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Jake Harwood
ENGR 1050
October 18, 2015
Carbon Nanotubes
Introduction
Carbon nanotubes (CNT) are the strongest materials that have yet to be discovered. Singlewalled carbon nanotubes (SWCNTs) have been reported to have up to an elastic modulus as high as 1
TPa, but also having a tensile strength of close to 60 GPa. This ranges from five to thirty times greater
than steels. Because of not only these values but also having only one sixth the weight of steel, CNT are
quickly drawing attention to themselves.
Figure 1
SWCNTs have three different structures. These structures, as shown in Figure 1, are the
armchair, zigzag, and the chiral. For the armchair structure, the hexagons are arranged parallel to the
axis of the nanotube. The armchair has electrical properties that are similar to metals. For example, this
type of structure is more conductive than copper. The zigzag and chiral structures are different in
arrangement, but similar in electrical properties. They both have the properties of semiconductors.
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There are multiple ways of creating carbon nanotubes, but the three major ones are arc
discharge, laser ablation, and chemical vapor deposition. The arc discharge was originally used to
produce C60 fullerenes but is now the most common way to create CNT. Both the arc discharge and
laser ablation method are used to create high quality CNTs. While these applications can only create a
small amount of CNTs, the chemical vapor deposition is used to create a large amount. But the one
down side to the chemical vapor deposition is that the CNTs are not as high of quality as the CNTS that
come from the arc discharge and laser ablation method.
Fundamental Concepts

Electronics: Carbon nanotubes are extremely conductive when they have a small diameter. In
theory, the armchair CNTs can carry a 4*10^9 A/cm^2 of electrical current. This is immensely
larger than that of coppers electrical density.

Communications: CNTs have been found to be able to control pulsed laser outputs over a wider
band than any of the semiconductors used today. This is a big leap for telecommunications.
Telecommunications uses semiconductors to create a pulse from a beam, since a constant beam
doesn’t do any good. The CNTs will do a better job at absorbing the beam than the
semiconductors do now and will cost less. Researchers are hopeful for the CNTs to be up scaled
to be of practical use for telecommunications.

Thermal Conductivity: Because of the high thermal conductivity, CNTs are promising to be used
as an effective thermal interface material for microelectronics and other cooling applications.
Once of the biggest problems right now with the use of these carbon nanotubes is that the
surface area is too small. If at a point of time they are able to up scale the CNTs then they would
be put into practical use for this but also many other uses.
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Carbon Nanotubes and armor
As mentioned before, the mechanical properties of carbon nanotubes are extreme. With high
tensile strength and elastic modulus that none other can compete with, scientist have turned their eyes
upon these carbon nanotubes for the use of armor. From police officers to national defense, carbon
nanotubes are slowly taking over the armor industry.
Before carbon nanotubes, if the U.S. government wanted to create vehicles for the army then
they would have to choose between having a vehicle that was made of steel or a fiber-reinforced
polymer-matrix body. Both have their pros and cons. While steel did excellent at protecting form bullets,
it was heavy and slow. This put a toll on the vehicle and also made it a vulnerable because it was too
slow. The fiber body was faster and didn’t take a heavy toll on the main frame of the car, but it couldn’t
protect the passengers from bullets. But now with CNTs they have made an advanced fiber-reinforced
polymer-matrix composites with carbon nanotube reinforcement. Now with the Humvees being made
of a carbon nanotube body, they can have the strength of steel without the cons of the steel.
CNTs have been looked at for the Humvees because of their high hardness. They can deflect the
projectile while their high strength combined with a high ductility helps with absorbing the projectiles
energy. All of this is done with little harm to the material. As shown in Figure 2, the projectile hits the
material. But because of the strength of the CNTs, the projectile cannot go throw the material. It’s only
able to push into it. Scientist are able to make it so that the energy of the impact is not focused in one
spot, they make it so that a certain area around the spot of impact absorbs energy as well. This helps so
that the impact does not hurt the user. With previous vests the material stopped the projectile, but still
injured the user by blunt force. With this new technology, the impact is does not hurt the user as much.
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When it comes to the protection of soldiers, police
officers, and special agents, their body armor has to be two
steps ahead of the newest weapon. Before the bullet proof
vests were heavy and not comfortable to wear. But now with
the invention of carbon nanotubes the vests are lightweight
and fit more comfortably on the user.
With light weight but still having a Young’s modulus of
about 1000 GPa and an estimated ballistic performance
parameter of 2700 m/s to 4326 m/s, this small material is the
new face of armor. By looking at Figure 3 the graph shows
the different materials used to make the body armor. Figure
3 compares the specific energy absorbed by the material
Figure 2
against the velocity of the projectile.
When it comes to utilizing the carbon nanotubes in the ballistic performance to body armor,
there are three different ways. The first way is incorporating the CNTs into PMCs (Polymer Matrix
Composites), ceramics or metals to increase the hardness or toughness. The second way is to use the
fibers of carbon nanotubes into a woven or non-woven fabric. This achieves an excellent ballistic
performance. The third way is to put the carbon nanotubes into other armor grade fibers. So for
example, you would have certain fibers like PBO or Kevlar and reinforce it with the carbon nanotubes.
This improves not only the energy absorption but also the elastic modulus of the material.
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Conclusion
At this day of age, the carbon nanotubes are the main guys for strength. But it wasn’t too long
ago that it was mainly steel and aircraft aluminum that was used for their strength. Everybody thought
that those were it. But now with new technology, we can look at the nanoscale and find ways to create
new materials. It will be interesting to see what happens in the future; what material will they come up
with next that can withstand the newest weapon. How much deeper will we look when it comes to the
atomic scale? Some people say that carbon nanotubes will be that last of it, that we will only be able to
mix the carbon with different elements to create allotropes of the CNTs. But people said that same thing
about steel. You just never know what these scientists will come up with next.
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