Annealing in the presence of boron

Boron has a smaller atomic radius than carbon and easily fits into the carbon lattice and can, for example, be found in the diamond lattice. The boron lowers the electrical resistivity and presumably acts as an electron acceptor site and, for valency reasons, some of the joins in 

Allen et al [130,131] showed that boron vapor increased the modulus and conductivity (Table 5.16) by increasing the crystallinity and helping to prevent shear in the crystallites. It is believed that the boron atoms hinder dislocation in the graphite lattice by a type of hardening process akin to the solid solution hardening effect in metallurgy. 

Fiber Type Boron (3 h at 2750X) % YM GPa TS GPa Extension % Resistivity cm 

Source Reprinted from Allen S, Cooper GA, Mayer RM, Paper presented at iP and PS Conference on Fibres and Composites, Brighton, Jun 1969. Reprinted with permission from Allen S, Cooper GA, Johnson DJ, Mayer RM, Carbon fibres of high modulus, Proc 3 Conf Industriai Carbons and Graphite, Soc Chem Ind, London, 456-461, 1970. Copyright 1976, The Society of Chemical Industry. 

Later work by FMI workers, Brewster, Nelson and Patton [134], showed that the boron deposits were confined to a surface layer on the fibers about 15mn thick, strengthening the fibers by healing surface defects such as holes and cracks. 

---