Abstract
In this study, the tribological behavior of an ammonium-based protic ionic liquid (PIL) as an additive in a base mineral oil (MO) is investigated on a steel-steel contact at room temperature and 100 °C. Tri-[bis(2-hydroxyethylammonium)] citrate (DCi) was synthesized in a simple and low-cost way, and the ionic structure of DCi was confirmed by proton nuclear magnetic resonance (1H NMR). The stability measurement of 1 wt% DCi to a MO was investigated, and the lubricating ability and anti-wear properties of DCi as an additive in MO were also examined using a custom-designed reciprocating ball-on-flat tribometer. Optical microscope and profilometry were used to obtain the worn morphology of the steel disks. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were carried out to investigate the wear mechanism and to analyze the surface interactions between the rubbing components. When 1 wt% DCi is added into the base MO, frictional performance is improved at both temperatures studied with a friction reduction of 29.0% and 35.5%, respectively. Moreover, the addition of 1 wt% DCi to MO reduced the wear volume 59.4% compared to the use of MO. An oxygen-richened tribolayer is confirmed by EDS on the disk surface when DCi was used as additive under 100 °C.
Highlights
It is estimated that the energy consumption from tribological contacts accounts for 23% which is around 119 EJ of the world’s total energy consumption [1]
When 1 wt% DCi is added into mineral oil (MO), lower friction coefficient at both temperatures are observed compared to MO, with friction reductions of 29.0% at room temperature, and 35.5% at 100 °C
In addition to these promising friction results, 1 wt% DCi+MO exhibits an excellent anti-wear performance at 100 °C where the wear reduction reaches up to 59.4% compared to MO
Summary
It is estimated that the energy consumption from tribological contacts accounts for 23% which is around 119 EJ of the world’s total energy consumption [1]. In order to reduce the energy losses and increase the energy efficiency of mechanical systems, one approach is to add additives, such as friction modifier additives or anti-wear additives, to the lubricant to obtain improved tribological performance [2]. ILs are synthetic salts that consist of cations and anions with melting point below 100 °C or even lower. The most commonly used cations of ILs are ammonium [4, 5], imidazolium [6], pyridinium [7], or phosphonium [8, 9], where the anions could be either organic or inorganic [10]. Oil-miscible ILs are explored and reported with promising anti-wear properties in early 2012 [13, 14], and since ILs used as lubricant additives have become a new topic
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