CNT is a tubular form of carbon with diameter as small as 1nm.Length: few nm to microns.CNT is configurationally equivalent to a two dimensional graphene sheet rolled into a tube.Fullerene -A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid or tube.
1 angstrom = 1.0 × 10-10 meters
The magnetic moment of a magnet is a quantity that determines the force that the magnet can exert on electric currents and the torque that a magnetic field will exert on it.Thermal stability is the stability of a molecule at high temperatures
Allotropy is the property of some chemical elements to exist in two or more different forms. covalent bond is the chemical bond that involves the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding.Field emission (FE) (also known as field electron emission and electron field emission) is emission of electrons induced by an electrostatic field
Involves condensation of C-atoms generated from evaporation of solid carbon sources. Temperature ~ 3000-4000K, close to melting point of graphite.Both produce high-quality SWNTs and MWNTs.MWNT: 10’s of m long, very straight & have 5-30nm diameter. SWNT: needs metal catalyst (Ni,Co etc.). Produced in form of ropes consisting of 10’s of individual nanotubes close packed in hexagonal crystals
hybridisation (or hybridization) is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties. Other carbon based compounds and other molecules may be explained in a similar way as methane. Take, for example, ethene (C2H4). Ethene has a double bond between the carbons.For this molecule, carbon will sp2 hybridise, because one π (pi) bond is required for the double bond between the carbons, and only three σ bonds are formed per carbon atom. In sp2 hybridisation the 2s orbital is mixed with only two of the three available 2p orbitals:
Diamond is considered to be the hardest material, and it is well known that graphite transforms into diamond under conditions of high temperature and high pressure. One study succeeded in the synthesis of a super-hard material by compressing SWNTs to above 24 GPa at room temperature. The hardness of this material was measured with a nanoindenter as 62–152 GPa. The hardness of reference diamond and boron nitride samples was 150 and 62 GPa, respectively. The bulk modulus of compressed SWNTs was 462–546 GPa, surpassing the value of 420 GPa for diamond.Already this property has been utilized to create the world's smallest rotational motor
Young's modulus, also known as the tensile modulus or elastic modulus, is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's law holds.Ultimate tensile strength (UTS), often shortened to tensile strength (TS) or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before failing or breaking.Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora.
INTRODUCTION Carbon nanotubes are :- • Allotropes of carbon with a cylindrical nanostructure. • Hexagonally shaped arrangements of carbon atoms that have been rolled into tubes. • Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1,significantly larger for any other material. • Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon called Graphene.
These sheets are rolled at specific and discrete “chiral “ angles, and the combination of rollingangle and radius decides the nanotubeproperties.They posses unusual properties, valuable fornanotechnology, electronics, optics, MechanicalEngg. and other fields of material science &Technology.
Timeline Of Carbon Nanotubes1952- L.V Radushkevich published tubes made up of carbonFrom Soviet Union.1976- koyama showed carbon fibers with Nano scale dia.1979- John Abrahamson presented evidence for CNT.1981-Soviet scientists chemical structural characterization ofCNTs.1987- Howard g. had patent for production of cylindricaldiscrete carbon fibrils.
They were discoveredIn 1991 by the Japaneseelectron microscopist SUMIO IIJIMA NECLaboratory in Tsukuba-- usedhigh-resolution transmissionelectron microscopy toobserve carbonnanotubes, And into theawareness of the scientificcommunity .
Most single-walled nanotubes(SWNT) have a diameter ofclose to 1 nanometre, with atube length that can be manymillions of times longer.The structure of a SWNT can beconceptualized by wrapping aone-atom-thick layer ofgraphite called graphene into aseamless cylinder.
The way the graphene sheet iswrapped is represented by a pair ofindices (n,m) called the chiralvector.The integers n and m denote thenumber of unit vectors along twodirections in the honeycomb crystallattice of graphene.If m = 0, the nanotubes are called The (n,m) nanotube naming"zigzag". If n = m, the nanotubes scheme can be thought of as a vector (Ch) in an infiniteare called "armchair". graphene sheet that describesOtherwise, they are called "chiral". how to "roll up" the graphene sheet to make the nanotube. T denotes the tube axis, and a1 and a2 are the unit vectors of graphene in real space.
Various Types Of SWNT Armchair (n,n) Zigzag (n,0)
Multi-walled nanotubes (MWNT)consist of multiple rolled layers(concentric tubes) of graphite.There are two models which can be used todescribe the structures of multi-wallednanotubes.• In the Russian Doll model, sheets of graphite are arranged in concentric cylinders.• In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or a rolled newspaper.(The Russian Doll structure is observed more commonly).
About MWNT The telescopic motion ability of inner shells and their unique mechanical properties will permit the use of multi-walled nanotubes as main movable arms in coming Nano mechanical devices.
Other carbon nanotube structures Toruscarbon nanotube bent into a torus (doughnut shape). Nanotori are predicted to have many unique properties, such as magnetic moments 1000 times larger than previously expected for certain specific radii. Properties such as magnetic moment, thermal stability, etc. vary widely depending on radius of the torus and radius of the tube.
Carbon nanobuds are a newly created material combining two previously discovered allotropes of carbon: carbon nanotubes and fullerenes. In this new material, fullerene-like "buds" are covalently bonded to the outer sidewalls of the underlying carbon. They good field emitters. In composite materials, the attached fullerene molecules may function as molecular anchors preventing slipping of the nanotubes, thus improving the composite’s mechanical properties.
Graphenated carbon nanotubes (g-CNTs) :-Graphenated CNTs are a relatively new hybrid thatcombines graphitic foliates grown along the sidewalls ofmulti walled or bamboo style CNTs use in super capacitorapplications. Peapod :-A Carbon peapod] is a novel hybrid carbon material whichtraps fullerene inside a carbon nanotube. Cup-stacked carbon nanotubes :-CSCNTs exhibit semiconducting behaviors due to thestacking microstructure of graphene layers.
Synthesis of Carbon NanotubesTechniques have been developed to produce nanotubesin sizeable quantities.some of them are:- Synthesis Chemical Arc Laser vapor discharge Ablation deposition (CVD)
Arc discharge• CNT production requires 3 elements ,I. Carbon feedII. Metal catalystIII. Heata) Two Graphite electrodes placed in an inert Helium atmosphere .b) When DC current is passed anode is consumed and material forms on cathode.c) For SWNT mixed metal catalyst is inserted into anoded) Pure iron catalyst + Hydrogen-inert gas mixture gives 20 to 30cm long tube.e) The nanotubes were initially discovered using this technique, it has been the most widely-used method of nanotube synthesis.
Laser Ablation• In the laser ablation process, a pulsed laser vaporizes a graphite target in a high-temperature reactor while an inert gas is bled into the chamber.• Nanotubes develop on the cooler surfaces of the reactor as the vaporized carbon condenses.• A water-cooled surface may be included in the system to collect the nanotubes.• The laser ablation method yields around 70% and produces primarily single- walled carbon nanotubes with a controllable diameter determined by the reaction temperature.• it is more expensive than either arc discharge or chemical vapor deposition.
Chemical vapor deposition (CVD)• During CVD, a substrate is prepared with a layer of metal catalyst articles, most commonly nickel, cobalt, iron, or a combination.• The diameters of the nanotubes that are to be grown are related to the size of the metal particles.• The substrate is heated to approximately 700°c.• To initiate the growth of nanotubes, two gases are bled into the reactor: a process gas (such as ammonia, nitrogen or hydrogen) and a carbon- containing gas (such as acetylene, ethylene, ethanol or methane).• Nanotubes grow at the sites of the metal catalyst;• The carbon-containing gas is broken apart at the surface of the catalyst particle, and the carbon is transported to the edges of the particle, where it forms the nanotubes.
Arc Discharge Method Chemical Vapor Deposition Laser Ablation (Vaporization) Connect two graphite rods Place substrate in oven, heat Blast graphite with intense to a power supply, place to 600 C, and slowly add a laser pulses; use the laserthem millimeters apart, and carbon-bearing gas such as pulses rather than electricitythrow switch. At 100 amps, methane. As gas to generate carbon gas from carbon vaporizes in a hot decomposes it frees up which the NTS form; try plasma. carbon atoms, which various conditions until hit recombine in the form of on one that produces NTS prodigious amounts of SWNTS Can produce SWNT and Easiest to scale to industrial Primarily SWNTS, with aMWNTs with few structural production; long length large diameter range that defects can be controlled by varying the reaction temperatureTubes tend to be short with NTS are usually MWNTS and By far the most costly,random sizes and directions often riddled with defects because requires expensive lasers
The The shortest The thinnesobservation The thinnest carbon t of carbon nanotube is freestandinthe longest the organic nanotube is g single- carbon compound armchair walled nanotubes cycloparaphe (2,2) CNT carbon (18.5 cm nylene, which with a was nanotube is long) was diameter of synthesized about 4.3 Åreported in 3 Å. in early 2009. in diameter. 2009.
Properties Of Carbon Nanotubes Carbon nanotubes are the strongest, flexible and stiffest materials yet discovered in terms of tensile strength and elastic modulus respectively. This strength results from the covalent sp2 bonds formed between the individual carbon atoms(which is stronger than the sp3 bonds found in Diamond & Alkenes). CNTs are not nearly as strong under compression. Because of their hollow structure and high aspect ratio, they tend to undergo buckling when placed under compressive, torsional or bending stress.
Hardness :-• The hardness(152 Gpa) and bulk modulus(462–546) of carbon nanotubes are greater than diamond, which is considered the hardest material.(:that of diamond is 150GPa & 420GPa).Kinetic Property:-• Multi-walled nanotubes, multiple concentric nanotubes precisely nested within one another, exhibit a striking telescoping property whereby an inner nanotube core may slide, almost without friction, within its outer nanotube shell thus creating an atomically perfect linear or rotational bearing, the precise positioning of atoms to create useful machines.
Electrical Properties:-Because of the symmetry and unique electronicstructure of graphene, the structure of a nanotubestrongly affects its electrical properties.-Very high current carrying capacity.Thermal Conductivity :-All nanotubes are expected to be very good thermalconductors along the tube.( Measurements show that aSWNT has a room-temperature thermal conductivity morethan copper.)
Optical properties:-EM Wave absorption :-• current military push for radar absorbing materials (RAM) to better the stealth characteristics of aircraft and other military vehicles. (There has been some research on filling MWNTs with metals, such as Fe, Ni, Co, etc., to increase the absorption effectiveness of MWNTs in the microwave regime).Thermal properties:-• All nanotubes are expected to be very good thermal conductors along the tube,but good insulators laterally to the tube axis. (Measurements show that a SWNT has a room-temperature thermal conductivity along its axis of about 3500 W·m−1·K−1;] compare this to copper, a metal well known for its good thermal conductivity, which transmits 385 W·m−1·K−1.)
Toxicity:-• Under some conditions, nanotubes can cross membrane barriers, which suggests that if raw materials reach the organs they can induce harmful effects such as inflammatory and fibrotic reactions.Crystallographic defect:-• As with any material, the existence of a crystallographic defect affects the material properties. Defects can occur in the form of atomic vacancies.
Advantages• Extremely small and lightweight.• Resources required to produce them are plentiful, and many can be made with only a small amount of material• Are resistant to temperature changes, meaning they function almost just as well in extreme cold as they do in extreme heat• Improves conductive, mechanical, and flame barrier properties of plastics and composites.• Enables clean, bulk micromachining and assembly of components.• Improves conductive, mechanical, and flame barrier properties of plastics and composites.
Disadvantages• Despite all the research, scientists still dont understand exactly how they work.• Extremely small, so are difficult to work with.• Currently, the process is relatively expensive to produce the nanotubes.• Would be expensive to implement this new technology in and replace the older technology in all the places that we could.• At the rate our technology has been becoming obsolete, it may be a gamble to bet on this technology.
• Nano electronics• Doping• Nano balance• Nano tweezers• Data storage• Magnetic nanotube• Nanogear
• Nanotube actuator• Molecular Quantum wires• Hydrogen Storage• Noble radioactive gas storage• Solar storage• Waste recycling• Electromagnetic shielding• Dialysis Filters• Thermal protection• Nanotube reinforced composites• Reinforcement of armour and other materials• Reinforcement of polymer• Avionics• Collision-protection materials• Fly wheels
Growth mechanism of Fullerene and CNT is still a mystery At present, they are not possible to grow in a controlled way Still not able to select size and helicity during growth Making connection between CNTs is uncontrollable now When bulk quantity is needed no manufacturing techniques are available Manipulation of CNTs is another problem