Aus Wissenschaft und Forschung / TAE-Plenarvorträge 36 Tribologie + Schmierungstechnik · 67. Jahrgang · 4/ 2020 1 Introduction It is known that different types of surface-affine additives (i.e. antiwear/ anti-corrosion/ anti-friction) can have very different adsorption behaviour on surfaces (e.g. [1-3]). The interactions can be synergistic or antagonistic in character and influences the near-surface chemistry of the sliding surfaces and therefore also the tribological performance of the system. For wear protection additives, it is for instance known that phosphor and sulfur containing layers are formed under tribo-conditions (e.g. [4,5]). If a friction modifier is added to the system, the question arises which interactions result and how the wear reduction performance is affected. In this presentation we will give an overview on an ongoing study of the adsorption of selected additives using novel in-situ approaches. The found correlations are also compared to tribo-experiments in order to answer the question whether synergistic effects in adsorption also lead to synergistic effects in wear reduction. 2 Results In an initial study, ZDTP and DTP were tested in combination with two different friction modifiers, a GMO and an organic friction modifier (OFM). As base oils mineral oil and PAO were used. The adsorption behavior was studied via quartz crystal microbalance with dissipation (QCM-D) using Fe 2 O 3 coated quartz crystals. The technique gives information on the amount of adsorbed additive (mass) as well as on the rigidity of the adsorbed layer (dissipation). The wear performance was tested in a ball-on-three disk tribometer. White light interferometry (WLI) was used to determine the wear volume and XPS depth profiles of the tri- In Situ Studies on the Competitive Adsorption of Lubricant Additives Martin Dienwiebel, Jennifer Honselmann, Jonas Wagner, Philipp Daum, Patrick Wilke, Thomas Rühle* * Martin Dienwiebel 1,2) Jennifer Honselmann 2)* Jonas Wagner 2) Philipp Daum 2) Patrick Wilke 3) Thomas Rühle 3) 1) Karlsruhe Institute of Technology KIT, MikroTribologie Centrum µTC, Straße am Forum 7, 76131 Karlsruhe, Germany 2) Fraunhofer IWM, MikroTribologie Centrum µTC, Straße am Forum 5, 76131 Karlsruhe, Germany 3) BASF SE, Carl-Bosch-Straße 38, 67, Ludwigshafen, Germany *Corresponding author: martin.dienwiebel@kit.edu Figure 1: Disssipation and adsorbed masses for two base oils. The green boxes indicate a synergistic effect in terms of wear; the red box indicates an antagonistic effect. The error bars are the standard deviation for three measurements Aus Wissenschaft und Forschung / TAE-Plenarvorträge 37 Tribologie + Schmierungstechnik · 67. Jahrgang · 4/ 2020 bofilms were acquired on selected systems. From the correlation of QCM-D and wear data we are able to conclude that initially adsorbed films that are viscoelastic lead to a third body formation during a tribo experiment which is more pronounced and there-by wear can be reduced (Figure 1). However, the results cannot provide information on the morphology of these films. There fore, in a subsequent experiment we combined the QCM-D technique with fluorescent im-aging of the additive adsorption using a 3D confocal laser scanning microscope (CLSM) see figure 2. Presently, these experiments are restricted to the ad-sorption of a single additive (i.e. a friction modifier). Surprisingly, we find that the friction modifier forms droplets in the oil which adsorb on the surface and there do not form a closed film. The calculated mass of the adsorbed droplet correlates reasonably well with mass found by QCM-D. References [1] M. Ratoi, V. B. Niste, H. Alghawel et al., “The impact of organic friction modifiers on engine oil tribofilms,” RSC Adv, vol. 4, no. 9, pp. 4278-4285, 2014. [2] Y.L. Wu, B. Dacre, “Effects of lubricant-additives on the kinetics and mechanisms of ZDDP adsorption on steel surfaces,” Tribology International, no. 30, pp. 445-453, 1997. [3] H. A. Spikes, “Additive-additive and additive-surface interactions in lubrication,” Lubrication Science, vol. 2, no. 1, 1989. [4] Z. Zhang, E. S. Yamaguchi, M. Kasrai et al., “Tribofilms generated from ZDDP and DDP on steel surfaces: Part 2, chemistry,” Tribology Letters, vol. 19, no. 3, pp. 221- 229, 2005. [5] H. Spikes, “The History and Mechanisms of ZDDP,” Tribology Letters, vol. 17, no. 3, pp.469-489, 2004. Figure 2: Schematic of the combined QCM-D and CLSM setup