Abstract
The use of solid lubricants such as graphene, graphene oxide, and other nanoparticles have gained notable attention in the tribological community to reduce friction and wear thus aiming at improved energy efficiency and sustainability. Tribological experiments unify rather extreme conditions such as high contact pressures, small contact areas, relative sliding motion, and rapid heating. This combination leads to mechanically- and/or thermally induced chemical, structural and microstructural modifications of the lubricating nanoparticles during rubbing thus altering their material’s properties. Due to the high sensitivity, we propose nanocalorimetry as the method of choice to shed more light on the thermally-induced processes and changes. As a model material for solid lubricants, we explore the transitions of graphene oxide under heating with 1000 °C/s up to 600 °C using quasi-adiabatic nanocalorimetry. We identify a strong exothermic runaway reaction at 317 °C. This runaway is preceded by exothermic reactions between 75–125 °C, which are correlated with the release of intercalated species and the formation of CO and CO2.
Highlights
In times of a continuously increasing population and energy demand as well as more environmental consciousness, new approaches to reduce energy consumption, increasing sustainability, have become more important than ever before
The involved contact pressures and sliding velocities can lead to rather high local temperatures, which go hand in hand with high heating and cooling rates
We propose nanocalorimetry as a method to quantitatively explore the thermally-induced material evolution, which has the overall potential to be correlated with processes going on in a tribological contact on the asperity level
Summary
In times of a continuously increasing population and energy demand as well as more environmental consciousness (global warming), new approaches to reduce energy consumption, increasing sustainability, have become more important than ever before. In this regard, tribology, which includes friction, wear, and lubrication, plays an important role since this topic is directly connected to transportation and industrial processes. Similar values have been extrapolated in other industrial branches such as the mining and paper industry [3,4] These numbers reflect the tremendous potential in terms of energy and sustainability by reducing tribology-related losses [5]. This approach becomes further complicated due to legal restrictions related to the Lubricants 2019, 7, 96; doi:10.3390/lubricants7110096 www.mdpi.com/journal/lubricants
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