In this chapter a series of electrochemically oxidized CF samples are produced using a commercial grade PAN precursor fibre and characterized using SEM, XPS, FT-IR and Raman spectroscopy. The application of the Raman spectroscopic techniques developed and demonstrated through the previous chapters, namely mapping and SERS, to this series of CF samples are given as examples of the potential to extend the use of these techniques to commercial CF.
The previous chapters of this thesis have demonstrated that Raman spectroscopy can be used in different ways to characterize CFs. Chapter 3 concentrated on the application of Raman mapping to investigate the heterogeneity of laboratory oxidized CF samples. The natural extension to that work is to apply the technique to CFs that have under gone surface oxidation in an environment more akin to commercial practice. The ability to access the Carbon Nexus facility to generate a series of CFs on a single tow line that replicates the main carbon fibre manufacturing line gives a unique opportunity to generate a customized set of CF samples of a commercial grade.
The use of SERS to detect the presence of size on the CF surface has proved challenging to date due to an Ag catalyzed degradation of the thin layer of size. However, the analysis of oxidized CF, with no size applied, using SERS has the potential to detect changes in the near surface of the CF. Previous work by Ishida et al. and Tadayyoni and Dando concluded that SERS detected more disorder in the near surface of graphite fibre compared to the spectra obtained using conventional Raman spectroscopy. Xu and Lu used SERS to compare CF before and after nitric acid oxidation as well as after reaction with maleic anhydride. Interpretation of their results however is complicated by insufficient information regarding the process utilized for the application of the Ag colloids as well as the potential Ag catalyzed degradation of species on the surface. SERS does not appear to have been widely utilized for the analysis of oxidized CF. Results from conventional Raman spectroscopy has suggested that oxidation with nitric acid results in a reduction in the amorphous carbon in conjunction with a sharpening of D and G bands and an increase in the D/G intensity ratio.
Similar results were obtained in this research as discussed in Chapter 3 in terms of a reduction in amorphous carbon; however no significant variation was observed in the D/G ratios and any apparent sharpening of D and G bands was attributed to the reduction in the A band. Others have concluded that no changes in the position or widths of the D and G bands occur with plasma surface treatment HM CF in contrast to Cuesta et al. that found a widening of D and G bands after plasma treatment. Both research groups did however conclude that an increase in the D/G ratio was observed after treatment. Variations in results are likely a combination of different CF samples and differences in the oxidation treatments
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