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The Effect of ZDDP and MoDTC Additives on the Friction Performance of DLC Coatings and Steel Cam Followers in Engine Oil – The Unique Role and Effect of MODTC Additives

Conduct friction tests using a pin plate test bench to simulate the sliding conditions of the cam follower. In the case of SAE5W-30 engine oil, the friction coefficient of steel pins sliding on steel discs increases from 0.11 to 0.12, while the friction coefficient of steel pins sliding on diamond-like carbon (DLC) coated discs decreases from 0.12 to 0.10. For 5W-20 oil containing friction improver MoDTC (dithiocarbamate phase), the friction coefficient of the steel pin sliding on the steel plate decreased significantly from 0.12 to 0.04. In contrast, the decrease in sliding of steel pins on DLC-coated discs is relatively small, from 0.11 to 0.08. In both situations, Zn, P, S, and Mo elements from ZDDP (Zinc dialkyl dithiophosphate) and MoDTC additives were not detected on the DLC-coated discs. In contrast, electron probe microscopy and X-ray photoelectron spectroscopy surface analysis detected these elements on the steel discs and pins.

Due to the inactive chemical properties of DLC materials, no frictional chemical reaction film has been formed on the DLC material. Therefore, in the case of steel pins sliding on DLC-coated discs, the increased friction caused by the formation of ZDDP-derived films and the decreased friction caused by the formation of MoDTC-derived films were significantly suppressed. It is believed that the frictional chemical reaction film helps to reduce friction significantly. Then, the lateral force of the thin film formed on the steel plate was measured using an atomic force microscope and a transverse force microscope. The lateral force of the film formed by 5W-30 oil is much higher than that formed by 5W-20 oil and MoDTC. This result is very consistent with the friction test results. From these results, it can be seen that the friction coefficient of the steel pin on the steel plate of 5W-30 oil is higher due to the high shear strength of the film formed by ZDDP. On the other hand, the very low friction coefficient survey in the steel pin disc combination of 5W-20 oil may be due to the formation of solid MoS2 lubricant by the MoDTC additive.


MODTC, also known as molybdenum dialkyl dithiocarbamate, is an organic molybdenum compound. It is usually used as an additive in lubricating oil, especially in engine oil for automobiles and other mechanical equipment. The molecular structure of MODTC contains molybdenum, sulfur, and organic groups, which give it excellent anti-wear and anti-friction properties.

The characteristics of MODTC

  1. Excellent wear resistance: MODTC can form a protective film on the metal surface, significantly reducing direct contact between metals and reducing wear.
  2. High-temperature stability: In high-temperature environments, MODTC can maintain its chemical stability, effectively protecting the engine from the impact of high-temperature wear.
  3. Environmentally friendly: Unlike other additives, MODTC produces fewer harmful substances during decomposition and has a smaller environmental impact.
  4. Strong interaction with metal surface: The sulfur and molybdenum atoms in MODTC molecules can strongly interact with the metal surface, determining a stable chemical adsorption layer.

Application of MODTC

  1. Automotive engine oil: MODTC is an important additive in automotive engine oil, which can significantly improve the anti-wear performance of the engine and extend its service life.
  2. Industrial lubricating oil: In the industrial field, MODTC is also widely used in various lubricating oils, such as gear oil, hydraulic oil, etc., to improve the operating efficiency and service life of mechanical equipment.
  3. Metal working fluid: In the metal working process, MODTC can be used as an additive for cutting or grinding fluids, effectively reducing tool wear and enhancing the surface quality of the workpiece.
  4. Besides the above applications, MODTC may play an important role in transportation fields such as aerospace, ships, and railways and industrial fields such as heavy machinery and power generation equipment.


TRUNNANO is a supplier of molybdenum disulfide with over 12 years of experience in the manufacturing of chemical materials. It accepts payments through credit cards, T/T, Western Union transfers, and PayPal. Trunnano will ship the goods to overseas clients through FedEx, DHL, and air or sea freight. If you are looking for high-quality MODTC, please get in touch with us and send us an inquiry.