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Application and research status of nano copper powder as lubricant additive

2019-06-06
1. Four characteristics of nanomaterials
Nano copper powder belongs to the category of nanometer materials, so it has four common effects of nanometer materials:
A.Quantum size effect: when the size of copper particle falls to the nanometer scale, the electron level near the Fermi level will change from the quasi-continuous level in bulk copper to discrete level, and the macroscopic optical, electrical, magnetic, mechanical and chemical properties of nano-copper powder will change significantly.
B.Surface effect: the specific surface area and the number of atoms on the surface of nanometer copper powder will increase rapidly with the decrease of particle size. There are many atoms on the surface with insufficient coordination, which have strong surface energy and can easily be combined with other atoms.
C.Small size effect: the particle size of nanometer copper powder is close to or even smaller than the wavelength of light wave and DE Broglie wavelength, and periodic boundary conditions will be destroyed, resulting in the melting point of nanometer copper powder will decline, and the light absorption will increase significantly.
D.Macroscopic quantum tunneling effect: nano-copper powder particles have the ability to penetrate potential barrier at the micro level. Therefore, when electronic devices develop into miniaturization, the macroscopic quantum tunneling effect must be taken into account to prevent electron overflow.

2. Uses and research status of nano copper powder as lubricant additive
Lubricating oil can not only greatly reduce the friction and wear of mechanical equipment caused by damage, but also play a role in rust and corrosion prevention, shock absorption and buffer, cooling, cleaning and cleaning, can extend the service life of mechanical equipment.The common lubricating oil products on the market generally consist of base oil and lubricating oil additives.Among them, base oil is the main component of lubricating oil, which is generally mineral base oil, synthetic base oil, biological base oil and other basic oils.In order to strengthen the performance of lubricating oil and enrich its functions, it is necessary to add an appropriate amount of additives in lubricating oil. Every update of lubricating oil products is inseparable from the development and progress of additive technology.Nano copper powder is a good solid lubricant due to its low shear force, especially suitable for high load, low rotation speed and high temperature environment.In recent years, nano-copper powder as lubricant additive has attracted more and more attention from scholars.

3. Types and development trend of lubricating oil additives
(1) Types of additives
According to the function of the additive, it can be divided into antioxidant, anti-corrosion agent, anti-wear anti-friction agent, detergent dispersant, viscosity enhancer, pour point depressant, extreme pressure agent, anti-foam agent, dispersant, etc. The diversification of their functions also improves the comprehensive performance of the lubricating oil.In accordance with the additive composition can be divided into type and no type additive, the model with additive mainly include: paraffin wax, alkyl sulfonate, polymer butadiene imide, naphthenic acid aluminum, alkyl disulfide generation of zinc phosphate (ZDDP), organic borate, N heterocyclic compounds, dithiocarbamate vinegar (DTC) derivatives, etc., including alkyl disulfide generation of zinc phosphate (ZDDP)
It is the most widely used type additive.The main additives are graphite, inorganic borate, sulfide, nano metal oxide, nano copper powder, etc.It can be seen from the above that most lubricating oil additives contain elements such as phosphorus and sulfur which cause serious environmental pollution and do not meet the standards of environment-friendly materials.The model-free additive nanometer copper powder has the characteristics of excellent anti-wear and anti-friction performance, strong extreme pressure performance, low shear strength and environmental friendliness, etc., and has achieved a good use effect in high-grade lubricating oil, which is also the most promising lubricating oil additive at present.

(2) Action mechanism and future development trend of additives
In the vast majority of lubricating oil additives containing sulfur, phosphorus, chlorine and other polar substances, it will be released with the heat generated by friction decomposition, and react with mechanical equipment friction on the surface of the metal materials, forming a layer of chemical adsorption film, have the effect of friction surface protection, anti-wear anti-friction: at the same time, these polar material reaction product will deposit in frictional contact surface, reduce the contact should be, the friction surface to smooth, to improve the environment of the friction surface, prevent friction occlusion, stuck phenomenon.
At present, the development direction of lubricant additive technology is mainly in the following aspects:
A.On the basis of energy conservation and environmental protection, we pursue higher scientific and technological content and higher technical level.
B.From a single component to a composite component with diversified functions;
C.Lubrizol, runinlian, chevron olenna, afton and other internationally renowned additives manufacturers continue to expand their own production capacity, increase market share, and promote industrial concentration;
D.With the rapid economic development of the asia-pacific region, according to the law of market development of maximizing benefits and local procurement and supply, lubricant additive manufacturers have an obvious trend to expand to the asia-pacific region.

(3) Research status of adding nano copper powder lubricating oil
By dispersing nano copper powder in lubricating oil and preparing uniform and stable suspension, nano copper powder lubricating oil with good anti-wear and anti-friction performance can be obtained.
Due to its large surface area, high diffusion performance and low shear force, nano copper powder, as a lubricant additive, can not only form a protective film on the friction surface, but also fill and repair the wear area, greatly reducing the friction coefficient and playing a good role in anti-wear and anti-friction.The anti-wear mechanism of nanometer copper powder has been a hot topic of scholars' research. Currently, the widely accepted theories are mainly as follows:

 A.Mechanism of tribochemical deposition film

The surface energy of nano copper powder is high. At the initial stage of friction, it will adsorb on the surface of metal matrix and form the physical deposition film of nanoparticles.Nanometer copper powder has a strong self-diffusion ability. With the progress of friction, nanometer copper powder will permeate and diffuse to the surface of metal matrix, forming solid solution, and even have chemical reaction with the matrix, forming a layer of wear-resistant chemical reaction film.These physical deposition film, solid solution, chemical reaction film can separate the contact surface of friction pair, so as to play a good anti-wear and anti-friction effect.

B. Action mechanism of "micro bearing"
The micro size of nano copper powder is very small, almost spherical, and it will play the role of micro ball bearing on the contact surface of friction pair, changing sliding friction into rolling friction, reducing friction resistance and friction coefficient, so as to play a good role of anti-wear and anti-friction.Due to the excellent plasticity of nano copper powder, it will be flattened and filled in scratches, furrows and other depressions under high load, chemical rotation speed and high wet friction environment, playing a good role in anti-wear and anti-friction.
At present, most researches on adding nano copper powder lubricating oil are still in the laboratory stage, and only a few high-end lubricating oil products add nano copper powder in the market.Scholars mainly focus on the improvement of anti-wear and anti-wear properties and extreme pressure properties of nano copper powder on oil products, but there are few reports on the harmful effects of nano copper powder on oil products, friction pair materials and other materials.In the future, the technical difficulties and development trend of adding nano copper powder lubricating oil are mainly as follows:
a.The surface energy of nano copper powder is high, and it is easy to agglomerate and settle in lubricating oil. Therefore, improving the dispersion stability of nano copper powder in lubricating oil is a prerequisite to ensure that it plays a good role in anti-wear and anti-friction characteristics.
b. Lubricating oil usually contains many additives to enrich its functions, so it is necessary to adapt and compatibility of nano copper powder with other common lubricating oil additives.
c. Whether nanometer copper powder has negative effects on the base lubricating oil and the lubricated mechanical parts themselves still needs to be further explored.
d. Strengthen the theoretical research on the anti-wear and friction reduction mechanism of nano copper powder, including the conditions under which its self-repairing effect occurs, and the evaluation standard of the repairing performance still needs to be supported by a set of formed theoretical system.