2.1 Morphology memory synthesis method
The main meaning is that the macrostructure of the initial solid reactants can be maintained to a certain extent before and after the synthesis reaction. In 1988, French Ledoux and his colleagues first proposed and used this method to prepare silicon carbide with high specific surface area and SiC materials with different structures. Later, people use this method to prepare silicon carbide nanowires, nanotubes, nano spheres and high specific surface silicon carbide.
2.2 Sol-gel and carbothermal reduction methods
Sol-gel method is to use contain Gao Huaxue compound as precursor of active components, the raw materials mixing in liquid phase, and hydrolysis, condensation reaction, in solution to form stable system of transparent sol, sol by retrogradation between colloidal particles slow convergence, form the three-dimensional network structure of the gel, gel filled with solvent, loss of mobility between network formed gel. After drying, sintering and curing, the gel is prepared into molecular and even nanostructured materials. Because of its low cost, simple process and relatively low reaction temperature, it has become a common method for preparing silicon carbide. Sol-gel method used to prepare silicon carbide powder, silicon carbide fiber and silicon carbide whisker, now it is also used to prepare some advanced silicon carbide materials such as nanowires, nanorods, nanoparticles or nano whiskers.
Uniform SiC can be obtained by sol – gel process. In the reaction process, carbon black, activated carbon, carbon fiber, phenolic resin, starch, sucrose and so on are generally used as carbon sources, and silica sol is used as silicon source. Some people also use organosilicone high polymers (that is, there are both carbon and silicon sources in the same molecule) by pyrolysis to obtain silicon carbide.
2.3 Carbon nanotube confinement reaction
Carbon nanotube confined reaction (CNT) is a method to synthesize one-dimensional nanomaterials by reacting CNTs with volatile metal oxides and chlorides. The premise of choosing this method is that because carbon nanotubes are resistant to high temperature and the vapor of carbon atoms is low, when a substance with a high vapor pressure is added to the system, it is possible for its molecules to migrate to the surrounding of carbon nanotubes, attach to its surface or diffuse into its interior. Because the reaction is confined to carbon nanotubes, the silicon carbide generated is only one-dimensional.
2.4 Chemical vapor deposition
Chemical vapor deposition (CVD) usually refers to the process of chemical reaction and condensation of reactants to produce a specific product. Chemical vapor deposition can be the thermal decomposition of a single compound that must have all the elements required for the product. In addition, by means of gas reaction between two or more substances, this method can be used in a variety of combinations. Its advantage is that high purity silicon carbide can be prepared.
2.5 Arc discharge method
Arc discharge is one of the most important methods for the preparation of nano-sized silicon carbide. The principle is that the arc discharge can make the temperature of the reaction as high as 2000℃, so that the synthesis of reactants can be accelerated, at the same time can promote the catalyst and other impurities at high temperature volatilization, get high purity nano silicon carbide particles and silicon carbide nanowires.
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May
