ABSTRACT
In the present world of development, technology is growing at a tremendous pace making works easier, faster, efficient, & compact. The introduction of nano-technology has revolutionized the world of science influencing each & every field. This paper aims at highlighting the technology that is emerging fast and is in latest use…nano carbon tubes ,a latest advent of nano technology.
Carbon Nano-tubes are an allotrope of carbon. These are a tubular material with a hexagonal honeycomb structure of a carbon atom connected to other carbon atoms. Carbon nano-tubes are known to have
excellent mechanical, electrically selective, high efficient hydrogen storage properties and be new and almost defect-free of all the existing materials. Carbon nano-tubes are called a new dream material in the 21st century and broadening their applications to almost all the scientific areas, such as aerospace science, bio-engineering, environmental energy, materials industry, medical and medicine science, electronic computer, security and safety, and science education with the development of science.
This paper deals with the basics of nano carbon tubes, history, their structures, different properties, types, various processing techniques and an analysis on these along with the perspective applications.
Introduction
As numerous researches has been reported on new physical phenomena and advanced properties of materials in the extremely infinitesimal areas of nanoscale size in recent years, a new area called
nanotechnologies came into being. These nanotechnologies have emerged as a future leader in areas, such as electronic information communications, medicine, material, production process, environment, and energy.
As new material properties of carbon nano-tubes, in particular, can be realized among other nano technologies, both the importance in basic research and industrial applicability are being in the great limelight
History
Fullerene, one of carbon allotropes (a cluster of 60 carbon atoms: C60) was discovered by KROTO and SMALLEY for the first time in 1985. Dr Sumio Iijima, a researcher of the NEC laboratories in JAPAN, in 1991 discovered thin and long straw shaped carbon nano-tubes during a TEM analysis of carbon clusters synthesized by arc-discharge method. He found that the central core of the cathodic deposit contained a variety of closed graphitic structures including nano-particles and nano-tubes, of a type which had never previously been observed. The nano-tubes range in length from a few tens of nanometers to several micrometers, and in outer diameter from about 2.5 nm to 30 nm. A carbon atom in nano-tubes forms a hexagonal honeycomb lattice of sp2 bond with 3 other carbon atoms. In 1992, Ebbesen and Ajayan reported that increasing the pressure in the chamber of an arc-evaporation had greatly improved the nano-tube yield on the cathode of graphite. In the year 1993 Bethune of IBM and Iijima of NEC independently synthesized carbon nano-tubes, using arc-discharge methods. In the Year 1998 using the plasma-enhanced chemical vapor deposition, a major breakthrough was made in synthesis and application of carbon nano-tubes by growing highly pure carbon nano-tubes vertically
aligned on a glass substrate. Since then, researches into synthesis and application have been vigorously conducted around the world.
STRUCTURE
A free carbon atom has the electronic structure 1s22s22p2. In order to form covalent bonds, one of the 2s electrons is promoted to 2p. In graphite, one carbon atom forms a strong ¥ò bond called as sp2 with three other adjacent atoms in a plane. The others in the p orbital have a weak ¥ð bond at 90o to this plane which gives the semi-metal characteristics.
There are two possible high symmetry structures for carbon nano-tubes, known as 'zig-zag' and 'armchair'. In practice, it is believed that most carbon nano-tubes do not have these highly symmetric forms but have structures called 'chiral' in which the honeycomb-shaped hexagons are arranged helically around the tube axis. The simplest way of specifying the structure of an individual tube is in terms of a vector, which is labeled as C, joining two equivalent points on the original graphene lattice. The cylinder is produced by rolling up the sheet such that the two end-points of the vector are superimposed. Fig 2. Shows the graphene sheet labeled. Each pair of
integers (n, m) represents a possible tube structure in this image. Thus the vector C can be expressed as
C = na1 + ma2
Where a1 and a2 are the unit cell base vectors of the graphene sheet. It can be seen that m = 0 for all zig-zag tubes, while n = m for all armchair tubes. All other tubes are 'chiral'. In the case of the two 'archetypal' nano-tubes which can be capped by one half of a C60 molecule, the zig-zag tube is represented by the integers (9, 0) while the armchair tube is denoted by (5, 5). The chiral angle, ¥è, is given by
¥è = sin-1{31/2m/2(n2+nm+m2)1/2}
PROPERTIE The strongest and most flexible molecular material because of C-C covalent bonding and seamless hexagonal network architecture.
Young’s modulus of over 1TPa vs. 70GPa for aluminum & 700GPa for C-fiber.
Maximum strain ~ 10% much higher than any material.
Thermal conductivity ~3000 W/mK in axial direction with small values in the radial direction.
Electrical conductivity six orders higher than copper.
Can be metallic or chirality’s based on 1. The tunable band gap 2.electrical properties can be tailored through application of external magnetic field, application of mechanical deformation…..
Very high current carrying capacity
Excellent field emitter; higher aspect ratio and a smaller tip radius of curvature which are ideal for field emission.
