Properties of graphitized carbon fiber-halogen residue compounds

Br 2 or ICl residue compound formation in TP 4104B and GY-70 fibers increases their electrical conductivity 3–5 times. It also decreases the tensile strength of the GY-70 fibers by increasing their cross-sectional area. In contrast, the tensile strength of the TP 4104B fiber remains unchanged on Br 2 or ICl residue compound formation. The TP 4104B/Br 2 residue compound loses only 1–2% of its weight and increases its resistance by only 5–10% when heated to 400°C in air; the ICl residue compounds of both fibers are unstable above 150°C. The temperature coefficient of resistivity of the unintercalated fibers (in the range 2–673 K) is attributed to a temperature dependent variation in the number of current carriers in the intercrystalline regions of the fibers and not to a finite resistance percolation path through the graphite crystallites. The magnetoresistance of the fibers from 2–200 K is attributed to a large resistance increase within the graphite crystallites. Both the temperature coefficient of resistivity and the magnetoresistance of the residue compounds are consistent with a metallic-like electron structure. The preparation of bromine residue compounds of individual TP 4104B fibers that had different bromine concentrations was not successful; fibers either intercalated Br 2 and formed the “full” residue compound or remained unintercalated.