Civil Engineering Reference
In-Depth Information
12.5.2 Carbon nanotubes (CNT)
Carbon nanotubes (CNTs), or nanotubes (NTs) as they are often referred
to, are cylinders constructed of carbon atoms (nanostructure) and are not
only organic but are good photosensitive material. Basically they consist of
a single sheet of graphite with a hexagonal lattice (Manna and Mahajan,
2007) which is constructed from linked carbon rings forming the tube,
capped at each end with a pentagonal carbon ring.
Nanotubes are made up of
n
rows and
m
columns and the link between
them defi nes exactly how they are formed. The structure has a length-to-
diameter ratio of 132,000,000 : 1 (Wang
et al.
, 2009), although this can vary,
which is signifi cantly larger than any other material. An NT is very thin,
being approximately 10,000 times thinner than a human hair and hollow in
the middle. Nanotubes are normally divided into two specifi c types, which
are specifi cally related to the amount of walls contained in the structure;
SWNTs (single-walled nanotubes) which have good light absorption pro-
perties and effi ciency, and MWNTs (multi-walled nanotubes) which have
slightly different properties. The SWNT, although any length, normally has
a diameter of approximately 1 nm, as the structure is basically a one atom-
thick layer of graphite which is wrapped until both ends meet, forming a
tube. Obviously it is harder to defi ne the size of the multi-walled nanotube
as this depends on the amount of walls. The main reason that the solar indu-
stry is interested in nanotubes as a third generation PV is related to the
properties associated with its materials and structure. The following points
are interesting facts about nanotubes commonly known in the industry:
They are as elastic as a rubber band.
Impressive thermal conduction which is twice that of diamond.
Withstand temperatures of 2700°C.
Do not react with other atoms.
Better electrical conductor than copper (100 times).
Depending on their structure, their electrical properties will either be
metallic or semiconductor.
Conduct at 10
9
amperes per square cm.
Thermal properties vary depending on the location - along the tube
there are good thermal properties whereas other locations in the tube
provide good insulation.
Electrical properties change depending on what material is attached to
them.
Although nanotubes have all these advantageous properties, their practical
implementation is still ongoing, with research and development looking
into ways to ensure they reach their maximum potential. Carbon nanotubes
are of interest in nanotechnology but are not limited to this fi eld; it is
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