More than 100 years ago, in addition to the structure, there is a material that is very similar to graphite, and that is hexagonal boron nitride (h-BN). It is a crystal composed of 56.4% nitrogen nuclei and 43.6% boron atoms. Because of its whiteness, it is also called "white graphite". Boron Nitride

h-BN has many excellent properties, among which the notable and commendable is that it is "slip". It can be seen from the figure above that the lattice structure of h-BN is very similar to graphite. The boron and nitrogen atoms are arranged staggered to form an infinite boundary network with a hexagon as a unit, that is, a single layer of h-BN; Such networks are stacked infinitely along the c-axis in the manner of ABAB... to form three-dimensional hexagonal boron nitride.

In each atomic layer, the boron atom and nitrogen atom are connected by a strong sp² hybrid covalent bond, the bond length is a=b=0.2504nm; each two adjacent atomic layers can rely on relatively Weak inter-atomic force-van der Waals (vanderWaals) force is connected, the bond length c=0.6661lnm. Therefore, the binding force of h-BN in the c-axis direction is very small, the distance between atoms is large, it is easy to slide between layers, and it has good lubricity even at high temperatures.

Generally speaking, lubricating oil additives change the form of the lubricating oil film adsorbed on the surface of the moving body to prevent the surface of the friction pair from contacting with the rough surface micro-protrusions during mutual movement, thereby improving the lubricity and anti-wear properties of the surface. At present, the use of nano-lubricating materials to prepare lubricating additives is the main method to improve the anti-friction and anti-wear performance of lubricating oil.

These nanomaterials mainly play two roles in lubricants, one is the "miniature ball bearing effect"; the other is the "self-repairing effect". They will enter the surface of the friction pair when the friction pair is working, and change the friction mode between the friction pairs-from pure sliding friction to sliding and rolling composite friction. Because the friction coefficient of rolling friction is an order of magnitude smaller than sliding friction, Friction and wear can be reduced.

Compared with the more reported metal nanoparticles (such as copper and iron), h-BN actually has more application advantages in lubricants. This is because although the soft nano-additives have excellent performance, they are quickly consumed during the use of lubricating oil, and the barrier effect between the friction pairs will gradually decrease, thereby reducing the service life of the lubricating oil; on the other hand, these metals Nanoparticles are mostly polyhedral in shape, and the surface atoms are distributed in a stepped manner. The activity is high. The effect on the lubricating oil is mainly completed by the self-repairing effect on the surface of the friction pair, and the "miniature ball bearing" effect is not obvious.

As an excellent solid lubricant, layered h-BN has the advantages of high carrying capacity, good stability at high temperature, and stable physical properties compared to liquid or semi-solid lubricants. It can be dispersed in heat-resistant lubricating grease, water or solvent and sprayed on the friction surface until the solvent evaporates to form a dry film; it can also be filled on the surface of resin, ceramic, metal, etc. as a heat-resistant and high-temperature self-lubricating material.