Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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5.4.3 Titania Matrix Titania (TiO2) is a semiconducting oxide with high photocatalytic ability. It finds application in many technological areas such as microelectronics, photocatalysis and sensors [95–97]. Titania is also an important bioceramic coating material for metal implants due to its excellent biocompatibility [98, 99]. Incorporating CNTs into titania can lead to the development of novel composite materials with advanced functional properties for photocatalytic, microelectronic and biomedical applications [100]. The techniques used for forming titania-CNT nanocomposites include heterocoagulation, sol-gel and hydrothermal treatment. Sun and Gao employed heterocoagulation to deposit titania on MWNTs [62]. In the process, ammonia-treated MWNTs were dispersed ultrasonically in water containing cationic PEI. Titania nanoparticles with sizes less than 10 nm were dispersed in water under sonication and the pH value was adjusted by adding NaOH. Titania drops were then added to the nanotube suspension under a pH of 8. Figure 5.24 shows the zeta potential vs pH curves for titania and NH 3-treated MWNTs measured in 1 mM NaCl solution. For zeta-potential measurements, the pH was adjusted with HCl for acidic suspension and with NaOH for basic suspension. Electronegative titania nanoparticles are attracted to positively charged surfaces of MWNTs, thereby forming a titania coating layer on the nanotube surface (Figure 5.25). In another study, Sun et al. coated SWNTs with titania nanoparticles by using TiCl4 precursor and PEI surfactant by the hydrothermal method [101]. Titania nanoparticles were formed by the hydrolysis of TiCl4 solution through the following reaction: TiCl4 þ 2H2O ! TiO2 þ 4H þ þ 4Cl : ð5:1Þ Figure 5.24 Zeta potential as a function of pH for titania and treated MWNTs with PEI. Reproduced with permission from [62]. Copyright Ó (2003) Elsevier. 5.4 Oxide-Based Nanocompositesj155
156j 5 Carbon Nanotube–Ceramic Nanocomposites Figure 5.25 TEM image showing titania coated MWNT surface. Reproduced with permission from [62]. Copyright Ó (2003) Elsevier. Acid-purified SWNTs were then added to the TiCl4 suspension. PEI addition is beneficial to assist the deposition of titania on nanotube surfaces. Jitianu et al. employed both sol-gel and hydrothermal techniques to coat titania on MWNTs [102]. For the sol-gel process, alkoxide precursor, that is, titanium tetraethoxide Ti(OEt)4 or titanium tetra-isopropoxide Ti(OPr)4) was mixed with ethanol/ isopropanol, water and nitric acid to form a titania sol under magnetic stirring. MWNTs were then mixed with the sol under stirring. The impregnated MWNTs were separated from the solution by filtration. For hydrothermal treatment, the precursor consisted of 15 wt% TiOSO4 in diluted sulfuric acid. MWNTs were then added to the TiOSO4 solution in water. Hydrothermal treatment was performed in an autoclave at 120 C for 5 h. Impregnated nanotubes prepared by the sol-gel and hydrothermal methods were further dried at high temperatures. MWNT surfaces prepared by solgel using Ti(OEt)4 precursor are coated with a continuous thin film (Figure 5.26(a)), and with TiO2 nanoparticles in the case of Ti(OPr)4 (Figure 5.26(b)). The microstructure of titania coated nanotubes prepared by hydrothermal method is shown in Figure 5.26(c). 5.4.4 Zirconia Matrix Zirconia-based ceramics are well recognized for their excellent mechanical, electrical, thermal and optical properties. They find a broad range of industrial applications including oxygen sensors, solid oxide fuel cells and ceramic membranes [103, 104]. The physical and mechanical properties of ziroconia can be further enhanced by adding low loading level of CNTs. Zirconia-CNT nanocomposites can be fabricated by hot-pressing [105], heterocoagulation [106] and hydrothermal crystallization [107, 108]. Shan and Gao fabricated ZrO2/MWNT nanocomposites by hydrothermal treatment of ZrOCl2.8H2O. They reported that full coverage of ZrO2 on nanotubes can be prepared only through the use of an acid medium [108]. In a weak alkaline solution, only few zirconia agglomerates adhere to the sidewalls of MWNTs. Hardly any adsorption of zirconia on nanotubes can be observed in a strong alkaline solution. They attributed the formation of zirconia coating on sidewalls of MWNTs to the
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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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206j 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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