Study On The Preparation And Characterization Of Microcoil Carbon Fiber

Materials with a 3D-helical/spiral-structure in micron size have recently aroused a great deal of interests. Among various 3D helical materials, microcoil carbon fiber is a major type of 3D helical carbon materials. Due to particular chiral conformations and the 3D-helical/spiral structure, it has unique combination of outstanding characteristics, such as super-elastic property, high electromagnetic waves absorption, high hydrogen absorption, etc, and thus can be used as micro-magnetic sensors, mechanical micro -springs, high elastic electric-conductors, etc. In the thesis, the preparation process of micro-coiled carbon fiber (MCCF) has been investigated, the morphology, microstructure of MCCF have been characterized. Research conclusions are obtained as follows:Author designs a suit of reaction apparatus, quartz tube is heated by electrically heating furnace. MCCFs have been successfully prepared by chemical vapor deposition method, using acetylene as carbon source, Ni powder as catalyst, hydrogen as carrier gas, and sulfur-containing compound (thiophene) as growth promoter, at 650℃-800℃. Preferable process parameters are decided with the endeavor of obtaining high yields and uniform diameter distribution of MCCFs, as followed: Ni powder as ascatalyst, reaction temperature 750℃, thiophene temperature 30℃, the ratio of H₂ to C₂H₂ 3:1, reaction time from 1.5 to 2h, graphite block setting vertically in the centre of quartz tube.The MCCFs generally have filmy forms macroscopically and the morphologies and microstructure of MCCFs are examined in detail through SEM observations, it is found that the products are pure MCCFs with the 3D-helical/spiral forms and with diameter of 3-6μm, length coil of 0.3-5mm, coil pitches of 0.6-0.9μm.The crystal structure features of MCCFs are studied by XRD and Raman. Research reveals that the interlayer spacing of MCCFs is larger than the spacing of normal graphite structure and turbostratic graphite structure, the microstructure is of poor degree of order, including a small quantity of amorphous carbon and crystal defects. After high temperature annealing(2500℃)of MCCFs were carried out, average grain dimensions of MCCFs grow larger, the content of crystalline carbon is clearly higher than the content of non crystalline carbon, and the crystallization degree of MCCFs is improved, air oxidation treatment can not only eliminate effectively noncrystal carbon,...