# Extreme pressure additive > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Extreme_pressure_additive > Markdown URL: https://mediated.wiki/source/Extreme_pressure_additive.md > Source: https://en.wikipedia.org/wiki/Extreme_pressure_additive > Source revision: 1326555209 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) '''Extreme pressure additives''', or '''EP additives''', are [additives](/source/oil_additive) for [lubricant](/source/lubricant)s with a role to decrease wear of the parts of the [gear](/source/gear)s exposed to very high pressures. They are also added to [cutting fluid](/source/cutting_fluid)s for [machining](/source/machining) of [metal](/source/metal)s. Extreme pressure additives are usually used in applications such as [gearboxes](/source/transmission_(mechanics)), while [antiwear additives](/source/antiwear_additives) are used with lighter load applications such as hydraulic and automotive [engine](/source/engine)s. Extreme pressure [gear oil](/source/gear_oil)s perform well over a range of temperatures, speeds and gear sizes to help prevent damage to the gears during starting and stopping of the engine. Unlike antiwear additives, extreme pressure additives are rarely used in [motor oil](/source/motor_oil)s. The sulfur or chlorine compounds contained in them can react with water and combustion byproducts, forming acids that facilitate [corrosion](/source/corrosion) of the engine parts and bearings.[http://www.pecuniary.com/faq/EP-additives.html pecuniary.com FAQ] {{webarchive |url=https://web.archive.org/web/20110715061411/http://www.pecuniary.com/faq/EP-additives.html |date=July 15, 2011 }} Extreme pressure additives typically contain organic [sulfur](/source/sulfur), [phosphorus](/source/phosphorus) or [chlorine](/source/chlorine) compounds, including [sulfur](/source/sulfur)-[phosphorus](/source/phosphorus) and sulfur-phosphorus-[boron](/source/boron) compounds, which chemically react with the metal surface under high [pressure](/source/pressure) conditions. Under such conditions, small irregularities on the sliding surfaces cause localized flashes of high [temperature](/source/temperature) (300-1000 °C), without significant increase of the average surface temperature. The [chemical reaction](/source/chemical_reaction) between the [additive](/source/Gasoline_additive)s and the surface is confined to this area. [[File:CH2 dtc 2.svg|thumb|class=skin-invert-image|[Methylenebis(dibutyldithiocarbamate)](/source/Methylenebis(dibutyldithiocarbamate)) is an additive in some extreme pressure [gear oil](/source/gear_oil)s, serving as an antioxidant and protecting metal surfaces.{{cite encyclopedia|title=Lubricants, 2. Components|encyclopedia=Ullmanns Encyclopedia of Industrial Chemistry |author=Theo Mang |author2=Jürgen Braun |author3=Wilfried Dresel |author4=Jürgen Omeis |doi=10.1002/14356007.o15_o04|year=2011|publisher=Wiley-VCH|isbn=978-3-527-30673-2 }}]] The early extreme pressure additives were based on [lead](/source/lead) salts of [fatty acid](/source/fatty_acid)s ("lead [soap](/source/soap)s"), "active sulfur" compounds (e.g. [thiol](/source/thiol)s and elementary sulfur), and chlorinated compounds. During the 1950s the use of lead soaps was eliminated and replaced by [zinc](/source/zinc) and phosphorus compounds such as [zinc dithiophosphate](/source/zinc_dithiophosphate).{{cite web|url=http://www.machinerylubrication.com/Read/496|title=Monitoring Active Sulfur in EP Gear Oils - And Other Options for Monitoring EP Additive Depletion|first=Arnold|last=Shugarman|access-date=7 October 2012}} Some of the EP additives are: * Dark inactive sulfurized fat * Dark active sulfurized fat * Dark active sulfur hydrocarbon * Short and medium chain chlorinated [alkane](/source/alkane)s (see [chlorinated hydrocarbon](/source/chlorinated_hydrocarbon)s and [chlorinated paraffins](/source/chlorinated_paraffins)) * [Ester](/source/Ester)s of [chlorendic acid](/source/chlorendic_acid) * Polymer [ester](/source/ester)s * [Polysulfide](/source/Polysulfide)s * [Molybdenum](/source/Molybdenum) compounds Aliphatic chlorinated hydrocarbons ([chlorinated paraffins](/source/chlorinated_paraffins)) are cheap and efficient, however they persist in environment and have strong tendency for [bioaccumulation](/source/bioaccumulation). Therefore, they are being replaced with alternatives. In [cutting fluid](/source/cutting_fluid)s, their role is largely confined to formulations for forming complex [stainless steel](/source/stainless_steel) parts. [https://web.archive.org/web/20041224170755/http://umweltbundesamt.de/umweltvertraegliche-stoffe-e/pressure.htm] The activity of halogenated hydrocarbons increases with decreasing stability of the [carbon-halogen bond](/source/haloalkane). At local contact temperatures ranging between 305-330 °C, the additive thermally decomposes and the reactive halogen atoms form a surface layer of iron halides on the part surface. Eventual failure of the contact point comes when the contact temperature exceeds the melting point of the iron halide layer. Under such conditions, small particles of [carbon](/source/carbon) are generated as well. Some compounds used in lubricant additives are chloroalkanes, trichloromethyl phosphine acids, organic esters of a-acetoxy-b,b,b-trichloroethyl phosphonic acid, trichloromethyl esters of [phosphoric acid](/source/phosphoric_acid), trichloromethyl derivates of sulfur, trichloroacetoxy compounds, esters or amine salts of [chlorendic acid](/source/chlorendic_acid), 1,2,3,4,7,7-hexachloro-5-dimethylbicyclo[2.2.1]-2-heptene, etc. Oil-soluble [organophosphate](/source/organophosphate)s, with or without zinc, have excellent high-pressure and antiwear properties, and provide [corrosion](/source/corrosion) protection especially in presence of chlorinated hydrocarbons. [Zinc dialkyldithiophosphate](/source/Zinc_dialkyldithiophosphate)s (ZDDP) start decomposing at 130-170 °C, while the activation temperature of [tricresyl phosphate](/source/tricresyl_phosphate) (TCP) typically exceeds 200 °C. Their reaction products form a chemically bonded lubricating film on the surfaces. [Polysulfide](/source/Polysulfide)s serve as carriers of inactive and active [sulfur](/source/sulfur).{{Cite journal |last=Liu |first=Zulong |last2=Liu |first2=Sheng |last3=Chen |first3=Jun |last4=Ren |first4=Xuemei |last5=Zhang |first5=Chi |last6=Jiao |first6=Yu |last7=Liu |first7=Shuchen |last8=Zhu |first8=Xiaodong |last9=Yan |first9=Yichao |last10=Lei |first10=Tianyu |last11=Chen |first11=Dongjiang |last12=Hu |first12=Yin |last13=Chen |first13=Wei |title=Dynamic Reconstruction of Polysulfides to Elemental Sulfur Enabling High-Performance Ah-Level Lithium-Sulfur Pouch Cells |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202525861 |journal=Advanced Functional Materials |language=en |volume=n/a |issue=n/a |article-number=e25861 |doi=10.1002/adfm.202525861 |issn=1616-3028}} [Molybdenum](/source/Molybdenum) compounds decompose under high pressure to form an in-situ deposited layer of [molybdenum disulfide](/source/molybdenum_disulfide). Molybdenum [dithiocarbamate](/source/dithiocarbamate)s are used as additives for [grease](/source/Petroleum)s. Sulfur containing extreme pressure additives can cause [corrosion](/source/corrosion) problems in gears with parts made of [bronze](/source/bronze), [brass](/source/brass) and other [copper alloy](/source/copper_alloy) when high temperature environments are encountered. ==References== ==See also== * [Metalworking](/source/Metalworking) Category:Oil additives --- Adapted from the Wikipedia article [Extreme pressure additive](https://en.wikipedia.org/wiki/Extreme_pressure_additive) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Extreme_pressure_additive?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.