Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

More documents

Recommendations

Info

sintered at 1500 C are responsible for its poorest fracture toughness and lowest bending stress. Reducing the sinter temperature to 1450 C leads to a marked increase of the bending stress (554 MPa) and VIF toughness (3.9 MPa m 1/2 ). The fracture toughness of nanocomposite increases with decreasing sinter temperature. Comparing the fracture toughness values of monolithic alumina sintered at the same temperature, it appears that the toughening efficiency of MWNT in alumina is very low. The fracture toughness of nanocomposite hot pressed at 1500 Cis even smaller than that of alumina sintered at 1500 C. There is no improvement in fracture toughness of the nanocomposite hot pressed at 1450 and 1400 C. The fracture toughness of nanocomposite hot pressed at 1350 C improves by nearly 33.3% compared with the single-phase alumina sintered at 1350 C. The poor toughness of the nanocomposite hot pressed at 1400–1500 C is attributed to the degradation of CNTs [Chap. 5, Ref. 53, Chap. 5, Ref. 69]. It is quite obvious that the hot-pressing temperature must be reduced to lower temperatures to preserve the structure of CNTs. In another study, Sun et al. employed SPS to consolidate the Al2O3/0.1 wt% CNT nanocomposite and single-phase alumina at 1300 C for 5 min [Chap. 5, Ref. 61]. Obviously, the addition of only 0.1 wt% CNT to alumina increases the fracture toughness by about 32.4% from 3.7 to 4.9 MPa m 1/2 . Compared with hot pressing, only one-tenth of CNT content is needed to improve the toughness of alumina by 33%. Figure 7.6(a) and (b) show SEM fractographs of Al2O3/0.1 wt% CNT nanocomposite. It is interesting to see from Figure 7.6(a) that the nanotubes are covered with matrix material, forming bridges across the crack. The crack bridging effect hinders the enlargement of the crack. Other alumina-sheathed nanotubes are broken and embedded in the matrix along the crack (Figure 7.4(b)). The crack bridging mechanism is responsible for the improvement of fracture toughness of such nanocomposite. This behavior is commonly observed in the polymer-CNT nanocomposites toughened by CNTs [20]. The polymer sheathed nanotubes bridge the matrix cracks effectively during tensile loading (Figure 7.7). Figure 7.6 SEM fractographs showing typical interactions between crack and alumina sheathed CNTs. Reproduced with permission from [Chap. 5, Ref. 61]. Copyright Ó (2002) The American Chemical Society. 7.3 Oxide-Based Nanocompositesj193
194j 7 Mechanical Properties of Carbon Nanotube–Ceramic Nanocomposites Figure 7.7 SEM micrograph showing crack bridging by polymer sheathed CNTs. Some nanotubes are sheathed by small polymer beads as indicated by the arrows. Reproduced with permission from [20]. Copyright Ó (2004) The American Chemical Society. Yamamoto et al. fabricated the Al2O3/0.9 vol% MWNT, Al2O3/1.9 vol% MWNT and Al2O3/3.7 vol% MWNT nanocomposites by dispersing acid-treated MWNTs in ethanol ultrasonically. Aluminum hydroxide and magnesium hydroxide were then added to the nanotube suspension under sonication. The resulting suspension was filtered, oven dried, followed by SPS at 1500 C under a pressure of 20 MPa for 10 min [Chap. 5, Ref. 71]. From the zeta potential measurements, aluminum hydroxide is positively charged over a wide pH range of 3–9 whilst acid-treated MWNTs is negatively changed in this pH range. Aluminum hydroxide particles are accumulated on MWNTs surfaces due to the electrostatic attraction, resulting in a homogeneous dispersion of nanotubes. Aluminum hydroxide precursor finally converted to a-alumina during SPS. The VIF test revealed that the addition of 0.9 vol% MWNT to alumina leads to an increase of fracture toughness from about 4.25 to 5.90 MPa m 1/2 . The toughness then decreases with increasing nanotube content. Figure 7.8 shows the variation of normalized fracture toughness vs nanotube content for the Al2O3/MWNTnanocomposites. In this figure, the fracture toughness value of nanocomposites is normalized to that of pure alumina. The normalized experimental result reported by Fan et al. [Chap. 5, Ref. 54] is also shown for comparison. Apparently, additions of CNTs up to 1 vol% CNTs can produce a beneficial toughening effect in alumina despite the employment of high sintering temperature (1500 or 1600 C). Above 1 vol% CNT, the toughening effect of CNTs diminishes as expected. Mukerjee and coworkers fabricated pure Al 2O 3,Al 2O 3/5.7 vol% SWNTand Al 2O 3/ 10 vol% SWNT nanocomposites through powder mixing in ethanol, ball milling and SPS at 1150 C for 3 min under 63 MPa [Chap. 5, Ref. 44, Chap. 5, Ref. 70]. The fracture toughness and hardness of these specimens were determined by indentation measurements. The indentation fracture toughness of pure Al2O3, Al2O3/5.7 vol% SWNT and Al2O3/10 vol% SWNT nanocomposites is 3.3, 7.9 and 9.7 MPa m 1/2 , respectively. All these specimens achieved a full density of 100% by sintering at 1150 C for 3 min (Chap. 5, Table 5.2). The structure and unique properties of SWNTs can be preserved at 1150 C for 3 min. Under these processing
Page 2 and 3:
Sie Chin Tjong Carbon Nanotube Rein
Page 4 and 5:
Sie Chin Tjong Carbon Nanotube Rein
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 28 and 29:
show TEM images of MWNTs synthesize
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
Page 78 and 79:
limited improvement in ultimate ten
Page 80 and 81:
Figure 2.18 SEM micrographs of the
Page 82 and 83:
Figure 2.19 (a) Low and (b) high ma
Page 84 and 85:
Figure 2.22 SEM micrographs of (a)
Page 86 and 87:
Figure 2.25 (a) TEM micrograph show
Page 88 and 89:
2.8 Transition Metal-Based Nanocomp
Page 90 and 91:
Figure 2.27 TEM image of electrodep
Page 92 and 93:
Figure 2.29 SEM micrographs of (a)
Page 94 and 95:
Figure 2.31 Schematic representatio
Page 96 and 97:
einforcement content SiCp/Al compos
Page 98 and 99:
Materials Science Forum, 534-536 (P
Page 100 and 101:
composite. Materials Science and En
Page 102:
111 Cha, S.I., Kim, K.T., Arshad, S
Page 105 and 106:
90j 3 Physical Properties of Carbon
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
100j 3 Physical Properties of Carbo
Page 117 and 118:
102j 3 Physical Properties of Carbo
Page 119 and 120:
104j 4 Mechanical Characteristics o
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
132j 5 Carbon Nanotube-Ceramic Nano
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158: 142j 5 Carbon Nanotube-Ceramic Nano
Page 185 and 186: 170j 6 Physical Properties of Carbo
Page 201 and 202: 186j 7 Mechanical Properties of Car
Page 207: 192j 7 Mechanical Properties of Car
Page 231 and 232: Table 8.1 Patent processes for maki
Page 233 and 234: 218j 8 Conclusions development of c
Page 235 and 236: 220j 8 Conclusions Figure 8.2 TEM m
Page 237 and 238: 222j 8 Conclusions increase in Vick
Page 239 and 240: 224j 8 Conclusions References 1 Cha
Page 241 and 242: 226j 8 Conclusions nano-matrix. Scr
Page 243: 228j Index l laser ablation 7 load
show all

Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?