利用广角(WAXD)和小角散射(SAXS)的方法,对PAN基炭纤维制备过程不同阶段纤维的微晶和微孔进行研究.WAXD结果表明,在炭化过程中,微晶尺寸变大,并沿着纤维轴方向取向.SAXS结果表明,制备过程过,新微孔进一步形成,微孔逐渐沿纤维轴排列,微孔的平均长度增大.基于传统分析方法,确立微孔为具有择优取向的圆柱状,其尺寸大小成log正态函数分布的散射模型,对二维散射图进行全谱拟合分析.将此方法运用于炭纤维,得出该模型可以准确描述微孔的相关特征.
Microstructural evolution in polyacrylonitrile (PAN) fibers at different temperatures during pre-oxidation and carbonization under stretching was studied by synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS).Microvoids were characterized by the classical SAXS method, and were compared with simulation results obtained by fitting 2D SAXS patterns to a model based on a dilute system of cylindrical microvoids randomly distributed and preferentially orientated along the fiber axis and having a log-normal size distribution.The WAXD results showed that the crystal size, d-spacing and preferred orientation decreased during pre-oxidation, and increased during carbonization.A diffraction peak for PAN fibers at 2θ=13.6° disappeared during the final stage of pre-oxidation, meanwhile a new peak at 2θ=23.6° appeared, whose intensity increased during carbonization, indicating the formation of the graphite structure.The average length of the microvoids increased, and new microvoids were formed, which became oriented along the fiber axis as the fiber manufacturing process proceeded.The length of microvoids from simulation results is consistent with that from the classical method, indicating that the model is valid to describe the microvoid structure of fibers.
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