Overview of ZDDP (Zinc Dialkyl Dithiophosphate) on Temperature Adaptability, Type Differences, Thermal Degradation Mechanism, and High-Temperature Performance

ZDDP, due to its unique chemical structure, can remain stable at higher temperatures, which is crucial for engine oils operating at high temperatures.

 

Temperature Adaptability of ZDDP:

ZDDP, due to its unique chemical structure, can remain stable at higher temperatures, which is crucial for engine oils operating at high temperatures. The thermal degradation temperature of ZDDP mainly occurs between 130-230 ℃, and it is generally believed that the rate of thermal degradation accelerates beyond 150 ℃, which coincides with the upper limit temperature that engine oils can come into contact with.

 

Type Differences of ZDDP:

The type differences of ZDDP mainly stem from the variations in its alkyl part, which are typically introduced by different alcohols. The differences in the raw alcohols used for various ZDDPs determine their distinct characteristics. For example, the ZDDP in diesel engine oil and gasoline engine oil differ because their oil requirements are different.

 

Thermal Degradation Mechanism of ZDDP:

The thermal degradation of ZDDP is an autocatalytic process, mainly divided into three steps:

1. Oxygen-sulfur exchange, where ZDDP, upon heating, has S replaced by O.

2. Nucleophilic cyclic reaction, resulting in the formation of -SR (alkylthio), which continues to attack P, producing phosphates and R2S.

3. In the presence of metal contact surfaces, a thermal film of ZDDP is formed.

The thermal degradation products mainly include solid precipitates of zinc phosphate, alkyl sulfides, thiols, olefins, and H2S, among which some volatile substances are known as ZDDP thermal volatiles.

 

Performance of ZDDP:

Thermal stability: Arylalkyl > Long-chain n-alkyl > Short-chain n-alkyl > Isoalkyl.

Anti-wear properties: Isoalkyl > Short-chain n-alkyl > Long-chain n-alkyl > Arylalkyl.

Hydrolytic stability: Arylalkyl > Alkyl > Isoalkyl.

Oxidation resistance: Isoalkyl > Alkyl > Arylalkyl.

The longer the alkyl carbon chain, the better the solubility of ZDDP, and the coefficient of friction will decrease.

Application of ZDDP:

In actual lubricating oil products, to balance performance, different types of ZDDP are often used in combination to achieve a balance between cost and performance. 

The interaction between ZDDP (zinc dialkyldithiophosphate) and MoDTC (molybdenum dithiocarbamate) and its impact on tribological properties also demonstrates the performance differences of ZDDP. The presence of MoDTC can enhance the friction-reducing ability of ZDDP. This synergistic effect may stem from the rough film formed by ZDDP, which provides areas of enhanced pressure and shear stress, allowing MoDTC to react on what would otherwise be a smooth surface.