Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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Figure 6.3 Effective d.c. electrical conductivity (s DC) vs MWNT concentration for 3Y-TZP/MWNT nanocomposites. Reproduced with permission from [21]. Copyright Ó (2006) John Wiley & Sons, Inc. zirconia material near the percolation threshold, the charge carrier can be transported across the fillers by tunneling through insulating zirconia. This behavior can be described by the fluctuation induced tunneling model which takes into account tunneling through potential barriers of varying height due to local temperature fluctuations [23]: where s exp½ T1=ðT þ T0ÞŠ ð6:8Þ T1 ¼ wAe 2 =8pk ð6:9Þ T0 ¼ 2 T1=pcw ð6:10Þ c ¼ð2 mV0=h 2 Þ 1=2 6.3 Percolation Concentrationj175 ð6:11Þ e ¼ 4 V0=ew ð6:12Þ where m and e are electron mass and charge k the Boltzman constant, V0 the potential barrier height, w the internanotube distance (gap width), and A the area of the capacitance formed by the junction. At constant temperature, Equation 6.8 can be further simplified to [24]: ln s w: ð6:13Þ Assuming the nanotube dispersion in the insulating matrix is homogeneous, the composite conductivity at a given temperature can be described by the behavior of a single tunnel junction where the gap width is w p 1/3 [25]. Accordingly, the d.c. conductivity should follow the following rule [24]: ln s p 1=3 : ð6:14Þ
176j 6 Physical Properties of Carbon Nanotube–Ceramic Nanocomposites Figure 6.4 Linear variation of ln sDC versus p 1/3 . Reproduced with permission from [21]. Copyright Ó (2006) John Wiley & Sons, Inc. Figure 6.4 shows the variation of electrical conductivity of the nanocomposites with p 1/3 . A linear relationship is observed for this plot indicating that tunneling conduction occurs in the nanocomposites. Figure 6.5 shows the dielectric constant vs filler concentration plot for the 3Y-TZP/ MWNT nanocomposites. The dielectric constant also rises abruptly by two orders of magnitude near the percolation threshold. From Equation 6.4, the nanocomposites with pc of 1.7 wt% yields a critical exponent s 0 ¼ 0.63 0.02. The conducting nanotube fillers are separated by thin dielectric ceramic layers, forming mini-capacitors across the matrix. The polarization effect between such filler clusters can improve the electric charge storage, thereby contributing to the enhancement of dielectric Figure 6.5 Dielectric constant vs MWNT concentration for 3Y-TZP/MWNT nanocomposites. Reproduced with permission from [21]. Copyright Ó (2006) John Wiley & Sons, Inc.
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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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226j 8 Conclusions nano-matrix. Scr
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228j Index l laser ablation 7 load
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