Boron carbide's properties and chemical properties

Boron carbide, also known as Black Diamond, is an organic form. The molecular form IS B₄C. It is usually a grayish-black fine powder. It is one of the three hardest materials known (the others are diamond and cubic boron nitride) and is used in many industrial applications. It has a Mohs hardness of 9.3. So what are the properties and chemical properties of boron carbide?

Basic properties of boron carbide  

1. Low density  

The density of B4C is smaller, 2.52g/cm3. In the homogeneous region.  

Due to the low density of boron carbide, under the condition of high density, its function can reach the standard of boron carbide high strength, high hardness and other excellent functions, so it can be used as light armor, to reduce the weight of tanks and other vehicles, save energy consumption.

2. Hardness and wear resistance  

B4C has super hardness and high wear resistance. In the homogeneous region, the Vickers hardness of B4C increases with the addition of C content. When the carbon content is 10.6%, the hardness is 29.1GPa. When the carbon content is 20%, the hardness 21 can reach 37.7GPa.  Its hardness remains high at high temperatures (>30GPa). Hardness changes with temperature can be shown by experience formula (10) :  

3. Coefficient of thermal expansion and specific heat capacity  

The melting point of boron carbide is 2450℃, the boiling point is 3000℃, and the thermal expansion coefficient is 5.73×10-6/℃(28-1770 ℃).

Chemical stability of boron carbide

Boron carbide is one of the most stable compounds, it is not easy to produce oxidation reaction below 600℃; When the temperature is above 600℃, the surface is oxidized into B2O3 film, which prevents the further oxidation of B4C. So B4C is now used as an antioxidant in refractory materials.  

B4C generally does not react with chemical reagents at room temperature; Above 800℃, B4C and Br form tribromine compound. At high temperatures, B4C reacts with metal oxides to form metal borides and carbon monoxide, resulting in FeB films with high microhardness (HV=24GPa) and wear resistance. Therefore, B4C can be used for the boriding of steel and alloy.