Carbon Nanotube Reinforced Composites: Metal and Ceramic ...
Carbon Nanotube Reinforced Composites: Metal and Ceramic ...
Carbon Nanotube Reinforced Composites: Metal and Ceramic ...
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Fan et al. prepared the Al2O3/0.5 wt% SWNT <strong>and</strong> Al2O3/1 wt% SWNT nanocomposites<br />
using heterocoagulation [Chap. 5, Ref. 54]. The colloidally-dispersed<br />
composite <strong>and</strong> monolithic alumina powders were hot pressed at 1600 Cinan<br />
argon atmosphere under a pressure of 20 MPa for 1 h. The r.d. values of monolithic<br />
alumina, Al2O3/0.5 wt% SWNT <strong>and</strong> Al2O3/1 wt% SWNT nanocomposites are<br />
99.8%, 99.5% <strong>and</strong> 99.1%. The bending strength of Al2O3, Al2O3/0.5 wt% SWNT<br />
<strong>and</strong> Al 2O 3/1 wt% SWNT nanocomposites is 356, 402 <strong>and</strong> 423 MPa, respectively.<br />
The VIF toughness of Al2O3, Al2O3/0.5 wt% SWNT <strong>and</strong> Al2O3/1 wt% SWNT<br />
nanocomposites is 3.16, 5.12 <strong>and</strong> 6.40 MPa m 1/2 .Additionof1wt%SWNTimproves<br />
the fracture toughness of alumina by 103% <strong>and</strong> bending strength by 18.8%.<br />
Crack bridging <strong>and</strong> pull-out of SWNTs can be readily seen in the SEM fractographs<br />
of Al2O3/1 wt% SWNT nanocomposite <strong>and</strong> is responsible for the toughening<br />
behavior of this material. It is noted that the mechanical properties of the<br />
Al2O3/0.5 wt% SWNT <strong>and</strong> Al2O3/1 wt% SWNT nanocomposites can be improved<br />
further by hot pressing the composite powders at lower temperatures. Hot pressing<br />
the nanocomposite at 1600 C leads to the degradation of SWNTs. It has been<br />
reported that that the structure of CNTs of alumina nanocomposites can be<br />
preserved by employing lower sinter temperatures up to 1250 C only. Above<br />
this temperature, CNTs convert to graphite <strong>and</strong> carbon nano-onion structures<br />
[Chap. 5, Ref. 53, Chap. 5, Ref. 59].<br />
Sun et al. investigated the effect of hot-pressing temperatures on the bending<br />
strength <strong>and</strong> fracture toughness of Al2O3/1 wt% MWNT nanocomposite [Chap. 5,<br />
Ref. 52]. The nanocomposite was prepared by the heterocoagulation route <strong>and</strong><br />
hot pressing. The later mechanical treatment was carried out at 1350–1500 Cin<br />
an argon atmosphere under 30 MPa for 1 h. Figures 7.4 <strong>and</strong> 7.5 show SEM<br />
Figure 7.4 (a) Low <strong>and</strong> (b) high magnification SEM micrographs<br />
showing the fracture surface of Al2O3/1 wt% MWNT<br />
nanocomposite sintered at 1500 C. Reproduced with permission<br />
from [Chap. 5, Ref. 52]. Copyright Ó (2005) Elsevier.<br />
7.3 Oxide-Based Nanocompositesj191