molybdenum additive is a special anti-wear, friction modifier that is commonly added to mineral and semi synthetic motor oil. This adds a layer of protection on the metal parts of your engine and helps eliminate those "tickling" sounds that come from underneath the hood - they are caused by metal-on-metal contact.

The Molybdenum atoms in this additive are sandwiched between layers of sulfur atoms and act as a lubricant that prevents metal surfaces from sliding together. As a result, this additive has some synergistic effects with other anti-wear additives, like zinc dialkyl dithiophosphate (ZDDP).

Friction Modifier Formulations

The friction modifying ability of MoDTC is influenced by the exchange between the molybdenum dithiocarbamate portion and the zinc dithiophosphate in ZDDP. This combination creates a complex molybdenum disulfide (MoS2) tribofilm on the metal surface.

Frictional performance of MoDTC is reduced in aged oils because of oxidative decomposition and hydrolytic instability. Casey used experimental blends of molybdenum esters and organic friction modifiers to increase the effectiveness of MoDTC in fresh oils.

In the study of Casey's work, she analyzed the oxidative stability and hydrolytic stability of a blend of molybdenum esters and molybdenum disulfide molecules. She found that the organic molybdenum esters could scavenge sulfur added to PCMOs from sources like ZDDP to form low-friction MoS2 films on the metal surfaces.

When tested in boundary lubrication conditions, molybdenum disulfide can significantly reduce frictional forces between metals by creating a tribofilm on each metal. However, when the frictional force is greater than that of the tribofilm, the MoS2 can decompose, releasing a layer of molybdenum dithiocarbamate and leaving an amorphous molybdenum disulfide coating on the metal.