Preparation And Properties Of Helical Carbon Nano-fibers

The helical carbon nano-fibers(HCNFs) as a novel carbon materials have the outstanding performance of low-density, high intensity, anti-temperature, corrosion resistant, wear rubbing and conductive ability. Furthermore, they have the wide applications in many fields such as microwave absorbent, composite, hydrogen storage, catalyst support due to their unique helical structure which make them possess excellent mechanical properties, elecctromagnetic performance and optical properties. In this thesis, the HCNFs were prepared by chemical vapor deposition (CVD) method, and electromagnetic properties and mechanical properties were carried out. Main content are as follows:In this paper, HCNFs were successfully prepared by CVD using nickel powder as catalyst, acetylene as carbon source, hydrogen as carrier gas and thiophene as growth promoter. The topography and micro-structure of single HCNFs, the double HCNFs were characterized by SEM, Raman and XRD. The double HCNFs had two typical carbon fiber structure: the flat shape and circular shape of cross-section in the fibers.The electromagnetic performance of HCNFs were measured in the frequency range of 8.2～12.4GHz. The research results on the electromagnetic properties of the HCNFs and HCNFs /nickel powder composite demonstrated that the electromagnetic performance had not been improved by the addition of nickel powder. The HCNFs were grown on different substrates such as nickel slice, nickel foam and SiC foam, and the electromagnetic properties of the several composites (substrate/ HCNFs) were studied. The effect of aperture size on electromagnetic performance of nickel foam/ HCNFs composites, the growth time on electromagnetic performance of SiC foam/ HCNFs composites were carried out respectively.In addition, due to ideal mechanical property of the HCNFs, preparation and property of the HCNFs /polyvinyl alcohol (PVA) composite materials were studied. First of all, the as-prepared HCNFs were purified by oxidation treatment, the purified product was characterized by SEM and EDS. The effect of the content of the HCNFs on the extension strength of composite was researched, and the results show that the extreme value of extension strength of composite was obtained as the content of helical carbon in matrix is 0.4%. Furthermore, the dispersion of the HCNFs in the matrix were characterized by SEM on fracture section of composite.