Master student Terekhova A.A., Ph.D.Dyakov I.A.

Tambov State Technical University, Russia

The use of carbon nanotubes in electrical engineering

Carbon nanotube is a long cylindrical graphite rolled strips with thickness up to several tens of nanometers and length up to several centimeters with a carbon frame structure. Under this structure include larger molecules are connected only to carbon atoms. At the ends of nanotubes are usually formed by hemispherical heads (Fig.1).

Carbon nanotubes come in different shapes and sizes – straight and curved, single layer and multilayer. Despite the fact that at first glance they seem very fragile, actually they are quite durable material that has been proven by many studies. It was found that carbon nanotubes are characterized by such properties as tensile and bending, i.e. under the influence of various mechanical loads the elements do not break and are broken, and this suggests that they can adapt to different voltages.

Fig. 1 Idealized model of single-layer carbon nanotubes

Due to characteristics such as bending strength and conductivity of carbon nanotubes used in many fields: as additives to polymers as absorber of electromagnetic waves, in the manufacture of various sensors and capacitors, to transform electricity, in the production of composites with the aim of strengthening their structure and properties.

Repeated experiments conducted by different scholars, show that carbon nanotubes are the most rugged and tough of all known materials - a material with a record

high values of ultimate tensile strength (~60 GPA) and young's modulus (≈ 1 TPA). It is connected with perfection of structure and the strong sp2 chemical bond between the carbon atoms that comprise the nanotube.

Nanotubes are also good heat conductors along the tube, showing properties, so-called, unimpeded conductivity or superconductivity. However, across the axis of the nanotubes have high thermal insulation properties.

An interesting feature of carbon nanotubes is that they can be metallic or semiconducting depending on their diameter and chirality. As a result of the synthesis is usually a mixture of tubes, two thirds of which have semiconducting properties, and one third metallic.

Metal tubes usually have a chair structure (Fig.2A) and semiconductor zigzag (Fig.2B) and spiral (Fig. 2B).

Metallic and semiconducting carbon nanotubes differing conductivity metal can conduct current at a temperature of 0 ° C, and the semiconductor only at elevated temperatures.

Widespread use of carbon nanotubes in electrical engineering possible due to the fact that they can transmit currents with a density higher than the most conductive metals, such as copper. So a single layer of nanotubes pass currents of density up to 109 A/cm2, and the multilayer is up to 100 µa/cm2, and copper at such values of current density melts.In addition, when the resistance is comparable to copper, and carbon nanotubes is four times easier.

Carbon nanotubes outperform copper by such indicators as the coefficient of thermal conductivity along the axis. For copper it is equal to 400W/(m×K), for nanotubes 500 -5500 W/(m×K).

Another advantage of nanotubes is due to cold emission of electrons, an along the tube axis of the electric field. The field strength in the vicinity of the top part hundreds of times higher than the one that exists in the volume, which leads to anomalously high values of emission current at a relatively low external voltage and allows the use of nanotube macroscopic system as a cold emission cathodes. The degree of emission of carbon nanotubes can be used in the manufacture of flat panel displays and touch control panels.

б)

Fig.2 Types of carbon nanotubes:

a – chair structure; b – zigzag structure; с – helical structure

The application of carbon nanotubes in the production of various electrical devices is one of the most promising directions of work of scientists around the world. Due to the properties of the nanotubes described above, their use in the production of, for example, cables and wires is quite beneficial. Due to its lightness and high conductivity cable, manufactured with the use of carbon nanotubes will significantly surpass its copper predecessor, which makes its production more profitable.

The authors propose to use carbon nanotubes in the manufacture of various parts of electrical machines. For example, the brush for electric machines that are special conductive parts of the current collection devices that provide a sliding contact between the stationary and rotating parts of the machine and serve to supply or drain current, when you add in the production of carbon nanotubes in them will last longer than usual. Or, for example, nanomodification coating of housings of electric motors will improve their heat-transfer properties. Such measures will allow to increase the service life of electric motors, which will significantly reduce costs in their operation.

Currently, due to their properties carbon nanotubes are one of the most promising materials used in many industries. Despite their shortcomings, such as toxicity, the use of nanotubes in electrical engineering due to the need to create a new material the properties of which will be an opportunity to reduce the cost of production and operation of electrical equipment.