Core carbon effective radius

The transverse radius of curvature of the graphene layers, n, increases from the core of a fiber to its surface, and graphene sheets near the fiber surface usually lie parallel to it. This structure is the cause of the notable skin/core effect and the low reactivity of the fiber surface. The reactivity of aromatic carbons is lower in-plane than at the layer edge. The turbostratic character of carbon in PAN based HM carbon fibers and the occurrence of elongated pores explain their low density (1.8-1.9 g/cm ). 

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