(2) Buckyballs
are also extremely stable and can withstand very high temperatures and
pressures.
(3) The
carbon atoms of buckyballs can react with other atoms and molecules, leaving
the stable, spherical structure still intact.
(4) New
molecules can be created by adding other molecules to the outside of a
buckyball and by trapping smaller molecules inside a backyball.
Use of
Buckyballs: -
(i)
Buckyball As Antioxidants: -
The medical field is one place that buckyballs appear to
have promising future. Buckyballs act as antioxidants, counteracting free
radicals in the human body.
A free radical is a molecule or atom
that has an unpaired electron which makes it very reactive. An antioxidant is a
molecule that can supply an electron and neutralize a free radical. The human
body normally has a balance of free radicals and antioxidants.
Buckballs can act as antioxidants to
neutralize free radicals. When a buckyball meets a free radical, the unpaired
electron in the free radical pairs up with one of the buckyballs delocalized
electrons, forming a covalent bond between the free radical and a carbon atom
in the buckyball.
(ii)
Drug Delivery With Buckyballs: -
Another use of buckyballs is to deliver
drugs directly to infected regions of the body. It turns out that such regions
have pH levels that differ from the pH of the healthy bits Researchers hope to
functionalize a buckyball by bonding it to molecules that react to changes in
pH.
Q.16 Discuss structure, properties and use of
carbon nanotubes.
Related
Questions -
Q. How carbon nanotubes are produced?
Discuss properties and uses of carbon nanotubes. (AKTU. 2009-10)
Q. What are carbon nanotubes? Explain
the CVD technique for its synthesization. (AKTU. 2010 - 11)
Ans. Structure of Carbon Nanotubes: -
A carbon nanotube is a cylinder of carbon atoms covalently
bonded together. Some of these cylinders are closed at the ends and some are
open. Each carbon atom is bonded to three other carbon atoms and forms a
lattice in the shape of hexagons (six-sided rings of carbon atoms), except near
the end.
The lattice can be oriented
differently, which makes for three different kinds of nanotubes. In armchair
nanotubes, there is a line of hexagons parallel to the axis of the nanotube. In
zigzag nanotubes, there is a line of carbon bonds down the center. Chiral
nanotubes exhibit a twist or spiral (called chirality) around the nanotube.
Producing
Nanotubes: -
Three methods have been developed to
produce carbon nanotubes in bulk quantities and at a lower cost.
1.
High-Pressure Carbon Monoxide Deposition (Hi PCO): -
This method involves a heated chamber through which carbon
monoxide gas and small clusters of iron atoms flow. When carbon monoxide
molecules land on the iron clusters, the iron acts as a catalyst and helps a
carbon monoxide molecule break up into a carbon atom and an oxygen atom. The
carbon atom bonds with other carbon atoms to start the nanotube lattice, the
oxygen atom joins with another carbon manoxide molecule to form carbondioxide
gas which then floats off into the air.
2.
Chemical-Vapor Deposition (CVD): -
In this method, a hydrocarbon (methane gas) flows into a
heated chamber containing a substrate coated with a catalysts such as iron
particles. The temperature in the chamber is high enough to break the bonds
between the carbon atoms and hydrogen atoms in the methane molecules¾resulting in
carbon atoms with no hydrogen atoms attached. Those carbon atoms attach to the
catalyst particles where they bond to other carbon atoms - forming a nanotube.
3.
Plasma Process to Produce Nanotubes: -
Methane gas used as the source of carbon, is passed through
a plasma tourch. One of the initial claims is that this process is 25 time more
efficient at producing nanotubes than the other two methods.
Properties
of Carbon Nanotubes: -
Some of the useful and unique properties of carbon
nanotubes are:
1.
Electrical Conductivity: -
Carbon nanotubes are metallic or
semiconductors depending upon the diameter and how they are rolled. In theory,
metallic nanotubes can have an electrical current density more than 1000 times
greater than metals such as copper and silver.
2.
Strength: -
Carbon nanotubes are the strongest
materials on earth in terms of tensile strength. The tensile strength of carbon
nanotubes is approximately 100 times greater than that of steel of the same
diameter.
3.
Stiffness: -
Nanotubes are not only strong but
also elastic. It takes a lot of force to bend a nanotube but it returns to its
original shape when the force is removed. Young’s modulus for carbon nanotubes
is about 5 times higher than that for steel.
4.
Thermal Conductivity: -
All nanotubes are very good thermal
conductors along the tube. This property is known as “blastic condition”.
Nanotubes have a thermal conductivity of more than 10 times that of silver.
Note that nanotubes are also good insulators laterally to the tube axis.
5.
Nanopolar Molecule: -
Carbon nanotubes are a little bit
sticky and form a nanopolar molecule.
6. Carbon nanotubes are light weight with a
density about one quarter that of steel.
7.
Toxicity: -
It has been proved that under some
conditions nanotubes are dangerous for human beings.
Use of
Carbon Nanotubes: -
1. With
nanotubes and nanowires, we can produce transistors and memory devices about a
nanometer wide. This can be used to reduce the size of the devices and wires as
the complexity of computer chips increases.
2. Nanotubes can produce materials with
toughness unmatched by natural and man-made materials. Due to its great
mechanical properties, nanotubes can be used to produce from everyday items
like clothes, sports gear to combat/bulletproof jackets and space-suits.
3. Nanoscale
electric motors have also been developed using nanotubes.
4. Chemical
vapours are also being detected using nanotubes. Sensors using carbon nanotubes
have shown to detect chemical vapours with concentrations in the parts per
billion (ppb).
5. Research
is being done to store hydrogen in nanotubes. If successful, this would act as
a fuel tank for hydrogen fuel cell-powered cars.
6. In
medical applications, the carbon nanotube can be used as a vessel for
transporting drugs into the body. It is especially being used for treatment of
cancer in destroying cancer cells.
Q.17 Explain the various applications of
nanotechnology. (AKTU. 2011 - 12, 12 -13)
Ans. Applications of Nanotechnology: -
Various applications of nanotechnology:
1.
Diagnostics: -
Nanotechnology is helping in medical diagnostics by
providing faster, cheaper and portable diagnostic equipments.
2.
Novel Drugs: -
Nanotechnology aids is delivery of
just the right amount of medicine to the exact spots of the body that need it.
3.
Energy: -
Nanotechnology will provide new methods to effectively
utilize out current energy resources. It will also present new alternative
fuels. Solar cells will also become cost effective.
4.
Water: -
Nanotechnology will provide efficient water purification
techniques. Water from the oceans can also be converted into drinking water.
5.
Superior, Light Weight Materials: -
The strength and light weight of nanomaterials make them
suitable for use in tear resistant clothes, body armour (bullet-proof
clothings), spouts materials etc.
6.
Computers: -
Computers can be made more powerful and smaller using
nanotechnology.
7.
Sensors: -
Sensors based on nanotechnology are more
sensitive and hence more effective.
Q.18. What is the value of critical field of a
super conductor at transition temperature. (AKTU. 2015 - 16)
Ans. The
critical magnetic field of a superconductor is a function of temperature. The
variation of Hc with temperature is given by
