Mechanism of formation of the texture and microtexture in as-spun then oxidized anisotropic pitch-based carbon fibers, part I: Radial with wedge type i1

Abstract

An anisotropic pitch made of a mixture of isotropic phase 1 (containing BT mesophase spheres) and a two-phase-disperse system 2.3 (edge-to-edge type of gel) was used for spinning fibers (radial with wedge type I1). The as-spun, then oxidized fibers were studied by optical microscopy (OM) and transmission electron microscopy (TEM). The sample preparation technique was thin sectioning (cross, oblique and longitudinal) for TEM and thin-sectioning residues for OM. The microtexture of a fiber is that of an edge-to-edge type of gel elongated uniaxially by spinning. The structure finally obtained is highly ordered. It is a combination of two orthogonal orientations of the aromatic layers. A dominant radial texture 2 (containing radial aromatic layers) is constantly prolonged parallel to the fiber axis. It is associated to sinuous channels 3, running radially in the fiber cross-sections. Inside them, the aromatic layer orientation is concentric. The sinuous channels themselves are constantly prolonged along the fiber axis as dotted slits, with well-aligned dots. The isotropic phase of the initial pitch is elongated as fibrils 1. A central pole is occupied by another fibril 1. The other fibrils are increasingly deformed when approaching the periphery of the fiber.