be accomplished in a single chamber with both a smaller footprint and residence time than for conventional carbonization. The process also affords the added advantage of rapid shutdown and start times because of minimal thermal inertia.
ORNL has demonstrated that advanced carbonization technology is capable of meeting the targets for scaling to the 25-ton-per-year (Carbon Fiber Technology Facility) production level. Specifications have been drafted and can be shared with interested parties. Current hardware can be used for experimental and demonstration purposes under a variety of customer agreements.