Tribochemistry in the analytical UHV tribometer

The knowledge of tribochemical reactions in boundary lubrication in the presence of lubricant additives is fundamental in order to improve chemical engineering of new molecules, multifunction compounds and to predict interactions between these additives. Experiments with in lubro, ex situ or post-mortem analyses are difficult and even dangerous to exploit because of numerous artefacts. We introduce two special approaches to simulate boundary lubrication tribochemistry. Basically, these approaches use a dedicated analytical UHV tribotester allowing in situ AES/XPS analysis of both counterfaces and introduction of partial pressure of gases during friction. The first model experiment is UHV friction on previously formed tribofilms from a lubricated test. The second experiment is gas phase lubrication with ethyl phosphate. The results reveal some fundamental aspects of the origin of friction-reduction by transfer of MoS2 single sheets. The reaction of friction-activated nascent surfaces with gases is also emphasised. (C) 2000 Elsevier Science Ltd. All rights reserved.