Tribological Performance Investigation of a Commercial Engine Oil Incorporating Reduced Graphene Oxide as Additive.

Hakan Kaleli,Dae-Eun Kim,Veli Uysal,Selman Demirtaş,Spiros H Anastasiadis,Ioannis Karnis,Minas M Stylianakis

doi:10.3390/nano11020386

Abstract

We investigated the tribological behavior of commercialized, fully synthetic engine oil upon the incorporation of reduced graphene oxide in seven different concentrations between 0.01 and 0.2 wt %. Stability of the prepared samples was assessed by turbidimetry and dynamic light scattering measurements, and their tribological properties through a reciprocating tribometer, using a steel ball on special cut steel blocks. The addition of 0.02 wt % of reduced graphene oxide led to an improvement of the tribological behavior compared to the pristine engine oil, by significantly lowering the friction coefficient by 5% in the boundary lubrication regime. Both the surfaces and the reduced graphene oxide additive were thoroughly characterized by microscopic and optical spectroscopy techniques. We also verified that a protective layer was formed between the worn surfaces, due to the presence of reduced graphene oxide. Carbon accumulation and various additive elements such as Ca, Zn, S and P were detected on the rubbing surfaces of both the ball and the block through energy-dispersive X-ray spectroscopy. Finally, it was shown that the wear scar diameter on the surface of the steel ball was lower by 3%, upon testing the engine oil sample containing reduced graphene oxide at concentration 0.02 wt %, compared to the control sample.

Highlights

We demonstrate for the first time the improvement of the tribological behavior of a conventional fully synthetic engine oil 5W-40, by Shell, through the addition of reduced graphene oxide (rGO) of different contents, in a range from 0.2 to 0.01 wt %, assisted by ultrasonication. rGO
We investigate the lubrication mechanism, which is due to the formation of a protecting layer on the sliding surfaces; carbon accumulation was detected on the surfaces, which originated from the rGO, and various elements such as Ca, Zn, S and P, because of other additives in the
3.1. rGO Analysis rGO was thoroughly characterized by several techniques before its incorporation rGO was thoroughly characterized by several techniques before its incorporation as as additive in the pristine 5W-40 Shell engine oil

Summary

Introduction

Liquid lubricants almost eliminate friction either by preventing sliding contact surfaces from severe or more frequent metal-to-metal contacts or by forming a low-shear, high-durability boundary film on the rubbing surfaces [1,2]. Depending on the sliding speed and other operating conditions, engine oils can effectively separate contact surfaces of rings and liners by reducing the frequency of direct metal-to-metal contact and, reducing friction and wear. Low friction means fuel savings, while reduced wear implies longer durability [2,3]. Due to these solid and liquid lubricants, the components of today’s engines and other mechanical systems can be safely and smoothly operated for long times. Graphene and its derivatives can serve as ideal solid or colloidal liquid lubricant additives due to their well-established lubricity, thermal stability, extraordinary electrical and mechanical properties and their impermeability to humidity and oxygen [4,5,6,7]

Methods

Results

Conclusion