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Introduction of six preparation methods of zirconium carbide (ZrC) ceramic powder

wallpapers Low Carbon 2020-06-23
Zirconium carbide (ZrC) ceramic material has a high melting point, high hardness, excellent mechanical properties, high electrical conductivity (thermal) rate and superior resistance to oxidation and ablation. As one of ultra-high temperature ceramic material systems, it can be used as a heat-resistant material For space vehicles and propulsion systems, such as the leading edge of the space shuttle wing, hypersonic scramjet engines, etc. The lattice structure of ZrC ceramic material is shown in Figure 1. Zr atoms form a compact cubic lattice, and C atoms are located in the octahedral gap of the mesh, so the crystal structure of ZrC belongs to the typical NaCl face-centred cubic structure. The ZrC lattice constant a=0.46930nm, the radius ratio of C atom and Zr atom is 0.481.
 
 Figure 1 Lattice structure of ZrC ceramic material

To prepare ZrC ceramic powder with uniform particle size and high purity, the researchers conducted some studies on the preparation of ZrC ceramic powder. At present, the preparation methods of ZrC powder mainly include electric arc furnace carbon thermal reduction method, self-propagating high-temperature synthesis method (SHS), sol-gel method and high energy ball milling method.

1. Electric arc furnace carbon thermal reduction method is currently the most effective method for industrial preparation. Its approach uses zircon sand or oblique zircon as a precursor and then generates ZrC through carbothermal reduction reaction at high temperature and high pressure. The reaction mechanism of the powder is: The temperature of the electric arc furnace should be strictly controlled during the reaction process. If the reaction temperature is too low, it will result in less SiO being eliminated, which will lead to the formation of ZrC powder containing more impurity phases Si and C. In turn, it affects the purity of ZrC powder. The ZrC powder prepared by the electric arc furnace carbon thermal reduction method has a simple equipment structure and simple operation. Still, its cost is higher, and the ZrC powder developed has a larger particle size. Figure 2 is ZrC ceramic powder made by carbothermal reduction using ZrO2 as the raw material. The dust has a uniform particle size, and the size is less than 200nm.
 
 Fig. 2 Nano-ZrC powder prepared by carbon arc furnace carbon thermal reduction method
 
2. Self-propagating high-temperature synthesis method (SHS) Self-propagating high-temperature synthesis method is a new technology that uses high reaction heat generated between reactants and synthesizes materials in a short time. The process flow for preparing ZrC powder using self-propagating high-temperature synthesis technology .

The use of self-propagating high-temperature synthesis method to prepare ceramic powder has the following characteristics: (1) The reaction process uses the chemical reaction to exotherm itself without the need for an external heat source; (2) The product of the desired composition and structure is obtained by the self-sustaining reaction of rapid automatic wave combustion (3) Control the processing speed, temperature, conversion rate and product composition and arrangement by changing the heat release and transmission speed. Figure3 shows the nano-ZrC powder prepared by self-propagating high-temperature synthesis technology; the particle size of the powder is uniform.
 Figure 3 Nano ZrC powder prepared by self-propagating high-temperature synthesis technology
 
3. Sol-gel method Sol-gel method has now become a new field of powder preparation technology is a method of making powder using a colloidal dispersion system. The basic principle of this method is: stir the metal alkoxide, water, alcohol and necessary catalysts to prepare a uniform solution, and form a wet gel through the hydrolysis and polycondensation reaction. After the damp gel is dried and heat-treated to create a bulk powder, and then proceed Superfine ceramic powder made by mechanical crushing or grinding. The sol-gel method has the advantages of preparing powder with uniform particle size and composition distribution and small particle size.
 
The advantages of the sol-gel method for preparing ceramic powder are: ① The raw materials used are high-purity inorganic salts or alkoxides to avoid the influence of impurity elements, so the ceramic powder made is of higher purity; ② The reaction is mainly in the liquid In the phase, it can realize the precise control of the chemical ratio of the material in a short time, and thus ensure the uniformity of the product particle size; ③ The reaction synthesis temperature of this method is low, which has a small cost effect. However, this method also has the characteristics of long preparation period and a relatively complicated operation.
 
 Figure 4 ZrC powder prepared by sol-gel method
 
4. Laser gas phase reaction method The laser gas phase reaction method uses Zr(OC4H9)4 as the precursor and uses laser pyrolysis to obtain Zr/O/C nanopowder first, which is then placed in an argon atmosphere and heat-treated at 1500°C. ZrC powder of about 40 nm was prepared. The advantage of the laser gas phase reaction method is that there is less pollution in the powder preparation process, and the particle size and stoichiometric ratio are elementary to control, the resulting powder particle size distribution range is very narrow, and the production efficiency is high.
 
Figure 5 shows the ZrC powder prepared by the laser gas phase reaction method.
Figure 5 is the ZrC powder prepared by the laser gas phase reaction method
 
5. High-frequency plasma method The preparation principle of high-frequency plasma method is: using high-frequency induction coil heating, using ZrCl4 carbon black and nano-active Mg as raw materials, high purity Ar as the carrier gas, loading the raw materials into high-temperature plasma The zone is quickly heated to the reaction temperature, and nano-scale ZrC powder is obtained through the gas-phase reaction. High-frequency induction thermal plasma belongs to electrodeless heating, which can avoid electrode pollution, high energy density, high temperature in the reactor, and significant temperature difference. No high-temperature treatment is required during the preparation process, which can effectively prevent particle agglomeration and help to obtain uniform particles. The dispersed ultrafine powder has a good application prospect. However, this process is a new type of powder preparation technology, the theory and method are not mature, and industrial production will take some time.

6. High-energy ball milling method High-energy mechanical ball milling method is to use the rotation or vibration of the ball mill to make the hard balls strongly impact, grind and stir the raw materials, and crush the mixed powder into fine particles. A large number of defects generated during the ball milling process reduce the activation energy, reduce the grain size and increase the temperature to increase the diffusion rate effectively, and can diffuse the non-diffused alloy elements through mechanical alloying to achieve the purpose of alloying.

Trunnano is one of the world's largest producers of nano carbides, of which nano zirconium carbide is one of the leading products. If you are interested in zirconium carbide, you can contact Dr Leo, email: brad@ihpa.net.

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Tag: Trunnano   Zirconium carbide   ZrC