Synthesis techniques of carbon nanotubes
Laser evaporation is an effective method for the preparation of single-walled carbon nanotubes. Single walled carbon nanotubes and single-walled carbon nanotube bundles were prepared by evaporation of carbon targets doped with Fe, Co, Ni or their alloy by high energy CO2 laser or Nd/YAG laser. The diameter of the tubes can be controlled by laser pulses. The researchers found that the shorter the laser pulse interval, the higher the yield of SWNTs, while the SWNT structure was not affected by the pulse interval time. Using CO2 laser evaporation method for single wall carbon nanotubes at room temperature, if the use of fast imaging technology and emission spectra can be observed in morphology of smoke and carbon containing debris flow evaporation in argon, the diagnostic technology makes the growth process of single wall carbon nanotubes tracking possible. The main disadvantage of laser evaporation (ablation) is that the purity of single walled carbon nanotubes is low and easy to entangle.
Carbon nanotube discharge using graphite electrode is one of the earliest studies in various synthetic techniques. The researchers did a lot of work in optimizing arc discharge for carbon nanotubes. In recent years, in addition to people by adjusting the current and voltage, pressure and velocity change, change the electrode composition, improved electrode feeding mode optimization of arc discharge process, but also through changes the arc medium, simplified arc device. In the process of preparing carbon nanotubes, arc method is mature by changing the arc discharge conditions, catalyst, electrode size, feed mode, the distance between the poles and the raw materials. The carbon nanotubes formed by arc method are straight and wall (multi wall or even single wall). But the production rate is low, the arc discharge process is difficult to control, and the preparation cost is too high. The industrial scale production needs to be explored.
The synthesis techniques of carbon nanotubes are mainly arc method, laser ablation (Zheng Fa) method, catalytic cracking or catalytic chemical vapor deposition (CCVD), and directional control growth method based on various synthesis techniques.
Catalytic pyrolysis is one of the widely used methods for preparing carbon nanotubes. The method mainly uses transition metal as catalyst, and is suitable for large-scale preparation of carbon nanotubes. The content of carbon nanotubes in the products is higher, but the defects of carbon nanotubes are more.
