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Purpose Interactions of different additive types for antiwear/friction modification on surfaces can be synergistic or antagonistic in nature. This paper aims to investigate whether there are interactions between different additives in the adsorption process and whether they synergistic or antagonistic. The yielded correlations will be validated with tribological experiments to answer the question whether synergistic effects in adsorption also lead to synergistic effects in wear reduction. Design/methodology/approach In a representative study, zinc dialkyl-dithiophosphate and dithiophosphate were elaborated in combination with two different friction modifiers, a glycerol monooleate and an organic friction modifier. As base oils, mineral oil and poly alpha olefine were used. The adsorption behavior was studied via quartz crystal microbalance with dissipation using Fe2O3 coated quartz crystals. The tribological performance was evaluated in a ball-on-three disk tribometer. White light interferometry was used to determine the wear volume and X-ray photoelectron spectroscopy depth profiles of the tribofilms were obtained on selected systems. Findings The combination of dithiophosphate and an organic friction modifier (OFM) revealed a synergistic effect in terms of wear. If the initially formed films are viscoelastic, the third body formation during a tribo experiment is more pronounced and thereby wear can be reduced. As a mechanism, the adsorption of the OFM on the formed antiwear layer is proposed. Originality/value Correlating the analytical findings with performance experiments provides further understanding of the interactions between different constituents and their implications on film formation processes and wear reduction mechanisms. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2019-0293/

Friction modifier additive technologies play a crucial role in controlling friction and wear of lubricated tribological systems. Novel additives are usually evaluated using formulations of varying concentrations. It can be very difficult to understand the underlying mechanisms in those laboratory tests because of the interaction of base oil with the additives. It thus can be insightful to perform model experiments in a controllable atmosphere. This can be achieved for instance by integrating a tribometer into a vacuum system comprising in-situ surface analytical methods.In this work, a nitrogen containing organic friction modifier is adsorbed from the gas phase onto a Fe2O3 surface. Different coating thicknesses are prepared by varying the duration of the vapor deposition, so that the influence of the coating thickness on the friction behavior can be investigated. The chemical composition of the coated surfaces is also analyzed by coupling to an XPS photoelectron spectrometer.Contrary to the assumption that layers are formed, this friction modifier accumulates in droplets on the Fe2O3 surface. The number of droplets as well as the radii of droplets increase with evaporation time. The chemical composition of the additive does not change as a result of the gas phase deposition. In the friction tests, the smallest friction values are found for a very low coverage of droplets. For larger droplets, friction increases due to a capillary neck of additive that forms between the sliding surfaces and is dragged along during the friction test.Using gas phase adsorption of a nitrogen containing organic friction modifier it was possible to establish a correlation between droplet morphology and the friction behavior.

Friction modifier additive technologies play a crucial role in controlling friction and wear of lubricated tribological systems. Novel additives are usually evaluated using formulations of varying concentrations. It can be very difficult to understand the underlying mechanisms in those laboratory tests because of the interaction of base oil with the additives. It thus can be insightful to perform model experiments in a controllable atmosphere. This can be achieved for instance by integrating a tribometer into a vacuum system comprising in-situ surface analytical methods.In this work, a nitrogen containing organic friction modifier is adsorbed from the gas phase onto a Fe2O3 surface. Different coating thicknesses are prepared by varying the duration of the vapor deposition, so that the influence of the coating thickness on the friction behavior can be investigated. The chemical composition of the coated surfaces is also analyzed by coupling to an XPS photoelectron spectrometer.Contrary to the assumption that layers are formed, this friction modifier accumulates in droplets on the Fe2O3 surface. The number of droplets as well as the radii of droplets increase with evaporation time. The chemical composition of the additive does not change as a result of the gas phase deposition. In the friction tests, the smallest friction values are found for a very low coverage of droplets. For larger droplets, friction increases due to a capillary neck of additive that forms between the sliding surfaces and is dragged along during the friction test.Using gas phase adsorption of a nitrogen containing organic friction modifier it was possible to establish a correlation between droplet morphology and the friction behavior.

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