Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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Chap. 5, Ref. 54, Chap. 5, Ref. 60]. The strengthening of such nanocomposites arises from effective load transfer from the matrix to nanotubes during mechanical loading. Homogeneous dispersion of CNTs in ceramics and strong nanotube–matrix bonding are prerequisites to achieve improved mechanical strength in the nanocomposites. 7.3 Oxide-Based Nanocomposites 7.3.1 Alumina Matrix 7.3.1.1 Deformation Behavior The mechanical properties of alumina-CNTnanocomposites depend strongly on the composite synthesis route and sintering process. The composite synthesis route controls the distribution of CNTs in the ceramic matrix and the interfacial bonding states. The later sintering process determines the final density of nanocomposite products. In general, homogeneous dispersion of nanotubes and strong CNT-matrix interfacial bonding are difficult to achieve using conventional powder mixing techniques. Ball milling of ceramic powders and CNTs in ethanol is essential to assist homogeneous dispersion but it beneficial effects depends greatly on the milling time, ball-powder ratio and type of ceramic powders. The heterocoagulation route shows promise because the alumina-CNT composite with better nanotube dispersion and strong interfacial bonding can be synthesized at the molecular level. Conventional hot pressing that combines composite powder consolidation and heat treatment at high temperatures is often adopted by researchers to fabricate nanocomposites due to its simplicity and versatility. Care must be taken in the selection of hot-pressing temperatures in order to avoid damage to the nanotubes at elevated temperatures. Peigney et al. [Chap. 5, Ref. 59] reported that the fracture strength of hot-pressed Fe-Al 2O3/4.8 wt% CNT nanocomposite is only marginally higher than that of monolithic alumina, but lower than that of the Fe-Al2O3 composites. Further, the fracture toughness values of Fe-Al2O3/8.5 vol% CNT and Fe-Al2O3/10 vol% CNTnanocomposites were lower than that of Fe-Al2O3 (Table7.1). Table 7.1 Mechanical properties of hot-pressed alumina and alumina-CNT nanocomposites. Materials Fe content (wt %) Fracture strength (MPa) 7.3 Oxide-Based Nanocompositesj189 Fracture toughness (MPa m 1/2 ) Fracture mode Al2O3 Ref [Chap. 5, Ref. 42] — 330 4.4 Intergranular Fe-Al2O3 Ref [Chap. 5, Ref. 42] 10 630 7.2 Mixed Fe-Al2O3/8.5 vol%CNT Ref [Chap. 5, Ref. 59] 8.38 400 5.0 Mixed Fe-Al2O3/10 vol% CNT Ref [Chap. 5, Ref. 59] 8.38 296 3.1 Intergranular
190j 7 Mechanical Properties of Carbon Nanotube–Ceramic Nanocomposites These nanocomposites were prepared by hot pressing of synthesized in situ composite powders at 1500 C. The relative density (r.d.) values of hot-pressed Fe-Al2O3/8.5 vol% CNT and Fe-Al2O3/10 vol% CNT composites are 88.7 and 87.3%, respectively. Therefore, the alumina-CNT nanocomposites exhibit inferior mechanical properties due to their porous nature. More recently, Maensiri et al. investigated the mechanical properties of alumina/ CNFnanocomposites reinforced with 1, 2.5 and 5 vol% CNF [19]. The nanocomposites were prepared by conventional powder mixing, ball-milling, followed by hot pressing at 1450 C. From SEM fractographs as shown in Figure 7.3(a)–(d)), agglomeration of CNFs can be readily seen in the Al2O3/5 vol% CNF composite. The bending stress of hot-pressed Al2O3, Al2O3/1 vol% CNF, Al2O3/2.5 vol% CNF and Al2O3/5 vol% CNF specimens is 414, 301, 279 and 219 MPa, respectively. Therefore, the bending strength of hot-pressed nanocomposites decreases with increasing filler content as a result of filler clustering and degradation of CNFs at high pressing temperature. The VIF toughness of hot-pressed Al 2O 3,Al 2O 3/1 vol% CNF, Al 2O 3/2.5 vol% CNF and Al 2O 3/ 5 vol% CNF specimens is 2.41, 2.50, 2.74 and 2.54 MPa m 1/2 , respectively. The Al2O3/ 2.5 vol% CNF nanocomposite exhibits the highest fracture toughness, but it is only improved by 13.7% compared with monolithic alumina. The toughening mechanism in Al2O3/2.5 vol% CNF nanocomposite is associated with the crack bridging effect of CNF (Figure 7.3(c)). Figure 7.3 SEM images showing fracture surfaces of (a) Al2O3; (b) Al 2O 3/1 vol% CNF; (c) Al 2O 3/2.5 vol% CNF; (d) Al 2O 3/5 vol% CNF specimens. Reproduced with permission from [19]. 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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132j 5 Carbon Nanotube-Ceramic Nano
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