Zinc dialkyldithiophosphates (often referred to as ZDDP) are a family of coordination compounds developed in the 1940s 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 synthetic oils used as lubricants.
Applications of Zinc Dithiophosphate ZDDP:
The main use of ZDDP is in anti-wear additives to lubricants such as greases, gear oils, and motor oils, which often contain less than 1% of this additive. It has been reported that zinc and phosphorus emissions may damage catalytic converters and standard formulations of lubricating oils for gasoline engines now have reduced amounts of the additive, though diesel engine oils remain at higher levels. Crankcase oils with reduced ZDDP have been cited as causing damage to, or failure of, classic/collector car flat tappet camshafts and lifters which undergo very high boundary layer pressures and/or shear forces at their contact faces, and in other regions such as big-end/main bearings, and piston rings and pins. Roller camshafts are more commonly used to reduce camshaft lobe friction in modern engines. There are additives, such as STP(R) Oil Treatment, and some racing oils such as PurOl, Brad Penn and Valvoline VR-1, which are available in the retail market with the necessary amount of ZDDP for engines using increased valve spring pressures. The same ZDDP compounds serve also as corrosion inhibitors and antioxidants.