Anti-wear additives: main types, mechanism of action and use in lubricants
2026-11-05
During the operation of lubricants, friction surfaces are exposed to load, temperature and relative motion. If the oil film does not completely separate the two metal surfaces, their micro-irregularities may come into contact. This leads to increased friction, wear and, in severe cases, damage to equipment parts.
Anti-wear additives- important functional components of lubricant formulations. They are designed primarily for operation in boundary and mixed lubrication conditions. The formation of a protective film on metal surfaces helps reduce direct contact between them and reduce wear of parts. Different chemical types of anti-wear additives differ in the reaction mechanism and the characteristics of the formation of the protective layer. Therefore, when choosing, it is necessary to take into account the properties of the base oil, equipment operating conditions and formulation requirements.
The article discusses the main types of anti-wear additives, their mechanisms of action, as well as the differences between anti-wear and extreme pressure additives. This will help to better understand their role in industrial lubricants.
1. What are Anti-wear additives?
Anti-wear additivesare functional components of lubricants designed to reduce wear of friction surfaces. They work most actively under conditions of boundary and mixed lubrication.
In full hydrodynamic mode, a continuous oil film is formed between the friction surfaces, which prevents direct contact of metals. However, when starting and stopping equipment, low rotation speeds, high loads or insufficient lubricant supply, film thickness may decrease. In certain zones, contact between microroughnesses of metal surfaces occurs.
Under such conditions, anti-wear additives are capable of forming a protective boundary film on the metal through physical adsorption or chemical reaction. This reduces the direct interaction of micro-roughness and helps reduce friction and wear.
Basic functionsAnti-wear additives:
- Reduced wear on metal surfaces.The formation of a protective film in the contact area reduces the likelihood of direct interaction between metal surfaces.
- Improved boundary lubrication.Additional protection is maintained even when the oil film does not completely separate the friction surfaces.
- Reduced friction losses.Some components improve shear characteristics at the interface.
- Increased equipment service life.Reducing wear on critical parts helps maintain stable operation of mechanisms.
At the same time, anti-wear additives do not replace the oil film formed by the base oil. Their effectiveness depends on the chemical structure of the components, the composition of the formulation and the operating conditions of the equipment.
2. Mechanism of action Anti-wear additives
The main mechanisms of action are the formation of an adsorption film and the formation of a protective layer as a result of a chemical reaction.
2.1. Adsorption film formation
Some polar organic compounds contain functional groups that can interact with metal surfaces. When lubricant enters the friction zone, such molecules are adsorbed on the metal and form a boundary layer with certain lubricating properties.
This group of compounds includes:
- fatty acids and their derivatives;
- alcohols;
- esters;
- other organic compounds with polar functional groups.
As a rule, the polar part of the molecule interacts with the metal surface, and the non-polar part is oriented towards the lubricant or neighboring molecules. The resulting adsorption layer changes the contact characteristics and helps reduce friction and surface wear.
2.2. Formation of a protective film as a result of a chemical reaction
Under the influence of temperature, pressure and friction, some anti-wear additives react chemically with the metal surface or its oxide layer. As a result, a protective reaction film is formed.
Such films may contain phosphates, sulfides and other inorganic reaction products. They are able to withstand a certain shear effect during friction, reducing direct contact of metal surfaces.
Typical representatives of this group include:
- organic phosphorus compounds;
- organic sulfur compounds;
- organic molybdenum compounds;
- Zinc dialkyldithiophosphate (ZDDP).
Protective films formed by various components differ in thickness, chemical composition, thermal stability and load-bearing capacity. Therefore, assessing anti-wear properties only by the name of the additive is not enough.
3. Main types of anti-wear additives and their features
3.1. Oxygen-containing organic compounds
This group includes fatty acids, alcohols and esters. Due to the presence of polar groups, such compounds are able to adsorb on a metal surface and form a boundary lubricating film.
Some carboxylic acids can react with metal to form metal soaps. Under certain conditions, such surface layers improve the lubricity of the contact and help reduce friction and wear.
Their effectiveness depends on the length of the molecular chain, the type of polar group, the properties of the metal surface and the operating temperature.
3.2. Organic phosphorus compounds
Organic phosphorus compounds are widely used as functional components of anti-wear formulations. Some phosphate esters are capable of reacting with a metal surface to form a protective film containing phosphorus.
Depending on the chemical structure of the compound and the reaction conditions, the composition of such a film may include iron phosphates and other phosphorus-containing products. Its thickness, structure and mechanical properties depend on the composition of the additive, temperature, surface condition and lubrication conditions.
The main functions of organic phosphorus compounds:
- formation of a reactive protective film on a metal surface;
- improvement of anti-wear properties under boundary lubrication conditions;
- combined use with other components to achieve the required lubricant characteristics.
Some phosphate esters may also have anti-corrosion or other additional properties. However, the specific effect is determined by the chemical structure of the substance and the test results of the finished formulation.
3.3. Organic molybdenum compounds
Organic molybdenum compounds are of interest for lubricant formulations that require a combination of anti-wear properties and friction reduction.
The most famous representatives include:
- MoDTC— molybdenum dithiocarbamate;
- MoDTP— molybdenum dithiophosphate.
Under suitable temperature conditions and friction, some organic molybdenum compounds are capable of forming molybdenum disulfide (MoS₂) and other molybdenum-containing reaction products on the friction surface.
MoS₂ has low shear strength, which improves the sliding of contacting surfaces. Therefore, such components are used in formulations where it is important to reduce the coefficient of friction.
Organic molybdenum compounds may also interact with ZDDP and other formulation components. This interaction affects the process of formation of the reaction film and its final characteristics. The result depends on the composition of the lubricant and operating conditions.
3.4. Zinc dialkyldithiophosphate (ZDDP)
ZDDP is one of the widely used multifunctional lubricant additives. It has both anti-wear and antioxidant properties and is an important component of many motor oils.
In the contact zone of friction surfaces, ZDDP enters into thermal or tribochemical reactions, as a result of which a protective film containing phosphorus, sulfur and zinc is formed on the metal. This film has a complex glass-like structure and a certain thickness, due to which it protects the metal surface during friction.
The anti-wear effectiveness of ZDDP is largely determined by the structure of the alkyl groups. What matters is the type of alkyl group - primary or secondary, the length of the carbon chain and the degree of its branching. Additives with different structures may differ in reactivity, film formation rate and thermal stability.
When developing formulations, it is necessary to take into account not only the anti-wear and antioxidant properties of ZDDP, but also compatibility with other components, as well as phosphorus content restrictions associated with the requirements for engine exhaust gas aftertreatment systems.
4. How are anti-wear additives different from extreme pressure additives?
Anti-wear additives and extreme pressure additives (EP additives) can form protective layers on friction surfaces and thereby reduce the risk of damage to parts. However, their main tasks and typical application conditions differ.
Anti-wear additivesDesigned primarily to reduce wear under moderate loads, under conditions of boundary and mixed lubrication.
EP AdditivesThey are mainly used for high loads and significant contact stresses. In areas of intense contact, under the influence of temperature and pressure, they enter into chemical reactions with the surface, forming protective layers. This helps reduce the risk of excessive wear, scuffing and seizing of metal surfaces.
The main differences are presented in the table:
| Criterion | Anti-wear additives | Extreme Pressure Additives |
| Main function | Reduced wear of friction surfaces | Protection against high loads and contact stresses |
| Typical Operating Conditions | Boundary and mixed lubrication | High loads and contact stresses |
| Mechanism of action | Adsorption or reaction film formation | Predominantly chemical formation of a protective film |
| Main task | Reduced surface wear | Prevents severe wear, scuffing and seizing |
| Typical Applications | Motor oils, hydraulic and circulating oils | Industrial gear oils, metalworking fluids |
It should be noted that the scope of action of these two groups is not completely isolated. Some chemical compounds can exhibit both anti-wear and extreme pressure properties at the same time. Their effectiveness is determined by their chemical structure, concentration in the formulation and actual operating conditions. Therefore, the differences between them cannot be reduced solely to the activation temperature.
5. Main Applications Anti-wear additives
Anti-wear additives are used in various lubricants for which it is important to control wear on friction surfaces.
5.1. Motor oils
An internal combustion engine contains many metal parts that operate under conditions of relative motion. During startup, shutdown and operation under high load, individual friction zones may be in boundary or mixed lubrication mode.
Anti-wear additives help protect parts such as camshaft lobes, valve lifters and other critical components, reducing the risk of wear. ZDDP is one of the common functional components of anti-wear motor oil formulations.
5.2. Hydraulic oils
In hydraulic systems, pumps, valves and other moving parts require reliable lubrication. Anti-wear additives help reduce wear on friction surfaces and maintain stable operation of hydraulic equipment under appropriate loads.
5.3. Industrial gear oils
During the meshing of gears, the contacting surfaces may experience significant loads and contact stresses. Depending on the gearbox design and operating conditions, when developing a formulation, it is necessary to take into account both the anti-wear and extreme pressure properties of the oil. This helps reduce the risk of damage to the working surfaces of the teeth.
5.4. Greases
Greases are widely used in bearings, mining equipment and various industrial machinery. Depending on the load, speed and operating conditions, components with anti-wear or extreme pressure properties can be added to the formulation.
6. How to choose suitable anti-wear additives?
When choosing anti-wear additives, it is not enough to focus only on one indicator of anti-wear effectiveness. The properties of the base oil, compatibility with other components and the actual operating conditions of the equipment must also be taken into account.
Main selection criteria:
1. Type of lubricant
Requirements for anti-wear properties vary depending on the intended use of the product. For example, motor oils, hydraulic oils, and industrial gear oils operate at different temperatures and loads and have different formulation systems. Therefore, the additive composition must match the specific type of lubricant.
2. Chemical structure and reactivity
Various anti-wear additives differ in their adsorption capacity, mechanism of protective film formation and reactivity. When choosing, it is necessary to take into account the required characteristics of the finished product and its operating conditions.
3. Compatible with base oil and other components
The additive must maintain good compatibility with the base oil and other functional components. It is especially important to evaluate the interactions of substances in additive packages, since competitive adsorption, mutual influence on chemical reactions, or the formation of sediment may occur between individual components.
4. Testing and confirmation of characteristics
The final choice should be based on the results of testing of the finished formulation. Depending on the purpose of the product, wear resistance, friction characteristics, oxidative stability, corrosion properties and other indicators are assessed.
For example, four-ball testing is used to evaluate the anti-wear and extreme pressure properties of lubricants. The specific test procedure is determined by the type of product and the applicable standards.
7. Main directions of development Anti-wear additives
As industrial equipment evolves and demands on its efficiency, service life and energy consumption increase, so do the requirements for anti-wear performance, friction control and operational stability of lubricants.
In the future, the development and application of anti-wear additives will pay special attention to the following areas:
- Multifunctionality.Development of chemical structures that allow combining anti-wear, anti-friction and antioxidant properties.
- Synergy of components.Optimization of compatibility Anti-wear additives with detergents, dispersants, antioxidants and other functional components.
- Phosphorus reduction and environmental adaptation.Development of recipes taking into account the requirements for specific equipment and environmental restrictions.
- Stability of characteristics.Increased attention to the ability to form a protective film, thermal stability and compatibility of components during long-term operation.
The practical effectiveness of anti-wear additives depends not only on the properties of the individual component, but also on the quality of the base oil, the development of a comprehensive formulation and control of the production process.
8. Development and production of additives for lubricants
Lansheng (Jinzhou) Chemistry LLC was founded in April 2018. The company specializes in the development, production and sales of lubricant additives and supplies products to lubricant manufacturers in China and abroad.
The company's production site occupies approximately 46,667 m². The company has 5 production lines and an annual production capacity of about 60,000 tons. The technical team consists of 9 R&D specialists and 12 engineering technical specialists. The company continues to develop product solutions and technical capabilities in the field of lubricant additives.
The range includes detergent additives, ashless dispersants, additive packages and other functional components. A closed production management system and intelligent process control allow us to pay special attention to product quality, batch consistency and customer requirements for the use of additives.
For lubricant manufacturers, when selecting components, it is important to consider not only individual performance indicators, but also compatibility with the base oil, interactions within the formulation, product stability and conditions for its further use.
If you are developing a new formulation or improving existing lubricants, contact us to discuss product requirements and possible applications.
Frequently asked questions (FAQ)
1. What is the main function of anti-wear additives?
The main task of anti-wear additives is the formation of an adsorption or reaction film on metal surfaces. This reduces direct contact between them and reduces wear under boundary and mixed lubrication conditions.
2. Does ZDDP belong to anti-wear additives?
Yes. ZDDP is a common multifunctional lubricant additive with anti-wear and antioxidant properties. It is widely used, in particular in motor oil formulations.
3. Can anti-wear additives and extreme pressure additives be used at the same time?
Yes. In some formulations these components are used together. In this case, it is necessary to take into account the operating conditions of the equipment, the type of lubricant and the compatibility of individual components.
4. How effectiveness is assessedAnti-wear additives?
Appropriate friction and wear test methods are used for evaluation, taking into account the intended purpose of the finished lubricant. For example, tests on a four-ball machine may be used, as well as additional tests taking into account actual operating conditions.
