Ionic Liquids as Alternative Lubricants for Special Applications

The still relatively unknown class of substances referred to as ionic liquids (ILs) is continuously gaining in interest and importance. This attunes for research as well as for industrial applications because of their outstanding and unique physical and chemical properties, which make them very interesting for various applications. These, under ambient conditions, mainly liquid compounds also offer several options for an optimization of process machines, with a high potential of performance increase and savings in investment and operating costs (Predel et al., Chem. Eng. Technol. 2007, 30, 1475). Furthermore, they offer the chance of conquering new areas in process technology like the lubricated compression of oxygen (Predel et al., Proceedings of the International Rotating Equipment Conference, 2008). For their commercial implementation in these fields, ILs have to fulfill a number of requirements, which have to be defined in detail for every specific application. ILs are also called designer substances, due to their tailor-made character with strongly differing properties depending on the ion structure. This attribute offers a great pool of possible candidates for any special application. A screening of the relevant parameters for lubrication applications, such as thermal stability, corrosiveness, wettability and tribological behavior, was carried out in several adequate experimental setups. The results are presented and an evaluation of the most promising candidates for lubrication applications was carried out. Furthermore, first results in the specific application of ILs as lubricants in a combustion engine are presented and an outlook for this specific topic will be given.