Lubricating properties of tungsten disulfide

Tungsten disulfide (WS2) has excellent thermal stability and oxidation resistance, sizeable compressive strength, strong load-bearing capacity, good wetting with the substrate, and is used in high-tech fields such as aviation, aerospace, military, and automotive industries. The working temperature range of tungsten disulfide in the atmosphere is -270-650 ℃. The friction coefficients of the three types of solid lubricants with the same parts added in the grease are: graphite> molybdenum disulfide> tungsten disulfide; and the maximum non-seizure load PB is tungsten disulfide> molybdenum disulfide> graphite. Molybdenum disulfide is thermally oxidized and degraded in the air at 360 ℃ to form MO3 and SO2, while tungsten disulfide only begins to oxidize and degrade at about 45℃ thermally. The resulting WO3 is also a high-temperature lubricant.

Lubricating mechanism of tungsten disulfide film

In the hard and soft metal friction pair, the hard metal is pressed into the soft metal under the load, and the furrow causes the contact area to increase, thereby increasing the friction force. When the hard metals slide relative to each other, the yield strength is enormous, and the friction force is large. The friction surface heats up and causes bite. A layer of film with low shear strength is coated on the surface of the hard metal substrate, which neither increases the contact area of the friction pair and reduces the shear strength, reducing friction and friction coefficient. Furrows will occur. Therefore, a thin film with a low shear strength is adhered to the friction surface of the hard metal substrate for lubrication, reducing the friction coefficient and reducing wear.

Dispersion of nano tungsten disulfide

The smaller the particle size of WS2, the better the adsorption and the better the lubricating effect. However, particle agglomeration affects its lubricating performance. Physical or chemical methods can disperse the modification. Physical methods are used to disperse the nanoparticles in the liquid medium, and the particles will re-aggregate due to the intermolecular forces after the external forces are canceled. The chemical dispersion changes the surface properties of the particles, improves the interaction between the particles and the liquid medium, and the particles, enhances the repulsion between the particles, and permanently inhibits flocculation and agglomeration. Combining physical dispersion and chemical dispersion, using physical means to deagglomerate, chemical methods to maintain stable dispersion, to achieve a better dispersion effect. Besides, the surface charge distribution of the particles can be changed by the adsorption of the dispersant, resulting in electrostatic stability and steric stabilization to enhance the dispersion effect.

When untreated, the average particle size of the suspended particles in the lubricating oil reaches ten μm, and the nano tungsten disulfide particles are obviously agglomerated. Still, with the increase of the ultrasonic dispersion and mechanical stirring treatment time, the particle size of the suspended particles decreases, 5.5 h. After that, the average particle size reached below one μm. After treatment, the agglomeration of nano tungsten disulfide particles changes from large to small, and the minimum agglomeration particle size is close to the size of the primary particles. According to Stokes' law, the sedimentation speed of ultrafine particles in the liquid medium becomes Proportionally. The particle size of nano tungsten disulfide agglomerates is significantly reduced, which improves their dispersion stability in lubricating oil. With the increase of the mass ratio of surface modifiers and nano tungsten disulfide particles, the stabilization time of the particles in the lubricating oil increases first and then decreases. When the mass ratio reaches 0.4, the stabilization time is the longest. With the increase of the amount of surface modifier, the surface of nano tungsten disulfide particles is gradually modified, preventing the agglomeration between particles, so that the dispersion stability of particles in lubricating oil is improved; when the amount of surface modifier exceeds a specific value, the surface Excess modifier causes flocculation and agglomeration of particles. The mass ratio of surface modifier to nano tungsten disulfide is 0.4-0.5. After nano-tungsten disulfide microencapsulation, it can also significantly improve dispersion stability and wear resistance in dispersion media. Measures for microencapsulation include the use of sodium carboxymethyl cellulose, PMMA in situ, or epoxy resin.

The two methods of using WS2 powder are:

1) Combine WS2 powder with moist lubricant (such as oil, grease and other synthetic lubricants)

Most lubricating oils adopt organic or inorganic, liquid or solid lubricating oil additives to improve the lubricating performance. Green engine oil is environmentally friendly and can be used to replace mineral-based engine oil that is prone to environmental pollution. Still, its base oil is susceptible to oxidation failure at high temperatures. Nano tungsten disulfide is surface-modified under the action of ultrasonic waves to reduce friction and anti-wear in lubricating oils, even under high-temperature oxidation conditions. The green engine oil containing nano tungsten disulfide has more excellent extreme pressure anti-wear performance and viscosity-temperature characteristics.

Add quality score 3% of the nano-WS2 added to the finishing oil has higher oil film strength and lower friction coefficient than the unadded lubricating oil. Add quality score 0. 5% of WS2 powder is added to the emulsified oil cutting fluid, and the surface quality of the workpiece is increased by 35% on average. Superfine WS2 particles have undergone surface chemical modification and adsorption modification surface modification, and are added to synthetic oil and mineral oil. The friction factor decreases with time. The surface of the wear spot is smooth, and the diameter is small, indicating anti-wear and anti-friction performance.

2) Coat WS2 powder on the substrate that needs (dry) lubricity:

The powder can be applied by spraying (120 psi) the substrate with dry (and cooled) pneumatic air. It does not require any adhesive and can be sprayed at an average room temperature. The coating film will be 0.5 microns thick. In an alternative application method, the powder can also be mixed with isopropyl alcohol, and the paste can be polished onto the substrate. Coating applications have been established in many areas, such as automotive parts, racing engines and other parts, aerospace parts, bearings (linear, ball, roller, etc.), shafts, marine parts, cutting tools, blades, cutting machines, knives, peeling Molding agents, precision gears, valve components, pistons, chains, mechanical components, and many other fields.

The application of tungsten disulfide in reliable lubrication has expanded from powder filling and dispersion in lubricating grease to the high-end field of film application. The lubrication mechanism of tungsten disulfide solid lubrication film still needs to be explored. Improving the performance of tungsten disulfide solid lubricating film by constructing the crystal structure and grain boundary characteristics of the film layer will become the leading research direction in the future.

Infomak is dedicated to the technology development of special oil additives, combined the Technology of nanomaterials developed dry lubricant and oil additives two series. Our products can significantly improve the performance of lubricating oil, improve energy efficiency, effectively protect the lubrication device and extend the oil change cycle, which can satisfy the lubrication oil constantly upgrading for high-end engine oil additives.

If you are looking for WS2 , please feel free to contact us.

Dry lubricant is a method of coating or plating a substance on the surface of the friction pair to form a thin film to reduce friction. The technology of using dry lubricant for lubrication is called robust lubrication technology. Reliable lubricating technology was first used in the military industry and was gradually promoted in some high-tech fields, which solved some severe problems of liquid lubricants.

Disulfide compounds that have application value as dry lubricants include tungsten, molybdenum, niobium, tantalum disulfide, diselenide, and ditelluride. MoS2 is currently widely used and representative, it is naturally formed, and other dichalcogenides are artificially synthesized. Among them, the representative products are tungsten disulfide (WS2), WS2 and other synthetic products. The impurity content is less than 0.5%, which is a costly and unique material. Where it is restricted, it will be introduced as a direct replacement for MoS2.

Both MoS2 and WS2 are excellent solid lubricating materials and have incredibly high application value in the field of ultra-solid lubrication. Since the late 1990s, major foreign developed countries have begun to apply friction components in the aerospace, precision instruments and ultra-high vacuum. At the same time, this technology is also referred to as the hard disk drive bearing of the computer, the rotation, sliding and other components in the ultra-high vacuum system.

MoS2 is a dark grey shiny powder, soluble in aqua regia and concentrated sulfuric acid, insoluble in water and dilute acid, can be used for maintenance and lubrication of processing and storage conditions, can form an efficient adhesion dry lubricant film, is to reduce wear and tear Special material for many problems in friction technology. MoS2 is the most common natural form of molybdenum, extracted and purified from the ore and used directly as a lubricant. Because MoS2 has a layered structure of hexagonal crystals, it is a beneficial oil additive. These layers can slide on each other, allowing free flow on steel and other metal surfaces, even under heavy pressure, such as bearing surfaces. Because MoS2 is formed by geothermal action, it has the chemical stability to withstand hot pressing. A small amount of sulfur and iron react and form a sulfide layer, which is compatible with molybdenum sulfide and maintains a lubricating film. MoS2 is inert to many chemicals and will complete its lubrication under vacuum, while graphite cannot. MoS2 has better thermal stability in an air environment lower than 400 ℃. When the temperature is higher than 400 ℃, MoS2 will be oxidized to MoS3 in a short time, and MoS3 is a kind of high-hardness particulate matter that adheres to friction Abrasive particles are formed on the secondary surface. But in a vacuum and inert gas environment, MoS2 can maintain a relatively stable structure at 1100 ℃.

WS2 is a new type of solid lubricant with similar characteristics to MOS2. Mohs hardness is low, it is easy to form a transfer film, the friction factor is slightly smaller than MOS2, and the thermal stability is higher; the air begins to decompose at 510 ° C, 650 ° C Completely decomposed, can be lubricated for a long time at 425 ° C; decomposed in vacuum at 1100 ° C, completely decomposed at 2000 ° C. WS2 has better lubrication performance than MOS2, and can completely replace MOS2.

Tungsten disulfide WS2 also has a layered hexagonal structure, similar to MoS2. Tungsten atoms and sulfur atoms are covalently bonded, and there are only sulfur atoms on the surface of the molecular layer. Weaker molecular bonds connect the sulfur atoms between the sheets. By combining Van der Waals forces between layers, compared with MoS2, WS2 has a more substantial layer spacing and a lower friction coefficient. Moreover, WS2 is insoluble in almost all media, including acids, alkalis, oils and water, but is more sensitive to free gaseous fluorine, hydrofluoric acid and hot sulfuric acid. Compared with MoS2, WS2 has better thermal stability than MoS2. In the air, the decomposition temperature of WS2 is 510 ℃. It will be rapidly oxidized at 539 ℃, and the decomposition temperature in a vacuum and inert gas is 1150 ℃. Compared to MoS2, WS2 has a broader temperature range.

Several domestic and foreign lubricant manufacturers have compared the lubricating properties of WS2, MoS2 and graphene. Through experiments, it was found that tungsten disulfide is not only more reliable than MoS2 but also more durable than graphene. Also, in high-radiation operating environments, WS2 has higher radiation resistance and can adapt to more complex operating environments. Therefore, manufacturers have shown a more substantial production interest in tungsten disulfide lubricants.

Through friction and wear test, study the friction performance comparison of WS2 and MOS2 solid lubricants. The results show that under normal temperature conditions, the friction factor of WS2 solid lubricant is similar to that of MOS2, but the film formation state of WS2 coating on the metal substrate is not as good as MOS2 coating; under high-temperature conditions, the friction factor of WS2 based coating is stable and the friction performance Better than MOS2 solid lubricating surface.

In the United States, the aerospace industry mainly uses MoS2 as a solid lubricating material. This is because the United States is also a major producer of molybdenum and has the convenience of taking resources locally. Tungsten, compared to molybdenum, tungsten is superior to molybdenum in terms of heat resistance, physical and chemical stability, and radiation resistance so that WS2 lubricant will be a better choice.

 Infomakis dedicated to the technology development of special oil additives, combined the Technology of nanomaterials developed dry lubricant and oil additives two series. Our products can significantly improve the performance of lubricating oil, improve energy efficiency, effectively protect the lubrication device and extend the oil change cycle, which can satisfy the lubrication oil constantly upgrading for high-end engine oil additives.

If you are looking for  MoS2 or WS2, please feel free to contact us.

Oil additives are an indispensable and essential component of lubricating oils, which are used to make up or improve the deficiencies of lubricating base oils and give them new properties. 

During the use of mechanical equipment, friction and wear often occur, which not only threatens the safety of the material but also causes enormous losses. There are two main ways to improve resistance and wear: under fluid lubrication or mixed lubrication conditions, improve the rheological properties of the lubricant to reduce shear stress; under mixed lubrication or boundary lubrication conditions, add a friction modifier to the grease to reduce the friction factor.

A friction modifier can better minimize wear. The mechanism is that when the metal surfaces that are in contact with each other mesh with each other due to load, local high temperature and high pressure will be generated. At this time, the antiwear agent reacts with the metal surface to form a reaction film with low shear strength. , To avoid direct contact between the two metal surfaces, play a role in reducing wear.

1.Ionic liquid friction modifier

Ionic liquids have the characteristics of extremely low volatility, good thermal stability, excellent viscosity-temperature performance, strong adsorption, etc. Under most working conditions, they can generate a boundary lubricant film on the surface of friction metal, which is an excellent performance modifier. . Dr. Liu's research group used ionic liquids in the field of tribology for the first time. Because of its excellent antiwear properties, the tribological properties of different types of ionic liquids have attracted full attention from researchers. Recent studies have shown that adding ionic liquids as friction modifiers to lubricating oils to improve their antiwear performance has good development prospects.

 Ionic liquids have excellent antiwear and anti-friction properties, which can effectively reduce the friction and wear of metal surfaces. Especially ammonium-based ionic liquids with flexible molecular structures can carry and convert more beneficial groups, so they are widely used. It is also a research hotspot.

2. Nanoparticle type friction modifier

Metal nanoparticles have small size effects and surface effects, which make them exhibit excellent antiwear performance, especially soft metal nanoparticles. Nano metal particles have more excellent antiwear properties than traditional friction modifiers because the nano surface is more comfortable to react on the metal surface to generate boundary lubrication. In recent years, researchers have done a lot of in-depth research on nanoparticle additives to solve a series of problems such as oil solubility, and found that whether it is a nano element, or its nitride, sulfur chemicals have excellent antiwear and anti-friction properties.

Nano-nitride, as a new type of dictionary modifier, can be embedded in the dents and pores on the metal surface under high temperatures and extreme pressure conditions to form a protective film. It is also possible to convert part of the sliding friction into rolling friction through the advantages of the nanoparticles' structure to further improve its antiwear performance.

 Nanoparticle antiwear agents have excellent tribological properties due to their structural advantages. Current research focuses on nano-element, nano-sulfide, nano-nitride, and nano-oxide. The screening of nanomaterials, the optimization of parameterization methods, and the improvement of modification methods will be the next research hotspots of nanoparticle friction modifiers.

3. Nitrogen-containing heterocyclic friction modifier

Nitrogen-containing heterocyclic compounds have good extreme pressure and antiwear properties, high thermal stability and good anti-oxidation and anti-corrosion properties, and have attracted extensive attention from researchers. C. Kajdas's "negative ion free radical" thought that the content of the N element in the nitrogen-containing heterocyclic additive will affect the resonance energy of the heterocyclic ring. As the content increases, the resonance energy decreases, thereby enhancing the activity of the friction reducer oil additive. It is easier to adsorb on the metal surface, and the antiwear performance is improved. During the friction process, the N element containing lone pairs of electrons undergoes a coordination reaction with some features on the surface of the friction pair, forming a reaction film of the nitrogen-containing heterocyclic metal complex, thereby reducing the wear on the cover of the friction pair.

The development trend of lubricating oil products is to extend the oil change period and improve fuel economy. The addition of friction modifiers can form a physical adsorption film or a chemical adsorption film on the friction surface, improve the lubrication condition of the friction pair, effectively reduce mechanical friction and wear, and reduce energy consumption.

Infomakis dedicated to the technology development of special oil additives, combined the Technology of nanomaterials developed dry lubricant and oil additives two series. Our products can significantly improve the performance of lubricating oil, improve energy efficiency, effectively protect the lubrication device and extend the oil change cycle, which can satisfy the lubrication oil constantly upgrading for high-end engine oil additives. Contact us.

Oil additives are additives that reduce the coefficient of friction of lubricants under boundary lubrication conditions. Lubricant energy-saving anti-friction additives appearing on the market generally belong to this kind of additives. In the fluid lubrication state, the surface of the Friction pair is entirely separated by the lubricating oil film. The friction force is proportional to the viscosity of the lubricating oil. The higher the thickness, the more excellent the viscous resistance. However, if the width of the lubricating oil is too low or the load on the friction pair is high, the lubricating film between the friction pairs is fragile, and the fluid lubrication state cannot be maintained. The boundary lubrication state of the direct contact of the friction pair is formed. The friction force is not related to the viscosity of the lubricating oil, but only depends on the chemical properties of the lubricating oil, that is, the surface-active substances present in the lubricating oil. Since most of the original surface-active materials in the lubricating oil are refined and removed during processing, it is necessary to add a Friction Modifier Additive to improve the lubricating performance of the refined oil. Friction modifier additive is based on this principle. Through the chemical action of the additives, the micro convex parts of the friction surface are softened and smoothed, or the additives are adsorbed on the surface of the friction pair, and the micro concave portions are filled to improve the state of the oil film on the surface of the friction pair. The friction force is reduced under severe boundary lubrication conditions, which can enhance the power, lower fuel consumption, and reduce wear. Friction modifier additive filling the depression can also improve the sealing of the combustion chamber of the engine and maintain the proper technical condition of the engine. Friction modifier additive is divided into solid suspension type and oil-soluble type.

1.Solid suspended lubricating oil additives

The robust suspension type was developed and applied earlier, and it is dispersed in the lubricant in the form of particles. The most famous solid suspension additives are molybdenum disulfide, graphite, and Teflon powder. Molybdenum disulfide and graphite are multilayer lamellar crystals. They have a strong adsorption force on the metal surface, but the interlayer shear resistance is feeble, so they have an excellent anti-friction and anti-friction effect in the boundary lubrication state. Resistant to high temperatures. Teflon powder is generally considered to be unable to form an adsorption film on the metal surface, but its particles can accelerate the running-in of the friction pair surface under boundary lubrication conditions, improve the smoothness, and reduce friction. The disadvantage of solid suspended oil additives is that the particles of lubricating oil additives may aggregate and delaminate during storage, and its anti-friction effect will be reduced. At the same time, the lubricating oil will become cloudy, the color will be darkened, and the appearance will be damaged. Most critically, there is also the possibility of particles clogging the filter or being separated from the lubricant by a centrifugal filter.

2.Oil Solubl lubricating oil additives

Due to the inherent disadvantages of oil-soluble lubricating oil additives, such additives have been gradually phased out in recent years. Vigorously develop oil-soluble lubricating oil additives that are entirely compatible with lubricating oils. Most of these lubricating oil additives are polar or active oil-soluble macro molecular compounds, such as fatty acids. In oil solution, a dimer molecule pair with extreme groups bonded to each other is formed. When the contact between the extremist group and the metal surface is much higher than the inter molecular dimer force when in connection with the metal surface, the dimer is gradually separated into single Molecules, and form a firm, tight, directional first adsorption layer on the metal surface and even hundreds of odd molecular layers. When the metal surface moves relatively under pressure, the end of the non-polar hydrocarbon chain of the directional molecule in the boundary adsorption layer on the isolated metal surface is relatively easy to slide relatively, the friction loss is small, and the friction coefficient may be as little as 0.01-0.02. It has a strong resistance to the pressure of the vertical metal surface. The more polar the lubricating oil additives are, the longer the hydrocarbon chain and the better the lubricating ability. The adsorption force between polar compound molecules and metals decreases with increasing temperature. When the oil temperature reaches 150-200 ° C, the polar molecules fall off, and the adsorption film is destroyed and fails.

In recent years, oil-soluble lubricating oil additives use compounds such as organic molybdenum, organic tungsten, natural boron, and ashless organic esters as friction modifiers, which not only have anti-friction properties at ordinary temperatures but also can react chemically at high temperatures. Improve the condition of the friction surface, make the friction surface smoother, and the friction coefficient is about 0.05. Although friction reducer oil additive often has both antiwear effects, it is different from antiwear and extreme-pressure antiwear additives. Friction reducer oil additive forms a friction-reducing adsorption film or a friction-improving film under boundary lubrication conditions. The role of antiwear agents or EP additives is to protect the friction surface from sticking, seizing or sintering when the lubricating film is broken, and its active chemical elements (sulfur, phosphorus, etc.) chemically react with the metal to form an antiwear protective film. The antiwear film can support higher loads than the boundary lubrication film, but the friction coefficient is much larger than the boundary lubrication film.

For automobiles, the boundary lubrication mainly occurs in the piston ring of the engine and its corresponding cylinder liner at the top dead center, and the surface of the main reducer gear. Besides, crankshaft bearings and connecting rod bearings will experience boundary lubrication when the engine starts, stops, and accelerates under heavy load or suddenly loads at a certain speed. When the camshaft and lifter, rocker arm and valve lifter of high compression ratio engine valve mechanism are operating under heavy load, the friction surface is also in the state of boundary lubrication. Therefore, adding appropriate friction reducer oil additive to automobile lubricating oil is an effective measure to reduce friction and save fuel. The fuel-saving rate is generally between 1% and 4%.

Antioxidants and antiseptics can inhibit oil oxidation and are mainly used in industrial lubricants, internal combustion engine oils, and process oils. A metal passivation agent is also an antioxidant. It does not have an antioxidant effect, but indirectly "passivates" metal activity, inhibits the catalytic effect of metals and their compounds on the oxidation of oil products, reduces oil damage, and prolongs oil life.

EP additives are additives that can form a high melting point chemical reaction film with metal surfaces under high-temperature and high-pressure boundary lubrication conditions to prevent melting, seizure, and scratching. Its role is to react its decomposition products with metals at high friction temperatures to produce compounds with lower shear stresses and melting points than pure metals, thereby preventing contact surface seizure and welding and effectively protecting metal surfaces. EP additives are mainly used in industrial gear oil, hydraulic oil, guide rail oil, cutting fat, and other oils with extreme pressure requirements to improve the intense pressure and wear resistance of oil products. Any additive that can make the lubricating oil increase the strength of the oil film, reduce the coefficient of friction, improve the antiwear ability, and reduce friction and wear between moving parts is called an oil-based agent.

Viscosity index improvers are oil-soluble, chain-like polymers with a relative molecular mass of tens of thousands to millions. When they are dissolved in the lubricating oil, they exist in the form of filaments at low temperatures, which has little effect on the viscosity of the lubricant. As the heat of the lubricant increases, the threads expand the effective volume increases and the resistance to the flow of the grease. The growth leads to a relatively significant increase in the viscosity of the oil. Based on the fact that viscosity index improvers have different forms and have different effects on thickness at different temperatures, they can increase viscosity and improve viscosity-temperature performance. Therefore, viscosity index improvers are mainly used to increase the viscosity index of lubricants, improve viscosity-temperature performance, and increase viscosity. It can be used to formulate thickener oil so that the formulated oil has excellent viscosity-temperature performance, makes it good at low-temperature stability, low fuel consumption, and has a specific antiwear effect. The role of the preservative is to form a strong adsorption film on the metal surface to suppress the contact of oxygen and water, especially water, on the metal surface so that the metal will not rust.

Rust inhibitors are mainly used in industrial lubricants and metal processing cooling lubricants, metal protective oils, etc. After the oil temperature drops to a certain level, it will lose fluidity and solidify. The function of the pour point depressant is mainly to reduce the freezing point of the oil and ensure that the oil can flow at low temperatures.

Pour point depressants are widely used in various types of lubricating oils. Typical representatives are alkyl naphthalene and poly-α-olefins. Oil products such as hydraulic oil and compressor oil may encounter the working conditions of normal start up and shutdown, and the circulation system of internal combustion engine oil, gearbox oil, and other agitation is more intense, often generating a lot of foam, causing energy transmission and oil supply failure. There are many anti foam methods, which can be divided into physical-mechanical anti foam and chemical anti foam. Most of the substances that are additives as anti foaming agents should have: a. Anti foaming agents cannot be dissolved in the lubricating oil; b. Anti foaming agents can be evenly dispersed in the lubricating oil; c. The surface tension of anti foaming agents is higher than that of lubricating oils small.

With the continuous improvement of the quality level of lubricating oils, car engine oil additives have included a variety of surface-active additives, such as antioxidants and antiseptics, metal salt detergents, dispersants, extreme pressure anti wear additives, and rust inhibitors. Test balance will not cause mutual interference and synergy between various additives. If an inappropriate engine additive is added again, it may be affected by the interference between different additives, and their regular performance may be modified, especially for high-quality G-class and higher engine lubricants, which cannot be ignored. Therefore, the selected car engine oil additives must be compatible with the original additives in the lubricating oil to properly exert its energy-saving and anti-friction effect. For the user, after adding energy-saving anti-friction agent in the lubricating oil, it is best to observe the lubricating oil frequently to grasp the change of its condition for a long time.

Infomak is dedicated to the technology development of special oil additives, combined the Technology of nanomaterials developed dry lubricant and oil additives two series. Our products can significantly improve the performance of lubricating oil, improve energy efficiency, effectively protect the lubrication device and extend the oil change cycle, which can satisfy the lubrication oil constantly upgrading for high-end engine oil additives. Contact us.

Lubricant additives are an indispensable and essential component of lubricating oils, which are used to make up or improve the shortage of lubricating base oils and to give them new properties. A country's lubricant consumption level can reflect the country's economic level and industrial conditions.The friction modifier is an essential part of lubricants.

What is friction modifier?

The friction modifier is usually a straight chain composed of multiple carbon atoms and a molecule with a polar group at the end. Among them, the last group is one of the main factors for the role of the friction modifier molecule. In general, the friction modifier works through physical adsorption and chemical reaction membranes. The lubricating film of the friction modifier that functions through physical adsorption is loosely adhered to each other by orderly and jointly arranged multiple molecular layers. The polarity of the molecules is tightly adsorbed on the metal surface. The formation of the physical adsorption layer is due to the molecular polarity, a friction modifier that dissolves in oil interacts with the metal surface through a strong adsorption force, the top end of the polar group is adsorbed on the metal surface, and the tail end of the hydrocarbon group is dissolved in the oil. It is oriented on the metal surface. All the molecules are neatly arranged in rows, perpendicular to the metal surface, forming a multilayer matrix of friction modifiers. The adsorption layer of this friction modifier is challenging to compress. Still, the hydrocarbon-based tail section is easily sheared during the friction contact process so that it can provide a lower friction coefficient. Friction modifiers that work through chemical reaction films are generally compounds containing metal elements. These compounds can produce a chemical reaction on the lubricated surface to provide a protective film under high-temperature conditions due to boundary lubrication. 

Although the specific reaction mechanism of the lubrication theory community has not been determined so far, from the effect of practical use, these chemical reaction films also have excellent anti-friction performance. In the case where the addition amount of friction modifier is very low, the friction coefficient can be significantly reduced. And this kind of chemical protective film also has excellent shear performance, and the sheared layer can be easily supplemented, which can continuously form a "dynamic balance" of the protective film on the lubricated surface. On the other hand, this kind of friction modifier also often has a particular ability to enhance extreme pressure. At the same time, it can reflect better synergistic performance with other differential friction modifiers, which is also very helpful for improving the PB value and PD value of oil products.

What does friction modifier do?

Energy-saving plays an essential role in alleviating global pressure on energy and the environment. As a kind of energy-saving technology, low friction technology needs further research and improvement. Reducing friction in the use of lubricating oil can be achieved through methods such as improving engine design, improving mechanical materials, and using energy-saving lubricating technologies. Currently, there are two ways to improve the energy-saving effect of lubricants by appropriately reducing the viscosity of the oil and adding a friction modifier. By reducing the friction coefficient between surfaces, fuel economy is improved, and energy loss is reduced. At present, the friction and wear tester and modern analysis technology are mostly used to study the friction reduction performance of friction modifier additives. I have a particular understanding of the production of different friction modifier additives.

Difference between friction modifier additive and EP additives

The difference between the friction modifier additive and the EP additives often causes some controversy, because the friction modifier and the EP additives are mainly used in boundary lubrication conditions, and they will form a physical or chemical reaction protective film on the surface of the friction pair of boundary lubrication.

The main difference between friction modifier additive and EP additives is their different mechanism and performance. Ep additives are generally compounds containing sulphur and phosphorus. These compounds can form a robust lubricating layer under severe load conditions. Boundary lubrication generates a higher temperature typically on the friction surface. These compounds will form a semi-plastic deposit protection film on the surface of the friction pair, which is not easy to shear. Therefore, the EP additives protects the close-contact metal surface and prevents the corresponding surface from being affected. Raised damage. Their primary role is to improve the load and extreme pressure performance of lubricating oil products, that is, the maximum non-seizure load (PB value) and sintering load (PD value), while protecting the friction surface of the engine. However, it is known from many tests and practices that most extreme pressure antiwear agents have little performance in improving friction and reducing friction coefficient.

For the friction modifier, one influential factor that we cannot ignore is the surface temperature of the friction pair, because the temperature can affect the thickness and elasticity of the film of the friction modifier. For physical adsorption membranes, the friction modifier occurs at relatively low heat with the adsorption of the metal surface. If the temperature is too high, enough energy provided by the environment can desorb molecules of the friction modifier from the metal surface and lose its effect.

On the contrary, for the chemical reaction protective film, sufficient surface temperature is required when the friction-reducing effect occurs. It can also be an instantaneous and high friction surface temperature. Only under high-temperature conditions can the chemical reaction be achieved. Form a protective layer. Under the trend of miniaturization and high power of the internal combustion engine and top temperature of the combustion chamber, the friction reducer oil additive capable of generating a chemical protective film will be increasingly valued and widely used.

Liquid moly oil additive

Oil-soluble organic molybdenum compounds have excellent anti-friction properties and can significantly reduce the friction coefficient of moving contact parts. Liquid moly oil additive is the best friction modifier. The moly oil additives currently developed mainly include dialkyl molybdenum thiosulfate (MoDTP), molybdenum dialkyl dithiocarbamate (MoDTC) and trinuclear molybdenum compounds. Although their friction reduction mechanism has not yet been determined, most opinions are that they produce a chemical reaction with the metal surface in the lubrication zone to create a chemical reaction film. A secondary structure film (<50 Dm) is formed on the surface, and MoS and MoO enter the metal surface. MoDTC, MoDTP, and trinuclear molybdenum compounds will decompose MoS on the surface of the micro convex body of the friction surface during the lubrication process. The MoS decomposed gathers in the concave valleys of the surface, thus making the friction surface smooth so that it can last effectively Reduce the friction factor. Liquid moly oil additive is split into organic groups and metallic molybdenum under the influence of higher thermal energy in the friction zone. Molybdenum diffuses on the friction surface and forms a low melting point substance with other metals, which reduces the friction factor and reduces friction losses.

Infomak is dedicated to the technology development of special friction modifier, combined the Technology of nanomaterials developed dry lubricant and oil additives two series. Our products can significantly improve the performance of lubricating oil, improve energy efficiency, effectively protect the lubrication device and extend the oil change cycle, which can satisfy the lubrication oil constantly upgrading for high-end engine oil additives. Contact us.

Regarding the anti-friction and anti-wear mechanism of nano-lubricants, it is mainly inclined to the following three cases: (1) the repair effect of nano lubricant additives; (2) nano lubricant additives form a film on the surface of friction pairs; (3) nano lubricant additives To the ball bearing.

1.Repair effect

Nanoparticles have the characteristics of small particle size. Nanoparticles added to the grease can deposit on the surface of the friction pair. Filling the pits generated during the operation of the machine can "repair" the friction pair to a certain extent and slow down the friction pair. Speed of wear to extend service life. Dr. Guo added nano copper powder to the steel/steel friction pair after working for a while and found that nano-copper particles were deposited on the surface of the substrate, filling the pits generated during the abrasion process, and repairing the surface of the friction pair to prevent it from further wear and tear.

2.Film on the surface of the friction pair

Nanoparticles have the characteristics of low melting point and high chemical activity. The local high temperature and high pressure generated by the friction pair during the working process can cause the nanoparticles to melt and spread to form a surface film. The surface film includes a chemical reaction film, a transfer film, and a deposition film.

Professor Liu's group used DDP-modified nano copper to conduct tribological tests under different loads and found that they exhibited certain anti-friction and anti-wear capabilities under various loads. They speculate that the reason is related to the formation of the film. Under low load, due to the large gap of the friction pair, the amount of nano copper powder deposited is small. At this time, the adsorption or reaction surface film formed by the modified layer is mainly used to support the load. ; Under high pressure, nano copper deposits more on the friction surface, and it is easy to form a thick deposition surface film, which reduces the degree of friction and wear of the friction pair. Chen Hanlin and others investigated the tribological properties of WS2 nano-powders added to lithium-based greases as nano lubricant additives. It was also found that during the friction process, tungsten disulfide nano-powders would adsorb and deposit on the surface of friction pairs. Under high temperature and high load conditions, a chemical reaction film containing Fe2O3, FeSO4, WO3, and Fe3O4 is formed, thereby reducing friction and reducing wear.

3.Ball-bearing action

For some harder nanoparticles, it is not easy to be compressed into a film under high-temperature and high-pressure working conditions, and friction between the friction pairs will form a "pebble," which acts as a "ball bearing" to support the load between the friction pairs and thus Improves abrasion and extreme pressure resistance of the grease.

Dr. Li Baoliang found that due to the characteristics of high hardness and the high melting point of Al2O3 particles, nano-Al2O3 particles play a role of "micro bearings and support pads" on the friction surface when they are inserted into the surface of the friction pair. Similar to "ball bearings", it improves the performance of extreme pressure and anti-wear.

Research development priorities and trends

The application of nano grease additives in tribology to tribology has achieved specific results, but in the future research process, the following aspects are worthy of our consideration:

(1) The wonderful grains of the nano-particles result in immense surface energy. In addition to the attractive force between the particles, it is easy for the particles to automatically aggregate to form larger massive aggregates, which will agglomerate and precipitate, and lose ultra-fine particles. Functional properties of fine grains. Therefore, the dispersion stability of nano oil additives in lubricating grease will become one of the focuses of future research;

(2) With the proposal of "green chemistry" in recent years, the next study of nano oil additives should be developed in the direction of "biodegradability and non-toxicity", and environmentally friendly lubricant additives should be designed to reduce environmental impact. damage;

(3) Nano additives and common oil additives have a synergistic effect. Among conventional oil additives and nano grease additives, the optimal proportion of the two is explored to achieve the best tribological properties of the grease.

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