Definition
Anti-wear (AW) additives form a protective film on metal surfaces to reduce wear under boundary lubrication conditions — the regime where the lubricant film is thin enough that asperities on opposing surfaces come into contact.
The most widely used anti-wear additive is ZDDP, which forms a glassy phosphate film on ferrous surfaces. Other classes include:
- Amine phosphates — used in hydraulic and gear oils where zinc content must be minimized
- Tricresyl phosphate (TCP) — aviation turbine oils and some industrial applications
- Sulfurized fatty esters — used in metalworking and gear applications
Anti-wear additives are distinct from Extreme Pressure (EP) additives, which activate at higher contact temperatures and pressures characteristic of gear tooth contact.