Noriyoshi Tanaka

MoS2 Production Mechanism of MoDTC

Automotive industries have strong interest in fuel economy. To enhance fuel economy, engine oils need to employ effective friction modifiers (FM). Molybdenum dithiocarbamate (MoDTC) is one of FM and superior in friction reduction performance to other FM especially in boundary lubrication regime. It is said that MoDTC produces MoS2 layer on the rubbing surface to reduce friction, and ZDDP has a synergistic effect with MoDTC to produce MoS2 layer effectively. In this paper, we analyzed the rubbing surfaces by several methods after rubbing with SRV tester to clarify the production mechanism of MoS2 layer. Results by EPMA showed that the combination of MoDTC and ZDDP decreased molybdenum intensity and increased sulfur intensity on lubricating surface compared to MoDTC alone. Results by XPS showed that MoDTC produced both of MoS2 and MoO3 layers while the combination of MoDTC and ZDDP produced only MoS2 layer selectively. Although ZDDP is an important sulfur supplier to MoDTC, at the same time ZDDP and MoDTC are under competing adsorption. We confirmed that a sulfur supplier to MoDTC played a very important role for producing MoS2 layer.