PAN基碳纤维在表面处理中的拉曼光谱研究

采用激光拉曼光谱研究了PAN基碳纤维在表面处理中的微结构变化，分析了表面处理前后碳纤维的一级拉曼光谱特性。结果表明：拉曼光谱中主要的D峰和G峰的拉曼频移、半高宽以及各个不同拉曼频移位置对应肩峰的积分面积比是表征碳纤维物相结构变化的重要参数。经过不同的表面处理，PAN基碳纤维的一级拉曼光谱参数发生了一定程度变化，D峰和G峰的拉曼峰位向高波数偏移，表征石墨微晶尺寸的R值有所提高，这说明在表面处理后碳纤维的石墨微结构受到刻蚀，微晶尺寸有所减小，石墨微晶的边界活性增大；此外，表征碳纤维结构有序程度和缺陷多少的D峰和G峰的半高宽均有减小，表征无定型碳结构或某种有机官能团的A峰和D″峰的相对积分面积减小，这说明与乱层石墨结构相比，碳纤维中存在的无定型碳结构更容易被刻蚀，经过表面处理之后无定型碳的物相比例减小，这与碳纤维XRD图谱中表观结晶度提高的规律相一致。因此，利用激光拉曼光谱可研究碳纤维物相结构的变化规律。

Raman Spectra of PAN-Based Carbon Fibers during Surface Treatment

Laser Raman spectroscopy was employed to characterize the microstructure changes of PAN based carbon fibers among different surface treatments, and the characteristics of first-order Raman spectra of carbon fibers during surface treatment were investigated in the present paper. The results show that the variety of carbon fibers’ phase structures can be represented by Raman spectroscopy parameters, such as the Raman frequency shifts of main D and G bands, FWHMs and additive bands’ area ratios at the positions of different Raman frequency shifts. During different surface treatment, some changes in the first-order Raman spectroscopy parameters of PAN based carbon fibers were observed, the Raman frequency shifts of D and G bands moved toward higher wavenumber, and the values of R(I_D/I_G) also improved, which can be used to measure the graphite crystallite size of carbon fiber. It is suggested that the graphite microstructure of carbon fibers is decomposed during surface treatment, the crystallite size is reduced, and the activity of the graphite crystallite boundary is improved. Moreover, the full-widths at half maximum (FWHM) of D and G bands both decrease, which can give information on the order of graphite microstructure and the quantity of defects in carbon fibers, and the relative bands’ areas of A and D″ bands also decrease, which can be attributed to the structure of amorphous carbon or some kinds of organic functional groups in carbon fibers. These differences among the spectra demonstrate that the structure of amorphous carbon in carbon fibers is easier to oxidize or decompose than multilayer graphite structure, so the relative proportion of amorphous carbon decreases during surface treatment. The conclusions obtained by Raman spectra are basically in agreement with the improvement of apparent crystallization degrees of carbon fibers during surface treatment, which were calculated by X-ray diffraction method. So the variety rules of carbon fibers’ phase structures can be investigated by laser Raman spectroscopy.