# Surface passivation by graphene in the lubrication of iron: A comparison with bronze

## TL;DR

This study investigates how graphene acts as a lubricant and passivates iron surfaces, reducing friction in steel-on-iron and bronze contacts through experimental analysis.

## Contribution

It provides experimental evidence that graphene passivates iron surfaces and reduces friction, clarifying its chemical lubricating mechanism.

## Key findings

- Graphene reduces the friction coefficient in steel-on-steel and steel-on-bronze contacts.
- Graphene passivates iron surfaces, decreasing surface energy and adhesion.
- Experimental results confirm the beneficial lubricating effect of graphene flakes.

## Abstract

It has been recently reported that graphene is able to significantly reduce the friction coefficient of steel-on-steel sliding contacts. The microscopic origin of this behavior has been attributed to the mechanical action of load carrying capacity. However, a recent work highlighted the importance of the chemical action of graphene. According to this work graphene reduces the adhesion of iron interfaces by reducing the surface energy thanks to a passivation effect. The aim of the present work is to clarify the still debated lubricating behavior of graphene flakes. We perform pin-on-disc experiments using liquid dispersed graphene solution as a lubricant. Two different materials, pure iron and bronze are tested against 100Cr6 steel. Raman spectroscopy is used to analyze the surfaces after the friction tests. The results of these tests prove that graphene flakes have a beneficial effect on the friction coefficient. At the same time they show a tendency of graphene to passivate the native iron surfaces that are exposed during sliding as a consequence of wear.