This program has demonstrated that wood, a composite structure with highly aligned cellulose fibers, can be converted in a highly controlled thermal process to a carbon material that retains the morphology of the cell structure present in the wood. The cellulose fibers are essentially converted to carbon fibers yielding a carbon with directional properties. The porous carbon monolith can then be shaped by conventional methods. The shaped carbon can then be converted to carbon/polymer composites, carbon/carbon composites, ceramics and ceramic composites. This technology has demonstrated the potential for elimination of several expensive processing steps as well as the cost of buying the carbon fibers. Specifically, no fiber lay-up or powder consolidation is required, and the final machining steps are minimized.

Results from wood carbonization characterization using thermal analy sis, density measurements, x-ray diffraction, and monitoring dimensional and acoustic velocity changes were presented. These data were used to identify the conditions under which wood can be carbonized without forming macro-defects. Mechanical test results were presented which demonstrated that carbonized tulip poplar (Liriodendron tulipifera) was 30% stronger than the precursor wood, and a carbon/polymer composite was 250% stronger than the precursor wood.

Among the characterization tools used in this study, nondestructive techniques played an integral role. In particular, x-ray radiography was shown to be instrumental in the evaluation of polymer infiltration and ceramic conversion uniformity. Ultrasonic evaluation provided insight into the effects of thermal treatment on carbonized wood characteristics. While these techniques were performed ex-situ, it is anticipated that in future work real-time nondestructive monitoring of critical process parameters will speed the development of this unique materials manufacturing approach.

As a first demonstration of this technology, Johns Hopkins University and Rotordynarnics-Seal Research (RSR), a small business located in North Highlands, California, recently completed a Phase I STTR (small business technology transfer) project, where it was demonstrated that a net shape silicon carbide race could be produced from carbonized wood. This silicon carbide race was successfully tested with a silicon nitride ball bearing by RSR. The Phase 2 follow-on contract has been approved pending matching funding where further optimization of the processing and testing of the bearing system will be done.