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Carbon Nanotubes are as deadly as asbestos 6-7-08
Carbon nanotubes can cause cancer such as deadly deadly lung cancer called
mesothelioma just as asbestos does, according to a new study published in the
Scientific journal Nature nanotechnology.
Canon nanotubes, 10,000 times thinner than a human hair show promise in making
plastic lighter and stronger. They can also be used to make tiny electronics.
If you work in any of these industries, please use every precaution you can
not to inhale or consume carbon nanotubes.
Cited below from wikipedia is some info on nanotubes:
Carbon nanotubes (CNTs) are allotropes of carbon with a nanostructure that can
have a length-to-diameter ratio greater than 1,000,000. These cylindrical carbon
molecules have novel properties that make them potentially useful in many
applications in nanotechnology, electronics, optics and other fields of
materials science. They exhibit extraordinary strength and unique electrical
properties, and are efficient conductors of heat. Inorganic nanotubes have also
been synthesized.
Nanotubes are members of the fullerene structural family, which also includes
the spherical buckyballs. The cylindrical nanotube usually has at least one end
capped with a hemisphere of the buckyball structure. Their name is derived from
their size, since the diameter of a nanotube is in the order of a few nanometers
(approximately 1/50,000th of the width of a human hair), while they can be up to
several millimeters in length (as of 2008). Nanotubes are categorized as
single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs).
The nature of the bonding of a nanotube is described by applied quantum
chemistry, specifically, orbital hybridization. The chemical bonding of
nanotubes is composed entirely of sp2 bonds, similar to those of graphite. This
bonding structure, which is stronger than the sp3 bonds found in diamond,
provides the molecules with their unique strength. Nanotubes naturally align
themselves into "ropes" held together by Van der Waals forces. Under high
pressure, nanotubes can merge together, trading some sp˛ bonds for spł bonds,
giving the possibility of producing strong, unlimited-length wires through
high-pressure nanotube linking.
Below are some applications of nanotubes, cited from wikipedia:
Structural
* clothes: waterproof tear-resistant cloth fibers
* combat jackets: MIT is working on combat jackets that use carbon nanotubes as
ultra strong fibers and to monitor the condition of the wearer. [1] Cambridge
university has developed the fibers and given a license to a company [2]
* concrete: In concrete, they increase the tensile strength, and halt crack
propagation.
* polyethylene: Researchers have found that adding them to polyethylene
increases the polymer's elastic modulus by 30%.
* sports equipment: Stronger and lighter tennis rackets, bike parts, golf balls,
golf clubs, golf shaft and baseball bats.
* space elevator: This will be possible only if tensile strengths of more than
about 70 GPa can be achieved. Monoatomic oxygen in the Earth's upper atmosphere
would erode carbon nanotubes at some altitudes, so a space elevator constructed
of nanotubes would need to be protected (by some kind of coating). Carbon
nanotubes in other applications would generally not need such surface
protection.
* ultrahigh-speed flywheels: The high strength/weight ratio enables very high
speeds to be achieved.
* Bridges: For instance in suspension bridges (where they will be able to
replace steel).
Electromagnetic
* artificial muscles[1]
* buckypaper - a thin sheet made from nanotubes that are 250 times stronger than
steel and 10 times lighter that could be used as a heat sink for chipboards, a
backlight for LCD screens or as a faraday cage to protect electrical
devices/airplanes.
* chemical nanowires: Carbon nanotubes additionally can also be used to produce
nanowires of other chemicals, such as gold or zinc oxide. These nanowires in
turn can be used to cast nanotubes of other chemicals, such as gallium nitride.
These can have very different properties from CNTs - for example, gallium
nitride nanotubes are hydrophilic, while CNTs are hydrophobic, giving them
possible uses in organic chemistry that CNTs could not be used for.
* computer circuits: A nanotube formed by joining nanotubes of two different
diameters end to end can act as a diode, suggesting the possibility of
constructing electronic computer circuits entirely out of nanotubes. Because of
their good thermal properties, CNTs can also be used to dissipate heat from tiny
computer chips. The longest electricity conducting circuit is a fraction of an
inch long. (Source: June 2006 National Geographic).
* conductive films: A 2005 paper in Science notes that drawing transparent high
strength swathes of SWNT is a functional production technique (Zhang et al.,
vol. 309, p. 1215). Additionally, Eikos Inc of Franklin, Massachusetts and
Unidym Inc.[2] of Silicon Valley, California are developing transparent,
electrically conductive films of carbon nanotubes to replace indium tin oxide
(ITO) in LCDs, touch screens, and photovoltaic devices. Carbon nanotube films
are substantially more mechanically robust than ITO films, making them ideal for
high reliability touch screens and flexible displays. Nanotube films show
promise for use in displays for computers, cell phones, PDAs, and ATMs.
* electric motor brushes: Conductive carbon nanotubes have been used for several
years in brushes for commercial electric motors. They replace traditional carbon
black, which is mostly impure spherical carbon fullerenes. The nanotubes improve
electrical and thermal conductivity because they stretch through the plastic
matrix of the brush. This permits the carbon filler to be reduced from 30% down
to 3.6%, so that more matrix is present in the brush. Nanotube composite motor
brushes are better-lubricated (from the matrix), cooler-running (both from
better lubrication and superior thermal conductivity), less brittle (more
matrix, and fiber reinforcement), stronger and more accurately moldable (more
matrix). Since brushes are a critical failure point in electric motors, and also
don't need much material, they became economical before almost any other
application.
* light bulb filament: alternative to tungsten filaments in incandescent lamps.
* magnets: MWNTs coated with magnetite
* optical ignition: A layer of 29% iron enriched SWNT is placed on top of a
layer of explosive material such as PETN, and can be ignited with a regular
camera flash.
* solar cells: GE's carbon nanotube diode has a photovoltaic effect. Nanotubes
can replace ITO in some solar cells to act as a transparent conductive film in
solar cells to allow light to pass to the active layers and generate
photocurrent.
* superconductor: Nanotubes have been shown to be superconducting at low
temperatures.
* ultra capacitors: MIT is researching the use of nanotubes bound to the charge
plates of capacitors in order to dramatically increase the surface area and
therefore energy storage ability.[3]
* displays: One use for nanotubes that has already been developed is as
extremely fine electron guns, which could be used as miniature cathode ray tubes
in thin high-brightness low-energy low-weight displays. This type of display
would consist of a group of many tiny CRTs, each providing the electrons to hit
the phosphor of one pixel, instead of having one giant CRT whose electrons are
aimed using electric and magnetic fields. These displays are known as field
emission displays (FEDs).
* transistor: developed at Delft, IBM, and NEC.
Chemical
* air pollution filter: Future applications of nanotube membranes include
filtering carbon dioxide from power plant emissions.[4]
* biotech container: Nanotubes can be opened and filled with materials such as
biological molecules, raising the possibility of applications in biotechnology.
* hydrogen storage: Research is currently being undertaken into the potential
use of carbon nanotubes for hydrogen storage. They have the potential to store
between 4.2 and 65% hydrogen by weight. This is an important area of research,
since if they can be mass produced economically there is potential to contain
the same quantity of energy as a 50l gasoline tank in 13.2l of nanotubes. See
also, Hydrogen Economy.[5]
* water filter: Recently nanotube membranes have been developed for use in
filtration. This technique can purportedly reduce desalination costs by 75%. The
tubes are so thin that small particles (like water molecules) can pass through
them, while larger particles (such as the chloride ions in salt) are blocked.
Mechanical
* oscillator: fastest known oscillators (> 50 GHz).
* nanotube membrane: Liquid flows up to five orders of magnitude faster than
predicted by classical fluid dynamics.
* slick surface: slicker than Teflon and waterproof.
In electrical circuits
Carbon nanotubes have many properties—from their unique dimensions to an unusual
current conduction mechanism—that make them ideal components of electrical
circuits. Currently, there is no reliable way to arrange carbon nanotubes into a
circuit.
The major hurdles that must be jumped for carbon nanotubes to find prominent
places in circuits relate to fabrication difficulties. The production of
electrical circuits with carbon nanotubes are very different from the
traditional IC fabrication process. The IC fabrication process is somewhat like
sculpture - films are deposited onto a wafer and pattern-etched away. Because
carbon nanotubes are fundamentally different from films, carbon nanotube
circuits can so far not be mass produced.
Researchers sometimes resort to manipulating nanotubes one-by-one with the tip
of an atomic force microscope in a painstaking, time-consuming process. Perhaps
the best hope is that carbon nanotubes can be grown through a chemical vapor
deposition process from patterned catalyst material on a wafer, which serve as
growth sites and allow designers to position one end of the nanotube. During the
deposition process, an electric field can be applied to direct the growth of the
nanotubes, which tend to grow along the field lines from negative to positive
polarity. Another way for the self assembly of the carbon nanotube transistors
consist in using chemical or biological techniques to place the nanotubes from
solution to determinate place on a substrate.
Even if nanotubes could be precisely positioned, there remains the problem that,
to this date, engineers have been unable to control the types of
nanotubes—metallic, semi conducting, single-walled, multi-walled—produced. A
chemical engineering solution is needed if nanotubes are to become feasible for
commercial circuits.
Metallic and semi conducting nanotubes
Most experimentally observed CNTs are multi-walled structures with outer most
shell diameters exceeding 10 nm Since current conduction in a MWCNT is known to
be mostly confined to the outermost single-walled nanotube and since band gap of
a SWCNT varies inversely with its diameter, MWCNTs are metallic in nature.
SWCNTs can be either metallic or semi conducting depending on the way the
roll-up of the graphene sheet occurs - an aspect termed as Chirality, and if all
the roll-up types are realized with equal probability, 1/3 of the SWCNTs end up
being metallic and 2/3 semi conducting. Thus, when CNTs are fabricated either by
arc growth, laser ablation or chemical vapor deposition (CVD), a mixture of
metallic and semi conducting nanotubes is formed.
Carbon Nanotube Interconnects
Metallic CNTs have aroused a lot of research interest in their applicability as
Very-large-scale integration (VLSI) interconnects of the future because of their
desirable properties of high thermal stability, high thermal conductivity and
large current carrying capacity. An isolated CNT can carry current densities in
excess of 1000 MA/sq-cm without any signs of damage even at an elevated
temperature of 250 degrees C, thereby eliminating electro migration reliability
concerns that plague Cu interconnects. Recent modeling work comparing the
performance, power dissipation and thermal/reliability aspects of CNT
interconnect to scaled copper interconnects have shown that CNT bundle
interconnects can potentially offer advantages over copper[6] Additionally, the
concept of hybrid CNT/Cu interconnects-employing CNT vias in tandem with copper
interconnects has been shown to offer advantages from a
reliability/thermal-management perspective. More information on state-of-the-art
of CNT interconnects (including their fabrication) can be found in the
literature.
Carbon Nanotube Transistors
Semi conducting CNTs have been used to fabricate field effect transistors (CNTFETs),
which show promise due to their superior electrical characteristics over silicon
based MOSFETs. Since the electron mean free path in SWCNTs can exceed 1
micrometer, long channel CNTFETs exhibit near-ballistic transport
characteristics, resulting in high speed devices. In fact, CNT devices are
projected to be operational in the frequency range of hundreds of GHz. Recent
work detailing the advantages and disadvantages of various forms of CNTFETs have
also shown that the tunneling based CNTFET offers better characteristics
compared to other CNTFET structures. This device has been found to be superior
in terms of sub threshold slope - a very important property for low power
applications.
Challenges in Electronic Design and Design Automation
Although CNT devices and interconnects have been separately shown to be
promising in their own respects, there have been few efforts to successfully
combine them in a realistic circuit. Most CNTFET structures employ the silicon
substrate as a back gate. Applying different back gate voltages might become a
concern when designing large circuits out of these devices. Several top-gated
structures have also been demonstrated, which can alleviate this concern.
Recently, a fully integrated logic circuit built on a single nanotube has been
reported. However, this circuit also employs a back-gate. Additionally, there
are still several process related challenges that need to be addressed before
CNT-based devices and interconnects can enter mainstream VLSI process. This
makes it an exciting and open field for research. Problems like purification,
separation of carbon nanotubes, control over nanotube length, chirality and
desired alignment, low thermal budget as well as high contact resistance are yet
to be fully resolved. Although these are serious technological challenges,
innovative ideas have been proposed to build practical transistors out of nano-networks.
Since lack of control on chirality produces a mix of metallic as well as
semi-conducting CNTs from any fabrication process and it is difficult to control
the growth direction of the CNTs, random arrays of SWCNTs (that are easily
produced) have been proposed to build thin film transistors. This idea can be
further exploited to build practical CNT based transistors and circuits without
the need for precise growth and assembly.
As fiber and film
One application for nanotubes that is currently being researched is high tensile
strength fibers. Two methods are currently being tested for the manufacture of
such fibers. A French team has developed a liquid spun system that involves
pulling a fiber of nanotubes from a bath which yields a product that is
approximately 60% nanotubes. The other method, which is simpler but produces
weaker fibers uses traditional melt-drawn polymer fiber techniques with
nanotubes mixed in the polymer. After drawing, the fibers can have the polymer
component burned out of them leaving only the nanotube or they can be left as
they are.
Ray Baughman's group from the NanoTech Institute at University of Texas at
Dallas produced the current toughest material known as of mid-2003 by spinning
fibers of single wall carbon nanotubes with polyvinyl alcohol. Beating the
previous contender, spider silk, by a factor of four, the fibers require 600 J/g
to break[7] In comparison, the bullet-resistant fiber Kevlar is 27–33 J/g. In
mid-2005, Baughman and co-workers from Australia's Commonwealth Scientific and
Industrial Research Organization developed a method for producing transparent
carbon nanotube sheets 1/1000th the thickness of a human hair capable of
supporting 50,000 times their own mass. In August 2005, Ray Baughman's team
managed to develop a fast method to manufacture up to seven meters per minute of
nanotube tape.[8] Once washed with ethanol, the ribbon is only 50 nanometers
thick; a square kilometer of the material would only weigh 30 kilograms.
In 2004, Alan Windle's group of scientists at the Cambridge-MIT Institute
developed a way to make carbon nanotube fiber continuously at the speed of
several centimeters per second just as nanotubes are produced. One thread of
carbon nanotubes was more than 100 meters long. The resulting fibers are
electrically conductive and as strong as ordinary textile threads.[9][10]