Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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commercialization of CNT-reinforced composites, the fabrication and consolidation methods must be both cost effective and competitive. Nanomaterials with unique physical properties, such as large surface area or aspect ratio have shown great potential for biological applications, including tissue engineering, biosensors, medical devices, and so on. The application of nanotechnology to biomedical engineering is a new frontier in orthopedics. Nanocomposites play a crucial role in orthopedic research since bone itself is a typical example of a nanocomposite [5, 6]. The fabrication of implant materials that mimic the structure and properties of human bones is a significant challenge for materials scientists. Bone is a composite material consisting of a calcium phosphate crystalline phase and an organic collagen matrix. The calcium phosphate phase in bones differs in composition from stoichiometric hydroxyapatite [Ca 10(PO4)6(OH)2] by the presence of other ions such carbonate, magnesium and fluoride of which the carbonate content is about 4–8 wt% [7]. Sintered hydroxyapatite (HA) cannot be used as a standalone load-bearing material for bones due to its brittle nature, so HA is mostly used as a coating material for bulk metallic implants. Therefore, CNTs with large aspect ratio, excellent flexibility, superior biocompatibility and bone cell adhesion appear to be suitable reinforcements for HA and other bioceramics. Apparently, orthopedic implant research is another area in which CNTs and their nanocomposites can be of significant importance [8]. Recently, Wang et al. reported that spark plasma sintered SiC/MWNTnanocomposites exhibit superior mechanical performance and biocompatibility [9]. These nanocomposites can be used for bone tissue repair and dental implantation on the basis of in vivo animal (rat) tests. Histological examination showed that there was little inflammatory response in the subcutaneous tissue, and newly formed bone tissue was observed in the femur after implantation for four weeks [9]. 8.2 Potential Applications of CNT–Ceramic Nanocomposites 8.2 Potential Applications of CNT–Ceramic Nanocompositesj217 In addition to thermal management applications in the electronic industries, ceramic–CNT nanocomposites with good thermal conductivity and fracture toughness are candidates for leading edge applications such as thermal barrier coatings (TBCs) for gas turbine engines since they can improve the performance of turbine blades operate at extreme thermal and mechanical conditions [4]. Ceramics with reduced thermal conductivity have been used as thermal barrier materials for TBCs of gas turbine engines. The CNT–ceramic nanocomposites for TBC applications can be fabricated by means of tape-casting or plasma-spraying techniques. Another possible area where ceramic–CNT nanocomposites can find useful application is light-weight armor made from boron carbide [10]. The inherently brittle nature of boron carbide can be overcome by incorporating CNTs, thus improving the ballistic performance considerably. It is anticipated that this novel emerging technology, nanotechnology, will have a substantial impact on biomedical engineering technology. At present, the
218j 8 Conclusions development of ceramic–CNT nanocomposites for biomedical engineering applications is still in its infancy. Such nanocomposites should possess excellent biocompatibility and mechanical properties similar to those of natural bones. The success or failure of orthopedic implants depends on the cell–surface behavior after embedding into the human body. In this regard, the potential application of HA/CNT nanocomposites as future hard tissue replacement implants in the biomedical engineering sector is considered in the next section. 8.2.1 Hydroxyapatite–CNT Nanocomposites Austenitic stainless steel, metallic Co–Cr–Mo and titanium-based alloys are widely used as implanted materials for artificial hip prostheses. They are suitable for loadbearing applications due to their combination of mechanical strength and toughness. However, the elastic modulus of metallic implants is not well matched with that of human bone, resulting in a stress shielding effect that can lead to reduced stimulation of bone tissue adhesion and growth. Furthermore, metallic alloys often suffer from pitting corrosion and stress-corrosion cracking upon exposure to human body environment. In this respect, ceramic composite materials offer distinct advantages over metallic alloys as implanted materials. It is recognized that ceramics possess excellent biocompatibility with bone cells and tissues. The intrinsic brittleness of ceramics precludes their use as bulk implants for load-bearing functions. Therefore, CNTadditions are needed in order to improve the toughness of ceramics. Moreover, CNT incorporation is beneficial in enhancing the wear resistance of ceramics. Wear failure of conventional implants that results in joint loosening is a potential threat to rehabilitation of the patients. Failed implants require additional surgical operations that markedly increase cost and recovery time. Successful performance of the HA–CNT nanocomposites depends greatly on the nanotube content and fabrication process. Hydroxyapatite is the main mineral constituent of human bones and teeth. An HA coating is generally deposited onto metal implants via plasma spraying. The major drawback of HA coating is its long term instability; HA tends to decompose into tricalcium phosphate (TCP), tetracalcium phosphate (TTCP) and non-biocompatible CaO during plasma spraying at elevated temperatures [11]. Delamination of HA coating from metal implants occurs readily due to its weak bond strength and chemical stability [12–14]. Bulk HA compacts prepared by conventional sintering generally exhibit low yield strength and fracture toughness [15]. High sintering temperature and long sintering time often result in grain coarsening and decomposition of HA. The fracture toughness of HA does not exceed 1 MPa m 1/2 and much lower compared with that of human bone (2–12 MPa m 1/2 ) [16]. In this respect, spark plasma sintering (SPS) with relatively low temperature and short sinter duration can be used to consolidate HA to obtain products with better mechanical property and reduced grain size [17]. Recently, there has been an increasing interest in the processing of HA-based ceramics with nanometer grain sizes [18]. This is because the features of synthetic
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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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