The production of grease accounts for a small proportion of the entire petroleum product field. According to a rough estimate, the annual output of oil worldwide is only about 1.16 million tons. Still, it occupies an essential position in the national economy and is necessary for maintaining various machinery and equipment. It plays a vital role in regular operation, reducing friction and wear during surgery, and extending the service life of machinery and equipment. In the field of lubrication engineering, the tribological behavior of grease largely depends on the performance of grease additives. The central role of grease additives is to improve and enhance performance. Often, the addition of different lubricant additives will cause the same grease performance the difference.

Nano science and technology are considered as a new technology facing the 21st century, and its excellent characteristics have attracted widespread attention of scientific researchers. In recent years, nano materials have shown significant application value and broad application prospects in the fields of light, electricity, and magnetism. At the same time, because nano particles have many excellent properties that traditional materials do not have, they exhibit distinctive and superior physics. Chemical properties have entered everyone's horizons. The research on the application of nano materials in grease is relatively smooth.

Previously, some scholars used nano materials as lubricant additives in lubricating oils. It was found that nano materials can be used as friction modifier additives and EP additives, which significantly promoted the reduction of friction and abrasion resistance and the carrying capacity of lubricants. The traditional lubricant additives currently in use have limitations in many aspects, so nano oil additives have been discovered by tribological researchers as a new type of the best oil additives for grease.

The advantages of nano particles as the best oil additives

(1) Nano particles have strong diffusion and self-diffusion capabilities, and it is easy to form a permeation layer or a diffusion layer with excellent abrasion resistance on the metal surface to achieve the anti-friction effect.

(2)Nano particles have the characteristics of small particle size, and they are approximately spherical. They can roll between friction pairs and play a role similar to "ball bearings". The form of friction changes from sliding friction to running friction, making friction The coefficient is reduced; (3) Nano particles can polish and strengthen the friction surface to support external loads and improve the carrying capacity.

Types of nano lubricant additives

(1)Nano elements grease additives

Professor Wang Peng and others investigated the tribological properties of the nano bismuth powder. They found that the quality of nano bismuth powder and the serpentine powder was studied using four-ball friction and abrasion tester under the condition that the total content of the fixed powder was 3% The effect of the ratio on the tribological properties of lithium-based greases. The results show that mixing the nano bismuth powder with serpentine powder as an additive is beneficial to improve the comprehensive tribological properties of lithium-based lubricants. When the mass ratio of the two powders is at 3:1, the composite lithium-based oil has the best tribological features and the best anti-friction and anti-wear effect.

As a transition element, copper has many outstanding characteristics in terms of physical and chemical properties, such as excellent corrosion resistance and mechanical properties, which makes it suitable for the environment in which grease is used. Researchers have found that adding an appropriate amount of nano copper to oil, and adding this grease to friction parts, has excellent anti-friction and anti-wear properties. After observation, it was found that a thin film with friction-reducing and the lubricating effect was formed on the surface of the friction pair, and the nano copper added at the same time would deposit to achieve the purpose of repairing the micro-scratch on the surface of the friction pair, which could significantly reduce the friction and wear of the friction pair.

Dr. Choi added nano copper powder to lithium-based grease. The test results show that nano copper can reduce the friction coefficient and reduce the wear on the friction surface.

Graphene is called "magic material" and has a strange and excellent performance in many fields. From the perspective of tribology, graphene is an excellent lubricating material, which can significantly reduce the friction coefficient and wear rate of friction pairs. Singh et al. Added graphene lubricant to lithium-based grease and tested its tribological properties. It was found that when its mass fraction is 0.4%, the friction coefficient, noise, and vibration of the friction pair are small, and pure grease without additives In comparison, the friction coefficient can be reduced by 30% when pure rolling friction occurs, and the friction coefficient can be reduced by 20% when mixed rolling and sliding friction occurs.

(2)Sulfide nano particles as grease additives

Tungsten disulfide is used as a new type of dry lubricant because of its particular layered hexagonal structure, which is liable to slip between layers, which makes it excellent in lubricating performance and low coefficient of friction. Professor Chen and others added the prepared nano tungsten disulfide powder to lithium-based grease and examined the tribological properties of the lithium-based oil. The results show that the added nano tungsten disulfide powder can significantly improve the tribological properties of lithium-based lubricants. During the friction process, nano tungsten disulfide powder generates adsorption deposition on the surface of the friction pair. Under high temperature and high load conditions, a chemical reaction film containing Fe2O3, FeSO4, WO3, and Fe3O4 is formed, which together produces a lubricating effect.

MoS2 has excellent lubricating properties. It has unique tribological features in harsh environments such as high vacuum, intense radiation, and high and low temperature. It can be used as aerospace grease additives. Cheng Yazhou et al. Prepared nano MoS2 powder and added it to the grease to conduct tribological performance tests. The test results show that the addition of a small amount of nano MoS2 powder has a significant effect on the extreme pressure performance and anti-friction and anti-wear properties of the grease. Influence, the result is pronounced.

In summary, nano lubricant additives have excellent application prospects in greases. In the future, nano-grease additives need to solve the problem of dispersion stability of particles, and they are developing in the direction of "green chemistry," laying a solid foundation for the large-scale practical application of nano-grease additives.

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