Abstract
Evolution of the radial distribution of a micro-crystalline structure within polyacrylonitrile monofilaments at various temperatures during carbonization was investigated via the method of synchrotron wide-angle X-ray diffraction (S-WAXD) and micro-scanning Raman spectroscopy. The result indicated that in the core region of the carbon fiber monofilaments, the Lc is lower while the interplanar spacing (d002) is higher compared with those in the skin region at 1300 °C. The difference between the skin and core regions in Lc and d002 constantly decreases as the heat treatment temperature increases. The results of micro-scanning Raman indicated that the micro-crystallites grow faster along the La direction, and the graphite degree is higher in the skin region than that in the core region. This is attributed to the fact that the removal of nitrogen element is the domain factor on the growth of a pseudo-graphite crystallite at relatively lower heat treatment temperatures. As the temperature rises, Lc is developed mainly in the core region with the closed packing of a graphite layer, while the crystallites in the skin region grow in both La and Lc directions, which are mainly affected by the disordered and boundary graphite structure.
Highlights
Polyacrylonitrile-based carbon bers (CFs) have been widely applied as a reinforcement in advanced composites due to their excellent performance.[1,2] compared with the ideal theoretical mechanical properties, carbon bers have rather relatively low tensile strength and modulus.[3]
Synchrotron wide-angle X-ray diffraction and Raman spectroscopy were applied to trace the evolution of the distribution of crystallite sizes and inter-planar spacing along the radial direction within CF mono laments
Synchrotron wide-angle X-ray diffraction (S-WAXD) experiments were performed at BL15U beamline at Shanghai Synchrotron Radiation Facility (SSRF)
Summary
Polyacrylonitrile-based carbon bers (CFs) have been widely applied as a reinforcement in advanced composites due to their excellent performance.[1,2] compared with the ideal theoretical mechanical properties, carbon bers have rather relatively low tensile strength and modulus.[3]. The mechanical properties of carbon ber were found to be strongly dependent on the radial structural distribution. As the temperature rises, the preferred orientations and crystallite sizes of the carbon ber increased accompanied by a growth in disorder and boundary carbon structure. According to the distribution of heat transferring, the growth rate of crystallites should be different in the radial direction of CF mono laments. Synchrotron wide-angle X-ray diffraction and Raman spectroscopy were applied to trace the evolution of the distribution of crystallite sizes and inter-planar spacing along the radial direction within CF mono laments. The mechanism of the formation and evolution of the heterogeneous radial structure was proposed to contribute to the theory of the relationship between the mechanical properties and structural heterogeneity of carbon bers
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