cement composites for electromagnetic interference shielding application

cement composites for electromagnetic interference shielding application

Construction and Building Materials 84 (2015) 66–72 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: ...

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Construction and Building Materials 84 (2015) 66–72

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Graphene oxide-deposited carbon fiber/cement composites for electromagnetic interference shielding application Juan Chen, Dan Zhao, Heyi Ge ⇑, Jian Wang Shandong Provincial Key Laboratory of Preparation and Measurement of Building Materials, University of Jinan, Jinan 250022, PR China School of Material Science and Engineering, University of Jinan, Jinan 250022, PR China

h i g h l i g h t s  Graphene oxide-deposited carbon fiber (GO-CF) was obtained.  The GO-CF showed good dispersion in water and cement matrix.  GO-CF was found to be more effective than CF in providing EMI shielding of cement.  SE of GO-CF/cement had a 31% increase than that of CF/cement in the mass of 0.4 wt.%.

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Article history: Received 4 December 2014 Received in revised form 28 February 2015 Accepted 8 March 2015

Keywords: Carbon fiber Graphene oxide Electromagnetic interference shielding Cement-based composite

a b s t r a c t Graphene oxide-deposited carbon fiber (GO-CF) was obtained by introducing GO onto CF surface through electrophoretic deposition method. GO-CF was found to be more effective than CF in providing electromagnetic interference shielding of cement-based composites. With 0.4 wt.% GO-CF and a shield thickness of 5 mm, a shielding effectiveness of 34 dB was attained at X-band region (8.2–12.4 GHz), which had a 31% increase than that of CF/cement (26 dB) in the same mass fraction. The GO-CF is believed a promising filler of cement-based composites for high electromagnetic interference shielding. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction With the rapid development of the electronics industry, the dominant frequency range of communication devices has shifted toward a higher range in order to enhance the data transfer rates [1]. As a result, the demand for the microwave absorbers and electromagnetic shields in this frequency range is greatly increasing, to solve the electromagnetic interference (EMI) problems, especially in the X band (8.2–12.4 GHz). Cement material which has rich resource and good environmental adaptability is attractive for the development of composites for EMI shielding [2–4]. However, cement is slightly conducting, so the use of a cement matrix needs to fill conductive fillers, such as carbon fiber (CF), carbon nanotube, carbon black, in composites to be electrically connected [5,6]. CF has aroused

⇑ Corresponding author at: Shandong Provincial Key Laboratory of Preparation and Measurement of Building Materials, University of Jinan, Jinan 250022, PR China. Tel.: +86 53182767151. E-mail address: [email protected] (H. Ge). http://dx.doi.org/10.1016/j.conbuildmat.2015.03.050 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.

tremendous attention due to its excellent properties, such as high conductivity, large aspect ratio and high thermal stability [7–10]. Ji Sun Im a used electrospinning and heat treatment methods to prepared CF and added additives (Fe2O3/BaTiO3/multi-walled carbon nanotubes) to increase the electromagnetic shielding effectiveness (SE), which observed an average of 37 dB over a frequency range of 800 MHz–4 GHz [7]. Chung attained a SE of 40 dB at 1 GHz in a cement-based composite containing 1.5 vol.% discontinuous 0.1 mm diameter CF [8]. Zhen-jun Wang investigated the electromagnetic SE of CF cement-based composites after freezing–thawing cycles [9]. Although CF has received much attention as it imparts cements with high electrical and EMI shielding properties, its further application is hampered due to the poor interfacial properties between CF and matrix as well as the poor dispersion in matrix. Normally CF volume fraction is typically less than 1% in a cement-based composite because of its poor dispersion. The cement paste with CF at 0.54 vol.% gave an effectiveness of 26 dB at 1.5 GHz [8], whereas the mortar with CF (isotropic pitch based, 3 mm long) at 0.84 vol.% gave an effectiveness of 15 dB at 1.5 GHz [10].

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Graphene oxide (GO) sheets have attracted enormous attention in recent years due to their remarkable properties and large specific surface area [11–14]. GO sheets bear various oxygen-containing groups, mainly epoxides and hydroxyls on their basal planes and carboxyls on the edges, which can facilitate the dispersion of GO in water [15,16]. Therefore GO has been accepted as a well agent to improve the interfacial properties between fiber and matrix [17]. Furthermore, the defects and groups in GO will arise relaxation processes [1,18–20], which is favorable in enhancing microwave absorbing ability. In this work, GO was introduced onto CF surface through the electrophoretic deposition method to improve CF hydrophilicity, thus to achieve the purpose of good CF dispersibility in cement matrix, excellent interfacial properties between CF and cement as well as higher EMI SE. The EMI SE of GO-CF/cement composite in the X-band frequency region (8.2–12.4 GHz) has been investigated for the first time. 2. Experimental 2.1. Materials Portland cement 42.5 was used. The sand met ISO standard. T700SC CF (12 K, 0.8 g/m), with an average diameter of 7–8 lm, was supplied by Toray Company, Japan. Graphite powder (8000 meshes, 99.95%) and methyl cellulose were purchased from Aladdin Industrial Corporation. Concentrated sulfuric acid (H2SO4), sodium nitrate (NaNO3), potassium permanganate (KMnO4), hydrogen peroxide (H2O2), and ammonium hydrogen carbonate (NH4HCO3) were of analytical grade and purchased from Sinopharm Chemical Reagent (Shanghai, China). 2.2. Preparation of GO The GO was synthesized by chemical exfoliation of flake graphite through a modified Hummers’ method [21,22]. Briefly, 3 g graphite powder, 1.5 g NaNO3 and 75 mL H2SO4 were sequentially added to a three-necked round-bottomed flask placed in an ice bath under stirring. 9 g KMnO4 was slowly added to the flask. Once it was thoroughly mixed, the ice bath was removed and the solution was stirred at 35 °C for 2 h. Then 150 mL of deionized water was slowly added to the solution, the temperature raised to 98 °C and 500 ml deionized water and 15 mL H2O2 slowly were added to the solution in turn. The mixture was filtered and washed with 10 wt.% HCl aqueous solution. Finally, it was purified by dialysis for one week to remove the remaining metal species and acid. Exfoliation of GO was realized in an aqueous solvent by sonication for 1 h, and the non-exfoliated GO was removed by centrifuge (4000 rpm, 10 min), which were the optimized conditions for this experiment. A well dispersed GO colloid solution was obtained and used to immobilize onto CF surface in the subsequent process. 2.3. Introduction of GO on CF The electrophoretic deposition method was used to introduce GO sheets on CF surface [23]. To exclude the possible effects of commercial sizing and to enhance the interfacial adhesion of GO/CF, the electrochemical corrosion method was firstly used to remove the commercial sizing before the introduction of GO on CF [24].

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The electrolytic treatment system of a potentiostat/galvanostat analyzer was established with CF used as the working electrode (positive), and a graphite cathode served as the counter electrode. During electrochemical corrosion, NH4HCO3 was used as the electrolyte solution. The direct voltage was 3 V. CF was treated for 5 min. Then CF was washed by distilled water twice and then used 1.5 mg/ml GO instead of NH4HCO3 as the electrolyte solution (as shown in Fig. 1). The direct voltage changed to 15 V. CF was treated for 40 min. After electrophoretic deposition, the GO-deposited CF (GO-CF) was washed with distilled water and then immersed in distilled water for 30 min to remove the residual GO absorbed on the GO-CF.

2.4. Mixing procedure and sample preparation The mortar mixtures were prepared in a mortar mixer. The CF and the GO-CF were cut to 3–5 mm before added to the mortar. They were used in the amount of 0.1%, 0.2%, 0.3%, 0.4% by mass of cement, respectively. Methyl cellulose was used as primary dispersant in the amount of 1% by weight of water. Water/cement (w/c) mass ratio was 0.48. Sand/cement (s/c) mass ratio was 1.0. Firstly the methyl cellulose was added in water and stirred. Then the CF or the GO-CF was added to form a uniform mixture. Finally the cement was mixed with this mixture (as shown in Fig. 2) and then cast in silicone molds. After 24 h, the specimens were removed from the molds and transferred to a moist-curing room for 7 days before EMI SE testing. The specimen size for EMI SE measurement was 22.6 mm  10 mm  5 mm and for the flexural strength/the compressive strength tests was 40 mm  40 mm 160 mm.

2.5. Characterization of specimens The morphology of GO was performed on an atomic force microscope (AFM) system (Veeco NsIV, USA). The GO sheets were dispersed in water and dip-coated onto freshly cleaved mica surface before testing. Scanning electron microscopy (FEI QUANTA FEG 250 fieldemission SEM system) was used to investigate the surface morphology of GO-CF. Fourier transform infrared (FTIR) measurement was performed on a Nicolet 380 infrared spectrometer (Thermo electron corporation, United States). The specimens were prepared by potassium bromide pellet technique. EMI SE was obtained according to the waveguide method using a network analyzer (Agilent, N5234A) equipped with an amplifier and a scattering parameter (S-parameter) test set over a frequency range of 8.2 GHz–12.4 GHz.

3. Results and discussion 3.1. The morphology and structure of GO sheets The GO sheets were dispersed in water for ultra-sonication and centrifuged to obtain a stable suspension (as shown in the photo of colloid suspension of GO (1 mg mL 1), Fig. 3(a)). GO sheets in water hydrolyze to form negatively-charged thin platelets that consist of single to multi-layer carbon [25]. The AFM image of the lamellae of GO is displayed in Fig. 3(b). The results indicate that single irregular layer of GO can be observed with a thickness about 1 nm. It suggests that the GO nanosheets suspension solution was obtained. As shown in Fig. 3(c), SEM image shows that the GO sheets appear typically flat yet wrinkled.

Fig. 1. Schematic of electrophoretic deposition.

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and CF-GO are shown in Fig. 4. For GO, the peak at 1056 cm 1 shows the presence of epoxy C–O. The characteristic peaks at 1618 cm 1 and 1730 cm 1 appear for aromatic [email protected] and carboxyl [email protected], respectively [26]. The peak at 3380 cm 1 shows the presence of stretching vibration of hydroxyl. For GO-CF, in comparison to CF, the spectrum exhibits about three additional peaks. The peaks at 3455 cm 1 (stretching vibration of hydroxyl), 1625 cm 1 (stretching vibration of [email protected]) and 1014 cm 1 (stretching vibration of epoxy C–O) demonstrate that GO has been introduced onto CF surface. 3.3. Surface topography of CF and GO-CF The SEM morphologies of CF, electrochemical treated CF and GO-CF are shown in Fig. 5. As shown in Fig. 5(a and b), CF has relatively smooth surface. After the electrochemical corrosion, CF surface appears some gullies. The electrophoretic deposition of GO on CF can be seen in Fig. 5(c). The GO sheets are tightly coated to the CF surface. The wrinkled and roughened textures of CF surface are due to the presence of flexible and ultrathin GO sheets. This indicates that the GO has been successfully immobilized on the CF surface. 3.4. The dispersion of GO-CF

Fig. 2. Schematic of sample preparation process.

3.2. The chemical structure of GO, CF and GO-CF FTIR is used to identify the type of oxygen functionalities and bonding configuration in GO and CF. The FTIR spectra of GO, CF

Water is normally used as the medium of cement paste. However, CF is hydrophobic, which makes it the poor dispersion in cement matrix. As shown in Fig. 6(a and b), GO-CF is better dispersed in water than CF. GO gained a lot of hydrophilic groups (carboxyl, hydroxyl and epoxy groups) through the oxidation process which made GO partially hydrophilic and guaranteed the stable existence in aqueous medium [16,17]. The introduction of GO on CF surface improved the hydrophilicity of CF surface, which could ameliorate its dispersibility in cement and its interfacial properties with cement matrix. As shown in Fig. 6(c), GO-CFs are evenly distributed in the cement matrix and some CFs lap together, which helps to form a conductive network. It can be seen in Fig. 6(d and e) that there are some tiny cement hydration products on the

Fig. 3. Dispersion of GO in water (a), AFM images of GO lamellae (b) and SEM image of GO (c).

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Fig. 4. FTIR spectra of GO, CF and GO-CF.

Fig. 5. SEM images of CF surface (a) CF, (b) CF treated by electrochemical corrosion, (c) GO-CF.

GO-CF surface (Fig. 6(e)), while CF surface is relatively smooth (Fig. 6(d)). The existence of GO plays a role in the template for the hydration of cement [27,28], which improves the interface bonding between CF and cement matrix. GO in the introduction of CF surface, therefore, not only can improve the hydrophilicity of GF surface, also can have the effect of influence of cement hydration, make the interface stronger. 3.5. EMI SE of specimens The EMI SE of a material can be expressed as SE (dB) = SEA + SER + SEM. SEA and SER are the shielding effectiveness due to absorption and reflection, respectively. SEM is multiple reflection effectiveness inside the material, which can be negligible when SEA >10 dB [29,30]. Fig. 7 shows the variation of the SE with frequency for the different fiber mass (in the amount of 0.1%, 0.2%, 0.3% and 0.4% by mass of cement, respectively) of CF/cement composite and GO-CF/cement composite. As shown in Fig. 7(a), SE of CF/cement composite increases with CF mass fraction. When CF mass fraction reaches 0.4%, SE reaches 26 dB, which has a 189% increases than that of the blank test sample with no CF. The SE value of GO-CF/ cement composites are shown in Fig. 7(b). Similarly, SE increases with GO-CF mass fraction. When GO-CF mass fraction reaches 0.4%, SE reaches 34 dB, which has a 278% increases than that of the blank sample. It is worth noting that the SE value of GO-CF/ cement composites have slightly increase than that of CF/cement composites below 0.3% mass fraction, however, there is a drastic increase of 31% with mass fraction of 0.4% GO-CF. In order to reveal the improvement of SE, SEA and SER were measured and calculated, respectively. The SEA and SER results are shown in Fig. 8. For the CF/cement composite, the SEA has been found to vary from 7 to 22 dB with

the increase of CF mass fraction while SER varies from 2 to 4 dB for the same increase. For the GO-CF/cement composite, SEA has been found to vary from 7 to 30 dB with the increase of GO-CF mass fraction while SER varies from 2 to 4 dB. It has been observed that for both the CF/cement composite and the GO-CF/cement composite, the dominant shielding mechanism is absorption, while the reflection value in SE is very low and it is a non-dominant factor in shielding mechanism. The comparison of Fig. 8(a and b) shows that SEA of GO-CF/ cement composite has an average increases of 35% than CF/cement composite, while SER of CF/cement composite and GO-CF/cement composite are almost the same by the comparison of Fig. 8(c and d). This indicates that, for GO-CF/cement composite, the increase of SE is mainly dominated by absorption increase. The increase in the absorption part should be attributed to the GO sheets uniformly immobilized on CF. It is well known that there are defects and groups in GO [19–21], which will arise two relaxation processes [31]. Firstly, defects can act as polarization centers, which would generate polarization relaxation under the altering electromagnetic field and attenuate electromagnetic wave, resulting a profound effect on the loss of microwave [32]. Secondly, there are oxygen containing chemical bonds such as [email protected], C–O in GO. The different ability to catch electrons between carbon atom and oxygen atom results in electric dipole polarization. Therefore, the electron motion hysteresis in these dipoles under alternating electromagnetic field induces additional polarization relaxation process which is favorable in enhancing microwave absorbing ability [33]. At low mass fraction of GO-CF, GO almost had no effect on the absorption of electromagnetic wave due to the low content of GO. With the increase of GO-CF, the function of the GO gradually displayed, the electromagnetic wave absorption efficiency of the composites increased. Meanwhile, when the GO-CF content reached 0.4 wt.%, the distance between the fibers was close enough

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Fig. 6. Dispersion of (a) CF, (b) GO-CF in water, dispersion of (c) GO-CF in cement and the interfacial of (d) CF, (e) GO-CF with cement matrix.

Fig. 7. SE analysis of (a) CF/cement composite and (b) GO-CF/cement composite with different fiber mass.

so that the existence of GO could help them form a conductive network or realize the tunneling effect. Thus, electronics could be transferred effectively and the electromagnetic shielding effectiveness was improved observably.

3.6. Mechanical properties of specimens The flexural strength and the compressive strength of the cement paste (with 0.4 wt.% CF/GO-CF) at 7 days and 28 days are shown in Fig. 9. The results indicate that the flexural strength and the compressive strength (7 days) of CF/cement and GO-CF/ cement composites have distinctly enhanced comparing with

those without CF. However, for 28-day strengths, the increases of CF/cement and GO-CF/cement compared with those without CF are unconspicuous. And both the strengths of GO-CF/cement and CF/cement are almost the same. The results suggested that the addition of CF could improve the early strength of cement. The deposition of GO onto CF has little influence on the mechanical properties of cement composites.

4. Conclusions GO sheets were introduced on CF surface successfully by the electrophoretic deposition method. The GO-CF showed good

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Fig. 8. SEA of (a) CF/cement composite and (b) GO-CF/cement composite and SER of (c) CF/cement composite and (d) GO-CF/cement composite with different fiber mass.

Fig. 9. The flexural (a) and compressive (b) strengths of the cement paste (with 0.4 wt.% CF/GO-CF) at 7 days and 28 days.

dispersion in water and cement matrix. For both the CF/cement composite and the GO-CF/cement composite, the SE increased with fiber mass fraction increase, and the dominant shielding mechanism was absorption. GO-CF was found to be more effective than CF in improving EMI shielding of cement-based composites, especially in 0.4 wt.% GO-CF content. With 0.4 wt.% GO-CF and a shield thickness of 5 mm, a SE of 34 dB was attained at X-band region (8.2–12.4 GHz), which had 31% increase than that of CF/cement composite in the same mass fraction. For GO-CF/cement composite, the increase of SE was mainly dominated by absorption increase. The GO-CF is believed a promising filler of cement-based composites for high EMI shielding. Acknowledgments This work is supported by Fund of the Science and Technology Program of the Higher Education Institutions of Shandong Province (J13LA06) and the National Natural Science Foundation of China (51272091 and 51401085).

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