Molded carbon-carbon composites based on microcomposite technology

A one-step, cost-effective processing methodology based on compression molding of a mixture of graphite particles and short fibers, both coated with a soluble polyimide adhesive was developed. This technique shows a considerable potential in decreasing the complexity of the current carbon-carbon fabrication procedures. The new process eliminates additional infiltration and densification steps following the initial carbonization, which reduces the processing time from 5 weeks to 3-5 days and saves energy. The structure and properties of the new carbon-carbon composites were characterized using optical and electronic microscopy, thermal analysis, density and porosity measurements, and mechanical properties (hardness and flexural strength). The flexural strengths ranged from 20-45 MPa. The densities ranged from 1.9 to 2.2 g/cc (which is close to pure graphite) while the porosity was as low as 3%. The CTE was approximately +/- 1 ppm/degrees C (R.T. to 550 degrees C). The thermal stability of the carbonized and graphitized specimens when heated in flowing air up to 500 degrees C and flowing nitrogen up to 1000 degrees C showed no observable weight loss. There are numerous applications for these materials which include: optical mirrors, medical implants, thermal radiators and parts for rotating equipment, etc. A car piston was successfully molded using a mixture of polymer coated graphite powder, flakes and chopped fibers.