Comparison Between the Action of Nano-Oxides and Conventional EP Additives in Boundary Lubrication

Valdicleide Silva Mello,Ana Emilia Diniz Silva Guedes,Marinalva Ferreira Trajano,Salete Martins Alves

doi:10.3390/lubricants8050054

Abstract

Additives are essential in lubricant development, improving their performance by the formation of a protective film, thus reducing friction and wear. Some such additives are extreme pressure additives. However, due to environmental issues, their use has been questioned because their composition includes sulfur, chlorine, and phosphorus. Nanoparticles have been demonstrated to be a suitable substitute for those additives. This paper aims to make a comparison of the tribological performance of conventional EP additives and oxides nanoparticles (copper and zinc) under boundary lubrication conditions. The additives (nanoparticles, ZDDP, and sulfur) were added to mineral and synthetic oils. The lubricant tribological properties were analyzed in the tribometer HFRR (high frequency reciprocating rig), and during the test, the friction coefficient and percentual of film formation were measured. The wear was analyzed by scanning electron microscopy. The results showed that the conventional EP additives have a good performance owing to their anti-wear and small friction coefficient in both lubricant bases. The oxides nanoparticles, when used as additives, can reduce the friction more effectively than conventional additives, and displayed similar behavior to the extreme pressure additives. Thus, the oxide nanoparticles are more environmentally suitable, and they can replace EP additives adapting the lubricant to current environmental requirements.

Highlights

A good lubricant is selected according to its ability to form a protective film on sliding parts, resist high temperatures, and support mechanical loads
The wear and friction performance at the boundary lubrication regime is controlled mainly by the lubricant additives, which form films on surfaces or create a layer of the sacrificial film [1]. This film formation depends on the nature and chemistry of additives added to the lubricant oil
The size of the and ZnO nanoparticles was around 4.5 nm and 10 nm, respectively, and their shape is near-spherical, CuO and ZnO nanoparticles was around 4.5 nm and 10 nm, respectively, and their shape is nearas can be seen in TEM images (Figure 2)

Summary

Introduction

A good lubricant is selected according to its ability to form a protective film on sliding parts, resist high temperatures, and support mechanical loads. The most commonly used additives are antioxidants and extreme pressure agents (EP) to act in boundary lubrication conditions. These EP additives prevent high wear caused by contact between metal to metal under high loads. The wear and friction performance at the boundary lubrication regime is controlled mainly by the lubricant additives, which form films on surfaces or create a layer of the sacrificial film [1]. This film formation depends on the nature and chemistry of additives added to the lubricant oil. These additives remain subject some restrictions on their use due to their environmental impacts [2,3]

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