Zinc dialkyl dithio phosphate
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Zinc dialkyl dithio phosphate (ZDDP, ZnDTP, or ZDP) is a family of zinc salts of dithio organophosphates. They are soluble in nonpolar solvents, so they easily dissolve in mineral and synthetic oils used as lubricants. They come under CAS number []. In aftermarket oil additives, the percentage of ZDDP ranges approximately between 2-15%.
The alkyl groups can be branched and linear alkanes between 1-14 carbons length, 2-butyl, pentyl, hexyl, 1,3-dimethylbutyl, heptyl, octyl, isooctyl (2-ethylhexyl), 6-methylheptyl, 1-methylpropyl, dodecylphenyl, and others.
A mix of zinc dialkyl(C3-C6)dithiophosphates come under CAS number []. List of other examples with their CAS numbers is here.
The main use of ZDDP is in anti-wear additives to lubricants (eg. greases, motor oils). To date it is the dominant anti-wear agent, present in most machine and motor oils in amount of about 1%. However for motor oil applications the amount of ZDDP has to be minimized, as the zinc and phosphorus emissions damage catalytic converters, .
ZDDP also has anticorrosive and antioxidant properties.
ZDDP is usually manufactured with dialkyldithiophosphates as intermediates, by a reaction of phosphorus pentasulfide with suitable alcohols. These intermediates are then neutralized by adding zinc oxide, yielding ZDDP.
ZDDP is a known eye irritant, capable of causing severe harm. Protective goggles are recommended when working with mixtures containing high concentration of ZDDP.
One of the zinc-free alternatives lies in using silver-based additives. [1]
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