Engine oil is often treated with friction modifier (FM) additives which adsorb to metal surfaces and, in a sliding contact, form low friction boundary layers. A trinuclear molybdenum compound called Moly Trimer (MT), with structure Mo3S7 organodithiocarbamate, is widely used as a FM because it breaks down during surface rubbing, in a mechanochemical reaction process, to form low friction layers of MoS2. We show using Quartz Crystal Microbalance (QCM) measurements that MT is a highly surface active material with a relatively strong free energy of adsorption. Surface analysis techniques reveal that it undergoes a surface catalyzed decomposition after the rapid adsorption process. It eventually reduces under rubbing to a mostly continuous layer of MoS2 inside the lubricated contact. Under the conditions studied, about 70 percent of the wear track area is covered with MoS2 of varying thickness.

Chemistry of trinuclear molybdenum compounds and impact on friction

255th National Meeting (2018)

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