ZDDP (Zinc Dialkyl Dithiophosphate), whose full Chinese name is zinc dialkyl dithiophosphate. It achieves multiple functions such as anti-oxidation, anti-corrosion, extreme pressure and anti-wear by decomposing in lubricating oil, forming a protective film on the metal surface, and neutralizing acidic substances and destructive oxides.

According to the industry standard SH 0394-1996, ZDDP is classified into different grades based on their performance, among which T202 and T203 are the two most representative ones. The core difference between them lies in the structure of the alkyl chain, which directly affects their thermal stability and application scenarios:

T202: Synthesized from short-chain primary alcohols. Its alkyl chain is relatively short, so its thermal stability is slightly lower, but it can form a protective film on the metal surface more quickly. It is more suitable for gasoline engine oil and some medium and low load working conditions.

T203: Synthesized from long-chain primary alcohols. Its alkyl chain is longer, which brings higher thermal stability and hydrolytic stability, enabling it to handle more demanding working environments. Therefore, it is particularly suitable for heavy-duty diesel engine oil, anti-wear hydraulic oil and medium-speed Marine oil.

In addition to T202 and T203, the ZDDP family also has other members to meet more specific requirements, such as T205A/T215. They usually have higher base numbers and better overall performance. However, the available public information about them is rather limited.

Main functions and application fields
As a multi-functional additive, the core functions of ZDDP are mainly reflected in the following aspects:

Antioxidant and anti-corrosion: ZDDP can eliminate free radicals produced by lubricating oil under high temperature and high pressure, interrupt the oxidation chain reaction of the oil, thereby delaying the process of lubricating oil deterioration and viscosity increase. At the same time, it can protect the metal surface from corrosion by acidic substances.

Extreme pressure anti-wear: Under boundary lubrication conditions (when the oil film is insufficient to completely separate the metal surface), ZDDP will decompose on the metal surface, forming a strong sacrificial protective film. This film prevents direct contact and wear between metals and is crucial for high-load engine components and gears.

Based on these outstanding functions, the ZDDP series of additives are widely used in:

Engine oil: Whether it is gasoline engine oil or diesel engine oil, they are the main application fields of ZDDP.

Industrial lubricating oils: such as anti-wear hydraulic oil, gear oil, etc.

Marine oil: especially medium-speed Marine engine oil.

Instructions for Use and Limitations
Although ZDDP has excellent performance, the following points should also be noted when using it:

Recommended addition amount: Usually 0.5% - 3.0%, depending on the oil formula and performance requirements.

Potential limitations

Corrosion of copper components: Lubricating oil with a high ZDDP content may cause corrosion to yellow metal components such as copper and bronze. Therefore, in systems containing such materials, it is necessary to carefully select or use zinc-free alternatives.

Environmental protection issue: ZDDP is not easily biodegradable and is toxic to aquatic organisms, which is a drawback from an environmental perspective.

Compatibility with exhaust gas after-treatment systems: Some modern high-performance engine exhaust gas after-treatment systems (such as catalytic converters) may be sensitive to phosphorus, and excessive phosphorus from the decomposition of ZDDP may cause catalyst poisoning. Therefore, the dosage needs to be controlled or low-phosphorus/phosphorus-free alternatives should be used.