Casting film production line
DATE：2021/5/14 8:59:37 / READ： / SOURCE：This station
Casting film production line
Carbon nanotubes
In 1991, Iijima, an electron microscope expert in the basic research laboratory of NEC company in Japan, accidentally discovered carbon molecules composed of tubular coaxial nanotubes when examining spherical carbon molecules produced in graphite arc equipment under a high-resolution projection electron microscope. This is the carbon nanotubes that are widely concerned today. From graphite, diamond to fullerene carbon, and then to carbon nanotubes, the structure of crystalline carbon is becoming more and more perfect. Before the discovery of carbon nanotubes, graphite was two-dimensional (plane), diamond was three-dimensional (volume), and C60 was zero dimensional (point). People will naturally think, is there still one-dimensional crystal carbon? Since the discovery of carbon nanotubes by Iijima in 1991, this question has finally been answered.① High resolution electron microscopy (HRTEM) was used to study the structure of carbon nanotubes (CNTs). It has been found that multi-layer CNTs are generally composed of several or dozens of single-walled CNTs with a spacing of about 0.34 mm, which is equivalent to the graphite (002) plane spacing. The diameter of CNTs ranges from 0.0 to tens of nanometers, and the side of each single-walled CNT is composed of hexagonal carbon atoms, Generally, it is tens of nanometers to micrometers. The ends are capped with a Pentagon of carbon atoms. There may be three types of structures in single-walled carbon nanotubes, including single-walled nanotubes (SWNTs), giant toothed pin rice tubes (MWNTs) and flexible nanotubes. The formation of these types of carbon nanotubes depends on how the hexagonal lattice two-dimensional graphite sheets of carbon atoms are "rolled up" to form a barrel shape.
② There are many methods for the preparation of carbon nanotubes. In addition to the DC arc discharge method using carbon rod as electrode, a large number of carbon nanotubes can also be obtained by the pyrolysis of hydrocarbons. Carbon nanotubes with tens of nanometers long can be grown by the pyrolysis of acetylene on catalyst particles such as CO or Fe, and some are coil shaped. Carbon nanotubes were also obtained by burning acetylene, benzene or ethylene in a low pressure chamber filled with oxygen and diluent. The growth of multi walled carbon nanotubes (MWCNTs) does not need catalyst. Single walled carbon nanotubes (SWCNTs) can grow only under the action of catalyst, but it is possible to grow MWCNTs with catalyst. Single walled carbon nanotubes (SWCNTs) were prepared by inserting Fe or Co catalyst into the tip of carbon rod of arc discharge anode.
③ Properties and applications carbon nanotubes have unique electrical properties, which is due to the quantum confinement of electrons. Electrons can only move along the nanotube's axial direction in a single-layer graphite sheet, and their radial motion is limited. Therefore, their wave vectors are axial and only need infinitesimal energy to excite an electron to an empty excited state, which is metallic. Therefore, most carbon nanotubes are good electrical conductors, which can give the engineering plastics antistatic and conductive properties after compounding with engineering plastics. Carbon nanotubes have the same thermal conductivity and unique mechanical properties as diamond. The tensile strength of carbon nanotubes is 100 times higher than that of steel, the elongation is several percent, and it has good bending property. These excellent mechanical properties make them have potential applications. For example, they can be used as reinforcing materials of engineering plastics, greatly improving the mechanical properties of engineering plastics.
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