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Carbon Nanotubes

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rhys davies

on 25 February 2013

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Transcript of Carbon Nanotubes

Carbon
Nanotubes The Background of Carbon Nanotubes By
Rhys Davies The current interest in Carbon Nanotubes (CNTs) came as a result of the synthesis of C60 and other fullerenes. What are Carbon Nanotubes? A Carbon Nanotube is a molecular-scale tube-shaped material, made of carbon, having a diameter measuring on the nanometer scale. The walls are made one atom thick sheets of graphene.

CNTs have remarkable properties:they are among the stiffest and strongest fibres known, and have good thermal conductivity/electronic properties The discovery that carbon could form stable, ordered structures other than graphite and diamond stimulated researchers worldwide to search for other new forms of carbon. A Japanese scientist, Sumio Iijima, discovered fullerene-related carbon nanotubes in 1991 using the same evaporator Structures of Carbon Nanotubes Carbon Nanotubes can either be found as Single Walled Nanotubes, Multi-wall Nanotubes or Double-wall Nanotubes. Single Walled Nanotubes
(SWNTs) Carbon Nanotubes have many structures, they differ in thickness, length, type of helicity and number of layers. A graphene sheet can be rolled into 3 different patterns: "Armchair", "Zig-Zag" and "Chiral". Each pattern refers to the arrangement of hexagons around the circumference.

The diameters of most SWNTs are 1nm, the tube length can be thousands of times larger.

The values of n and m determine the chirality, or "twist" of the nanotube. The pattern of a nanotube sheet depends on the pairs of indicies Multiwall Nanotubes Multi-walled nanotubes consist of multiple rolled layers of graphene

Mulitwall nanotubes are easier to produce in larger quantities than Single wall nanotubes, as multiwall nanotubes are cheaper.

Two common models are the: Russian Doll and Parchment. Properties Carbon nanotubes can be either: semiconducting or metallic

Most fiber materials lack either stiffness, strength or tenacity, however carbon nanotubes have a distinctive combination of these properties

Carbon nanotubes are also excellent conductors of heat and energy compared with other materials

This explains why there is such a variety of uses for carbon nanotubes Macroscopic Properties Microscopic Structure There are two types of bonding related to Carbon nanotubes, Covalent and Van der Wall.

The strength in the nanotubes comes from the sp2 covalent bonds between the carbon atoms

Helicity and diameter of carbon atoms in the nanotube shell determine whether a nanotube is metallic Carbon nanotubes are the strongest/stiffest materials discovered yet, in relation to tensile strength and elastic modulus. Fibre Material Specific Density Youngs Modulus (Tpa) Strength (GPa)
Carbon Nanotube 1.3-2 1 10-60
HS Steel 7.8 0.2 4.1
Kevlar 49 1.4 0.13 3.6-4.1
Carbon Fibre 1.7-2 0.2-0.6 1.7-5
Polyacrylonitrile
Fibreglass 2.5 0.07/0.08 2.4/4.5 Uses of Carbon Nanotubes The properties of carbon nanotubes make them ultimate carbon fibres.
Their properties allow them to be used in a variety of applications: Current Uses of Carbon Nanotubes:
Atomic Force Microscope Tips
Bicycle Components
Biosensors for harmful gases
Low power, fast computer chips
Touchscreen displays for mobile phones

Potential Uses include:
Space Elevator
Synthetic Muscles
Body Armour
Water Proof Fabrics Batteries Research by the Massachusetts Institute of Technology has lead to the discovery that carbon nanotubes can be used to replace the cathode in a lithium ion battery as well as the negative annode.

This new battery demonstrated an increased capacity for charge by around a third and using carbon nanotubes for battery electrodes can produce a tenfold increase in the amount of power expected of a conventional rechargeable lithium battery. Lithium Ion Batteries Three components make up lithium-ion batteries: An anode(negative electrode), a cathode (positive electrode) and an electrolyte

A lithium-ion battery is a family of rechargeable batteries.

During discharge, charged lithium ions move from the negative electrode to the positive electrode, and back when charging Carbon Nanotubes in Lithium Batteries A base material is dipped in solutions containing carbon nanotubes

These materials are then alternated on a surface, this allows them to bond tightly, as they have complementary charges.

“By integrating charged molecules on the nanotubes, they can assemble in a way that produces a highly porous electrode resulting in a greater number of nanotubes accessible for Li-ion storage and release."
Dr. Paula Hammond How They Work 1. A heat source, generally a laser or high voltage spark, is used to set an end of the nanotube alight.

2. The heat generated from the burning fuel passes enters the centre of the nanotube.

3.A thermal wave is created Comparison with Lithium-ion Battery The power density of lithium ion batteries: 300 to 1,500 W/kg. Carbon nanotubes increase the power density 10x, therefore the power density could reach 15,000 W/kg.

The cycle durability of lithium ion batteries is between 400-1200 cycles, maximum. Carbon nanotube lithium ion batteries can last 1000 cycles easily. Alternative Method A spray technique has been developed to increase the time of producing the layers

Layers can now be laid down within seconds rather than the 15-20 minutes it normally takes. The structure of the nanotube influences its electrical properties. Carbon nanotubes deform plastiaclly, the material becomes permanently stretched. Most nanotubes are good conductors of heat. At room temperature single walled nanotubes have a thermal conductivity of around 3500W·m−1·K−1. Future of Carbon Nanotube Lithium-Ion Batteries Electrical cars: are in need of a battery that requires a small charging time for a high power output. Carbon nanotube batteries could fit this requirement. Rechargeable Devices:As lithium ion batteries are often found in rechargeable devices, carbon nanotube batteries may start to become more popular CNTs are not as strong under compression.
They usually undergo buckling when placed under compressive, torsional, or bending stress. They may, also, be suitable for hybrid cars
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