Materials Science and Engineering B 132 (2006) 307–310

Preparation and characterization of carbon fibers coated byFe3O4 nanoparticles

Jing Xu a, Haibin Yang a,b,∗, Wuyou Fu a, Yongming Sui a,Hongyang Zhu a, Minghui Li a, Guangtian Zou a

a National Laboratory of Superhard Materials, Jilin University, Changchun 130012, PR Chinab Institute of Materials Science & Engineering, Henan Polytechnic University, Jiaozuo 454003, PR China

Received 4 March 2006; received in revised form 24 April 2006; accepted 29 April 2006

Abstract

Carbon fibers have been successfully coated with Fe3O4 nanoparticles coating layers via sol–gel method combined with annealing under vacuum.The phase structures and morphologies of the composite have been characterized by XRD and FESEM. The results show that a complete anduniform Fe3O4 nanoparticles coating on carbon fibers can be obtained in the temperature range of 300–550 ◦C. The coating layers with thicknesscfi©

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a. 800 nm are composed by Fe3O4 nanoparticles of mean sizes ca. 30 nm. The surface properties of Fe3O4 nanoparticles detached from carbonbers/Fe3O4 composite have been analyzed by XPS and FTIR.2006 Elsevier B.V. All rights reserved.

eywords: Fe3O4 nanoparticles; Carbon fibers; Sol–gel

. Introduction

With the fast development of information and communicationechnology in recent years, microwave absorptive materials draw

ore and more attention because of their widespread applica-ions for electromagnetic compatibility (EMC) [1–3]. They aremportant parts of stealthy defense system for aircraft, sea orand vehicles, and essential parts of absorbing and shielding thenvironmental pollution from microwave irradiation. Magneticbsorption materials continue to play a leading role in the inves-igation and application of microwave absorption materials [4].owever, the conventional absorption materials, such as ferrite

nd metal, are quite heavy. The problem restricts their useful-ess in many applications [5,6]. One of the ways to overcome theroblem is to couple ferrite and metal materials with low den-ity materials. Carbon fibers (CFs) are dominant in low densityaterials because of their low density, high strength, and per-

ect electrical property [7,8]. CFs coated by magnetic materialsan decrease the weight of the microwave absorptive compos-te, and improve the conductivity and strength of the composite.t has been demonstrated that iron-coated CFs can be obtained

by electrochemical method and used as electromagnetic radia-tion absorptive composite [9,10]. Huang et al. reported nickeland copper/nickel can be loaded on CFs for EMI shielding byelectroless method [11].

However, very little work has been done for combining ferritewith CFs. Huang et al. prepared CFs coated with barium ferriteby sol–gel method and analyzed its electromagnetic propertiestheoretically [12]. Even though the composite is an absorbingmicrowave absorbing materials, it still has some limitations,such as high density and high-temperature treat. Magnetite(Fe3O4) has attracted long-standing interest in nanostructuresynthesis because of its extensive applications in ferrofluid, andultrahigh density magnetic storage media [13,14]. Magnetite(Fe3O4) as a type of relatively low density ferrite can be obtainedin a relatively low temperature (compared with barium ferrite).However, little work has been done to couple CFs with Fe3O4nanoparticles so far.

In this paper, Fe3O4 nanoparticles have been coated onCFs by sol–gel method based on the reaction of ferric nitrateand ethylene glycol under vacuum in the temperature rangeof 300–550 ◦C. The Fe3O4 coating layers with thickness ca.

∗ Corresponding author. Tel.: +86 431 5168763; fax: +86 431 5168258.E-mail address: yanghb@jlu.edu.cn (H. Yang).

800 nm are composed by Fe3O4 nanoparticles of mean sizesca. 30 nm. The Fe3O4 coating on CFs surfaces can be furtherfunctionalized with a large variety of other nanostructure mate-

921-5107/$ – see front matter © 2006 Elsevier B.V. All rights reserved.

oi:10.1016/j.mseb.2006.04.038

308 J. Xu et al. / Materials Science and Engineering B 132 (2006) 307–310

Fig. 1. The scheme of the procedure used to synthesize the CFs/Fe3O4 composite.

rials by utilized the chemistry of Fe3O4 nanoparticles to createnovel multilayer coating on CFs. And the magnetic, thermal,and microwave absorption properties of CFs/Fe3O4 would beconsidered in near future.

2. Experimental

2.1. CFs and chemicals

PAN-based CFs with 6–8 �m in diameter and 3 mm in lengthwere supplied by Jillin Carbon Group Co., Ltd. Chemicals, ferricnitrate (Fe(NO3)3·9H2O), ethylene glycol (C2H6O2), nitric acid(HNO3, 65%) and acetone (C3H6O), used in the experiment areof analytical grade and used without further purification.

2.2. Preparation of CFs/Fe3O4 composite

The synthesis procedure for the CFs/Fe3O4 composite isillustrated in Fig. 1 and exhaustively described as follows: beforedeposition, CFs were immersed in acetone for 2 h to clean theCFs surfaces, then CFs were treated with HNO3 (65%) for 24 h atroom temperature to introduce various functional groups (suchas COOH, OH, and CO) on CFs surfaces. These functionalgroups can act as nucleation sites for Fe3O4 nanoparticles onCFs. A 0.2 mol ferric nitrate was firstly dissolved in 100 ml ethy-l

coating solution. Then 2 g of acid-treated CFs were immersedin the above sol. The system was ultrasonically dispersed for2 h at room temperature, and then the excess sol was filteredfrom CFs with the precursor of Fe3O4 (CFs/precursor). Afterbeing dried at 120 ◦C, CFs/precursor was further annealed atdifferent temperatures under vacuum for 2 h. After repeating theprocess several times, CFs would be coated by a uniform Fe3O4nanoparticles layer.

2.3. Characterization

The morphologies, particle size, and thickness of Fe3O4nanoparticles coating on CFs were investigated by a field emis-sion scanning electron microscopy (FESEM, JSM-6700F). Thephase structures of CFs/precursor annealed were character-ized by X-ray powder diffraction (XRD, D/Max-rA) with CuK� radiation (λ = 0.15418 nm). Thermal analysis (TG-DTA)of the CFs/precursor was conducted in N2 on a thermal ana-lyzer (TA, SDT-2960) at a heating rate of 10 ◦C/min fromroom temperature to 900 ◦C. The residual organic materials onthe surface of Fe3O4 nanoparticles were examined by X-raydiffraction photoelectron spectroscopy (XPS, ESCALAB MarkII) and Fourier transform infrared spectrophotometer (FTIR,UV-3101).

Fv

ene glycol with vigorously stirring for 2 h at 40 ◦C, to be used as

Fig. 2. TG-DTA curves of CFs/precursor in N2.

ig. 3. XRD patterns of CFs/precursor annealed at different temperatures underacuum for 2 h: (a) 250 ◦C, (b) 300 ◦C, (c) 550 ◦C and (d) 700 ◦C.

J. Xu et al. / Materials Science and Engineering B 132 (2006) 307–310 309

3. Results and discussion

3.1. Characterization of CFs/Fe3O4 composite

A typical TG-DTA curve for CFs/precursor is shown in Fig. 2.The TGA curve exhibits three distinct weight loss steps andthe DTA curve shows three exothermic peaks. The first obvi-ous weight loss step in the temperature range of 150–250 ◦C isaccompanied with an exothermic peak around 200 ◦C in the DTAcurve. We believe this result is due to the combustion of organicresidue in the CFs/precursor. The second weight loss step inthe temperature range of 250–320 ◦C and the broad exothermicpeak around 290 ◦C in the DTA curve are considered as a resultof crystallization of Fe3O4 phase. Almost no weight loss wasobserved from 300 to 530 ◦C, implying the unique presence ofCFs/Fe3O4 in this temperature range. The exothermic peak at620 ◦C in the DTA curve and the weight loss process continued

until about 680 ◦C are presumed to be associated with the crys-tallization of �-Fe phase. The XRD analysis was carried out toprobe the composition at different temperatures (Fig. 3), whichconfirmed the results of TG-DTA.

Fig. 3 shows the XRD patterns of CFs/precursor annealed atdifferent temperatures under vacuum for 2 h. At 250 ◦C (Fig. 3a),no other diffraction peaks except the (0 0 2) peak of graphiteappears, indicating that the Fe3O4 coating layer on CFs has notbeen formed. Fig. 3b and c illustrate that CFs/Fe3O4 compositecan be obtained in the temperature range from 300 to 550 ◦C.The diffraction peaks at 2θ = 35.48◦, 62.62◦, 30.12◦, 57.02◦,and 43.12◦ can be assigned to (3 1 1), (4 4 0), (2 2 0), (5 1 1)and (4 0 0) planes of Fe3O4 (JCPDS 88-0866), respectively. Noother diffraction peaks can be observed but those of graphiteand Fe3O4, indicating that the coating layer is only consistedof Fe3O4 nanoparticles. When CFs/precursor were annealed at700 ◦C (Fig. 3d), the phase of �-Fe appears and the (0 0 2) peak of

Fc

ig. 4. FESEM micrographs of (a) bare CFs, (b) multiple CFs/Fe3O4 composite, (c) soating layer.

ingle CFs/Fe3O4 composite, and (d) the magnified view of Fe3O4 nanoparticles

310 J. Xu et al. / Materials Science and Engineering B 132 (2006) 307–310

Fig. 5. XPS spectrum of Fe3O4 nanoparticles separated from CFs/Fe3O4 com-posite of O 1s.

graphite still remains, showing that the CFs/precursor changed toCFs/�-Fe at high-temperature under vacuum. No obvious peakscorresponding to ferrite nitrite or other iron oxide, such as �-Fe2O3 and �-Fe2O3, are detected (Fig. 3).

Fig. 4 shows the FESEM micrographs of bare CFs,CFs/Fe3O4 composite (CFs/precursor annealed at 300 ◦C). Thediameters of bare CFs with smooth surfaces are about 6–8 �m(Fig. 4a). The direct evidence of the formation of Fe3O4 nanopar-ticles coating on CFs is given by FESEM in Fig. 4b. It is apparentthat almost all CFs have been fully coated with uniform Fe3O4nanoparticles without separated Fe3O4 nanoparticles conglom-erations next to the coating layers. The ca. 800 nm thicknessof coating layer is observed distinctly in Fig. 4c, and Fig.4dis the magnified micrograph of Fe3O4 nanoparticles coating,which reveals that the perfect coating are composed of Fe3O4nanoparticles with sizes of about 30 nm.

3.2. The surface properties of Fe3O4 nanoparticlesdetached from CFs/Fe3O4 composite

To analyze the surface properties of Fe3O4 nanoparticles,we separated Fe3O4 nanoparticles from CFs/Fe3O4 composite.XPS analysis (Fig. 5) was performed to characterize the surfaceproperties of Fe3O4 nanoparticles detached from CFs/Fe3O4composite. The oxygen 1 s peak is deconvoluted into three spec-tral bands at 530.6, 532.0, and 533.4 eV. The most intense peakaTartanVtc

Fig. 6. FTIR spectrum of Fe3O4 nanoparticles detached from CFs/Fe3O4 com-posite.

some organic materials have been absorbed on Fe3O4 nanopar-ticles.

4. Conclusions

Fe3O4 nanoparticles have been successfully coated on CFssurfaces by sol–gel method. The CFs/Fe3O4 composite ispresent at 300–550 ◦C, and the Fe3O4 coating layers with thick-ness ca. 800 nm are composed by Fe3O4 nanoparticles of meansizes ca. 30 nm. The surface properties of Fe3O4 nanoparti-cles separated from CFs/Fe3O4 composite have been studied byXPS and FTIR analysis. The results indicate that some organicresidue exist with Fe3O4 nanocrystalline. CFs/Fe3O4 compos-ite is potential microwave absorbing materials, and the magneticproperties and microwave absorption properties of CFs/Fe3O4will be considered in our future work.

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[

[[

[[

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