Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

98j 3 Physical Properties of Carbon Nanotube–Metal Nanocomposites
Table 3.3 CTE values of the Sn–37%Pb alloy and its CNT-reinforced composites.
Material CTE (10 6 ºC 1 )
63%Sn–37%Pb 25.8 1.2
63%Sn–37%Pb/0.01% SWNT 25.2 0.9
63%Sn–37%Pb/0.03% SWNT 24.6 1.1
63%Sn–37%Pb/0.05% SWNT 23.4 0.7
63%Sn–37%Pb/0.08% SWNT 21.2 1.3
63%Sn–37%Pb/0.1% SWNT 20.8 1.4
63%Sn–37%Pb/0.3% SWNT 19.8 1.1
63%Sn–37%Pb/0.5% SWNT 19.2 0.9
PCB 18
SWNT 1.6
Reproduced with permission from [27]. Copyright Ó (2006) Elsevier.
composite solder reinforced with nanotubes which closely matches that of the PCB
can address the major reliability concern [29].
3.3
Electrical Behavior of Metal-CNT Nanocomposites
Up till now, the electrical behavior only of Al-CNTnanocomposites has been reported
in the literature. Xu et al. measured the electrical resistivity of Al/MWNT nanocomposites
filled with 1, 4 and 10 wt% CNTs from room temperature down to 4.2 K [31].
The composites were prepared by hand grinding MWNTs with Al powder, followed
by hot pressing. Figure 3.6 shows the variation of electrical resistivity with temperatures
for the Al/MWNT nanocomposites. The resistivity of all composites decreases
linearly with temperature from 295 down to 80 K. At temperatures 80 K, the
resistivity of the composites approaches zero. The loss of electrical resistance of
nanocomposites at low temperatures is somewhat similar to that of superconducting
materials. The mechanism for zero resistance of the nanocomposites at low temperatures
could be attributed to the ballistic conduction of CNTs. MWNTs conduct
current ballistically and do not dissipate heat. It has been theoretically predicted that
ballistic conduction occurs without resistance in CNTs due to the disappearance of
scattering. When scattering occurs during electric conduction very few ballistics are
produced [32].
Xu et al. demonstrated that the electrical resistivity of Al (3.4 mW cm) increases
to 4.9 mW cm by adding 1 wt% MWNT [31]. The resistivity further increases to
6.6 mW cm when 4 wt% MWNT is added. The reported experimental resistivity of
individual CNT is in the order of 10 6 –10 4 W cm, being much lower than that
of aluminum. They attributed the increase in resistivity of the nanocomposites to
agglomeration of CNTs at grain boundaries. The agglomerates enhance the scattering
of the charge carrier at grain boundaries, thereby reducing the conductivity.
Similarly, the resistivity of the 2024 Al/3 wt% CNFnanocomposite also shows a linear