为优化PAN基碳纤维结构,采用AES表征PAN纤维在低温碳化与高温碳化后C,N,O沿纤维径向的分布,并用以阐明预氧化碳化过程径向差异的形成机理.结果表明：预氧丝径向结构不均匀,由外向内氧化程度降低;预氧时物理阻隔与化学阻隔导致径向形成氧浓度梯度,热物理传递与化学反应放热导致径向形成温度梯度.低温碳化时,热物理传递与化学反应放热形成温度梯度加剧了预氧时的径向差异;纤维分3部分,最外层氧含量低,由氧化程度高的预氧皮层外部强烈脱氮脱氧形成,最内层由氧化程度低的预氧芯层转化而成;中间是过渡层,一部分由氧化程度较高的预氧皮层内部少量脱氧脱氮而成,氧含量高,而后过渡到预氧程度低的低含氧量芯部.高碳丝径向组分差异变小,纤维分两部分,外层厚度仅为纤维直径的10%,是碳含量逐渐降低的过渡性皮层,其余部分为组成均一的芯层.
To optimize the structure of PAN-based carbon fiber,PAN fiber was stabilized and carbonized at different temperature,optics microscope and Auger Electron Spectroscopy（AES） were applied to character the radial heterogeneity structure of resulted fibers.The result shows that,the radial structure is non-uniformity in stabilized fibers;the thickness of skin part is one-third of fiber′s diameter.Skin part is darker than the core and contains more oxygen.After low-temperature carbonization,along the direction of radius,fibers can be divided into three parts：the outer part that is 1 μm-thick and contains 95% carbon atoms formed by the intense denitrogenation and deoxidization reaction in the skin part of stabilized fibers,the inner part with less oxygen caused by the core part of stabilized fibers,and the middle part that is a transition part,of which the content of oxygen firstly increases with increasing depth,and then decreases.During high temperature carbonization process,the fiber contains two distinct parts,the outer part with higher carbon content is about 10% of the diameter while the inner part contains about 1.7% nitrogen atoms and less than 0.6% oxygen.
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