Understanding anti-wear additives
Lubricants are more than just oils—they’re complex formulations enhanced with chemical additives to perform under demanding conditions. Two essential additive types are Anti-Wear (AW) and Extreme-Pressure (EP) additives. While these terms are sometimes used interchangeably, they differ significantly in both chemistry and function. This blog post (part one of two) explores the role of AW additives and sets the stage for understanding EP agents in our next post.
What Do AW and EP Additives Do?
Both AW and EP additives are designed to protect metal surfaces in boundary and mixed lubrication regimes—conditions where metal-to-metal contact is likely due to insufficient lubricant film thickness. These additives create a protective barrier to minimize friction, wear, and ultimately extend component life.
But how they form this barrier is where things get interesting.
How Anti-Wear Additives Work?
AW additives typically consist of molecules with a polar head and an oil-soluble tail, much like a surfactant. The polar head is attracted to metal surfaces, allowing the additive to physically adsorb onto the metal and form a protective layer.
Figure 1: Polar heads of AW additives adsorb onto metal surfaces, forming a protective film.
As metal surfaces continue to rub against each other under heat and pressure, this adsorbed layer transitions to a chemisorbed film. This means it bonds chemically to the surface, creating a much stronger, more resilient coating.
Figure 2: Under higher heat, the adsorbed AW layer transforms into a chemically bonded film for added protection.
Common Anti-Wear Additives
One of the most widely used AW additives is Zinc Dialkyldithiophosphate (ZDDP). It’s found in:
- Engine oils
- Hydraulic fluids
- Transmission fluids
- Certain greases
ZDDP not only protects against wear—it also acts as an antioxidant and corrosion inhibitor. However, it starts to break down at temperatures between 130°C to 170°C, limiting its effectiveness in high-temperature applications.
For those, we turn to Tricresyl Phosphate (TCP), a phosphorus-based additive that performs well above 200°C. It’s ideal for:
- Turbine oils
- Silver component systems (where zinc is incompatible)
What About PTFE?
You may have heard of PTFE (commonly known by the brand name Teflon) being used as an aftermarket engine oil additive. While PTFE is excellent for reducing friction on frying pans, its effectiveness in engine oils is debated. Even DuPont, the company behind Teflon, has never officially endorsed PTFE for use in lubricating oil formulations.
When AW Isn’t Enough
AW additives are great up to a point—but they have limits. When the pressure and temperatures exceed their capacity, Extreme-Pressure (EP) additives step in. These compounds are specifically formulated to handle severe operating conditions and we’ll explore them in our next blog post.
Stay tuned for part two, where we’ll delve into the chemistry, functionality, and applications of EP additives.