Zinc Dialkyldithiophosphate (ZDTP)
Definition
The primary anti-wear additive in motor oils, contributing zinc, phosphorus, and sulphur to the additive package. The Zn/P ratio and S/P ratio are measurable by ICP-OES and are brand-distinctive features used in lubricant forensic comparison.
- Function
- Primary anti-wear additive in motor oils
- Elements contributed
- Zinc, phosphorus, sulphur
- Measured by
- ICP-OES
- Forensic use
- Zn/P and S/P ratios distinguish oil brands
Common questions
Why are Zn/P and S/P ratios more useful for brand comparison than raw element concentrations?+
Ratios cancel out dilution and volume effects that would otherwise make raw concentration values vary between samples of the same product, isolating the relative additive formulation that differs consistently between brands rather than between individual bottles or sampling conditions.
Does engine use change the ZDTP-derived ratios over time?+
Yes, ZDTP is consumed as it performs its anti-wear function during operation, and metal wear particles enter the oil, so a used oil sample's Zn/P and S/P ratios can drift from the fresh-oil formulation, meaning comparisons work best when fresh reference oil or a degradation correction is available.
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