Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

flakes with platelets of 400 mm are recommended due to their low cost and excellent
thermal conductivity.
The size of integrated circuits (IC) continues to decrease as the demand for IC in
wireless communication and personal computers increases. Miniaturization of IC
chips and increasing processing speed reduces the heat transfer surface area and
increases power. Local overheating in the central processing unit of computers can
cause the breakdown of the whole system. Accordingly, heat dissipation is the most
common problem that limits the performance, reliability and miniaturization of
microelectronics. Further, rapid technological advancement in nanotechnology has
led to the development of novel nanoelectronic devices with multifunctional properties
[11–13]. Conventional metal-matrix composites reinforced with large volume
content of ceramic microparticulates cannot cope with the fast development of
electronic devices. Thus, composites reinforced with a low loading level of carbon
nanotubes (CNTs)show great promise for thermal management applications. At
present, only polymer-based composites reinforced with CNTs have been developed
into thermal interface materials (TIM) for heat dissipation in electronic components.
For instance, Huang et al. fabricated a prototype TIM film consisting of aligned CNT
arrays embedded in an elastomer [14]. They achieved a 120% enhancement of
thermal conductivity in the nanocomposite film reinforced with 0.4 vol.% CNT.
However, the thermal conductivity of such nanocomposite film (1.21 W m 1 K 1 )is
far less small than the theoretical thermal conductivity of aligned nanotubes.
Various unique properties of CNTs have generated interest among many
researchers to use them as nanofillers for metals. The Young s modulus of CNTs
predicted from theoretical simulations and measured experimentally is of the order
of 1000 GPa. The tensile strength of MWNTs determined experimentally is 150 GPa.
Further, theoretical prediction reveals an extremely high value of 6000 W m 1 K 1 for
the room temperature thermal conductivity of an isolated SWNT. The measured
room temperature thermal conductivity of an individual MWNT is 3000 W m 1 K 1 .
The combination of high strength, stiffness, aspect ratio and flexibility make
CNTs ideal reinforcement materials for high performance composites employed
for structural engineering and space applications. Despite these advantages, research
studies on the thermal and electrical conducting behaviors of metal/CNT nanocomposites
are very scarce. Nevertheless, there are tremendous opportunities for
materials scientists to develop novel metal-matrix nanocomposites with fascinating
properties.
3.1.1
Thermal Response of Metal-Matrix Microcomposites
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The thermal expansion behavior of ceramic particulate-reinforced MMCs is controlled
by several factors including size, distribution and content of reinforcing
particles. In general, internal stresses are created within the composite during the
cooling from processing temperature due to the mismatch in thermal expansion of
the constituents. The thermal expansion behavior of a composite is quantified by the
coefficient of thermal expansion (CTE) defined as the change in unit length of a