TEM study on the inhomogeneity of oxygen diffusion distances in single polyacrylonitrile-based carbon fibers

Abstract

Accurate measurement of oxygen diffusion distances (ODDs) is important but difficult in the production of polyacrylonitrile (PAN)-based carbon fibers. Traditionally, the ODDs were deemed to be homogeneous in a single fiber and paid no attention. Herein, the skin widths of carbon fibers with the skin-core structure were proposed to assess the ODDs, and the ODDs were investigated by transmission electron microscopy. The ODDs were first found to be homogeneous for the commercially noncircular carbon fibers, while they were uniform in every direction for the circular single carbon fibers. The inhomogeneity of the ODDs was unrelated to the surface and cross-sectional morphologies of carbon fibers, and it was considered to result from the density difference at the edge of a single PAN precursor fiber. These findings not only deepen the understanding of the effect of the PAN precursor fiber shapes on the oxygen diffusion during stabilization, but also provide an opportunity for optimizing the stabilization conditions according to the density difference at the edges of single PAN precursor fibers.