Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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Figure 6.6 Dielectric constant vs frequency for 3Y-TZP/MWNT nanocomposites. Reproduced with permission from [21]. Copyright Ó (2006) John Wiley & Sons, Inc. constant of nanocomposites [16]. Figure 6.6 shows the dielectric constant vs frequency plot for the 3Y-TZP/MWNT nanocomposites at room temperature. The dielectric constant of pristine 3Y-TZP and 3Y-TZP/MWNT nanocomposites containing nanotubes up to 1 wt% is quite low and independent of frequency. At MWNT concentration 2 wt%, the dielectric constant increases significantly. A pronounced dependence of the dielectric constant on frequency is observed for the 3Y-TZP/ MWNT nanocomposites with MWNT concentration 2 wt%. In this regard, the dielectric behavior can be described by Equation 6.6. The dielectric constant can reach 11 200 at 10 3 Hz for the 3Y-TZP/4 wt% MWNT nanocomposite. 6.4 Electromagnetic Interference Shielding Electromagnetic interference (EMI) shielding has received increasing attention in the electronic and communication industries due to the devices emit radiation at microwave and radio frequencies. The EMI of a material refers to its capability to reflect and absorb electromagnetic radiation at high frequencies. Thus, shielding and absorbing are two main methods to prevent and attenuate EMI radiation. The EMI shielding effectiveness (SE) of a material is expressed as the ratio of transmitted power (ET) to incident power (EI) of an electromagnetic wave and measured in decibels (dB) [26, 27]: SE ¼ 10 log ET EI 6.4 Electromagnetic Interference Shieldingj177 : ð6:15Þ In general, electrical conducting materials such as metals, graphite, conducting polymers and polymer-based composites have been used for EMI shielding
178j 6 Physical Properties of Carbon Nanotube–Ceramic Nanocomposites applications [28]. Carbon nanotubes with excellent electrical conductivity show attractive applications for EMI shielding. Introducing conductive CNTs into insulating polymers and ceramics is a simple and effective way to increase their EMI effectiveness. The EMI behavior of CNT-polymer nanocomposites is well documented in the literature because they are easy to process [29–31]. In contrast, less information is available on the EMI behavior of CNT–ceramic nanocomposites. Xiang et al. studied the EMI shielding properties of hot-pressed SiO 2/MWNT nanocomposites in the frequency range of 8–12 GHz (X-band) and 26.5–40 GHz (Ka-band) [32, 33]. They reported that the EMI SE of the nanocomposites increases with increasing nanotube content. Further, the SiO2/10 vol% MWNT nanocomposite exhibits the highest SE value of 66 dB at 34 GHz. This demonstrates a possible use of such material for commercial applications in the broad-band microwave frequency. The improvement of shielding effectiveness is primarily attributed to improvement of the conductivity (Table 6.2). MWNTs with excellent electrical conductivity and high aspect ratio can easily form conducting networks within a silica matrix. The conducting networks would interact and attenuate the electromagnetic radiation effectively. For the purpose of comparison, silica composites reinforced with carbon black (CB) nanoparticles of 24 nm were also prepared under the same conditions. The EMI SE values of the SiO2/10 vol% CB composite at 10 and 34 GHz are quite low (i.e., 10–11 dB) due to the low aspect ratio of CB particles. In addition to EMI SE, another material parameter typically used to characterize the microwave interaction is the complex permittivity (e ). The dielectric permittivity of a material is commonly given relative to that of free space, and is known as relative permittivity (er), or dielectric constant. The dielectric responses of the polymer nanocomposites at various frequencies are described in terms of the complex permittivity (e ) given by the following equation: e* ¼ e 0 ie 00 and the dissipation factor (tangent loss) which is defined as: ð6:16Þ tan d ¼ e 00 =e 0 : ð6:17Þ Table 6.2 Electrical conductivity and EMI shielding effectiveness of SiO2/MWNT and SiO2/CB nanocomposites. MWNT or CB content (vol %) Conductivity (S m 1 ) SE at 10 GHz (dB) SE at 34 GHz (dB) MWNT composites CB composites MWNT composites CB composites MWNT composites 2.5 6.49 · 10 12 — 7 — 12 — 5 4 3.17 · 10 12 22 4 41 10 7.5 21.8 — 26 — 53 — 10 57.4 8.77 · 10 3 32 10 66 11 Reproduced with permission from [33]. Copyright Ó (2007) Elsevier. CB composites
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Sie Chin Tjong Carbon Nanotube Rein
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Sie Chin Tjong Carbon Nanotube Rein
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Contents Preface IX List of Abbrevi
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5 Carbon Nanotube-Ceramic Nanocompo
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Preface Carbon nanotubes are nanost
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XII List of Abbreviations HIP hot i
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1 Introduction 1.1 Background Compo
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Figure 1.2 Transmission electron mi
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1.3 Synthesis of Carbon Nanotubes 1
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MWNTs can be as high as 70% of the
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Figure 1.7 In situ TEM images recor
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1.3 Synthesis of Carbon Nanotubesj1
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show TEM images of MWNTs synthesize
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Since then, large efforts have been
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1.3.4 Patent Processes Carbon nanot
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1.4 Purification of Carbon Nanotube
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Table 1.3 Patent processes for the
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Figure 1.13 Schematic illustration
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1.5 Mechanical Properties of Carbon
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Figure 1.14 Carbon nanotubes in hig
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Figure 1.15 In situ tensile deforma
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Table 1.7 Theoretical and experimen
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Nomenclature ~a 1 , ~a 2 Unit vecto
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carbon nanotubes. Physical Review L
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70 Jang, I., Uh, H.S., Cho, H.J., L
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108 Shelimov, K.B., Esenaliev, R.O.
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Bonnamy, S., Beguin, F., Burnham, N
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2 Carbon Nanotube-Metal Nanocomposi
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isostatic pressing. In certain case
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This implies the absence of effecti
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coating material, the plasma gun an
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Table 2.4 Changes in the size and v
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Figure 2.6 (a) Low and (b) high mag
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Figure 2.8 SEM micrographs showing
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Figure 2.11 Bright field TEM microg
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Figure 2.13 TEM image of bulk Al/5
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2.5 Magnesium-Based Nanocomposites
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limited improvement in ultimate ten
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Figure 2.18 SEM micrographs of the
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Figure 2.19 (a) Low and (b) high ma
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Figure 2.22 SEM micrographs of (a)
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Figure 2.25 (a) TEM micrograph show
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2.8 Transition Metal-Based Nanocomp
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Figure 2.27 TEM image of electrodep
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Figure 2.29 SEM micrographs of (a)
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Figure 2.31 Schematic representatio
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einforcement content SiCp/Al compos
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Materials Science Forum, 534-536 (P
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composite. Materials Science and En
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111 Cha, S.I., Kim, K.T., Arshad, S
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90j 3 Physical Properties of Carbon
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100j 3 Physical Properties of Carbo
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102j 3 Physical Properties of Carbo
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104j 4 Mechanical Characteristics o
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Page 231 and 232: Table 8.1 Patent processes for maki
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228j Index l laser ablation 7 load
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