Theoretical and Experimental Study of the Friction Behavior of Halogen-Free Ionic Liquids in Elastohydrodynamic Regime

Karthik Janardhanan,Patricia Iglesias

doi:10.3390/lubricants4020016

Karthik Janardhanan, Patricia Iglesias

Open Access

https://doi.org/10.3390/lubricants4020016

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Abstract

Ionic Liquids have emerged as effective lubricants and additives to lubricants, in the last decade. Halogen-free ionic liquids have recently been considered as more environmentally stable than their halogenated counterparts, which tend to form highly toxic and corrosive acids when exposed to moisture. Most of the studies using ionic liquids as lubricants or additives of lubricants have been done experimentally. Due to the complex nature of the lubrication mechanism of these ordered fluids, the development of a theoretical model that predicts the ionic liquid lubrication ability is currently one of the biggest challenges in tribology. In this study, a suitable and existing friction model to describe lubricating ability of ionic liquids in the elastohydrodynamic lubrication regime is identified and compared to experimental results. Two phosphonium-based, halogen-free ionic liquids are studied as additives to a Polyalphaolefin base oil in steel–steel contacts using a ball-on-flat reciprocating tribometer. Experimental conditions (speed, load and roughness) are selected to ensure that operations are carried out in the elastohydrodynamic regime. Wear volume was also calculated for tests at high speed. A good agreement was found between the model and the experimental results when [THTDP][Phos] was used as an additive to the base oil, but some divergence was noticed when [THTDP][DCN] was added, particularly at the highest speed studied. A significant decrease in the steel disks wear volume is observed when 2.5 wt. % of the two ionic liquids were added to the base lubricant.

Highlights

Almost all of the machines that we use today run on some source of energy
This paper studies the tribological effects of the addition of two halogen‐free ionic liquids to a synthetic oil in steel–steel contact using a ball‐on‐flat reciprocating tribometer
This paper studies the tribological effects of the addition of two halogen-free ionic liquids to synthetic oil in steel–steel contact using a ball‐on‐flat reciprocating tribometer

Summary

Introduction

Almost all of the machines that we use today run on some source of energy. a fair amount of this energy is lost as frictional force has to be overcome. Lubricants are important fluids as they are responsible for reducing friction, removal of wear particles and, minimizing loss of energy [1]. In the transportation industry, overcoming friction is one of the main focus areas as, in passenger cars for example, almost one third of the total energy is used to overcome friction in the tires, brakes, transmission and the engine [2]. It is estimated, that between 1% and 1.55% of a country’s Gross Domestic Product (GDP) can be saved if friction and wear losses in mechanical parts were reduced. It is estimated that approximately 11% of the total energy consumed in the U.S

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