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Properties And Application of Boron Carbide Ceramic

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Update time : 2020-01-13 15:41:42
Boron carbide ceramic is an essential part of new ceramics, which has a high melting point, high hardness, low density, wear resistance, and corrosion resistance. It is widely used in the field of nuclear energy, bulletproof armor, and wear-resistant materials.

At present, the depth and strength of the research on boron carbide ceramics are increasing. In addition to the emergence of new methods for the synthesis of high-purity and ultra-fine boron carbide powder, researchers are also committed to the development of advanced and practical sintering technology.

 

Ceramics boron carbide properties

Boron carbide ceramics are very hard. Its microhardness is about 50000mpa (50gpa), next to diamond (90-100gpa), and CBN (80-90gpa). Its grinding efficiency can reach 60% - 70% of a diamond, 1-2 times of SiC, 1-2 times of corundum's grinding ability. It has excellent acid-base resistance and a small coefficient of thermal expansion (4.5x10-6 ℃), so it has excellent thermal stability. It can absorb thermal neutron qualitatively, but it has a weak impact on resistance and high brittleness.
Boron carbide can resist air corrosion at 1000 ℃, but it is easy to oxidize in an oxidation atmosphere at higher temperatures. Boron carbide has a high resistance to acid and alkali, and is not wetted by most of the molten metals, and has high stability in contact with these substances.

 

 

Preparation of boron carbide ceramics

Boron carbide ceramics can be created by various methods. To obtain dense B4C, hot pressing sintering is generally used.
The B4C obtained by hot pressing sintering can reach 98% of the theoretical density. The preparation is carried out in a vacuum burning pressing furnace or a standard fiery pressing furnace. The warm pressing temperature is 2100 ℃, the pressure is 80-100mpa, the temperature is kept for several minutes, and the pressure needs to be maintained when the heat is reduced.

Due to the weak thermal shock resistance of B4C, the cooling should be slow. The hot pressing temperature should not be too high. When it reaches 2150 ℃, the B4C-C eutectic liquid phase will appear, but if the temperature is too low, the product density will below. Boron carbide ceramic products with high density and hardness can be obtained by using B4C ultrafine powder.

In addition to hot pressing sintering, there is no pressing sintering. But the requirements of pressureless sintering for carbide powder and sintering temperature range are very high. The results show that an essential condition for the densification of pure boron carbide by pressureless sintering is to use ultrafine powder ≤ 3um, and the oxygen content is low enough. The sintering temperature range is 2250-2350 ℃.
 
The primary way of pressureless sintering with additives is to remove the oxide layer of boron carbide by additives, to improve the activation of grain boundary and volume diffusion by increasing the density of point defects or dislocations, to obtain a higher frequency (90-95%) at a slightly lower temperature (2000-2200 ℃). The results show that when Al and Si are used as sintering aids respectively and sintered at 2050 ℃ and atmospheric pressure for 180min, the relative density of the composite ceramics is more than 93%, including 298mpa bending strength of the boron carbide ceramics containing Al and 344mpa bending strength of the boron carbide ceramics containing Si.

Besides, there are also hot isostatic pressing sintering and discharge plasma sintering methods for boron carbide ceramics, which will not be described here. However, hot pressing is a standard method to prepare pure boron carbide ceramics.

 

 

Application of boron carbide ceramics

1. Bulletproof armor field

Due to its lightweight, super high hardness, and high elastic modulus, B4C ceramics are the best materials for a bulletproof vest, helmet, and armor.

At present, boron carbide ceramics are widely used in ceramic armor materials. Compared with other bulletproof materials, B4C ceramics are lighter and more difficult. It is especially suitable for armed helicopters and other aircraft as bulletproof armor materials, which can effectively resist shells. Boron carbide ceramics, produced by BAE Systems Advanced Ceramics, have been used as the "interceptor" bulletproof clothing for the US military.
 

2. Wear-resistant technology

In the field of wear-resistant technology and engineering, various nozzles made of B4C with high hardness are used for the desander nozzle and the nozzle for high-pressure jet water cutting of ship rust removal. Boron carbide is used as the abrasive material for other hard materials such as cemented carbide and engineering ceramics in the process of polishing, fine grinding or grinding, which can significantly reduce the cost of grinding process.
 

3. Thermoelectric couple

Based on the thermoelectric property of B4C, a temperature differential couple capable of measuring 2200 ℃ was prepared by sintering in Japan and Germany, which was used for the measurement and control of high temperature. Because of its high thermal electricity and stability, it can be used reliably for a long time, and the temperature can be measured repeatedly.
 
Boron carbide ceramics is much significant, which has many excellent properties and has been widely used. And in the future, it will be more.