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- Reddy, Akepati Bhaskar, Dr. 1990-, et al.
(författare)
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Ionic liquids enhance electrical conductivity of greases: an impedance spectroscopy study
- 2024
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Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 683
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Tidskriftsartikel (refereegranskat)abstract
- Ionic liquids (ILs) have emerged as viable solutions for developing new-age lubricants, both as neat lubricants and lubricant additives. Enabled by the presence of discrete ions, ILs have the possibility to render electrically conductive lubricants, which is a feasible strategy for developing lubricant systems compatible with modern e-drive conditions. However, this requires the characterization of the electrical properties of lubricants, which is a bottleneck for developing electrically conductive greases, given their complex architecture. This work introduces an electrochemical impedance spectroscopy measurement methodology to evaluate grease samples' electrical properties. Compared to the commonly used conductivity meters, this method, through its multi-frequency alternating current (AC) impedance approach, can effectively distinguish the individual contributions of the bulk and the sample-electrode interface to the measured electrical response. Impedance spectra of grease samples are obtained using an electrochemical cell with parallel plate electrodes, mounted on a temperature-controlled cell stand and coupled with a potentiostat. The grease's bulk conductivity is extracted by fitting the impedance data to relevant equivalent electrical circuits. The bulk conductivity of lithium complex grease doped with ILs is evaluated and compared to greases with conventional conductivity additives (copper powder and conductive carbon black). The analysis of temperature-dependent conductivity reveals the rather different conductivity mechanisms for different additives. For greases doped with ILs, a comparison against the electrical conductivity of neat ILs reveals that, in addition to the ion dissociation, the interaction of the ions with the different grease components (base oil, thickener) is crucial in defining the grease conductivity.
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- Reddy, Akepati Bhaskar, 1990-, et al.
(författare)
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On electric conductivity of greases
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The development of new lubricant systems compatible with modern e-drive conditions, including stray voltages and currents, has gained momentum in recent years. One of the strategies being widely evaluated to achieve these goals is the development of conductive lubricants. Greases, however, have a complex architecture that renders measurement and analysis of their electrical properties challenging; this has severely limited the implementation of the strategy for this class of materials. In this work, a measurement methodology implementing electrochemical impedance spectroscopy to evaluate the electrical properties of grease samples is introduced. Compared to the commonly used conductivity meters, this method, through its multi-frequency alternating current (AC) impedance measurement approach, is able to effectively distinguish the separate contributions of the bulk and the sample-electrode interface to the measured electrical response. Thus, the bulk conductivity of a range of greases with different electrical properties could be obtained independently of their interfacial behavior at the electrode. The temperature-dependent bulk conductivity of lithium complex grease doped with different ionic liquids and non-ionic solids (copper and carbon black powders) has accordingly been evaluated and the rather different conductivity mechanisms explained. Bulk ionic conductivity of neat ionic liquids has also been measured using a liquid sample-specific electrochemical cell, which aids in the interpretation of the ionic liquid based greases.
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- Reddy, Akepati Bhaskar, 1990-
(författare)
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Sustainable Lubrication and Tribotronics enabled by Ionic Materials
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Developments in machine design play a crucial role in the global endeavor towards sustainability. The potential for energy conservation and emission reduction has pushed lubrication research to the forefront, with the lubricant considered to be a vital machine component. As a result of the need for high machine efficiency and longevity, as well as that of greener lubricants, ionic liquids (ILs) are gaining attention for lubrication applications, especially in combination with biodegradable oils. ILs also present a unique opportunity for developing active lubrication, tribotronic systems. To make them an industrially viable option, however, an in-depth understanding of IL lubrication behavior is required. In this doctoral work, investigations of the tribologically relevant ionic boundary films formed by non-halogenated ILs dispersed in a carrier medium (polar solvent or bio-oil) were conducted using a variety of tribological techniques and neutron reflectance. The effect of external actuation by electric potential on the extent, ionic composition, and tribological relevance of the interfacial boundary films was also studied. The results revealed that the ionic architecture and the condition of IL in the oil play an important role in defining the lubricity of the adsorbed boundary films. Clear electroresponsivity was also observed across methods, with the relative concentration of cations and anions in the interfacial film and the lubricating film thickness changing with the electric potential bias. It was established that the anions, playing an anchor role on the surface, are crucial for the formation of robust load-carrying boundary films. A methodology using electrochemical impedance spectroscopy was developed for measuring and characterizing the electric conductivity of complex lubricating greases with ionic and non-ionic additives. According to these measurements, the electrical characteristics of greases depend on the interactions of IL with the grease matrix. Overall, this work contributes towards the development of sustainable lubrication and tribotronic systems using ILs.
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