AW additive
Encyclopedia
AW additives, or antiwear additives, are additives
for lubricants to prevent metal-to-metal contact between parts of gear
s.
EP additives are usually used in applications such as gearboxes
, while AW additives are used with lighter loads such as bushings.
AW additives typically contain zinc
and phosphorus
compounds.
Some popular AW additives are:
Some formulations use colloid
al PTFE (Teflon), but its efficiency is controversial.
Many AW additives function as EP additives, for example organophosphate
s or sulfur
compounds.
The mechanism of function of TCP and ZDDP is explained in EP additive
s.
Under extreme pressure conditions, the performance of AW additives becomes insufficient and designated EP additive
s are required.
See also:
Oil additive
Oil additives are chemical compounds that improve the lubricant performance of base oil . By utilizing the same base stock, many different oils can be manufactured, each with its distinctive properties. Additives comprise up to 5% by weight of some oils.Nearly all commercial motor oils contain...
for lubricants to prevent metal-to-metal contact between parts of gear
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
s.
EP additives are usually used in applications such as gearboxes
Transmission (mechanics)
A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...
, while AW additives are used with lighter loads such as bushings.
AW additives typically contain zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
and phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
compounds.
Some popular AW additives are:
- zinc dithiophosphate (ZDP)
- zinc dialkyl dithio phosphateZinc dialkyl dithio phosphateZinc dialkyldithiophosphates are a family of coordination compounds invented by Castrol that feature zinc bound to the anion of dithiophosphoric acid. These uncharged compounds are not salts. They are soluble in nonpolar solvents, and the longer chain derivatives easily dissolve in mineral and...
(ZDDP), probably the most widely used in formulated engine oils, also acts as a corrosion inhibitorCorrosion inhibitorA corrosion inhibitor is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy. The effectiveness of a corrosion inhibitor depends on fluid composition, quantity of water, and flow regime...
and antioxidantAntioxidantAn antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When... - Tricresyl phosphateTricresyl phosphateTricresyl phosphate, abbreviated TCP, is an organophosphate compound that is used as a plasticizer and diverse other applications. It is a colourless, viscous liquid, although commercial samples are typically yellow...
(TCP), used for high-temperature operation, often used as an AW and EP additive in turbine engine lubricants, and also in some crankcase oils and hydraulic fluidHydraulic fluidHydraulic fluids, also called hydraulic liquids, are the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water...
s - HalocarbonHalocarbonHalocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms resulting in the formation of organofluorine compounds, organochlorine compounds, organobromine compounds, and organoiodine compounds...
s (chlorinated paraffinsChlorinated paraffinsChlorinated paraffins are a complex mixture of polychlorinated n-alkanes and were introduced in the 1930s. The chlorination degree of CPs can vary between 30 and 70%. CPs are subdivided according to their carbon chain length into short chain CPs , medium chain CPs and long chain CPs...
), for extreme pressure operations - Glycerol mono oleate
- Stearic acidStearic acidStearic acid is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH316CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates...
, adhering to surfaces via reversible adsorption process under 150 °C, which limits its use to mild contact conditions.
Some formulations use colloid
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...
al PTFE (Teflon), but its efficiency is controversial.
Many AW additives function as EP additives, for example organophosphate
Organophosphate
An organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactors that are essential for life...
s or sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
compounds.
The mechanism of function of TCP and ZDDP is explained in EP additive
EP additive
Extreme pressure additives, or EP additives, are additives for lubricants with a role to decrease wear of the parts of the gears exposed to very high pressures...
s.
Under extreme pressure conditions, the performance of AW additives becomes insufficient and designated EP additive
EP additive
Extreme pressure additives, or EP additives, are additives for lubricants with a role to decrease wear of the parts of the gears exposed to very high pressures...
s are required.
See also:
- EP additiveEP additiveExtreme pressure additives, or EP additives, are additives for lubricants with a role to decrease wear of the parts of the gears exposed to very high pressures...
s - Oil additiveOil additiveOil additives are chemical compounds that improve the lubricant performance of base oil . By utilizing the same base stock, many different oils can be manufactured, each with its distinctive properties. Additives comprise up to 5% by weight of some oils.Nearly all commercial motor oils contain...