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 [68649-42-3][link]. 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 [84605-29-8][link]. 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, .
The mechanism of function of ZDDP lies in chemical reaction with the surface of the metal gears under high pressure and temperature. Pressure concentrates on small unevennesses on the surfaces in contact; pressure and temperature at these points sharply rises. At such conditions, ZDDP decomposes and forms a layer of iron phosphate or iron sulfate, effectively chemically polishing the surfaces. The zinc polyphosphates and polythiophosphates also form a thin layer of glass that becomes fluid at 230 °C, further lubricating the surfaces. If higher local temperatures are desired, molybdenum compounds are used. [link]
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. [link]
External links
- For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].
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