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What is friction modifier?
Friction modifier is an additive that reduces the friction coefficient of lubricating oil under boundary lubrication conditions. Its function is mainly to form a lubricating protective film on the metal surface to avoid direct contact between metal peaks so that the mixed lubrication and boundary lubrication conditions The friction coefficient is reduced, the friction resistance and wear are reduced, and the fuel-saving purpose is achieved.
Differential friction modifier includes carboxylic acids and their derivatives, amides, imides, amines and their derivatives, phosphorus and phosphoric acid derivatives, organic polymers, and organometallic compounds. Organometallic compounds are widely used in internal combustion engine oils. A class of products, such compounds include molybdenum dithiocarbamate (MoDTC), MoDTP, organic molybdenum mixtures, and so on. With the increase in environmental protection requirements, friction modifiers containing sulfur and phosphorus have been restricted. The role of environmentally friendly friction modifiers that do not contain metals, sulfur, and phosphorus is more prominent.
Type and working mechanism of friction reducer oil additive
1. Types and mechanism of organic friction modifier
(1) Types of organic friction modifiers
Usually, there is a polar group at one end of the organic friction modifier oil. This opposing group is one of the leading factors in the effectiveness of friction modifiers. From the chemical structure division, the commonly used organic friction modifier oil mainly includes ① carboxylic acid or its derivatives; ② imide, amine, and its products; ③ phosphorus or phosphonic acid derivatives; ④ organic polymers.
(2)what does friction modifier do?
The mechanism of action of organic friction modifier oil usually has the following three forms:
①Form a chemical reaction film. Such products mainly include saturated fatty acids, phosphoric acid, and thiophosphoric acid, and sulfur-containing fatty acids. The mechanism is similar to that of anti-wear agents. The friction modifier additive reacts with the metal surface to form a protective film, thereby reducing friction. But the most fundamental difference between the two is that the chemical reaction film of the friction modifier oil appears under milder load and temperature conditions in the mixed lubrication state, and the chemical activity of the friction modifier additive is required to be relatively high, such as a chemical structure similar to thrive. Stearic acid is an exception. In theory, as the temperature increases, the anti-friction effect of stearic acid should decrease due to the desorption of molecules from the metal surface. However, experiments have shown that with the rise in temperature, stearic acid forms a chemical reaction film, and the anti-friction effect is enhanced;
②Form a physical adsorption film. Such products mainly include long-chain carboxylic acids, esters, ethers, amines, amine-based compounds, and imides. The friction modifier additive dissolved in the oil is adsorbed on the metal surface by the polar groups of the molecules, and the long hydrocarbon chain is dissolved in the oil, perpendicular to the metal surface, resulting in a multilayer matrix of the friction modifier additive molecules. The thickness and anti-friction effect of the friction modifier additive film on the metal surface are related to the following parameters: (1) the more robust the polarity of the polar group, the greater the thickness and strength of the friction modifier film on the metal surface; (2) friction modifier The additive's hydrocarbon straight chain is conducive to the production of more muscular anti-friction cinema; (3) The chain length of the base oil and the chain length of the friction modifier additive are similar, which is beneficial to produce a stronger anti-friction film, but the chain length ratio of the friction modifier additive The chain length of the base oil has a more significant impact; (4) The increase in temperature can improve the thickness and strength of the friction modifier additive film, but if the weather is too high, the friction modifier molecules may be desorbed from the metal surface;
③Form a polymer. Such products mainly include unsaturated complex esters, methacrylates (esters), unsaturated fatty acids, and sulfurized kinds of paraffin. The formation of friction reducer oil additive is a particular case. It does not form a solid film but forms a liquid film under contact temperature and load, and the metal surfaces on both sides of the film do not react. The formation of this polymer requires the following characteristics: (1) Relatively low activity; (2) The polymer has good mechanical and thermal stability and is insoluble in the lubricating oil; (3) A healthy formation between the polymer and the metal surface Adsorption or chemical bond; (4) Polymer film formation speed is fast.
2. Other friction reducer oil additive types and their working principles
①Metal organic compound type friction reducer oil additive
Types of metal-organic compound friction modifiers mainly include molybdenum or copper compounds, such as molybdenum dithiophosphate, dithiocarbamate, copper oleate, salicylate or ester, and hydrocarbyl dithiophosphate Wait.
The mechanism of action of metal-organic compound friction reducer oil additive: (1) Molybdenum may penetrate into the rough surface, (2) form a polymer film, (3) form polymorphic molybdenum disulfide (the most acceptable theory), (4) A thin metal film that is easy to shear due to the selective transfer of metal (copper). The mechanism of action of metal-organic compound friction modifiers is not fully known.
②Non-oil-soluble friction modifier
The more classic non-oil-soluble friction modifiers are graphite, molybdenum disulfide, and the newly emerged Teflon (polytetrafluoroethylene), polyamide, graphite fluoride, borate, etc. The mechanism of action of this type of friction modifier is mainly to form a layered structure with a low shear rate or to form a ductile or plastic layer on the metal surface, resulting in a reduction in friction.
③The main difference of Differential friction modifier
Relatively speaking, the molybdenum-based metal-organic compound is very active in the boundary lubrication state, but the organic friction modifier is more involved in the mixed lubrication state.
The effect of organic friction modifier is more significant than the use of low-viscosity oil to compensate for the growth of mixed lubrication. To a certain extent, the molybdenum-based metal compound shows the same effect as the organic friction modifier. Still, the latter offers a small friction coefficient in the mixed lubrication state, especially under the most demanding low-speed and high-load conditions. The organic friction modifier mainly acts in the form of an absorption layer, which occurs at relatively low temperatures. The molybdenum compound acts as a polymer of MoS2 and needs to be present in a high-temperature environment. Besides, although molybdenum-based metal compounds can improve fuel economy, there are data showing that adding them to base oils or fully formulated engine oils increases TEOST deposit levels, which is undesirable.
Besides, although the molybdenum-based metal compound friction modifier is widely used in Japan and can improve fuel economy by 0.3%, the program VIB engine test limits its use. Therefore, it is more important to select a useful organic friction modifier to improve fuel economy.
The improvement of the quality of internal combustion engine oil requires the development of related oil additives technology. To improve the performance of internal combustion engine oil, friction modifier plays a significant role. Its effect and research trends are mainly manifested in the following aspects:
(1) Strengthening of single-dose function and developing towards multi-function;
(2) The result of ashless additives and the enhancement of processes, replacing or partially replacing the current ash metal additives, such as nitrogen or boron compounds;
(3) The exploration of friction modifier to find more effective types of additives, especially the research of individual rare earth element (tungsten) additives, is expected to make good progress;
(4) Research on additives that can replace metal sulfophosphates to reduce the impact of phosphorus on engine systems;
(5) Research on adding Jing compound technology to meet better economic principles and comprehensive performance;
(6) The study on the action mechanism of a friction modifier guides people to better understand its action mechanism and apply it to actual internal combustion engine oil formulations.
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