Thermo-oxidative stability of ionic liquids was evaluated by three bulk-scale tests. The changes in chemical and physical properties such as viscosity, deposit formation, weight loss and TAN were obtained. The results are discussed in terms of chemical structure of ionic liquids. TFSI derivatives exhibit good thermo-oxidative stability in comparison with BF4 derivatives. As chain length of alkyl group in imidazolium-cationic moiety increases, the thermo-oxidative stability of the molecule decreases. Water contaminant promotes the thermo-oxidative degradation of ionic liquids. Reaction mechanism via radical intermediates is proposed herein.
Lubricant additive technology to improve lubricant performances is an important issue for ionic liquids to be applied practically. Effects of carboxylic acids with different carbon chain length in ionic liquid on tribological properties were examined. Solubility of carboxylic acids was dependent on the chain length of carboxylic acids and imidazolium cations. The carboxylic acids reduced friction and wear in comparison with additive free one. It was found that friction reducing properties of carboxylic acid depended on their chain length. Interestingly, additive response of ionic liquids was found to be superior to those for conventional ester oil as base oil. Surface images obtained by an optical microscope clearly show that the additive depressed chemical wear by ionic liquids especially at low load. Surface analysis with EPMA supported films of carboxylic acids as a cause of improvement of friction property. Therefore, the mechanism of carboxylic acids was considered to provide adsorbed film which accompanied with low friction and anti-wear properties.
The most important role of a hydraulic fluid is transmission of power among various roles. A bulk modulus of the fluid is crucial for hydraulic systems, particularly for high-pressure hydraulics. In theory, compression energy losses are in diverse proportional to the effective bulk modulus of the fluid, and response speed and stability depend directly on the square root of it. Conventional mineral oils have pretty low bulk modulus, compared to water-based hydraulic fluid. On the other hand, the water-based fluids are disadvantageous in lubricity and evaporation. Under the circumstances, we've searched for available oily high bulk modulus fluid, and found organic compounds with water-level bulk modulus.
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