Editing Lubricant (section)

=== Additives ===

{{main|Oil additive}}

A large number of additives are used to impart performance characteristics to the lubricants. Modern automotive lubricants contain as many as ten additives, comprising up to 20% of the lubricant, the main families of additives are:<ref name=Fundamentals/>
* [[Pour point]] depressants are compounds that prevent crystallization of waxes. Long chain [[alkylbenzene]]s adhere to small crystallites of wax, preventing crystal growth.
* [[Anti-foaming agent]]s are typically [[silicone]] compounds which increase [[surface tension]] in order to discourage foam formation.
* [[Viscosity index improver]]s (VIIs) are compounds that allow lubricants to remain viscous at higher temperatures. Typical VIIs are [[polyacrylate]]s and [[butadiene]].
* [[Antioxidant]]s suppress the rate of oxidative degradation of the hydrocarbon molecules within the lubricant. At low temperatures, free radical inhibitors such as hindered phenols are used, e.g. [[butylated hydroxytoluene]]. At temperatures >90&nbsp;°C, where the metals [[Catalysis|catalyze]] the oxidation process, dithiophosphates are more useful. In the latter application the additives are called [[metal deactivator]]s.
* [[Detergent]]s ensure the cleanliness of engine components by preventing the formation of deposits on contact surfaces at high temperatures.
* [[Corrosion inhibitor]]s (rust inhibitors) are usually alkaline materials, such as alkylsulfonate salts, that absorb acids that would corrode metal parts.
* [[AW additive|Anti-wear]] additives form protective 'tribofilms' on metal parts, suppressing [[wear]]. They come in two classes depending on the strength with which they bind to the surface. Popular examples include [[tricresylphosphate|phosphate ester]]s and [[zinc dithiophosphate]]s.<ref>{{Cite journal|last=Spikes|first=H.|date=2004-10-01|title=The History and Mechanisms of ZDDP|journal=Tribology Letters|language=en|volume=17|issue=3|pages=469–489|doi=10.1023/B:TRIL.0000044495.26882.b5|s2cid=7163944|issn=1023-8883}}</ref> 
* [[EP additive|Extreme pressure]] (anti-scuffing) additives form protective films on sliding metal parts. These agents are often sulfur compounds, such as dithiophosphates.
* [[Friction modifier]]s reduce friction and wear, particularly in the boundary lubrication regime where surfaces come into direct contact.<ref>{{Cite journal|last=Spikes|first=Hugh|date=2015-10-01|title=Friction Modifier Additives|journal=Tribology Letters|language=en|volume=60|issue=1|pages=5|doi=10.1007/s11249-015-0589-z|issn=1023-8883|hdl=10044/1/25879|s2cid=137884697|url=http://spiral.imperial.ac.uk/bitstream/10044/1/25879/2/post%20review%20Friction%20modifier%20additives.pdf|hdl-access=free|access-date=23 September 2019|archive-date=22 September 2017|archive-url=https://web.archive.org/web/20170922050548/http://spiral.imperial.ac.uk/bitstream/10044/1/25879/2/post%20review%20Friction%20modifier%20additives.pdf|url-status=live}}</ref> 
<!--* [[Friction modifier]]s
* Stickiness improver
* Complexing agent (in case of greases)
Note that many of the basic chemical compounds used as detergents (example: calcium sulfonate) serve the purpose of the first seven items in the list as well. Usually it is not economically or technically feasible to use a single do-it-all additive compound. Oils for [[hypoid]] gear lubrication will contain high content of EP additives. Grease lubricants may contain large amount of solid particle friction modifiers, such as graphite, molybdenum sulfide.-->

In 1999, an estimated 37,300,000 tons of lubricants were consumed worldwide.<ref>{{Cite book |doi=10.1002/14356007.a15_423|chapter=Lubricants and Lubrication|title=Ullmann's Encyclopedia of Industrial Chemistry|year=2003|last1=Bartels|first1=Thorsten|last2=Bock|first2=Wolfgang|last3=Braun|first3=Jürgen|last4=Busch|first4=Christian|last5=Buss|first5=Wolfgang|last6=Dresel|first6=Wilfried|last7=Freiler|first7=Carmen|last8=Harperscheid|first8=Manfred|last9=Heckler|first9=Rolf-Peter|last10=Hörner|first10=Dietrich|last11=Kubicki|first11=Franz|last12=Lingg|first12=Georg|last13=Losch|first13=Achim|last14=Luther|first14=Rolf|last15=Mang|first15=Theo|last16=Noll|first16=Siegfried|last17=Omeis|first17=Jürgen|isbn=978-3527306732}}</ref> Automotive applications dominate, including electric vehicles<ref>{{Cite book|last1=Beyer|first1=Monica|last2=Brown|first2=Gareth|last3=Gahagan|first3=Michael|last4=Higuchi|first4=Tomoya|last5=Hunt|first5=Gregory|last6=Huston|first6=Michael|last7=Jayne|first7=Doug|last8=McFadden|first8=Chris|last9=Newcomb|first9=Timothy|last10=Patterson|first10=Suzanne|last11=Prengaman|first11=Christopher|last12=Shamszad|first12=Mariam|date=2019-12-12|chapter=Lubricant Concepts for Electrified Vehicle Transmissions and Axles|chapter-url=https://www.jstage.jst.go.jp/article/trol/14/5/14_428/_article/-char/ja/|pages=428–437|doi=10.2474/trol.14.428|title=Tribology Online|volume=14|issue=5|s2cid=210160024|access-date=17 February 2020|archive-date=17 February 2020|archive-url=https://web.archive.org/web/20200217161625/https://www.jstage.jst.go.jp/article/trol/14/5/14_428/_article/-char/ja/|url-status=live}}</ref> but other industrial, marine, and metal working applications are also big consumers of lubricants. Although air and other gas-based lubricants are known (e.g., in [[fluid bearing]]s), liquid lubricants dominate the market, followed by solid lubricants.

Lubricants are generally composed of a majority of base [[oil]] plus a variety of additives to impart desirable characteristics. Although generally lubricants are based on one type of base oil, mixtures of the base oils also are used to meet performance requirements.