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Five Important Methods of Boron Carbide Production

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Update time : 2020-01-17 15:30:29
Boron carbide has excellent properties and is widely used. Boron carbide is second only to diamond and cubic boron nitride in hardness. It has many advantages, such as high melting point, low density, high strength, broad neutron absorption cross-section, excellent thermoelectric performance, and good mechanical stability. And we can use it in aerospace, national defense, nuclear energy, and wear-resistant technology.

At present, the carbothermal reduction is the primary method for the industrial production of boron carbide. Besides, the practices of boron carbide production include self-propagating thermal reduction, mechanochemical method, direct synthesis, sol-gel method, and so on.

1. Carbothermal reduction
The carbothermal reduction method usually uses boric acid or boric anhydride as raw material and carbon as a reducing agent to carry out high-temperature reduction reaction in an electric arc furnace. At present, this method is the primary method of industrial production of boron carbide, which has the advantages of simple response and low cost.

 

Boric acid and carbon black were used as raw materials and kept at 1700-1850 ℃ for 0.5-1.0 h. The boron carbide powder with high purity was calcined. The carbon content was 20.7%, close to the theoretical value. However, the disadvantages of this method are: it needs to be carried out at a higher temperature, which consumes a lot of energy; the boron carbide production is easy to agglomerate, which needs to be crushed; the product is mixed with unreacted carbon, which needs to be removed by subsequent treatment.

2. Self-propagating thermal reduction
The self-propagating thermal reduction method uses carbon black (or coke) and boric acid (or boric anhydride) as raw materials, active metal substance (usually mg) as reducing agent or flux, and the heat generated by self-propagating combustion reaction of metal substance are used to synthesize boron carbide. The reaction equation is as follows: 6mg + C + 2b2o3 = 6mgo + B4C 

This method has the advantages of low initial reaction temperature (1000-1200 ℃), energy saving, fast reaction, and simple equipment. The synthesized B4C powder has high purity and excellent particle size (0.1 - 4.0 μ m) and generally does not need to be crushed.

Using Na2B4O7, Mg, and C as raw materials, Jiang et al. Prepared B4C powder with a particle size of 0.6 μ m by self-propagating thermal reduction. But the MgO produced by the reaction must be removed by additional process, and it is challenging to eliminate.

3. Mechanochemistry
The mechanochemical method uses boron oxide powder, magnesium powder and graphite powder as raw materials, using the rotation or vibration of the ball mill to make the harder ball milling medium impact, grind and stir the raw materials vigorously, and induce the chemical reaction at a temperature slightly higher than the room temperature to prepare boron carbide powder. The preparation temperature of this method is low, so it is a promising preparation method.

Deng et al. Prepared B4C powder with B2O3: C: Mg mass ratio of 10:1:11 by the mechanochemical method. The particle size of the powder was 100-200 nm. According to yogurt et al., the best mass ratio of Mg: C is 9:2 - 10:1. However, MgO, the by-product of this method, is challenging to be obliterated, and it usually takes a long time for ball milling.

 

4. Direct synthesis
The direct boron carbide production method is to prepare by thoroughly mixing the carbon powder and boron powder and reacting in a vacuum or inert atmosphere of 1700 - 2100 ℃. The purity of boron carbide prepared by direct synthesis is high, and the B / C ratio in the reaction is easy to control. Still, the preparation process of boron carbide used for synthesis is relatively complex and high cost. Therefore, this method has some limitations.

5. Sol-gel method
Sol-gel method (Sol-gel) refers to the technique of solidifying inorganic or metal alkoxides through the solution, sol, and gel, and then heat-treated to obtain stable compounds. The superiority of this method is that the mixture of raw materials is more uniform, the reaction temperature is low, the product is bulky, and the particle size of B4C powder is small.

Sinha et al. Mixed the boric acid and citric acid under the conditions of pH=2-3 and 84-122. Transparent and stable gold gel can be formed. When heated to 700 degrees in a vacuum furnace, the porous soft borate citric acid precursor can be obtained. The precursor is kept under vacuum for 1000-1450 at 2h, and the B4C powder with a particle size of about 2.25 M can be obtained.

Luoyang Tongrun team studied the effect of reaction time, temperature, and different raw material ratio on the B4C in the boric acid citric acid gel reaction system. When controlling the initial mass rate of boric acid and citric acid to 2.2:1, the content of free carbon in the product was 2.38% when the reaction temperature was 1500 3.5H. However, the production efficiency of this method is low, and it isn't effortless to get large-scale applications.

With the development of today's science and technology, boron carbide plays a more and more critical role in industry and life. Therefore, a suitable boron carbide production will be an essential determinant of the development of boron carbide in the future.
 

Luoyang Trunnano Tech Co., Ltd (TRUNNANO) is a professional Boron Carbide Powder manufacturer with over 12 years experience in chemical products research and development. If you are looking for high quality Boron Carbide B4C Powder, please feel free to contact us and send an inquiry.

 
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