Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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show TEM images of MWNTs synthesized from thermal CVD over Ni/Al catalyst at 450 C [59]. Long nanotubes having a diameter of about 15 nm exhibit typical coiled, spaghetti-like morphology. Some metal catalysts appear to locate at the tip of nanotubes. TEM image of MWNTs produced at 650 C clearly shows an interlayer spacing between graphitic sheets of 0.34 nm (Figure 1.9(c)). A metal nanoparticle can be readily seen at the tip of the tube formed at 650 C, thus indicating that a tip growth mechanism prevails in this case (Figure 1.9(d)). Despite the fact that the thermal CVD method produces tangled and coiled nanotubes, this technique is capable of forming aligned arrays of CNTs by precisely adjusting the reaction parameters [53, 56–58, 61–63]. For practical engineering applications in the areas of field emission display and nanofillers for composites, formation of vertically aligned nanotubes is highly desirable. To achieve this, a gaseous precursor is normally diluted with hydrogen-rich gas, that is, NH3 or H2. Lee et al. reported that NH3 is essential for the formation of aligned nanotubes [61]. Choi et al. [62] demonstrated that the ammonia gas plays the role of etching amorphous carbon during the earlier stage of nucleation of nanotubes. Both synthesis by C2H2 after ammonia pretreatment, and synthesis by NH3/C2H2 gas mixture without ammonia treatment favor alignment of nanotubes. Figure 1.10(a) shows the morphology of nanotubes synthesized by flowing C2H2 on a Ni film at 800 C without ammonia pretreatment. Apparently, coiled nanotubes are produced without NH3 treatment. However, well-aligned nanotubes can be formed on the Ni film with ammonia pretreatment prior to the introduction of C2H2 gas (Figure 1.10(b)). Figure 1.10 Surface morphology of CNTs synthesized by C2H2 gas mixture on 20 nm thick Ni films: (a) without and (b) with ammonia treatments. Reproduced with permission from [62]. Copyright Ó (2001) Elsevier. 1.3 Synthesis of Carbon Nanotubesj13
14j 1 Introduction 1.3.3.2 Plasma-enhanced CVD Plasma-enhanced CVD (PECVD) offers advantages over thermal CVD in terms of lower deposition temperatures and higher deposition rates. Carbon nanotubes can be produced at the relatively low temperature of 120 C [64], and even at room temperature [65] using plasma-enhanced processes. This avoids the damage of substrates from exposure to high temperatures and allows the use of low-melting point plastics as substrate materials for nanotubes deposition. The plasma Sources used include direct current (d.c.), radio frequency (r.f.), microwave and electron cyclotron resonance microwave (ECR-MW). These Sources are capable of ionizing reacting gases, thereby generating a plasma of electrons, ions and excited radical species. In general, vertically aligned nanotubes over a large area with superior uniformity in diameter and length can be synthesized by using PECVD techniques [54, 66–70]. Among these Sources, microwave plasma is commonly used. The excitation microwave frequency (2.45 GHz) oscillates electrons that subsequently collide with hydrocarbon gases, forming a variety of C xH y radicals and ions. During plasmaenhanced deposition, hydrocarbon feedstock is generally diluted with other gases such as hydrogen, nitrogen and oxygen. Hydrogen or ammonia in hydrocarbon Sources inhibit the formation of amorphous carbons and enhance the surface diffusion of carbon. This facilitates formation of vertically aligned nanotubes. By regulating the types of catalyst, microwave power and the composition ratios of gas precursor, helix-shaped and spring-like MWNTs have been produced [71]. 1.3.3.3 Laser assisted CVD Laser assisted CVD (LCVD) is a versatile process capable of depositing various kinds of materials. In the process, a laser (CO2) is used to locally heat a small spot on the substrate surface to the temperature required for deposition. Chemical vapor deposition then occurs at the gas–substrate interface. As the spot temperature increases and the reaction proceeds, a fiber nucleates at the laser spot and grows along the direction of laser beam [72]. LCVD generally has deposition rates several orders of magnitude higher than conventional CVD, thus offering the possibility to scale-up production of CNTs. Focused laser radiation permits growth of locally defined nanotube films. Rohmund et al. reported that films of vertically aligned MWNTs of extremely high packing density can be produced using LCVD under conditions of low hydrocarbon concentration [73]. The use of LCVD for producing nanotubes is still in the earlier development stage. Compared with PECVD, only few studies have been conducted on the synthesis of CNTs using LCVD [50, 73, 74]. 1.3.3.4 Vapor Phase Growth This refers to a synthetic process for CNTs in which hydrocarbon gas and metal catalyst particles are directly fed into a reaction chamber without using a substrate. VGCFs can be produced in higher volumes and at lower cost from natural gas using this technique. In 1983, Tibbets developed a process for continuously growing vapor grown carbon fibers up to 12 cm long by pyrolysis of natural gas in a stainless steel tube [75]. However, the diameters of graphite fibers produced are quite large, from 5 to 1000 mm depending on the growth temperature and gas flow rate.
Page 2 and 3: Sie Chin Tjong Carbon Nanotube Rein
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Page 6 and 7: Contents Preface IX List of Abbrevi
Page 8 and 9: 5 Carbon Nanotube-Ceramic Nanocompo
Page 10: Preface Carbon nanotubes are nanost
Page 13 and 14: XII List of Abbreviations HIP hot i
Page 16 and 17: 1 Introduction 1.1 Background Compo
Page 18 and 19: Figure 1.2 Transmission electron mi
Page 20 and 21: 1.3 Synthesis of Carbon Nanotubes 1
Page 22 and 23: MWNTs can be as high as 70% of the
Page 24 and 25: Figure 1.7 In situ TEM images recor
Page 26 and 27: 1.3 Synthesis of Carbon Nanotubesj1
Page 30 and 31: Since then, large efforts have been
Page 32 and 33: 1.3.4 Patent Processes Carbon nanot
Page 34 and 35: 1.4 Purification of Carbon Nanotube
Page 36 and 37: Table 1.3 Patent processes for the
Page 38 and 39: Figure 1.13 Schematic illustration
Page 40 and 41: 1.5 Mechanical Properties of Carbon
Page 42 and 43: Figure 1.14 Carbon nanotubes in hig
Page 44 and 45: Figure 1.15 In situ tensile deforma
Page 46 and 47: Table 1.7 Theoretical and experimen
Page 48 and 49: Nomenclature ~a 1 , ~a 2 Unit vecto
Page 50 and 51: carbon nanotubes. Physical Review L
Page 52 and 53: 70 Jang, I., Uh, H.S., Cho, H.J., L
Page 54 and 55: 108 Shelimov, K.B., Esenaliev, R.O.
Page 56 and 57: Bonnamy, S., Beguin, F., Burnham, N
Page 58 and 59: 2 Carbon Nanotube-Metal Nanocomposi
Page 60 and 61: isostatic pressing. In certain case
Page 62 and 63: This implies the absence of effecti
Page 64 and 65: coating material, the plasma gun an
Page 66 and 67: Table 2.4 Changes in the size and v
Page 68 and 69: Figure 2.6 (a) Low and (b) high mag
Page 70 and 71: Figure 2.8 SEM micrographs showing
Page 72 and 73: Figure 2.11 Bright field TEM microg
Page 74 and 75: Figure 2.13 TEM image of bulk Al/5
Page 76 and 77: 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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104j 4 Mechanical Characteristics o
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132j 5 Carbon Nanotube-Ceramic Nano
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186j 7 Mechanical Properties of Car
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Table 8.1 Patent processes for maki
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218j 8 Conclusions development of c
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220j 8 Conclusions Figure 8.2 TEM m
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222j 8 Conclusions increase in Vick
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224j 8 Conclusions References 1 Cha
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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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