The contribution of XANES spectroscopy to tribology

Nicholls, Mark A.; Najman, M.N.; Zhang, Z; Kasrai, M.; Norton, P. R.; Gilbert, Benjamin

doi:10.1139/v07-093

Cited by 49 publications

(45 citation statements)

References 58 publications

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“…The main peak was observed at 2152.5 eV, shifted by ~2.5 eV from the peak observed for unreacted ZDDP (see Figure 3). This shift is in agreement with the previous XANES studies done on ZDDP tribofilms [47,56]. Previous XANES studies on phosphates with different cations [57] show that P K-edge appear to be the same whether the cation is Fe or Zn.…”

Section: In-lubro Analysis Of Lubricant Tribofilms Formed On Steel Ansupporting

confidence: 93%

“…Figure 11 shows the S K-edge XANES spectra (obtained in He environment) of ZDDP and ZDDP+MoDTC tribofilms and model compounds. The concentrated ZDDP spectrum shows an S K-absorption edge at 2471.9 eV which is consistent with what is observed in literature [53,55,56] when similar films were analysed in vacuum environment. Tribofilm spectra showed a peak consistent with the concentrated additive spectrum.…”

Section: In-lubro Analysis Of Lubricant Tribofilms Formed On Steel Ansupporting

confidence: 91%

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In-situ reflection-XANES study of ZDDP and MoDTC lubricant films formed on steel and diamond like carbon (DLC) surfaces

Morina

Zhao

Mosselmans

2014

Applied Surface Science

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Chemical characterisation of boundary lubricated interfaces is essential for developing mechanistic models that describe lubricant additive interactions with the surface and their effect on tribological performance. In this study the potential for using the synchrotron-based reflection mode X-ray absorption spectroscopy (XAS) technique for in-situ chemical characterisation of lubricant films has been studied.

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Section: In-lubro Analysis Of Lubricant Tribofilms Formed On Steel Ansupporting

confidence: 93%

Section: In-lubro Analysis Of Lubricant Tribofilms Formed On Steel Ansupporting

confidence: 91%

In-situ reflection-XANES study of ZDDP and MoDTC lubricant films formed on steel and diamond like carbon (DLC) surfaces

Morina

Zhao

Mosselmans

2014

Applied Surface Science

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“…P K-edge XANES has been applied to studies of phosphate minerals (Okude et al 1999;Ingall et al 2011), phosphate glasses (Yin et al 1995;Nicholls et al 2004); and soils (Beauchemin et al 2003;Prietzel et al 2010 and references therein;Kar et al 2011;Xiong et al 2012). On the other hand, a substantial amount of P L-edge data comes from the thin film and tribology literature where phosphorous and sulfur are key ingredients in lubricants (Kasrai et al 2003;Nicholls et al 2007 and references therein). Recently Kruse et al (2009) have reviewed the phosphorous L 2,3 -edge XANES of a number of commonly used crystalline and organic reference compounds.…”

Section: Phosphorousmentioning

confidence: 99%

X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

Henderson

Groot

Moulton

2014

Reviews in Mineralogy and Geochemistry

262

155

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In addition to the XANES region, at higher energies the extended X-ray absorption fine structure (EXAFS) region is found. The spectral shape in the near-edge region is determined by electronic density of states effects and gives mainly information about the electronic properties and the local geometry of the absorbing atom. The EXAFS region is dominated by single scattering events of the outgoing electron on the neighboring atoms, providing mainly information about the local geometric structure around the absorbing site. In this chapter we will focus on XANES. XANES SpectroscopyIn XPS the ground state (Ψ 0 ) is excited to the ground state plus a core hole (c), where the electron (ε) is excited to higher energy, while in XAS the ground state is excited with a coreto-valence excitation (cv). The XPS binding (E B ) is defined as the photon energy (Ω) minus the measured kinetic energy of the electron (E k ) and corrected for the work function (φ):The work function is the minimal energy to emit an electron from the material. In metals the XAS edge energy can be assumed to be equal to the XPS binding energy, because exactly at the XPS binding energy a transition is possible to the lowest empty state. Experimentally the XAS edge energy can be slightly higher than the XPS binding energy, for example if the transition to the lowest empty state is forbidden by selection rules. Single electron excitation approximation and selection rulesIn first approximation XANES can be described as the excitation of a core electron to an empty state. In the Fermi golden rule, the initial state wave function is rewritten as a core wave function and the final state wave function (ε) as a valence electron wave function (ν). This implicitly assumes that all other electrons do not participate in the X-ray induced transition. In this approximation, the Fermi golden rule can be written as:The X-ray absorption selection rules determine that the dipole matrix element is non-zero if the orbital quantum number of the final state differs by one from the initial state (∆L = ± 1, i.e., s → p, p → s or d, etc.) and the spin is conserved (∆S = 0). In the dipole approximation, the shape of the absorption spectrum should look like the partial density of the (∆L = ± 1) empty states projected on the absorbing site, convoluted with a Lorentzian. This Lorentzian broadening is due to the finite lifetime of the core-hole, leading to an uncertainty in its energy according to Heisenberg's principle. The single electron approximation gives an adequate simulation of the XANES spectral shape if the interactions between the electrons in the final state are relatively weak. This is the case for all excitations from 1s core states (K-edges).

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“…The ex-situ studies were carried out mainly using X-ray photoelectron spectroscopy (XPS) [19,22], Raman spectroscopy [23,24], Fourier transform infrared spectroscopy (FT-IR) [25] and X-ray absorption spectroscopy (XAS) [26,27]. The XAS studies investigated the reactions of different oil additives including ZDDP [14,28,29], ashless alkyldithiophosphate (DDP) [28,30], potassium triborate [31], phosphate ester additives [32], and other different organosulfur additives [33].…”

Section: Introductionmentioning

confidence: 99%

“…In addition, several other studies [26,36] examined the effect of detergents and dispersants on the decomposition reactions and the synergy between the different oil additives. Some of these XAS measurements were combined with X-ray photoelectron emission microscopy (X-PEEM) [27,31,37] and Photoelectron Emission Microscope by Synchrotron Undulator Illumination technique [38]. A review of the different contributions of these various XAS techniques to tribology was provided by Nicholls et al [27], which highlighted the importance of XAS especially in studying the reactions of oil additives and the composition of the formed tribofilms.…”

Section: Introductionmentioning

confidence: 99%

An in situ synchrotron XAS methodology for surface analysis under high temperature, pressure, and shear

Dorgham

Neville

Ignatyev

et al. 2017

Review of Scientific Instruments

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The complex tribochemical nature of lubricated tribological contacts is inaccessible in real time without altering their initial state. To overcome this issue, a new design of a pin-on-disc tribological apparatus was developed and combined with synchrotron X-ray absorption spectroscopy (XAS). Using the designed apparatus, it is possible to study in situ the transient decomposition reactions of various oil additives on different surfaces under a wide range of realistic operating conditions of contact pressure (1.0–3.0 GPa), temperature (25–120 °C), and sliding speed (30–3000 rpm or 0.15–15 m/s). To test the apparatus, several tribological tests were performed at different shearing times ranging from 2.5 to 60 min. These tests were carried out under helium atmosphere at a temperature of 80 °C, contact pressure of 2.2 GPa, and sliding speed of 50 rpm. The XAS experiments indicate that the zinc dialkyldithiophosphate antiwear additive decomposes in the oil to form a tribofilm on the iron surface at different reaction kinetics from the ones of the thermal film. The tribofilm composition evolves much faster than the one of the thermal film, which confirms that the formation of the tribofilm is a thermally activated process similar to the one of the thermal film but accelerated by shear. Furthermore, the results indicate that the sulfur of the formed film, whether a tribofilm or a thermal film, appears initially in the form of sulfate, with some sulfide, which under heat or shear is reduced into mainly sulfide.

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The contribution of XANES spectroscopy to tribology

Cited by 49 publications

References 58 publications

In-situ reflection-XANES study of ZDDP and MoDTC lubricant films formed on steel and diamond like carbon (DLC) surfaces

In-situ reflection-XANES study of ZDDP and MoDTC lubricant films formed on steel and diamond like carbon (DLC) surfaces

X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

An in situ synchrotron XAS methodology for surface analysis under high temperature, pressure, and shear

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