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Preparation of Nano Carbon Fibers and Porous Carbon Fibers and the Research on Their Radar Absorbing Properties

Author: ZhangLiang
Tutor: LiGuang
School: Donghua University
Course: Materials Science
Keywords: Carbon Nanofibers Porous carbon fibers Composites Microwave absorbing Polymer blends
CLC: TQ340.7
Type: Master's thesis
Year: 2010
Downloads: 266
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Abstract

Weaponry, stealth technology has become an important means to enhance defense and strike capability in modern warfare, and radar absorbing stealth materials is one of the keys of the stealth technology. The carbon material is absorbing materials has been the development of the most promising absorbing materials best overall performance, not only absorbing, and can enhance, can be used as a structural radar absorbing materials. Therefore, the development of different forms of carbon materials research as absorbents filled to composite resin prepared absorbing performance has important theoretical significance and application value. Paper selected polyacrylonitrile (PAN) as a carbon precursor polymer, poly (methyl methacrylate) (PMMA) is the thermal decomposition polymer, prepared by two co-dissolved in dimethylformamide (DMF) of PAN / PMMA Blends solution. Using wet molding prepared PAN / PMMA blend fibers, PMMA component was prepared nano carbon fibers and a porous carbon fibers are removed after pre-oxidation and carbonization. Microwave absorbing properties to add them to the epoxy resin in the composite material. The main work includes the following aspects: strain-controlled dynamic rheometer dynamic rheological properties of PAN / PMMA blend solution, when the PAN molecular weight, molecular weight 50000 (PAN5) and a molecular weight of 80,000 (PAN8 ), blend solution logG 'with logω relationship presents a different change, that PAN5/PMMA the logG' performance in the low range of frequency ω out of the obvious deviations logG'α2logω the relationship, while PAN8/PMMA basic linear relationship Description PAN5/PMMA blend solution presents obvious non-uniform structure. This is consistent with the results obtained for both stability of the blend solution observed PAN5/PMMA solution was allowed to stand for 12-24 hours delamination, while PAN8/PMMA blend solution distinct layers in the same standing time. The blend solution cast film formation, the sectional morphology of the film was observed by SEM. The results showed that the PAN and PMMA blends showed a respective phase structure, the percentage of high quality components tend to form a continuous phase. When PAN molecular weight increase, the size of dispersed phase is significantly reduced. Prepared by wet spinning mass percentage of 3:7 and 7:3 PAN / PMMA blend fibers. In the fibers, the two-phase distribution is different, i.e., when the PAN molecular weight of 80 000, showing the same phase distribution of the blend film; while when the molecular weight of 50,000 PAN, PAN tend to forming the continuous phase structure. Spinning speed and drafting multiple possible to control the size of the dispersed phase of the blend fibers. PAN / PMMA blend fiber raw yarn after the pre-oxidized and carbonized, and the dispersed state of the phase of the morphology of the resulting carbon fiber and the original yarn of the PAN. PAN as the continuous phase of the original wire, corresponding to obtain a porous carbon fiber, the pore diameter of 2-5um, When the PAN as the dispersed phase, the resultant carbon nanofiber having a diameter of 80-150nm. Changing the temperature of the carbonized able to control the degree of graphitization of the carbon material obtained. With the carbonization temperature is increased, the conductivity increases, the conductivity was 7.6 × 10 to 1 S / cm at 1000 ℃ conductivity of 1200 ° C was 2.3 × 10 2 S / cm. 2-8wt% of the proportion of epoxy resin made by mixing standard Samples tested them 8GHz-12GHz complex permittivity of the resulting carbon material as absorbents. Sui absorbing agent content increases, the permittivity real portion and the imaginary part increases; loss tangent is also increased with increasing the content of the Absorbing agent. Thus by theoretical simulation of electromagnetic waves of different thickness composite reflectivity, and the composite monolayer structure to guide the design and preparation. 2-8wt% of absorbents content for a single-layer structure composite absorbing performance Agilent HP8722ES type vector network analyzer, using the bow method reflectivity test results showed that: a certain thickness (3mm) composite materials in the 8-12GHz peak reflectance of the electromagnetic wave with the increase of the content of the absorbents smaller; absorbents content of 8wt%, the reflectance peak frequency corresponding to the low frequency movement. Results and theoretical simulation of the actual test results. Comparative porous carbon fibers and nano carbon fibers two absorbing agent, under the same content, the porous carbon fiber composite material has a lower reflectance, and the reflection peak is less than-10dB in a wider frequency range. For example: Absorbing agent content of 8wt%, and the sheet material with a thickness of 3mm, the porous carbon fiber composite material of minimum reflectance of-20dB of the absorbents. The frequency range of 8-12GHz are less than-10dB; carbon nanofiber absorbents, the minimum reflectance of-16dB, and less than-10dB at around 2GHz. Absorptive mechanism discussed, absorbents absorption of electromagnetic waves and multiple reflections decay of two mechanisms-based. In the porous carbon fiber as the absorbing agent, and to increase the path of reflection of electromagnetic waves, is conducive to further attenuation of electromagnetic waves. This work using carbon materials as absorbents composite material design and preparation of content, the results have a reference value.

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