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Project VII – Tribochemistry Studied by Surface-Analytical Tools
Contributors: N. Spencer, C. Kajdash
Tribochemistry, the study of reactions that are induced by tribological conditions, is of ever-increasing importance in a world that is energy conscious, environmentally conscious and generally searching for a more sustainable overall materials balance during use cycles. Current major challenges for the field include the replacement of the many existing, highly effective lubricant additives with alternatives that are equally (or more) effective, but more environmentally benign. To achieve this end, the mechanisms by which the current additives function must be better understood, and this is one of the goals of our tribochemistry efforts.
One of our approaches has been to employ a combination of imaging surface analytical techniques with classical tribometry under very carefully controlled conditions. Specifically, pin-on-on-disk experiments are carried out under various conditions with a given set of lubricants and additives. The chemical state of the surface and near-surface region is then analyzed with techniques such as iXPS and ToF-SIMS, in order to make a correlation between tribological conditions, lubricant chemistry, surface reactions, and ultimate tribological performace. This work is now being extended into a combinatorial-type approach, where many relevant parameters can be examined and correlated in parallel. One aspect of this work that has been somewhat neglected by the community until now is the prediction of tribochemical reactions for relevant systems. Collaboration with theoretical chemists with this goal in mind could be extremely productive.
Another approach used in our laboratory is the use of newly developed in situ approaches to tribochemical investigation. Using an iron-coated attenuated total reflectance (ATR) device in an FTIR spectrometer, we have been able to monitor the reaction pathways of specific additives while the tribolochemistry is actually occurring. Additionally, we have been able to monitor the progress of physical processes during sliding, such as polymer transfer.
In addition to the more traditional additives alluded to above, we have also begun looking at aqueous, protein-lubricated systems. These function highly effectively in biological environments, although their mechanisms are not well understood. Using a combination of surface functionalization and in-situ protein-binding analysis techniques, we are trying to explore protein-mediated lubrication, with the ultimate goal of application of biologically inspired lubrication in non-biological systems.
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