Tribological Behaviour of Rare-Earth Lubricating Oils

Abstract

Exhaust gas recirculation (EGR) is being used widely to reduce and control the NOx emissions from internal combustion engines. However, the use of EGR leads to rise in soot emission and contamination of lubricating oil. Soot-contaminated lubricating oil has been shown to accelerate engine wear. At the same time, zinc dialkyldithiophosphate (ZDDP) which is widely used in lubricating oil as highly active extreme pressure and anti-wear additive may harmfully affect the internal combustion engine and its exhaust gas purifying installation. It is an important for the engine lubricating oil to look for new type lubricating oil additives without or low phosphorus. Rare-earth is the general name of 17 elements, including scandium, yttrium and lanthanide series. It is potential for the rare-earth compounds as new type and efficient lubricating oil additives because most of rare-earth compounds have hexagonal crystal layer structure. Current research results showed that the application prospects of some rare-earth compounds in the tribology field were extremely vast, such as oil, grease, water and coating lubrication systems etc. This chapter will mainly focus on the recent developments on the tribological behaviour of lubricating oils containing rare-earth elements, including the preparation and lubricating mechanism of rare-earth nanoparticles, surface modification for the rare-earth inorganic compound, rare-earth additives with potential application, synergistic effect of the rare-earth compounds and other additives, and the research tendency on the rare-earth lubricating additives, especially the influence of rare-earth elements on the tribological performance of carbon films and its friction-reduced catalyst function etc. which will be helpful to understand and develop the lubrication role of the rare-earth elements as additives in the lubricating oils.