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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44j 2 <strong>Carbon</strong> <strong>Nanotube</strong>–<strong>Metal</strong> Nanocomposites<br />
Table 2.1 Typical reinforcement materials for MMCs.<br />
Continuous Fiber C, B, SiC, Al2O3, Si3N4<br />
Short fiber SiC, Al2O3<br />
Whisker TiB, SiC, Si3N4, Al2O3, SiO2<br />
Particulate SiC, TiC, B 4C, Al 2O 3,TiB 2,Si 3N 4, AlN<br />
than 99%. The physical <strong>and</strong> mechanical properties of CFs prepared from a PAN<br />
precursor are listed in Table 2.2 [2], which shows that commercial grade CFs use a<br />
lower cost, modified textile-type PAN. Three different grades of fibers for the<br />
aerospace category are derived from different combinations of mechanical stretching,<br />
heat treatment <strong>and</strong> precursor spinning. <strong>Carbon</strong> fibers can also be prepared<br />
from pitch through spinnerets <strong>and</strong> subsequent heat treatment somewhat similar to<br />
those of PAN-based fibers. The pitch Sources include petroleum, coal tar <strong>and</strong> asphalt.<br />
It is noted that the large crystallite size <strong>and</strong> better orientation of pitch-based fibers<br />
give rise to higher modulus, thermal conductivity <strong>and</strong> lower thermal expansion when<br />
compared with PAN-based fibers [3].<br />
Such MMCs are generally fabricated by powder metallurgy (PM) <strong>and</strong> liquid metal<br />
routes. The PM route is mainly used for making discontinuously reinforced MMCs<br />
with a near net shape capability The process involves initial mixing of metal powders<br />
<strong>and</strong> ceramic particulates, followed by cold pressing <strong>and</strong> sintering, or hot pressing/hot<br />
Table 2.2 Properties of PAN-based carbon fibers.<br />
Property<br />
Commercial,<br />
st<strong>and</strong>ard<br />
modulus<br />
St<strong>and</strong>ard<br />
modulus<br />
Aerospace<br />
Intermediate<br />
modulus<br />
High<br />
modulus<br />
Tensile modulus/GPa 228 220–241 290–297 345–448<br />
Tensile strength/MPa 380 3450–4830 3450–6200 3450–5520<br />
Elongation at break, % 1.6 1.5–2.2 1.3–2.0 0.7–1.0<br />
Electrical resistivity/mO cm 1650 1650 1450 900<br />
Thermal conductivity/W m –1 K –1<br />
20 20 20 50–80<br />
Coefficient of thermal expansion,<br />
axial direction, 10 6 K<br />
0.4 0.4 0.55 0.75<br />
Density, g cm –3<br />
1.8 1.8 1.8 1.9<br />
<strong>Carbon</strong> content, % 95 95 95 þ99<br />
Filament diameter, mm 6–8 6–8 5–6 5–8<br />
Manufacturers Zoltek,<br />
Fortafil,<br />
SGL<br />
Reprinted from [2]. Copyright Ó (2001) ASM International.<br />
BPAmoco, Hexcel,<br />
Mitsubishi Rayon,<br />
Toho, Toray,<br />
Tenax, Soficar,<br />
Formosa