Types of superhard materials

No matter how superhard materials are defined, in popular terms, superhard materials mainly refer to diamond and cubic boron nitride and related materials.

Diamond

Diamond is the hardest substance known in nature and has extremely high thermal conductivity as well as a large band gap and high dispersion.

These excellent physical properties make diamond in industrial cutting, heat transfer equipment manufacturing, optical device manufacturing, and electronic equipment manufacturing has an irreplaceable important position. The excellent properties of diamond, especially the super hardness, come from the hybridization of its electronic states, so that the four valence electrons are involved in bonding, forming a three-dimensional covalent bond network.

CBN

The cubic boron-nitrogen structure corresponding to diamond, because it also has a covalent bond network composed of SP3 bonds, so that it also has a high hardness, in fact, cubic boron-nitrogen hardness is second only to diamond superhard materials. Although the hardness of cubic boron nitrogen is less than diamond, it has better thermal stability and chemical stability, making it more used in high temperature devices.

On the one hand, we vigorously research and develop the derivative hard materials related to artificial diamond and cubic boron nitride to meet the needs of current industrial and scientific and technological development, and on the other hand, we spare no effort to explore other new types of superhard materials.

Fullerite

Undoubtedly, the successful synthesis of fullerite has extraordinary significance for the processing of a series of materials such as super-strong metals. However, the industrial production of fullerite still needs to solve the related problems such as ultra-high pressure.

Carbon nitride

The structure of carbon nitride was proposed in 1985. This compound has the same structure as silicon nitride. At that time, it was predicted that its hardness might be greater than diamond.

Wurtzite type boron nitride

A small amount of wurtzite type boron nitride may exist in nature. It has a similar structure to diamond, but is composed of different atoms. In wurtzite boron nitride, boron atoms and nitrogen atoms are tetrahedral, but the angle between adjacent tetrahedra is different, the hardness of wurtzite boron nitride may be related to the toughness of the atomic bond.

The Langsdale Stone

In terms of crystal structure, Lonsdale stone, also known as hexagonal diamond, is an allotropic crystal of hexagonal lattice carbon, which is a rare mineral in nature and formed when graphitic meteorites hit the Earth's surface. It was named in honor of Irish crystallographer Kathryn Lonsdale.

Heterogeneous diamond

Heterogeneous diamond is a kind of superhard material containing boron, carbon and nitrogen, also known as cubic boron-carbon-nitrogen, is a polycrystalline material of nanocrystalline grains and ultrafine powders, slightly blue-black.

Metal boride

The electron state density of metal borides reflects its metal properties, and the extensive covalent bond between boron atoms and metal atoms and boron atoms can lead to high hardness, so it causes the attention of the superhard materials industry, in addition, it needs high temperature and high pressure conditions to synthesize like carbon-based superhard materials, and it is easy to synthesize in large quantities at room temperature and pressure. At present, the metal borides that are being explored are osmium diboride, rhenium boride, ruthenium diboride and boron carbide. Because osmium (Os), rhenium (Re) and other metals have high electron density, large bulk elastic modulus, small atomic radius, and directional bonding with boron can be highly controlled.

Nanostructured superhard materials

Nanostructured superhard materials belong to the non-intrinsic class of superhard materials, such as nano-grained diamond aggregates, which have proved that their hardness and toughness are greater than ordinary large-grained diamond. One common form is polymerized diamond nanorods, which have a hardness of 150GPa and are known as one of the hardest materials.