ABSTRACT:
For the first time in the human history, we are close to being able to manipulate the basic forms of all the things, living and inanimate, take them apart and put them together in almost anyway the mind can imagine.
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The sophistication with which scientists are learning to engineer matter at the nanometer scale is giving us unprecedented mastery of a large part of our environment. The world of the future will be defined by how we use this mastery. Nanotechnology is engineering at the molecular (groups of atoms) level. It is the collective term for a range of technologies, techniques and processes that involve the manipulation of matter at the smallest scale(from 1 to 100 nm2).
Carbon nanotubes have been under scientific investigation for more than fifteen years because of their unique properties that predestine them for many potential applications. The field of nanotechnology and nanoscience push their investigation forward to produce carbon nanotubes with suitable parameters for future applications. Carbon nanotubes are one of the most commonly mentioned building blocks of nanotechnology.
With one hundred times the tensile strength of steel, thermal conductivity better than all but the purest diamond and electrical conductivity similar to copper, but with the ability to carry much higher currents, they seem to be a wonder material.
Field effect transistors using carbon nanotubes came into existence, these have a extremely good properties.
CARBON NANOTUBES:
Evolution of Nano
Importance of Nano in present day scenario
Moores Law
Greatness of Carbon
Graphene
Carbon nanotube
Synthesis of CNT
Properties of CNT
Purification methods
Real time applications
GREATNESS OF CARBON:
Carbon is the 4th most abundant element in the Universe by mass after( Hydrogen, Helium and Oxygen).
Forms more compounds that any other element, with almost 10 million pure organic compounds.
Abundance, unique diversity and unusual polymer forming ability at the temperatures makes the element the chemical basis of life.
CARBON NANOTUBES:
Carbon nanotubes are long, thin cylinders of carbon which were discovered in 1991 by Sumio Iijima.
A sheet of graphene rolled in cylindrical structure results in Carbon nanotube of 1 atom thickness and diameter in nano scale.
Nanotubes have a very broad range of electronic, thermal, and structural properties that changes due to change in length, diameter and chirality or twist.
Types of Carbon Nano Tubes:
Single walled:
In these single walled nano tubes are narrower than the multi walled nano tubes ,the diameters typically in the range of 1-2nm ,and tend to be curved rather than straight. In these SWNT only single layer of grephene .Catalyst is required for synthesis .Bulk synthesis is difficult as it requires proper control over growth and atmospheric condition .In these SWNT Purity is poor and less accumulation in body .Characterization and evaluation is easy .It can be easily twisted and are more pliable. These tubes are used to make super strong amour bodies .These single walled nano tubes are used as elastic property and used to make bullet proof vests.
Multi walled:
Multi walled nano tubes consists of multiple layers of graphite rolled in on themselves to for a tube shape .There are two models which can be used to describe the structures of multi walled nano tubes .In these MWNT multiple layer of grephene and can be produced without catalyst Bulk synthesis is easy .Purity is high ,more accumulation in body .It has very complex structure .It can not be easily twisted.
Synthesis:
Laser ablation:
A pulsed or continuous laser is used which will vaporize a graphite target in an oven at 1200c . Oven is filled with helium& argon gas .In order to keep the pressure at 500 torr ,Since the optimum background gas as catalyst mixture is the same as in the arc discharge process Laser ablation method is similar to arc discharge method .This method is vey expensive so it is mainly used for SWNT’s laser vapourization results in higher yield of SWNT’s with narrow size distribution than those produced in arc discharge process .Catalyst used for SWNT is NI:Y (4.2:1 At%).
Arc Discharge Method:
Arc Discharge method has been reported for producing carbon nano tubes .In these method nano tubes are produced through arc vapourization of two carbon rods placed end to end with a distance of 1mm in an environment of inert gases such as helium argon at pressure b/w 50 to 100 amps driven by 20v which will create high temperature discharge b/w two electrodes ,due to this anode wil get evaporated and rod shaped tubes will be deposited on cathode.Bulk production of CNT’s depends on uniformity of plasma arc and temperature of depositon The Main principle is carbon nano fibres are good at absorbing energy so they can absorb the energy coming from the bullet .The inherent property of elasticity makes the bullet to rebound .Its is 100% stronger thean steel.Lighter than aluminium.Conduct electricity as copper .These fibres can be used as space elevators .
Purification Of CNT’s:
Nanotubes usually contain a large amount of impurities such as metal particles ,amorphous carbon ,and multishell .These are different steps in purification of nano tubes .
Air Oxidation:
The Carbon nano tubes are having less purity ,the average purity is about 5-10%.So,Purification is needed before attachment of drugs onto CNT’s .Air oxidation is useful in Reducing the amount of amorphous carbon and metal catalyst particles (Ni,Y).
Acid Reflexing:
Refluxing the sample in strong acid is effective in reducing the amount of metal particles and amorphous carbon ,different acids used were hydrochloric acid (HCL),nitric acid(HNO3)and sulphuric acid (H2so4)bt HCL is identified to e ideal reflexing acid .
Surfactant aided sonication, filtration and annealing:
After the acid reflexing ,the CNT’s were purer but ,tubes were entagled together ,trapping most of the impurities,such as carbon particles and catalyst particles ,which were difficult to remove with flitration .so,surfactant –aided sonication was carried out .sodium dodecyl benezene sulphonate (SDBS) aided sonication with ethanol or methanol ,as organic solvent were preferred cz it took the longest ime time fr CNTS to settle down ,indicating an even suspension state was achieved .The sample was then filtered with un ultra filtration unit and annealed at 1273k in N2 for 4H .Annealing is effective in optimizing the CNT structures .It was provided the surfactant –aided sonication is effective to untangle CNT’s thus to free the particulate impurities embedded in the entanglement .Nano tube can also be purified by multistep purification method .
Real time applications:
Carrier for drug delivery:
Carbon Horns (CNHs) are the speherical aggregates of CNT’s with irregular Horn like shape .Research studies have proved CNT’s CNH’s as a potential carrier for drug delivery system .
Genetic Engineering:
In Genetic engineering ,CNT’s and CNH’s are used to manipulate genes and atoms in the development of bio imaging geneomas protemics and tissue engineering .The unwound DNA (single stranded )winds around SWNT by connecting its specific neucletoids and causes change in its electrostatic property .this creates its potential application diagnostics and in therapeutics Nano tubes and nanohorn’s can adehere various antigens on their surface ,hence act as source of antigen in vaccines .Hence by use of nanotubes ,use of dead bacteria as source for antigen which is sometimes dangerous can be avoided .
Pseudo spark switches:
These are switches which work upon principle of field emission, this emission is achieved by triggering.
Generally the triggering methods are
Surface discharge triggering
Optical triggering
Pulsed low-current glow discharge triggering
But cnt’s have a good emitting properties when compared from above methods.
For field emission cnt’s are used as cold cathode emitters.
The field emission characteristics of cnt’s are mostly reported at high vacuum pressures of 10^-6 and 10^-7 torr.
Usage of cnt’s for field emission resulted in good properties and working of pseudo spark switches in both high pressure and low pressure vacuum..
