Effect of the oxygen-induced modification of polyacrylonitrile fibers during thermal-oxidative stabilization on the radial microcrystalline structure of the resulting carbon fibers

Amorphous carbon fiber from polyamide 6 (PA6) precursor was produced using a multi-step procedure consisting of oxidative stabilization in air at 180℃ in the presence of cupric chloride impregnation, pre-carbonization at 250℃ and carbonization at temperatures ranging from 500℃ to 1000℃ in nitrogen. The results obtained from thermal analysis data suggested that cupric chloride impregnation enhanced thermal stability. During the oxidative stabilization process, a polymorphic structure consisting of α- and γ-phases was eliminated due to the decrystallization process. The pre-carbonization step was found to be necessary to enhance the thermal stability of oxidatively stabilized PA6 fiber prior to carbonization. The results suggested that the pre-carbonization step improved the aromatization and crosslinking reactions. The results obtained from the experimental data suggested that the carbonization temperature had an effective role on the molecular structure and properties of the resulting carbon fibers. The carbon fibers obtained from stabilized and pre-carbonized PA6 fibers showed physical and structural changes with rising temperature. They were characterized by a reduction in fiber diameter, linear density, carbon fiber yield, hydrogen and nitrogen content values due to the removal of non-carbon elements together with increases in the values of density, crystallite thickness, carbon content, C/H ratio and electrical conductivity values. The results obtained from X-ray diffraction, IR spectroscopy and elemental analysis suggested that the crystalline structure was totally lost and converted to a carbonized structure at 500℃ and above due to the formation of an amorphous carbon structure during carbonization reactions.

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Study on the Electric Properties of Carbon Fibers and its Application for the Preparation of Carbon/Carbon Composites

Materials Science Forum ◽

10.4028/www.scientific.net/msf.809-810.707 ◽

2014 ◽

Vol 809-810 ◽

pp. 707-710

Author(s):

Xian Feng Xu ◽

Ling Zhi Chai ◽

Hui Li ◽

Ling Sheng Zeng

Keyword(s):

Carbon Fibers ◽

Gas Flow ◽

Chemical Vapor ◽

Deposition Process ◽

Electric Properties ◽

Carbon Composites ◽

Microcrystalline Structure ◽

Initial Voltage ◽

Growth Center ◽

The Relationship

Acetylene (C2H2) was used as carbon source gas, nitrogen (N2) as dilution gas. The electric properties of carbon fibers was briefly discussed by energizing the carbon fibers in vacuum condition which were applied for the preparation of carbon/carbon composites by the method of chemical vapor deposition. The deposition mechanism and microstructure of pyrolytic carbons in carbon fibers under different deposition crafts were also discussed. Results indicate that the greater the initial voltage, the higher the temperature, we can change the deposition temperature by changing the initial voltage according to the relationship between the brightness and the surface temperature of carbon fibers. The surface of carbon fibers will be etched in the process of electrifying which would make the pyrolytic carbons preferred deposition on the etching point which became the growth center in the early deposition process. The pyrolytic carbons deposited with a spherical microcrystalline structure under the gas flow of C3H6/N2=2:3, When the rate of gas flow is C3H6/N2=1:2, The pyrolytic carbons deposited with a spherical microcrystalline structure after deposited for 0.5h, but after deposited for 1h, the deposition of large patches of molecular is dominant which lead to that: from a macro perspective, the pyrolytic carbons were a layered structure, From a microscopic perspective, they were a spherical microcrystalline structure with different size.

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