Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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The real part (e 0 ) correlates with the dielectric permittivity and the imaginary part (e 00 ) represents the dielectric loss. The tangent loss or dissipation factor represents the ability of the material to convert the absorbed electromagnetic energy into heat [34]. Figure 6.7(a)–(c) show the complex permittivity spectra vs frequency for the SiO2/ MWNT nanocomposites. At 26.5 Hz, the real part of permittivity increases sharply with increasing MWNT content and reaches a value of 21 for the SiO2/10 vol% MWNT nanocomposite. The e 00 and tan d spectra display a similar increasing trend with filler content. The e 00 and tan d values of the SiO2/10 vol% MWNT nanocomposite at 26.5 Hz approach 28 and 1.3, respectively. The large e 00 and tan d values give rise to high EM attenuation by absorbing the incident radiation and dissipating it as heat. The dramatic enhancement of complex permittivity can be attributed to the addition of MWNTs with superior electrical conductivity and large aspect ratio. It can be concluded that the EMI properties of insulating ceramics can be tailored effectively by simply adding CNTs having superior load-bearing capacity and EM absorption characteristics. 6.5 Thermal Behavior 6.5 Thermal Behaviorj179 By analogy to the electrical properties, the thermal conductivity of ceramics should be markedly improved after the addition of CNTs with very high thermal conductivity. Individual MWNT has unusually high thermal conductivity of 3000 W mK 1 [Chap. 1, Ref. 157]. Isolated SWNT has even higher conductivity of 6000 W mK 1 . Accordingly, a thermal percolation network is expected to form in the CNT–ceramic nanocomposites as in the case of electrical percolation. This allows for rapid heat flow along the percolating nanotube networks and further enhancement of thermal transport. However, the thermal conductivity of the CNT–ceramic nanocomposites is much smaller than the value predicted from the intrinsic thermal conductivity of the nanotubes and their volume fraction. Further, enhancement in thermal properties is considerably lower than the corresponding improvement in electrical properties [35–37]. This is due to the formation of Kapitza contact resistances at the nanotube–matrix interface [8, 9, 38–41]. It is well recognized that the interface plays an important role in heat conduction through CNT composites. The resistance at the nanotube–ceramic and nanotube–nanotube interfaces restricts heat transport along percolating pathways of CNTs. When a phonon travels along nanotubes and encounters nanotube–ceramic and nanotube–nanotube interfaces, it is blocked and scattered at these sites. On the basis of MD simulations, Huxtable et al. demonstrated that heat transport in a nanotube composite material is restricted by the exceptionally small interface thermal conductance, resulting in the thermal conductivity of the composite becomes much lower than the value estimated from the intrinsic thermal conductivity of the nanotubes and their volume fraction [38]. Table 6.3 gives a typical example of the modest improvement in thermal conductivity of silica by adding MWNTs. Dense SiO 2/MWNT nanocomposites were prepared by ball milling of composite slurries followed by SPS treatment at 950–1050 C
180j 6 Physical Properties of Carbon Nanotube–Ceramic Nanocomposites Figure 6.7 Complex permittivity spectra as a function of frequency for SiO2/MWNT nanocomposites: (a) real permittivity, (b) imaginary permittivity and (c) loss tangent. Reproduced with permission from [33]. Copyright Ó (2007) Elsevier.
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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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