The carbon nanotubes are another carbon allotropic form, they have many interesting properties and promise many applications.
What are carbon nanotubes?
They are cylindrical molecules made of carbon atoms with a diameter on nanometric scale and length on micrometric or millimetric scale. They consist of a rolled graphene sheet, linking opposite extremities.
![carbon nanotube from graphene](https://www.electricalelibrary.com/wp-content/uploads/2022/05/cnt-from-graphene-1.jpg)
![cocentric carbon nanotubes](https://www.electricalelibrary.com/wp-content/uploads/2022/05/Nanotubo-de-carbón-de-4-capas-1.jpg)
![carbon nanotubes](https://www.electricalelibrary.com/wp-content/uploads/2022/05/dressel2-1-1024x926.jpg)
Properties
The carbon nanotube’s properties depend on if it has single or multiple walls and how it’s rolled.
Graphene winding
![rolling carbon nanotubes](https://www.electricalelibrary.com/wp-content/uploads/2022/05/sensors-19-02464-g001-1-1024x937.jpg)
The two numbers in parentheses (n,m) form the chiral vector (\vec{C}_{h}).
\vec{C}_{h}=n\vec{a}_{1}+m\vec{a}_{2}=(n,m)
Where \vec{a}_{1} and \vec{a}_{2} are unitary vectors, whose modules are equal to 1.
![carbon nanotube vectors](https://www.electricalelibrary.com/wp-content/uploads/2022/05/sensors-19-00392-g002-1-1024x805.jpg)
Obtaining the chiral vector \phi formula.
\vec{C}_{h}\cdot \vec{a}_{1}=\left| \vec{C}_{h}\right|\cdot \left| \vec{a}_{1}\right|\cdot cos\phi
\phi=cos^{-1}\left ( \frac{2n+m}{2\sqrt{\left ( m^{2}+n^{2}+mn\right )}} \right )
The tube’s diameter (d).
d=\frac{a\sqrt{3(n^{2}+mn+m^{2})}}{\pi }
Where a is the length of covalent bond between two carbon atoms, which is 1.42 Å (angstrom).
1 Å = 1\times 10^{-10}m
The integral numbers m and n determine if a nanotube is a conductor or a semiconductor.
Other properties of carbon nanotubes (CNT)
- All nanotubes have great tensile strength, they are 100 times stronger than steel with only 1/6 of density.
- Are excellent heat conductors. Thermal conductivity can reach 6000 W/m\cdot K (watt per meter times Kelvin).
- Since they are made of graphene, Young module (measures resistance to elastic deformation) is close to 1000 GPa, it read gigapascals.
- Carbon nanotubes kill the living cells when they come into contact with the latter.
Some application examples
- Composite materials with nanotubes of multiple walls can have higher resistance to weariness and break, with less weight.
- The conductors CNT have better conductivity than copper. They can one day be used in electric energy transmission.
- It’s possible to put semiconductor nanotubes in field effect transistors, to make the connection between drain and source terminals. Creating high-performance smaller circuits.
![transistor with a carbon nanotube](https://www.electricalelibrary.com/wp-content/uploads/2022/05/2-Figure1-1-1.png)
![carbon nanotubes in digital circuits](https://www.electricalelibrary.com/wp-content/uploads/2022/05/431fd-dc8ecf15-8bec-4348-ae44-af24f0999724-1.jpg)
- Can be used in electrochemical and biological sensors.
![hydrogen sensor with carbon nanotubes](https://www.electricalelibrary.com/wp-content/uploads/2022/05/id2887-1.jpg)
Carbon nanotubes still are very expensive to mass manufacture.