Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics

Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia

A methodology for Raman characterisation of MoDTC tribofilms and its application in investigating the influence of surface chemistry on friction performance of MoDTC lubricants

In this study, Raman spectroscopy has been employed to understand the influence of surface chemistry on friction in a tribocontact. Tribotests were conducted using molybdenum dialkyldithiocarbamate (MoDTC) lubricant in a steel/steel sliding contact. First, surface chemistry during the high friction regime, at the beginning of the test, and at the low friction regime, after long test durations, is investigated. Second, the influence of temperature on the surface chemistry of the resulting wear scars was investigated. The results show that at the beginning of tribotests with MoDTC lubricant, iron oxides are formed at the tribocontact which results in high friction. At longer test durations, adsorbed MoDTC on the ferrous surface decomposes to form MoS2 and low friction is observed. Surface chemistry at the tribocontact has been found to vary depending on the test temperature. At high temperatures, MoS2 is formed which provides friction reduction while at low temperatures, molybdenum oxide species and amorphous sulphur-rich molybdenum (MoSx) species are formed which do not provide friction reduction. Furthermore, it has been shown that MoS2 formed within the tribocontact at high temperatures has a slightly disordered crystal structure as a result of tribological processes