Synthesis and characterisation of carbon nanotubes grown on silica fibres by injection CVD

Carbon nanotube grafted primary reinforcing fibres are under development for a new generation of hierarchical composites. Pure and nitrogen-doped multi-walled carbon nanotubes (MWCNTs) were grown on silica fibres using the injection chemical vapour deposition method. The morphology and size of the nanotubes were controlled by varying the growth time. The surface structure of the silica fibres after the grafting process was studied by electron microscopy following focused ion beam sectioning; the images confirmed a base growth mechanism and a shallow iron-rich layer. Thermogravimetric analysis indicated a shorter induction period and a faster growth rate for pure rather than nitrogen-doped MWCNTs. Raman characterisation of the grafted MWCNTs showed a decreasing intensity ratio of the D to G modes, moving from the tip to base in both cases; a detailed comparison of different characteristic Raman ratios is provided, using both the peak intensity and the area for the D, G, and G′ signals.