Electromagnetic shielding and absorption properties of fiber reinforced cementitious composites

In order to investigate the electromagnetic shielding effectiveness (SE) and absorbing properties of fiber reinforced concrete, steel fiber, carbon fiber and synthetic polyvinyl alcohol (PVA) fiber reinforced concrete were researched. The results show that with the increase of fiber volume fraction, the SE and trend of frequency change of corresponding fiber reinforced concrete are enhanced. When the volume content of steel fiber is 3%, the SE of concrete is above 50 dB and its frequency is above 1.8 GHz. Moreover, in the range of 8-18 GHz, steel fiber, carbon fiber and PVA fiber all can improve the microwave absorption properties of concrete. The concrete with 0.5% carbon fiber can achieve the best absorbing property, the minimum reflectivity is about -7 dB; while steel fiber optimal volume fraction is 2%. The reflectivity curve of PVA fiber reinforced concrete fluctuates with the frequency, and the minimum value of the reflectivity is below -10 dB. The results show that fiber reinforced concrete could be used as EMI(electromagnetic interference) prevention buildings by attenuating and reflecting electromagnetic wave energy.     

Effect of nano-silica modification on the tensile property of SMA/GF/CF/epoxy super hybrid woven fabric composites

Tensile properties of epoxy casts together with shape memory alloy (SMA), glass (GF) and carbon (CF) woven fabric reinforced epoxy matrix super hybrid composites were investigated, respectively. In order to enhance the mechanical strength of this advanced material, two categories of modifications including matrix blending and fiber surface coating by nano-silica were studied. Scanning electron microscopy (SEM) and fiber pull-out tests were adopted to complement the experimental results, respectively. Experimental results reveal that the toughness of epoxy matrix is enhanced significantly by adding 2wt% nano-silica. The failure mechanism of SMA reinforced hybrid composites is different from that of GF/CF/epoxy composites. Compared with the matrix modification, the fibers modified by coating nano-silica on the surface have better tensile performances. Moreover, the fiber pull-out test results also indicate that composites with fiber surface modification have better interfacial performances. The modification method used in this paper can help to enhance the tensile performance of the mentioned composite materials in real engineering fields.     

几何混杂钢纤维水泥基材料的断裂性能研究

采用不同几何尺度混杂钢纤维增强水泥基材料的断裂性能,结果表明,在纤维体积分数一定的情况下,几何混杂钢纤维对水泥基材料强度和断裂韧性的改善优于单一尺度钢纤维。选用适当混杂比的几何混杂钢纤维增强水泥基体,可制备出断裂性能较好的GHFRCC材料。     

Electromagnetic Interference Shielding Properties of Electroless Nickel-coated Carbon Fiber Paper Reinforced Epoxy Composites

Carbon fibers(CFs) were coated with a nickel-phosphorus(Ni-P) film using an electroless plating process. The morphology, elemental composition and phases in the coating layer of the CFs were investigated by scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD), respectively. Wet paper-making method was used to prepare nickle coated carbon fiber paper(NCFP). Vacuum assisted infusion molding process(VAIMP) was employed to manufacture the NCFP reinforced epoxy composites, and carbon fiber paper(CFP) reinforced epoxy composites were also produced as a comparison. Electromagnetic interference(EMI) shielding properties of the composites were measured in the 3.22-4.9 GHz frequency range using waveguide method. Both NCFP and CFP reinforced epoxy composites of 0.5 mm thickness exhibited high EMI shielding effectiveness(SE) at 8wt% fiber content, 35 d B and 30 d B, respectively, and reflection was the dominant shielding mechanism.     

纤维体积分数对单向C/C复合材料导热系数的影响

采用无维布叠层的方式获得不同纤维体积分数的单向长炭纤维预制体,以化学气相渗透(CVI)增密技术制备了单向C/C复合材料.讨论了C/C复合材料的导热机理以及纤维体积分数对单向C/C复合材料导热系数的影响.研究表明,材料沿纤维方向的导热系数约为垂直纤维方向的10倍;材料沿纤维方向的导热系数在不同热处理温度下都随纤维体积分数的增加而增加,而材料垂直纤维方向的导热系数在低热处理温度下随纤维体积分数的提高而略增,但在高热处理温度下随纤维体积分数的提高先增加再降低.     

表面处理对碳纤维在水泥浆体中分散性的影响

碳纤维的分散性是决定碳纤维混凝土的力学性能和机敏特性的重要因素。研究采用交流电测量新拌水泥浆不同部分的电阻率 ,结合数理统计方法计算电阻率的标准偏差和变异系数 ,进而对碳纤维在水泥浆体 (砂浆 )中分散的均匀性进行了评价。利用这种评价均匀性的方法 ,研究了碳纤维表面处理对其分散性的影响。     

MDF水泥的碳纤维增强研究

研究了碳纤维作为MDF水泥增强材料的可行性以及它的增强效果．探讨了各种因素对MDF水泥性能的影响,分析了碳纤维增强MDF材料的结构特征．研究结果表明,碳纤维作为MDF水泥的增强材料能够显著提高MDF水泥的抗弯强度、断裂韧性和耐水性能。碳纤维在复合材料中呈三维均匀分布．形成空间网络结构,这是碳纤维增强MDF水泥的主要原因。     

Effects of carbon nanotubes on mechanical and 2D-3D microstructure properties of cement mortar

To study the influence of multi-wall carbon nanotubes （MWCNTs） on the mechanical and microstructural properties of cementitious composites, 0.00, 0.02, 0.08, 0.10, and 0.20 wt% of multi-wall carbon nanotubes were added into cement mortar, in which the cement-sand ratio was 1：1.5. The flexural and compressive strengths of cement mortar at the age of 3, 7, 28 and 90 d and the fracture performance at the age of 28 d were determined, its 2D micrograph was tested by means of SEM, and the 3D defects distribution was firstly determined with or without CNTs by means of XCT （X-ray computerized tomography）. The results showed that 0.08 wt% of CNTs improved the compressive strength and flexural strength by 18% and 19~A, respectively, and a significant improvement of its fracture property was observed. Moreover lower addition of carbon nanotubes to cement mortars can improve its microstructure and decrease the defects significantly compared to the cement mortar without CNTs. With the increase of the content of CNTs, the mechanical properties of cement mortars presented to be declined largely due to the agglomeration of CNTs.     

表面处理碳纤维增强羟基磷灰石复合材料研究

对碳纤维进行表面氧化处理和对氨基苯甲酸表面处理,以这种表面改性碳纤维与羟基磷灰石陶瓷复合,制备表面改性碳纤维增强羟基磷灰石复合材料,研究各种碳纤维的含量对复合材料的抗弯强度、断裂韧度的影响。结果表明,表面氧化改性碳纤维可以显著提高材料的性能,其断裂韧度可达基体断裂韧度的2倍,抗弯强度可达基体抗弯强度的2．48倍。尤其是对氨基苯甲酸表面处理的碳纤维的效果更好,其断裂韧度可达基体断裂韧度的2．25倍,抗弯强度可达基体抗弯强度的3倍。     

Sn/C纳米复合材料的合成及其电化学嵌放锂性能

用SnCl4和葡萄糖的水热反应合成SnO₂/碳质复合材料,然后在氮气气氛中热处理使SnO₂被碳热还原为Sn纳米粒子,制备得到Sn/C纳米复合材料.用X-射线衍射(XRD), 透射电镜(TEM)和X-射线电子散射能谱(EDX)对样品进行表征.结果显示Sn纳米粒子具有球形的形貌,并均匀地分散在无定形的碳材料中.对于Sn质量分数58.5%和32.3％的Sn/C复合材料,Sn纳米粒子的平均粒径分别为51和20 nm.电化学测试结果显示,Sn/C复合材料具有高的电化学贮锂可逆容量和良好的循环稳定性.讨论了Sn/C纳米复合材料的形成机理及其循环稳定性能改善的原因.     

碳纤维增强水泥基复合材料的力学性能研究进展

碳纤维(Carbon Fibers, CFs)作为增强相运用在复合材料中一直是研究热点。综述了CFs的种类、分散方式及其在水泥基复合材料中分散性的评估方法、CFs表面涂层改性的制备工艺及其优缺点。通过改善CFs在水泥基体中的分散性和对CFs表面进行涂层改性处理,可以制备性能良好的碳纤维增强水泥基复合材料（CFRC）。同时,对CFRC力学性能的影响因素进行了系统的探讨及研究,包括水灰质量比、养护龄期、成型工艺、硅粉掺量、外加剂、CFs掺量和长度等。总结出进一步提高CFRC力学性能的关键在于改善CFs在水泥基体中的分散性和相容性,并为今后制备高性能CFRC提供参考。     

Electroless nickel plating on the surface of carbon fibers

The electroless nickel plating on the surface of carbon fibers was prepared by pretreating the carbon fibers in order to increase their conductivity,and consequently enhance the EMI shielding effectiveness of the composites.The relationship between the performance of depositing coat and pH value,temperature,reaction time and the way of agitation was studied.Results show that the depositing quality is stable under pH between 4.5 and 5.0,temperature between 75 ℃ and 85 ℃,reaction time for 10 min and air agitation.The uniform and compact nickel layer deposited on carbon fibers was proved by XRD and SEM,and the electrical resistivity of carbon fibers with nickel coating was tested.Results indicate that the electrical resistivity of carbon fibers with electroless nickel plating is decreased by an order of magnitude compared with that of carbon fibers.It means that nickel coating can greatly improve the electromagnetic interference shielding properties of carbon fibers.     

Preparation and properties of C/C-SiC brake composites fabricated by warm compacted-in situ reaction

Carbon fibre reinforced carbon and silicon carbide dual matrix composites(C/C-SiC) were fabricated by the warm compacted-in situ reaction.The microstructure,mechanical properties,tribological properties,and wear mechanism of C/C-SiC composites at different brake speeds were investigated.The results indicate that the composites are composed of 58wt%C,37wt%SiC,and 5wt%Si.The density and open porosity are 2.0 g.cm~(-3) and 10%,respectively.The C/C-SiC brake composites exhibit good mechanical properties.The ...     

Influence of surface state on moisture sensitivity of carbon fiber and its composite interfacial properties

The influence of surface state on the moisture sensitivity of carbon fiber was analyzed by applying a T800 grade carbon fiber with five different surface conditions, namely, with and without surface oxidation, in the presence or absence of sizing agent. The interfacial properties of their composites in the presence of two epoxy matrices (respectively EP07 and EP10) were also characterized by micro-droplet tests. The overall results show that both oxidized and sizing-coated fibers have higher moisture equilibrium content than that of the pristine unsurface-treated fiber, due to higher amount of activated carbon groups. After moisture absorption of the carbon fibers, almost all the fiber/epoxy systems show decrease in the interfacial shear strength and the unsurface-treated fiber system exhibits the largest decline. Moreover, both interfacial shear strength and interlaminar shear strength of carbon fiber/EP10 composite demonstrate better water resistance performance than that of the carbon fiber/EP07 composite, consistent with DSC results of the two resins.     

竹纤维/水泥复合材料力学性能和耐久性的试验研究

利用竹纤维制备了水泥基复合材料,采用正交试验法得到了纤维掺量、纤维长度、减水剂和水灰比四个因素的最佳试验条件.在此基础上测试了该复合材料在不同龄期抗压强度和抗折强度.针对竹纤维的机械性能在碱性水泥浆中会逐渐恶化的缺点,对竹纤维表面预涂了乳液并进行了耐久性对比测试.结果表明,加入预处理的竹纤维制备出的水泥基复合材料的力学性能和耐久性得到了显著改善.     

Effects of carbon nanotubes by electrophoretic deposition on interlaminar properties of two dimensional carbon/carbon composites

Carbon nanotubes(CNTs) were deposited uniformly on carbon cloth by electrophoretic deposition(EPD). Thereafter, CNT-doped clothes were stacked and densified by pyrocarbon via chemical vapor infiltration to fabricate two-dimensional(2 D) carbon/carbon(C/C) composites. Effects of EPD CNTs on interlaminar shear performance and mode Ⅱ interlaminar fracture toughness(GⅡc) of 2 D C/C composites were investigated. Results showed that EPD CNTs were uniformly covered on carbon fibers, acting as a porous coating. Such a CNT coating can obviously enhance the interlaminar shear strength and GⅡc of 2 D C/C composites. With increaing EPD CNTs, the interlaminar shear strength and GⅡc of 2 D C/C composites increase greatly and then decrease, both of which run up to their maximum values, i e, 13.6 MPa and 436.0 J·m-2, when the content of EPD CNTs is 0.54 wt%, 2.27 and 1.45 times of the baseline. Such improvements in interlaminar performance of 2 D C/C composites are mainly beneficial from their increased cohesion of interlaminar matrix, which is caused not only by the direct reinforcing effect of EPD CNT network but also by the capacity of EPD CNTs to refine pyrocarbon matrix and induce multilayered microstructures that greatly increase the crack propagation resistance through "crack-blocking and-deflecting mechanisms".     

石墨烯关联材料包覆修饰高性能纤维的研究进展

碳纳米管、石墨烯、氧化石墨烯等石墨烯关联纳米材料具有很高的强度、模量、韧性和很大的表面积, 可用于充当复合材料的增强体或涂覆修饰纤维类增强体的表面。本文综述近年来采用石墨烯关联材料来修饰纤维,从而改善纤维强化复合材料中纤维和基体树脂之间界面性能的研究进展。首先概述碳纳米管、石墨烯、氧化石墨烯3种碳纳米材料的性能和应用,然后分别介绍他们在碳纤维和玻璃纤维表面的几种修饰方法,阐述在玻璃纤维表面协同包覆碳纳米管和氧化石墨烯时,纤维表面与树脂基体的浸润性、啮合作用和协同效应。最后,对下一步包覆的研究重点提出展望,指出在研制新型促进剂、偶联剂及协同包覆常规纤维等方面,尚需深入研究。     

Electrical resistance behavior of vinylester composites filled with glass-carbon hybrid fibers

Vinylester (bismethacryloxy derivative of a bisphenol-A type EP resin, VE) composites with glass-carbon hybrid fibers (CF-GF) weight fraction of 50%, were prepared by the compress molding method. The distribution of carbon fiber in the hybrids was observed by stereomicroscope. The electrical resistance behavior of the composites filled with different carbon fiber (CF) weight contents (0.5% to 20%) was studied. The experimental results show that the electrical resistance behaviors of CF-GF/VE composites are different with those of CF/VE composites because carbon fibers’ conducting networks are broken by the glass fibers in the CF-GF/VE composites. The carbon fibers distribute uniformly in the networks of glass fibers (GF) like single silk and form the semi-continuous conducting networks. Composite filled with GF-CF hybrid has a higher percolation threshold than that filled with pure CF. At that time, the resistivity of CF-GF/VE composites varies little with the temperature increasing. The temperature coefficient of resistivity in GF-CF/VE composite is less than 317 ppm and the variation of the resistivity after ten thermal cycles from 20 °C to 240 °C is less than 1.96%. Funded by the Natural Science Foundation of Hubei Province (No. 2007ABA028)     

Damage self-diagnoses feasibility of fiber-reinforced concrete structure

The seepage theory was used to explain the variation between the specific resistance of the carbon fiber reinforced cement concrete and the carbon fiber volume ratio. The electro-dynamic seepage was observed in the cement. The longer the carbon fiber is, the smaller the critical volume to produce the electro-dynamic seepage phenomenon will be. However, the forming and stirring process is harder. In general, the average length of carbon fiber is 5 mm. Under the condition of three-point bending load, the specific resistance changes with the loading process, and a good correlation could be obtained according to the load-deflection relationship. The experimental results reveal that the carbon fiber reinforced cement based composites can be used as sensors to self-diagnoses of the damage.     

Microstructural and Mechanical Characterization of SiBNC Coated Carbon Fibers Prepared via PIP Method

The preparation of SiBNC ceramic oxidation-resistant coating on carbon fiber via precursorsolution infiltration and pyrolysis(PIP) method was presented and discussed in detail. Moreover, the microstructures and the components of the coating were characterized. The experiment results showed that the 0.5% polyborosilazane(PBSZ) solution in the coating preparation gave fewer defects, in contrast with the 1% and the 5% PBSZ solutions. The strength of the carbon fiber coated with SiBNC-0.5 wt%(3.08 GPa) was decreased by 12%. Compared with uncoated carbon fiber, the starting oxidation temperature and the reaction activation energy of the coated carbon fibers(SiBNC-0.5 wt%) have increased by about 300 ℃ and 104%, respectively. The oxidation resistance of the SiBNC coated carbon fiber was improved dramatically.