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Study on the Electromagnetic Interference of CFRC Composites by Reflectivity

Kezhi LI,Chuang WANG,Hejun LI,Gengsheng JIAO,Jian WEI,

材料科学技术学报 , 2008,
Abstract: The influence of dispersion of carbon fibers in carbon-fiber-reinforced cement-based composites (CFRC) on the mechanical properties of the composites was discussed. The microstructure of the fracture surface of the CFRC samples was observed with a scanning electron microscope (SEM). The electromagnetic interference (EMI) was evaluated indirectly by reflectivity in the Naval Research Laboratory (NRL) testing system. The reflectivity of the electromagnetic radiation by the composites was measured in the frequency range of 8.0-18.2 GHz for different carbon fiber contents of 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% (in wt pct), respectively. The results showed that the reflectivity decreased with the growing fiber content till the percentage of 0.6%.The minimum reflectivity was -23 dB, far less than -10 dB, and the composites were strong wave absorbers.After this percentage, the curve increased abruptly as the fiber content proceeded. The electromagnetic waves were gradually reflected. When the fiber content reached 1.0% finally, the maximum reflectivity -7.5 dB appeared and there was stronger reflection. The shielding mechanism includes mainly reflection, absorption,and multiple reflections.
Hybrid Carbon Fibers/Carbon Nanotubes Structures for Next Generation Polymeric Composites  [PDF]
M. Al-Haik,C. C. Luhrs,M. M. Reda Taha,A. K. Roy,L. Dai,J. Phillips,S. Doorn
Journal of Nanotechnology , 2010, DOI: 10.1155/2010/860178
Abstract: Pitch-based carbon fibers are commonly used to produce polymeric carbon fiber structural composites. Several investigations have reported different methods for dispersing and subsequently aligning carbon nanotubes (CNTs) as a filler to reinforce polymer matrix. The significant difficulty in dispersing CNTs suggested the controlled-growth of CNTs on surfaces where they are needed. Here we compare between two techniques for depositing the catalyst iron used toward growing CNTs on pitch-based carbon fiber surfaces. Electrochemical deposition of iron using pulse voltametry is compared to DC magnetron iron sputtering. Carbon nanostructures growth was performed using a thermal CVD system. Characterization for comparison between both techniques was compared via SEM, TEM, and Raman spectroscopy analysis. It is shown that while both techniques were successful to grow CNTs on the carbon fiber surfaces, iron sputtering technique was capable of producing more uniform distribution of iron catalyst and thus multiwall carbon nanotubes (MWCNTs) compared to MWCNTs grown using the electrochemical deposition of iron. 1. Introduction The attractive properties of carbon nanotubes [1] (CNTs) might be attributed to their unique and minimum defect nanostructure. Single wall carbon nanotubes (SWCNTs) possess exceptional mechanical [2, 3], thermal, and electric properties [4] compared to graphite, Kevlar, SiC, and alumina fibers. The strength, elastic modulus, and fracture properties of CNTs are an order of magnitude higher than most common composites used in civilian and military applications [5–8]. Moreover, CNTs reinforcement was proven to increase the toughness of the polymers and composite to absorb impact energy [9–12]. Most research to date had focused on using CNTs as a reinforcement or as a filler in a polymeric matrix by dispersing and perhaps subsequently aligning single- or multiwalled CNTs in the matrix [13, 14]. Alignment and dispersion are critical factors that are difficult to control experimentally using oft-repeated mixing methods. CNTs embedded in a polymeric matrix form aggregates of themselves that are not only poorly adhered to the matrix but also concentrate stresses, compromising the effect of the CNTs as reinforcement. Sonication [15] and calendaring [16] have been used to mitigate this problem, but these techniques are not effective beyond ~3% CNTs weight fraction due to the formation of aggregates [17]. The extreme difficulty in uniformly dispersing CNTs in polymer matrices arises from the large surface area of CNTs [18]. Dispersion and extrusion

SUN Mingqing,LI Zhuoqiu,MAO Qizhao,SHEN Darong,

材料研究学报 , 1998,
Abstract: The influence of the content of carbon fiber, cement matrix and curing period on Seebeck effect of carbon fiber reinforced cement (CFRC) is discussed in this paper. The results show that the thermoelectric power (TEP) reaches its maximum when carbon fibers in the amount of 1.0% by weight of cement are used. As the curing period extends, TEP becomes steady. Cement matrix makes Iittle influence on TEP.
Strength Improvement of CVD SiC Fibers by Electrochemical Surface Treatment
Xinchun CHANG,Jianqiang WANG,Nanlin SHI,Zhuangqi HU,

材料科学技术学报 , 1998,
Abstract: An electrochemical sudece-treatment method has been used for modifying surface condition of large diameter CVD SiC (W core) fibers. The average tensile strength of the fibers was increased obviously from 2270.1 to 3002.9 MPa. X-ray photoelectron spectroscopy (XPS) studies on the treated fiber sudece indicate that a silicon-oxide film (primarily α-SiO2) has formed,accompanying the precipitation of amorphous carbon as the products of an anode oxidation reaction. In addition, the substantial increase of fiber strength through the electrochemical treatment may be described to the formation of oxide films and elimination of defects on the fiber surface.
The Effect of Admixtures on Electrical Conductance of CFRC

MAO Qizhao,YANG Yuanxia,LI Zhuoqiu,SHEN Darong,

无机材料学报 , 1997,
Abstract: The effects of various specially made admixtures on properties of CFRC were studied. Theresults reveal that by using MKC, together with proper manufacturing technologyt the electricalconductivity, dispersion of fibre in cement and compression sensibility of CFRC are much improved,compared to the corresponding plAlN CFRC values. In addition, CKH can improve the electricalconductance of CFRC evidently.

MAO Qizhao,ZHAO Binyuan,SHEN Darong,LI Zhuoqiu,

材料研究学报 , 1997,
Abstract: The polarization of carbon-fiber hardened cement paste (CFRC) at electric conduction is studied. The results show, the polarization has a notable effect on the electric conductivity of the CFRC.But the polarization can be controlled by adjusting the content of carbon fiber. the measuring voltage and current. The polarization decreases with curing age.So the electric resistence of CFRC can be measured by a direct current.
Fabrication and Properties of Carbon Fibers  [PDF]
Xiaosong Huang
Materials , 2009, DOI: 10.3390/ma2042369
Abstract: This paper reviews the research and development activities conducted over the past few decades on carbon fibers. The two most important precursors in the carbon fiber industry are polyacrylonitrile (PAN) and mesophase pitch (MP). The structure and composition of the precursor affect the properties of the resultant carbon fibers significantly. Although the essential processes for carbon fiber production are similar, different precursors require different processing conditions in order to achieve improved performance. The research efforts on process optimization are discussed in this review. The review also attempts to cover the research on other precursor materials developed mainly for the purpose of cost reduction.
Self-adjustment of Carrying Capacity of Concrete Embedded with CFRC

材料科学技术学报 , 2006,
Abstract: By heating up the embedded carbon fiber reinforced cement based material (CFRC), the carrying capacity and deformation of concrete member could be adjusted. The relationship between temperature difference and expansion strain of CFRC was demonstrated, and the temperature-deformation-load effect of concrete embedded with CFRC was studied. Heating the CFRC up to different temperatures resulted in different degree of inner pre-stress in concrete. Thus, the load capacity of concrete could be regulated owing to counteracting the pre-stress.
Piezoresistivity in Carbon Fiber Reinforced Cement Based Composites
Bing CHEN,Keru WU,Wu YAO,
,Keru WU and Wu YAO

材料科学技术学报 , 2004,
Abstract: The resu lts of some i nteresti ng investigation on the piezoresistivity of ca rbon fi ber reinforced cement based com posites (CFRC) are presented with the prospect of developing a new nondestructive testing method to assess the integrity of the composite. The addition of short carbon fibers to cement-based mortar or concrete improves the structural performance and at the same time significantly decreases the bulk electrical resistivity. This makes CFRC responsive to the smart behavior by measuring the resistance change with uniaxial pressure. The piezoresistivity of CFRC under different stress was studied, at the same time the damage occurring inner specimens was detected by acoustic emission as well. Test results show that there exists a marking pressure dependence of the conductivity in CFRC, in which the so-called negative pressure coefficient of resistive (NPCR) and positive pressure coefficient of resistive (PPCR) are observed under low and high pressure. Under constant pressures, time-dependent resistivity is an outstanding characteristic for the composites, which is defined as resistance creep. The breakdown and rebuild-up process of conductive network under pressure may be responsible for the pressure dependence of resistivity.
Carbon fibers and textiles and some of their applications
Kalu?erovi? Branka V.,Milovanovi? Ljiljana M.,Babi? Biljana M.
Hemijska Industrija , 2002, DOI: 10.2298/hemind0209369k
Abstract: Production process and characteristics of PAN based carbon fibers and cellulose based carbon textile are presented. In the case of carbon fibers attention is paid to changes during the carbonization process in the range of 400-1000°C. The change of diameter and weight loss as well as tensile strength and Young's modulus were examined. For carbon textile it was interesting to show their adsorption characteristics as activated material. The nitrogen adsorption isotherms correspond to the microporous adsorbent which is suitable for adsorption of both gaseous and liquid adsorbats.
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