Ionic Liquids as Alternative Lubricants for Special Applications

Abstract

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. IntroductionThe development of ionic liquids (ILs) reaches back to the beginning of the 20 th century when the first species were designed, which are liquid at ambient conditions. These compounds, which are also called room-temperature molten salts, had their first main application in electrochemisty [1][2][3]. In the beginning of the 1980s, the groups around Seddon and Hussey began to use these liquids as non-aqueous, polar solvents for the examination of transition metal catalysis [4,5]. These works were the first efforts in order to establish ILs in research.Since the 1990s, ILs are now gaining more and more in interest as well as in importance due to their outstanding unique physical and chemical properties, which offer extremely promising employments in several areas of chemical engineering. Some industrial processes such as the BASIL process [6] and the hydrosilation process [7] show that ILs are no longer a curiosity in chemical laboratories but on the way to become a common good in the chemical industry. In addition, there are also several possible applications in process technology, such as the compression of oxidative gases, hydraulic load transmission, vacuum technology, lubricating applications, and as a versatile "green" engineering liquid [8][9][10][11]. ExperimentalFor the parameter screening, several experimental setups...

Self-lubricating, wear resistant protic ionic liquid-epoxy resin

“…Room-temperature ionic liquids (ILs) [11,12] contain bulk organic cations and organic or inorganic anions and show a unique combination of properties such as their low volatility, non-flammability, and their high thermal stability which are most relevant for tribological applications. ILs have shown excellent tribological performance, not only in lubrication of metal alloys and ceramic materials under severe sliding conditions [13][14][15][16][17][18][19][20][21][22][23][24][25], but also in the very difficult task of achieving the reduction of friction coefficients and wear rates of thermoplastic polymers and epoxy resins, where they have been used both as external lubricants and as additives [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. Ionic liquids are also making an increasing impact in the field of polymer science, in particular on the development of new epoxy networks and composite materials by acting as curing agents, plasticizers, and as dispersants of nanophases in the epoxy matrix [35][36][37][38][39].…”

Lubricity Improvement of Imidazolium Cation-based Ionic Liquids Treated with Carbon Dioxide

“…Ionic liquids are attracting attention as novel lubricants because they have the main characteristics required of a lubricant, such as flame retardancy, thermal stability, and extremely low vapor pressure 1), 2) . Additives improve the anti-wear ability of hydrocarbon-based lubricants by the formation of a boundary film which was produced by the reaction between the additive and the frictional surface.…”

Assessing Boundary Film Forming Behavior of Phosphonium Ionic Liquids as Engine Lubricant Additives

“…Since 2001, many studies have reported on the tribological properties of ionic liquids (ILs) as an additive in mineral and/or synthetic base oils [3,[6][7][8][9][10], and others on their use as engine lubricants [3,4,7,11,12]. ILs have some key inherent properties that make them suitable for an engine environment, such as high thermal stability, very low volatility, non-flammability, detergency in being a solvent, they are non-corrosive, have good wettability, and excellent tribological performances [3,7].…”