In chemistry, structures called nanotubes tube with a diameter of nanometer order. There nanotubes of many materials such as silicon or boron nitride, but generally, the term applies to carbon nanotubes. carbon nanotubes have a structure that can be seen from a graphite sheet rolled on itself. Are being actively studied for their fundamental interest for chemistry and technological applications. It is, for example, the first substance known to mankind can sustain indefinitely its own weight, a necessary condition for building a space elevator.
properties of nanotubes
The nanotubes usually have a high length-to radio as the radio is usually less than a few nanometers, however, the length can be even 105 nm. Because of this feature can be considered as one-dimensional.
nanotubes are characterized by a large electronic complexity. These structures can withstand a wide range of behaviors. Starting with the semiconducting behavior to present, in some cases, superconductivity. This wide range of conductivity is determined primarily by geometric relations, ie according to their diameter, twist and the number of layers of composition.
As the ability to carry current, it is known that can arrive at quantities of approximately one billion A/cm2. We must also say that all these properties do not depend on the length of the tube, unlike what happens in everyday cables.
stability and robustness of the links between carbon atoms, provides the ability to be one of the strongest fibers that can be manufactured today. On the other hand, faced with intense deformation efforts are able to deform significantly and kept in a elastic regime. Moreover, these mechanical properties could be improved by attaching several nanotubes in bundles, or ropes. Thus, although it broke a nanotube, as they behave as independent units, the fracture would not spread to adjoining units. In other words, the nanotubes can act as extremely strong springs with small efforts and, compared to higher loads can deform dramatically and return later to its original shape.
thermal conductivity of nanotubes can be as high as 6000 W / mK at room temperature. Also are extremely thermally stable, being stable even at 2800 ° C in vacuum and 750 ° C in air. The properties of nanotubes can be modified by encapsulating metals inside, or even gases. In this sense, would be an extraordinary hydrogen storage. As you know one of the major technical problems for the development of fuel cells is the storage of this element. Main
manufacturing methods
The "laser ablation" is a process of vaporizing a graphite target by radiating a laser pulse at a high temperature reactor in the presence of an inert gas. The nanotubes are formed when vaporized graphite in contact with the cold surface, condensing on the reactor walls.
download arc: The arc discharge is a type of continuous electric discharge that generates intense light and heat. Occurs between two electrodes faced in an atmosphere of inert gas at low pressure. For graphite electrodes, a current is strong which makes carbon atoms sublimate from the electrode surface, forming a plasma around them. In an open-air arc, and normal pressure, the positive electrode reaches a temperature of 3,000 ยบ C.
CVD (Catalytic Vapor Phase) to initiate the growth of nanotubes, two gases are mixed in reactor. A process gas (such as ammonia, nitrogen, hydrogen, etc.) And a gas used as carbon source (such as acetylene, ethylene, ethanol, methane, etc.).. The nanotubes grow on the side of the metal catalyst. Gas containing carbon is broken on the surface of the catalyst particles, and carbon is transported to the limits of the particle, where the nanotubes are formed. This mechanism is still under study. Applications
supercapacitors: nanotube-enhanced ultracapacitors (either single or multiple wall) combine high durability and power of commercial supercapacitors with higher storage density characteristic of chemical batteries. They can therefore be used in many energy storage applications.
hydrogen storage: the large surface area and tubular structure of nanotubes makes carbon that may be useful for hydrogen storage. Hydrogen is added to the nanotubes by chemisorption, since the carbon bonds that form the nanotube offer capacity up to saturation incorporating hydrogen.
transistors, field transistors, semiconductor nanotubes can be inserted between two electrodes (source and drain) in field effect transistors (FET), called CNTFET, to create a highway for the movement of electrons. As a result, without missing commuted CNTFET and consume less energy than a silicon device. In addition, switching speeds can reach terahertz switch which is 104 times faster than current processors.
Memories: Other devices may experience great advances with the introduction of carbon nanotubes in its construction is, without doubt, the random access memory (RAM). Given that the characteristics of an ideal memory of this type would be a large storage capacity, access to rapid and random data, a low power consumption, a low price per bit stored, easy integration in integrated circuit technology and, if possible, the non-volatility of the data after turning off the computer, have tried to design reports in whose operation play an essential role of carbon nanotubes.
Other industrial applications
By adding small amounts of nanotubes to polymers, changing their electrical properties and this gives rise to the first industrial applications: biomedical, automotive, aerospace, packaging, conductive inks, materials extremely black sports.
Source: SOBER LONGAR ESTEBAN
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