Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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HA nanocrystals resemble more closely the mineral constituents of human bone. Moreover, HA nanocrystals facilitate osteoblast (bone-forming cell) adhesion and cell proliferation [19, 20]. The molecular building blocks of cells such as proteins, nucleic acids, lipids and carbohydrates are confined to nanometer scales. In this context, nano-HA with a large surface area enhances cell activities and promotes adsorption of proteins from body fluids [21–23]. In general, grain refinement of HA to nanoscale enhances its strength, but reduces its toughness considerably. To restore its toughness, CNTs with excellent high flexibility are incorporated into nano-HA. It has been reported that CNTs exhibit excellent biocompatibility and superior osteoblast adhesion [24, 25]. In this respect, biocomposites having nanonano structure are considered to be potent implant materials for bone replacement function. Up till now, very little information is available in the literature relating the synthesis and structure of nano-HA/CNT composites [26, 27]. Zhao and Gao used in situ chemical precipitation to prepare nano-HA/MWNT nanocomposite powders [27]. In the process, MWNTs were dispersed initially in anionic SDS solution, forming electronegative charges on nanotube surfaces [Chap. 5, Ref. 62]. Carbon nanotube suspension was then added to calcium nitrate solution in which Ca 2 þ ions adsorb preferentially onto MWNTs due to the electrostatic attraction. Subsequently, di-ammonium hydrogen phosphate [(NH4)2HPO4] was dissolved in dilute NH3.H2O solution and added to the nanotube mixture solution. The PO4 3 ions reacted in situ with Ca 2 þ , forming amorphous HA precipitates on MWNTs (Figure 8.1(a)). Precipitation of nano-HA on nanotubes occurred via the following reaction [28]: 10CaðNO3Þ 2 þ 6ðNH4Þ 2 HPO4 þ 8NH4OH ! Ca10ðPO4Þ 6 ðOHÞ 2 þ 20NH4NO3 þ 6H2O: Nanocrystalline HA precipitates can be obtained through proper hydrothermal treatment (Figure 8.1(b) and Figure 8.2). Such nano-HA/2 wt% MWNTpowders were hot-pressed at 1200 C. The compressive strength of nano-HA/2 wt% MWNT Figure 8.1 X-ray diffraction patterns of HA/MWNT before and after hydrothermal treatments for 10 and 20 h. Reproduced with permission from [27]. Copyright Ó (2004) Elsevier. 8.2 Potential Applications of CNT–Ceramic Nanocompositesj219
220j 8 Conclusions Figure 8.2 TEM micrographs of HA/MWNT (a) before and (b) after hydrothermal treatment for 20 h. Inset in (a) is EDX spectrum of HA/MWNT. Copper in the spectrum originates from sample holder. Reproduced with permission from [27]. Copyright Ó (2004) Elsevier. composite is 102 MPa, compared with 63 MPa of pure HA. This corresponds to about 63% improvement in mechanical strength. In the case of micro-nano HA/CNT composites, several processing techniques such as laser surface alloying [29, 30], plasma spraying [31, 32], sintering and hot pressing [33–35] and SPS [3] have been used to fabricate them. The fabrication processes employed for the fabrication of HA–CNTnanocomposites are summarized in Table 8.2. The high temperature environments of laser surface alloying and plasma spraying can cause serious degradation of the quality of CNTs. Further, laser surface alloying route results in the formation of undesired TiC phase [29]. Thus, pressureless sintering at lower temperature (1100 C) [33] and SPS with short processing time [3] are more effective processes to consolidate the HA and CNT powder mixtures. The HA/CNT powder mixtures can be prepared by the in situ synthesis route or through proper mixing of HA and nanotubes. The in situ route can be further classified into chemical vapor deposition (CVD) synthesis [36] and solution precipitation techniques [37, 38]. The in situ CVD technique involves the initial formation of Fe2O3/HAprecursor, followed by calcination in a nitrogen atmosphere and reduction in hydrogen of the Fe2O3/HAprecursor to yield Fe/HA catalyst and a final exposure to CH 4/N 2 gas mixture at 600 C [38]. Figure 8.3(a) and (b) show typical SEM and TEM images of the in situ synthesized Fe-HA/CNT powder. As expected, the length of CVD-grown nanotubes is of the order of several tens of micrometers (Figure 8.3(a)). HA particles are strongly bonded and accumulated on the outer surface of MWNTs (Figure 8.3(b)). The synthesized HA/CNTpowders were cold compacted and sintered at 1000 C in vacuum for 2 h. As aforementioned, hot pressing in situ CVD-synthesized Fe-Al2O3/CNT nanocomposite powder at 1500 C yields low density and poor mechanical strength due to the degradation of CNTs at high temperatures [Chap. 5, Ref. 42, Chap. 5, Ref. 59]. The synthesized Fe-HA/CNTpowders were cold compacted and sintered at 1000 C, thus the integrity of CNTs is preserved. As a result, sintered Fe-HA/CNT nanocomposite containing 2 wt% CNT and 1.5 wt% Fe exhibits a 226%
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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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132j 5 Carbon Nanotube-Ceramic Nano
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