Roman Heuberger

ETH Zurich, Zürich, Zurich, Switzerland

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Publications (4)4.51 Total impact

  • Roman Heuberger · Antonella Rossi · Nicholas D. Spencer ·
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    ABSTRACT: Phosphorothionates are anti-wear lubricant additives and potential replacements for zinc dialkyldithiophosphates. In this study, ball-on-disc tests have been carried out combinatorially under extreme pressure (EP) conditions (100–350 MPa at 10 N load). The tests were performed in oil containing triphenyl phosphorothionates substituted with alkyl chains of different lengths. Imaging, small-area and angle-resolved X-ray photoelectron spectroscopy were performed following the tribotest to probe the modification, removal and growth of the surface film. The films were composed, depending on the test conditions, of (i) iron phosphate, (ii) iron phosphates with sulphates or (iii) a mixture of iron phosphates with sulphides and sulphates. With increasing load, the dimensional wear coefficients decreased. Upon increasing temperature from 30 to 150°C, the wear became more severe. These findings suggest the formation of a tribochemical film with some EP performance, despite the severe tribological test conditions applied in this work. Copyright © 2008 John Wiley & Sons, Ltd.
    Lubrication Science 04/2008; 20(2):79 - 102. DOI:10.1002/ls.56 · 1.03 Impact Factor
  • Roman Heuberger · Antonella Rossi · Nicholas D. Spencer ·
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    ABSTRACT: Combinatorial testing has been performed on zinc dialkyldithiophosphate (ZnDTP)-containing lubricants, to investigate the effects of contact pressure on the formation of tribochemical films. Contact pressures ranging from 25 to 500MPa were applied in ball-on-disc tribotests with oscillating load. Both the ball and the disc were investigated by means of small-area and imaging X-ray photoelectron spectroscopy (XPS). The thickness and the composition of the reaction layer were estimated from the XPS data. The thickness of the reaction layer in the tribologically stressed areas of the ball and of the disc increased with both temperature and contact pressure. The reaction layer mainly consisted of short-chain poly(thio)phosphates, shorter chains being observed at higher contact pressures. At high pressures, the presence of a thick, high-toughness short-chain poly(thio)phosphate layer can explain the lower friction and dimensional wear coefficients observed. On the ball, similar anti-wear film formation mechanisms were observed as on the disc, zinc sulphide being deposited in the post-contact region.
    Tribology Letters 09/2007; 28(2):209-222. DOI:10.1007/s11249-007-9267-0 · 1.74 Impact Factor
  • Roman Heuberger · Antonella Rossi · Nicholas D. Spencer ·
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    ABSTRACT: Antiwear additives, such as zinc dialkyldithiophosphate (ZnDTP), find application in many different industrial sectors. Although it is understood that certain ZnDTP concentrations need to be used to achieve an effective antiwear performance, there has been very little work published concerning the effect of temperature on the interactions of the additive and its adsorption mechanism on steel. In this article, 100Cr6 (52100) steel ball-on-disc experiments under solutions of zinc dialkyldithiophosphate (ZnDTP) in poly-α-olefin (PAO) were performed at different temperatures, ranging from 25 to 180°C. The discs were analysed after the experiments by means of small-area, imaging and angle-resolved X-ray photoelectron spectroscopy (XPS). The composition of the reaction film was found to change as a function of the applied temperature and also to vary within the film as a function of depth: Longer polyphosphate chains were found at higher temperatures as well as towards the outer part of the reaction film.
    Tribology Letters 03/2007; 25(3):185-196. DOI:10.1007/s11249-006-9166-9 · 1.74 Impact Factor
  • N. D. Spencer · R. Heuberger · J. Antifakos · A. Rossi ·
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    ABSTRACT: The tribochemical mechanism of phosphorus-containing additives is important to understand, even if the ultimate aim is to replace them with something more environmentally benign. In a combinatorial experiment that explored a range of temperatures (RT-180°C), loads, two additives, and two substrate pairings, it was observed that zinc dialkyldithiophosphate (ZnDTP) reacted with steel surfaces to produce phosphate at room temperature, pyrophosphate at 130°C, and polyphosphate at 180°C. Metal-ceramic pairings did not seem to produce long-chain polyphosphates at 150°C. It was also observed that metal-metal pairings appear to benefit more from the presence of the additives than ceramic-metal pairings, which suggests that the role of the additives is largely to inhibit microwelding of the asperities across the sliding plane.
    World Tribology Congress III; 01/2005

Publication Stats

73 Citations
4.51 Total Impact Points

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  • 2008
    • ETH Zurich
      • Surface Science and Technology Group
      Zürich, Zurich, Switzerland
  • 2005
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland