用径向分布函数法对三种不可石墨化碳结构的研究

STRUCTURAL STUDY OF THREE KINDS OF NONGRAPHITIZED CARBON BY USE OF RADIAL DISTRIBUTION FUNCTION METHOD

本文应用广角X射线散射径向分布函数(RDF)法对三种典型的不可石墨化碳的结构及其随温度的转化进行了研究。在使用“去负法”对RDF进行截尾效应校正时,对Kaplow等的方法作了修正,发展成为“小r区降零过正法”,由自编的计算程序得到了不可石墨化碳的RDF,结果较为满意。由RDF曲线取得的基本结构参数是表征不可石墨化碳结构带本质性的基本数据。研究表明,在被测定的三种不可石墨化碳中,除主要为sp^2杂化键的石墨层片结构外,还存在着显著含量的sp^3杂化轨道碳一碳键。这说明,具有四面体结构的碳一碳交联键将芳香结构的层片状分子彼此联接,以及这些碳原子以层片内部缺陷处的sp^3杂化的间隙原子形式,存在于这三种不可石墨化碳中。其中,聚丙烯腈(PAN)基碳纤维在原子空间排布上受到原丝纺丝过程中拉伸张力的影响,而碳黑则受缺陷原子及层面皱折的制约,玻璃碳则由于乱带型碳网骨架的存在,形成了多微孔、低密度的结构特征。

This paper deals with the structure and its change due to heat treatment of three kinds of typical non-graphitized carbon, namely, pAN-based carbon fiber, carbon black and glassy carbon, by use of radial distribution function (RDF) in wide-angle X-ray scattering. Negative cut-off correction for termination error in RDF is modified, and 'zero-replacement in small r region and positive-setting' method is developed. Satisfactory results are obtained by use of the self-compiled computer program. It is demonstrated that the structural parameters obtained from RDF curve provide some essential criteria for the characterization of non-graphitized carbon.From our results it is indicated that the carbon—carbon bonds in the three kinds of non-graphitized carbon are mainly of sp^2 hybridized bonds as well as sp^3 hybridized bonds with considerable amount of carbon atoms. It is suggested that the carbon—carbon bonds with tetrahedral type cross-linkages are covalently linked with laminar layer molecule of aroma structure, as well as the interstitial atoms with sp^3 hybridized bonds and strain within aromatic nuclei is also extended over these kinds of nongraphitized carbon. In conclusion, the structure of pAN-based carbon fiber is governed by the fibril structure of the original pAN fiber and the tensile force in spinning operation. The structure of carbon black is confined by the defect atoms and lamellar wrinkling, and the glassy carbon is characterized by its multimicro-pores and low density due to the existence of the random ribbon-like carbon network.