Oil additives can be chemical compounds that increase the lubricant properties of base oils (or "base stock") or oil. A manufacturer can use the same base stock to make different oils but can choose different additives depending on their specific needs. Some oils may contain up to 5% of additives.
Nearly all commercial motor oils have additives, regardless of whether they are petroleum-based or synthetic. The American Petroleum Institute (API Service SA) motor oils do not contain additives and are thus incapable of protecting modern engines. The application determines the type of additives used, e.g. The oil for a diesel engine that has direct injection in a pickup truck (API Service CJ-4) contains different additives to the oil used in small gasoline-powered outboard motors on boats (2-cycle engine oils).
For modern internal combustion engines to work properly, oil additives are essential. The oil could become contaminated, leak out, crack, or fail to protect the engine parts at all temperatures. Additives for oils inside gearboxes and automatic transmissions are just as important. Additives that control viscosity, lubricity, chemical breakdown control, and contaminant control are some of the most important. Some additives allow lubricants that are subject to extreme pressures, temperatures, and high levels of contamination to perform better.
Since the 1930s, detergent additives have been used to remove oil impurities that could otherwise cause deposits (oil slime) on engine parts. Magnesium sulfonates are the most common detergent.
The oxidation of metals within an engine is impeded by corrosion or rust-inhibiting substances.
Antioxidant additives slow down the oil stock's degradation by oxidation. Organic amines, phenols, and other phenols are two examples of common additives.
To prevent oil from oxidizing, metal deactivators form a protective film on metal surfaces.
Bases can be used to prevent the chemical decomposition in base stock oils that are contaminated with acids. Oil will tend to accumulate acids when it is exposed to heat and oxidation from air and combustion gases.
You might find carbocyclic acid, ketones, and esters in used gear oil. As discussed below, formulated oils contain both organic and inorganic bases and detergents. This means that some, but not all, of these contaminants, can be neutralized. The TAN can measure the degradation of gear oil and its longevity.
Chemical structure of a zinc dialkyldithiophosphate, a typical antiwear agent found in many motor oils.
Alkaline additives can be used to neutralize acids and prevent the formation of sulfates within a working oil. KOH (potassium hydroxide) is a strong base that can be found in formulated oils. It is an effective neutralizer in the refining of petroleum and will be present in small quantities in formulated oils.
The following additives can perform similar functions in motor oils: magnesium and calcium sulfonates, salicylates and phenates. These detergent additives were mentioned earlier. It is necessary to measure the alkalinity of a formulated oils to determine its Total Base Number (TBN). This number refers to the amount of KOH in the oil. Each unit represents a mg of KOH per gram. TBN will decrease as the additive package is degraded until the motor oil has to be replaced. The oil's continued use will lead to sludge, varnish and metal corrosion. The TBN (total oil content) is an important indicator of motor oil's longevity and degradation.
Viscosity modifiers increase an oil's viscosity at higher temperatures. This improves its viscosity index, or VI. This reduces oil's tendency to thin at high temperatures. A VI enhancer will make oil viscousier and more lubricating at low temperatures. Multi-grade oils are often modified with viscosity modifiers. Some synthetic oils can be engineered without viscosity modifiers to meet multi-grade specifications. Many viscosity modifiers can be plastic polymers. Virtually all oils need a certain viscosity range to work properly. Oils will lose their viscosity over time, and eventually, they will need to be replaced.
Pour point depressants increase oil's flowability at lower temperatures.
By reducing friction between moving components, friction modifiers (or friction reducers) can be used to increase fuel economy. Friction modifiers affect the lubricity and viscosity of base oil. Whale oil was once used.
Extreme pressure agents are able to bond to metal surfaces and keep them from touching at high pressure.
Antiwear additives and wear inhibiting additives create a protective film around metal parts to help keep them separate. Zinc dialkyl dimiophosphate and zinc dithiophosphates can be used.
Nanoparticles can create diamond-like carbon coatings. This improves embeddability and achieves Superlubricity. This technology was developed in collaboration with Argonne National Laboratory, Pacific Northwest National Laboratory, and the foundation for TriboTEX. NASA Spinoff Magazine featured this technology for its ability to increase longevity.
Inorganic Fullerene like Tungsten Disulfide IF-WS2 nanoparticles have a hollow sphere (Fullerenelike) morphology. They provide high lubricity, antifriction and impact resistance (upto 35 GPa). Professor Reshef Tene at the Weizmann Institute of Science discovered the IF-WS2 particles. IF-WS2 particles are more resilient to extreme pressure and load than standard lubricant additives, which have platelet-like structures but have moderate tribological characteristics. The IF-LWS2 particle can be purchased in dry powder or as a dispersion with oil, water, or solvent. These dispersions can be used to make a variety of lubricants, greases, metalworking fluids and coatings.
Unintentional oil additives can cause wear metals. However, large metal particles and impurities can be removed in situ with either magnets or oil filters. Tribology studies the wear of materials.
Dispersants prevent contaminants (e.g. To prevent oil from coagulating, dispersants keep contaminants (e.g. soot) suspended within the oil.
Anti-formats (defoamants), which prevent the formation of air bubbles in the oil, can cause loss of lubrication and pitting.
Antimisting agents stop the oil from atomizing. Silicones are a common antimisting agent.
Wax crystal modifiers can be used to improve oil filters' ability to separate oil from wax. This additive is used in refining and transporting oil but not for lubricant formulation.
Gasket conditioners cause seals and gaskets to swell to prevent oil leakage.