Organosulphurs compounds have been used for many years as Extreme Pressure (EP) and Anti Wear (AW) additives in a wide range of metal working applications. These additives act in severe conditions by building up a reaction film (tribofilm) on the metallic surfaces. Several interpretations have been proposed to explain the (EP) and the (AW) properties of these compounds, but the detailed mechanisms and surface reactions products are still largely unknown. To better understand the tribochemistry of these compounds, we developed a new device in our laboratory called “Environmentally Controlled Tribometer”. This apparatus permits to study the interaction of one or several additives on different metallic surfaces using a gas having the same chemical function as the additive. After friction experiments, in-situ surface analyses (XPS and AES) were carried out on the tribofilm, to clearly identify the reactions products in order to understand the tribochemical mechanism. In this paper, we simulate the metal working lubrication of steel by the gas phase lubrication. The results show a clear difference in tribological behaviour and surface products between triboreactivity on nascent and oxidized surfaces. These observations gave us new information to better understand the tribochemical reactions of these additives. The comparison between the liquid phase lubrication and the gas phase lubrication results validates this methodology.

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