Zinc Secondary Dialkyl Dithiophosphate (ZDDP or ZnDTP) is one of the most important and widely used additives in engine oils, hydraulic fluids, and industrial lubricants. It serves as a multifunctional additive with excellent anti-wear, antioxidant, and corrosion inhibition properties.
🧪 Chemical Structure & Type
- ZDDP is a zinc salt of dialkyl dithiophosphoric acid.
- The “secondary” designation refers to the type of alkyl group attached — secondary alkyl groups (e.g., isopropyl, sec-butyl) generally provide better thermal stability and anti-wear performance than primary alkyls.
🔧 Main Functions of Zinc Secondary Dithiophosphate
| Function | Mechanism |
|---|---|
| Anti-wear | Forms a protective tribochemical phosphate glass film on metal surfaces under heat/pressure |
| Antioxidant | Scavenges free radicals and hydroperoxides, slowing base oil degradation |
| Corrosion inhibitor | Protects ferrous and non-ferrous metal parts from rust and oxidation |
🔍 Why “Secondary” ZDDP Is Often Preferred
| Secondary ZDDP | Primary ZDDP |
|---|---|
| Better wear protection | Lower wear protection |
| Slightly more oxidation stability | Slightly less stable |
| More thermally active (activates sooner) | Activates at higher temperatures |
✅ Secondary ZDDP is more commonly used in high-performance and modern formulations.
⚙️ Typical Applications
- Passenger car motor oils (PCMO)
- Heavy-duty diesel oils (HDMO)
- Hydraulic fluids
- Greases
- Industrial gear oils
🧪 Treat Rates and Levels
| Application | Typical ZDDP Content |
|---|---|
| Older API SJ/SL/SM oils | 1000–1400 ppm phosphorus |
| Modern API SN/SP oils | ~800 ppm phosphorus (max) |
| Racing/off-road oils | Up to 2000 ppm phosphorus |
⚠️ Modern oils have reduced ZDDP content to protect catalytic converters and emission systems, particularly in gasoline engines.
✅ Advantages
- Proven, reliable anti-wear performance
- Good oxidative stability for long oil life
- Cost-effective multifunctional additive
- Synergistic with other additives (e.g., detergents, MoDTP)
❌ Limitations
- High phosphorus content can poison catalytic converters
- Not suitable for low-SAPS (sulfated ash, phosphorus, sulfur) oils used in diesel engines with DPFs
- Environmental concerns in used oil disposal due to zinc and phosphorus
Zinc secondary dialkyl dithiophosphate (ZDDP) are organic compounds used as a corrosion inhibitor and anti-wear additive in lubricants. The most commonly used ZDDP is zinc dialkyldithiophosphate, typically made of a mixture of dialkyldithiophosphates and zinc salts. It contains a zinc atom bound to two sulfur atoms and two phosphorous atoms. It is used in engine oils, gear oils, and hydraulic oils to limit wear and tear on engine components and reduce friction. Other additives such as detergents, dispersants, and antioxidants are often added to enhance its properties. It is typically used in concentrations of 1-2%.
Zinc Secondary Dialkyl Dithiophosphate (ZDDP), a kind of antioxidant and anti-corrosion agent. This product features excellent anti-oxidation and anti-wear performance, which can effectively solve the problem of engine cam and tappet’s abrasion and corrosion. It can be widely applied to various oils, especially for high grade gasoline engine oil.
Zinc Secondary Dialkyl Dithiophosphate is a type of additive commonly used in engine oils and lubricants. It is part of a class of compounds called ZDDP (Zinc Dialkyl Dithiophosphate).
ZDDP additives provide several important benefits to engine oils:
- Wear Protection: ZDDP acts as an anti-wear agent, forming a protective film on metal surfaces to reduce friction and wear. This is particularly important in high-stress areas such as the engine camshaft and valve train.
- Anti-Oxidation and Thermal Stability: ZDDP helps to prevent oil degradation and maintain the oil’s viscosity at high temperatures. This reduces the formation of sludge and deposits, ensuring the oil remains effective in lubricating and protecting engine components.
- Anti-Corrosion Properties: ZDDP additives help to protect engine parts against corrosion and rust, particularly during periods of engine inactivity or storage.
- Compatibility with Older Engines: ZDDP additives were originally developed for use in older engines with flat-tappet camshafts. These engines require a high level of anti-wear protection, which ZDDP additives provide. However, modern engines with roller camshafts typically require lower levels of ZDDP due to different camshaft designs.
While ZDDP additives provide many benefits to engine oils, it’s important to note that their usage has declined in recent years. This is because ZDDP can interfere with the effectiveness of some emission control systems, particularly catalytic converters. Therefore, in order to meet stricter emission standards, newer engine oils often contain reduced levels of ZDDP or alternative anti-wear additives.
Zinc Secondary Dialkyl Dithiophosphate is an additive commonly used in engine oils for its anti-wear, anti-oxidation, thermal stability, and anti-corrosion properties. However, its use has decreased over time due to compatibility issues with certain emission control systems.
Zinc Secondary Dialkyl Dithiophosphate (ZDDP) is a foundational anti-wear and antioxidant additive used in lubricants to:
- Protect engine components under high pressure and temperature
- Extend oil life
- Resist rust and corrosion
It remains critical for internal combustion engines, especially in older vehicles, performance engines, and certain industrial applications.