The dependence of B retentivity on carbon crystallinity

Boron was doped into different carbon fiber reinforced carbon (CFRC) composites made of PAN-based carbon fibers and pitch-based carbon fabrics as the reinforcement and phenolic resin as the matrix, and the composites were heated at different temperatures (2000 and 2300 °C) to evaluate the preferential retentivity of B in carbon. The composites were chosen to create a competitive situation with different crystallinity unlike in one carbon sample with the same crystallinity. It was found that the retentivity is higher in the order of phenolic resin, PAN-based carbon fibers and pitch-based carbon fabrics, that is the exactly overturn of the order of initial crystallinity. B retentivity was also higher at 2000 °C than at 2400 °C; it seems to be B atoms at 2000 °C are located both substitutionally and interstitially. Due to the different retentivity of carbon, crystallinity of the composites was changed accordingly.