The cost of boron carbide is low, but the thermal stability is not good, although silicon nitride is the hardest material, but the cost is too expensive. Silicon carbide ceramics combine the advantages of both together, and are widely used in many fields.
Boron carbide (boron carbide), alias black diamond, the formula B4C, usually gray black powder. Is one of the three most hard known materials (the other two are diamond, cubic boron nitride), armor for tank cars, bodyguards and many industrial applications. The Mohs hardness is 9.3.
It was discovered in the 19th century as a by-product of metal boride research until it was scientifically studied in the 1930s. Boron carbide can be obtained by reduction of boron trioxide with carbon in an electric furnace. Boron carbide can absorb large amounts of neutrons without forming any radioactive isotopes, so it is an ideal neutron absorber in nuclear power plants, while neutron absorbers are mainly responsible for controlling the rate of mitosis. Boron carbide in the nuclear reaction furnace is mainly made control rod-shaped, but sometimes because of the need to increase the surface area and made it into powder.
Because of the low density, high strength, high temperature stability and good chemical stability characteristics. In the wear-resistant materials, ceramic reinforced phase, especially in light armor, reactor neutron absorber and so on. In addition, compared with diamond and cubic boron nitride, boron carbide is easy to manufacture, low cost, and therefore more widely used, in some places can replace expensive diamond, common in grinding, grinding, drilling and other applications
Silicon nitride is an important structural ceramic material. It is a super-hard material, self-lubricated, and wear-resistant, for the atomic crystal, high temperature antioxidant. And it can resist the hot and cold impact in the air heated to more than a thousand degrees, the rapid cooling and then a sudden heating will not be broken. It is precisely because the silicon nitride ceramic has such excellent characteristics, it is often used to manufacture bearings, turbine blades and other mechanical components.