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Reducing the friction and wear of the main friction pairs of mechanical equipment, reducing energy consumption, and reducing environmental pollution are the three major issues facing the design, manufacture, and use of modern machinery. Lubricants are the key factors. EP additives and anti-friction additives are the most important among lubricants. Commonly used engine oil additives. Adding EP additives to the grease under pressure can reduce friction, wear and sintering of mechanical parts, and lubricate the machine, thereby improving the working efficiency of the device and extending the service life of the device. Traditional EP additives and anti-friction additives usually contain sulfur, phosphorus, and organometallic salts, while new engine oil additives are developing towards ashless, low phosphorus, and low sulfur.
Research and Application Status of Various Extreme Pressure Antiwear Additives
1. Phosphorus EP additives
Phosphorus-containing organic compounds, engine oil additives, have been used as extreme pressure anti-wear additives for a long time, and have obtained a wide range of industrial applications. They are currently one of the most widely used additives with the best anti-wear effects. There are many types of phosphorus EP additives. According to their active elements, they can be divided into phosphorus type, phosphorus nitrogen type, sulfur phosphorus type, sulfur phosphorus nitrogen type, and sulfur phosphorus nitrogen boron type. Phosphorus anti-wear agents have been around for a long time, mainly in phosphate and phosphite series.
2. Nitrogen-containing heterocyclic EP additives
Nitrogen-containing heterocyclic compounds and their derivatives have good anti-ware, anti-oxidation performance, dispersion performance, rust prevention performance, and anti-corrosive performance. They are hot research topics in the field of tribology in recent years. The nitrogen heterocyclic additives are divided into thiazole derivatives, thiadiazole derivatives, oxazolines, benzotriazole derivatives, imidazoline derivatives, pyridine, and imidazoline, diazine derivatives, and triazine derivatives, etc.
3. Boron-containing EP additives
As a new type of inactive EP additives, boron-based additives are receiving more and more attention due to their unique chemical stability. From the perspective of chemical structure, boron-based EP additives can be divided into organic borate and inorganic borate. Boron-containing EP additives not only have excellent thermal oxidation stability and sealing adaptability, but also have no corrosion effect on copper at high temperatures. Steel has excellent anti-rust performance, and at the same time, is conducive to improving the operating environment. It has the excellent bearing capacity and anti-friction and anti-wear properties. It has superior performance than sulfur and phosphorus additives. It has been used in industrial gear oils and two-stroke oils.
The boron-based additives with broad development prospects are organic borate esters. A large number of studies have found that almost all of the organic borate esters have friction reduction and oxidation resistance, and some have anti-wear effects. Besides, its thermal stability is excellent, and it is non-corrosive to copper at high temperatures, has excellent rust resistance to steel, and also has good sealing adaptability, non-toxic and odorless, which is beneficial to environmental protection. These advantages are incomparable with traditional phosphorus and sulfur extreme pressure anti-wear additives.
4. Organic metal salts EP additives
Organometallic salts are an essential class of oil additives, and their applications are quite extensive. According to the structural characteristics of the compounds, organic metal salt EP additives can be divided into the following categories: 1) metal dialkyl dithiocarbamates, 2) zinc alkyl dithiophosphate, 3) polymers containing active metal elements (Mainly EDTA water-soluble metal complex). However, in recent years, environmental regulations have become increasingly stringent, and the demand for ashless oil additives has been increasing, so oil additives containing metal elements have been increasingly challenged.
Zinc dialkyl dithiophosphate (ZDDP) has many functions, such as anti-oxidation, anti-corrosion, extreme pressure, and anti-wear. It is widely used in other industrial oils.
Molybdenum compounds have excellent tribological properties and occupy a significant position in lubricating materials. Organic molybdenum additives have various functions such as anti-wear, anti-friction, extreme pressure, and anti-oxidation, which have attracted full attention from academia and industry. Experiments show that molybdenum dithiocarbamate has good intense pressure and anti-wear properties, especially with zinc dialkyldithiophosphate, which shows a perfect anti-wear synergy effect.
5. Nano-friction reducing oil additive
With the rapid development of nanotechnology and surface analysis technology, many scholars expect to use nanoparticles as a breakthrough in the event of new lubricant additives. Nanomaterials used as additives for lubricants are mainly of the following categories: (1) layered inorganic substances such as graphite, MoS2, etc .; (2) nano soft metals such as Cu, Al, Ni, etc .; (3) nano oxides, such as Al2O3, ZnO, etc .; (4) Compounds containing active element S, such as PBS, ZnS, etc .; (5) Inorganic borate salts, such as Cu3 (BO3) 2, Ni3 (BO3) 2, etc .; (6) Rare earth compounds, such as rare earth fluoride LaF3, rare earth oxide La2O3, CeO2, and rare earth hydroxide La (OH) 3, etc. Unique earth compounds have great potential for development as lubricant additives. They have the advantages of high-temperature resistance, good oil solubility, and low pollution. Therefore, new multifunctional rare earth organic sophisticated additives have been continuously developed.
With the increase of people's awareness of environmental protection and the increasingly stringent environmental regulations, the development trend of new extreme pressure anti-wear additives in the future is as follows:
(1) Under the premise of not reducing the extreme pressure anti-wear performance, improving the thermal oxidation stability and reducing the phosphorus consumption to extend its service life is the development direction of phosphorus intense pressure anti-wear agents;
(2) To find out the compounding rule and mechanism of other absolute pressure anti-wear agents, and to develop boron-containing agents with hydrolytic stability is the development direction of intense boron pressure anti-wear agents;
(3) The green synthesis method is used to obtain a multifunctional nitrogen-containing heterocyclic derivative lubricating additive with high yield, low cost, and ideal effects; meanwhile, in-depth research on its friction mechanism by applying new characterization methods is nitrogen-containing Development direction of ring lubricant additives;
(4) As an emerging technology, nano engine oil additives solve its agglomeration and cost problems, and research on the compounding rule with conventional additives in lubricants is the development direction of extreme nanoparticle pressure anti-wear agents.