Young's modulus, thermal conductivity, electrical resistivity and coefficient of thermal expansion of mesophase pitch-based carbon fibers

摘要

Although there are several reported correlations among structural parameters, Young's modulus (E), thermal conductivity, electrical resistivity and coefficient of thermal expansion of carbon fibers in the longitudinal direction, a single physical model has not yet been established to explain quantitatively these properties. Here a model of continuous defective graphene nanoribbons (dGNR), which are arranged in stacks, is presented to predict a number of properties of mesophase pitch (MPP)-based carbon fibers in a single physical framework. Reported in situ tensile tests and other works support the assumption that, for MPP-based carbon fibers with E > 350 GPa, slightly misaligned perfect graphene regions of the dGNR are longitudinally in series with defective regions of an approximately constant length δ = 3 nm. The longitudinal properties of the dGNR depend strongly on the average longitudinal concentration of defective regions (x) of length 8, which can be estimated from the X-ray diffraction in-plane longitudinal coherence length (L_(a||)). The model was applied with success to high- and ultra-high-modulus commercial MPP-based carbon fibers; other fibers were also discussed. The values for the properties of the defective regions were determined and are consistent with the proposed model structure; relative values and scaling factors between properties were discussed.