Carbon Nanotubes

CARBON NANOTUBES

Introduction

Carbon nanotubes (CNTs) are allotropes of carbon. In a nano structure length-to-diameter ratio exceeds 1,000,000. Nanotubes are members of the fullerene structural family, which also includes buckyballs. Whereas buckyballs are spherical in shape, a nanotube is cylindrical, with at least one end typically capped with a hemisphere of the buckyball structure.

The chemical bonding of nanotubes are composed entirely of sp2 bonds, they align themselves into “ropes” held together by Van der Waals forces.

In 1952 Radushkevich and Lukyanovich published clear images of 50 nanometer diameter tubes made of carbon in the Soviet Journal Of Physical Chemistry.

Types of Carbon

Single Walled

Most Single-Walled Nanotubes (SWNT) have a diameter closed to 1 nanometer, with a tube length that can be many thousands of times longer. The structure of SWNT can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene into a seamless cylinder.

The way the graphene sheet is wrapped is represented by a pair of induces (n,m) called the chiral vector. The integer’s n and m denote the number of unit vectors along two directions in the honeycomb crystal lattice of graphene. If n=m, the nanotubes are called “armchair”. Otherwise, they are called “chiral”. The micro electro-mechanical scale which is currently the basis of modern electronics and the most basic building block of this system is the electric wire, and SWNTs can act as excellent conductors.

Multi-Walled

MWNT consist of multiple layers of graphite rolled in on themselves to form a tube shape. In the Russian Doll model, sheets of graphite are arrange in concentric cylinders, e.g. a(0,8) single-walled nanotube (SWNT) within a larger (0,10) single-walled nanotube.
In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or a rolled up newspaper.

Fullerite

Fullrites are the solid state manifestation of fullerene. Being highly incompressible nanotubes forms, polymerized single-walled nonotubes (P-SWNT) are a class of fullerits.
These are comparable to diamond in terms to hardness.

Torus

A nanotube is theoretically described carbon nanotube bent into a torus (doughnut shape).
Nanotube have many unique properties, such magnetic moments 1000 times larger than previously expected for certain specific raddi. Properties such as magnetic moment, thermal stability, etc. vary widely depending on radius of the torus and radius of the tube.

Nanobud

Carbon nanotubes are materials formed by combining two allotropes of carbon nanotubes and fullerens. In the fullere – like “buds” are conveniently bounded to the outer sidewalls of the underlying carbon nanotube.
In particular the have been found to be exceptionally good field emitters.

Properties

1. Strength

Carbon nanotubes are the strongest and stiffest material on earth, in terms of tensile strength and elasticity respectively. This strength results from the covalent sp2 bonds formed between the individual carbon atoms. Under excessive tensile strain, the tubes will undergo Plastic deformation and higher pressure causes bulkiness.

2. Kinetic

Multi-walled nanotubes, multiple concentric nanotubes precisely nested within one another, exhibit a striking telescoping property whereby an inner nanotube core may slide, almost with in the friction, within its outer nanotube shell thus create an automatically perfect linear or rotational bearing. Already this propertyhas been utilized to create the World’s Smallest Rotational Motor.

3. Electrical

Electrical properties of nanotubes are of two types A) Metallic and B) Semiconductor.
Metallic semiconductor can have an electrical current density more than 1,000 times greater than metals such as silver and copper.

4. Thermal

All nanotubes are expected to b very good thermal conductors along the tube, exhibiting a property known as” BLAAICTIC CONDUCTION”. It is predicted that carbon nanotubes will be able to transmit up to 6000 watts per meter per Kelvin at room temperature; compare this to copper, a metal known for its good thermal conductivity. The temperature stability of carbon is estimated to be up to 2800 degrees Celsius in vacuum and about 750 degree Celsius in air.

5. One-Dimensional Transport

Due to their nanoscale dimensions, electron transport in carbon nanotubes will takes place through quantum effects and will only pro[agate along the axis of the tube because this special transport property, carbon nanotubes are frequently referred to as “one – dimensional ” in scientific articles.

6. Toxicity

Results from various scientific tests on cells have so far proven confusing; with some results indicating to be highly toxic and others show no signs of toxicity. A recent research shows that once they are inside the cell, they accumulate in the cytoplasm and cause cell death.

Potential and Current Applications

The joining of two carbon nanotubes with different electrical properties to form a diode has been proposed. The strength and flexibility of carbon nanotubes makes them of potential use in controlling other nanoscales structures, which suggest they will have an important role in Nanotechnology Engineering. Carbon nanotubes have already been used as composite fibers in polymers to improve the mechanical, thermal and electrical properties of the bulk product.

1. Structural

Because of the great mechanical properties of the carbon nanotubule, a variety of structures has been proposed ranging from everyday items like clothes and sports gear to combat jackets and space elevators. However the space elevators will require further efforts in refining carbon nanotube technology.

2. In electrical Circuits

Carbon nanotubes have many properties – form their unique dimensions to an unusual current conduction mechanism-that make them ideal components of electrical circuits.
Nanotubes transistors can be grown in bulk, not very differently from silicon transistors.
The nanotubes made integrated memory circuits was made in 2004.

Depending on subtle surface features a nanotubes may act as a plain conductor or as a semiconductor.

3. As a Vessel for Drug Delivery

The nanotube’s versatility structure allows it to be used for a Varity of tasks in and around the body.