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Lubrification par la phase gazeuse : tribochimie des additifs phosphorés et boratés

Abstract : Automotive lubricants are very complex systems due to numerous additives mixed with base oils. In order to better design lubricants, it is necessary to understand the mechanisms of reaction of each additives and also the interactions between additives. Consequently, to better understand these mechanisms, a new approach was developed during this study based on the experimental simulation of the boundary lubrication by gas phase lubrication: low molecular weight molecules simulating the heavy lubricant additives were introduced under ultra high vacuum (UHV). Tests were carried out in a new Environmentally Controlled Tribometer (ECT) developed in the laboratory, which is also connected to a chemical analysis device. This technique allows the simplification of the tribosystem and the in situ study of the tribofilm formation mechanisms by XPS/AES analysis. Different kinds of molecules were used: trimethylborate (TMB), trimethylphosphite (TMPi) and trimethylphosphate (TMPa) to simulate respectively the borate and the phosphorous additives usually used as gear lubricants. The experimental simulation by gas phase lubrication was corroborated by comparison with liquid phase lubrication. Moreover, optical microscopy observations as well as chemical analysis gave rise to tribofilm formation. Experiments made in presence of TMB have confirmed literature observations by the formation of a non sacrificial tribofilm composed of mineral borate. Experiments made with phosphorous molecules allowed to clearly identify differences between phosphates and phosphites. Phosphites induce iron phosphide formation. The possible mechanism of the iron phosphide like compound was proposed thanks to the in situ analysis. The binary blends of gases allowed us to study the effect of synergisms and antagonisms interactions between additives.
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Submitted on : Tuesday, May 20, 2008 - 10:38:18 AM
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David Philippon. Lubrification par la phase gazeuse : tribochimie des additifs phosphorés et boratés. Matériaux. Ecole Centrale de Lyon, 2007. Français. ⟨tel-00280892⟩

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