Revealing the interface nature of ZDDP tribofilm by X-ray photoelectron spectroscopy and atom probe tomography

Abstract

Purpose To decrease wear and friction, zinc dialkyldithiophosphate (ZDDP) has been used in engine oil for several decades, but the mechanism of the tribofilm formation is still unclear. The purpose of this study is to characterize the chemical details of the tribofilm by using high-resolution approaching. Design/methodology/approach An ISO VG 100 mineral oil mixed with ZDDP was used in sliding tests on cylindrical roller bearings. Tribofilm formation was observed after 2 h of the sliding test. X-ray photoelectron spectroscopy (XPS) and atom probe tomography (APT) were used for chemical analysis of the tribofilm. Findings The results show that the ZDDP tribofilm consists of the common ZDDP elements along with iron oxides. A considerable amount of zinc and a small amount of sulfur were observed. In particular, an oxide interlayer with sulfur enrichment was revealed by APT between the tribofilm and the steel substrate. The depth profile of the chemical composition was obtained, and a tribofilm of approximately 40 nm thickness was identified by XPS. Originality/value A sulfur enrichment at the interface is observed by APT, which is beneath an oxygen enrichment. The clear evidence of the S interlayer confirms the hard and soft acids and bases principle. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0035/

Tribochemistry evolution of DDP tribofilms over time using in-situ synchrotron XAS

“…1. Hsu [28] also showed that a sulfur-rich base layer exists between the oxide layer on the metal surface and the ZDDP tribofilm. Dörr et al [29] suggested that sulphide species are dominantly formed from fresh oils but sulfate species increase in concentration when degraded oils are used.…”

Atmospheric pressure matrix‐assisted laser desorption/ionization mass spectrometry of engine oil additive components

“…The composition of these tribofilms has been extensively investigated by various measurement techniques, such as X-ray photoelectron spectroscopy (XPS), 8,[10][11][12][13] X-ray absorption spectroscopy, [14][15][16] and transmission electron microscopy (TEM) combined with focused ion beam (FIB) cutting. 17 Other available techniques include X-ray absorption near edge structure (XANES), 16,18 RAMAN spectroscopy, 19 scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), 8,[20][21][22] Fourier-transform infrared (FTIR) spectroscopy, 23,24 electrospray ionization mass spectrometry (ESI-MS), 25,26 high-field asymmetric waveform ion mobility spectrometry coupled with mass spectrometry (FAIMS-MS), 27 or dynamic time-of-flight secondary ion mass spectrometry (TOF-SIMS). 28 Direct surface analysis techniques such as desorption electrospray ionization (DESI-MS) 29 oil analysis and direct analysis in real time coupled with mass spectrometry (DART-MS) 30 have been applied for quantitative analysis of a commercial lubricant antioxidant additive in a base oil, while mass spectrometric imaging (MSI) by means of laser desorption/ionization reflectron time-of-flight mass spectrometry (LDI-RTOF-MS) was used to analyse ex situ oil components applied as lubricant additives in a tribological layer of a tribologically stressed surface.…”

“…The composition of these tribofilms has been extensively investigated by various measurement techniques, such as X‐ray photoelectron spectroscopy (XPS), 8 , 10 , 11 , 12 , 13 X‐ray absorption spectroscopy, 14 , 15 , 16 and transmission electron microscopy (TEM) combined with focused ion beam (FIB) cutting. 17 Other available techniques include X‐ray absorption near edge structure (XANES), 16 , 18 RAMAN spectroscopy, 19 scanning electron microscopy (SEM) with energy‐dispersive X‐ray spectroscopy (EDS), 20 , 21 , 22 Fourier‐transform infrared (FTIR) spectroscopy, 23 , 24 electrospray ionization mass spectrometry (ESI‐MS), 25 , 26 high‐field asymmetric waveform ion mobility spectrometry coupled with mass spectrometry (FAIMS‐MS), 27 or dynamic time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). 28 …”

Influence of temperature on wear performance of greases in rolling bearings

“…With increasing temperature, the patches become larger and progress towards a continuous tribofilm (Spikes, 2004; Brizmer et al , 2017). Glassy phosphates are part of a characteristic ZDDP-based tribofilm, which mainly consists of Zn, P, S, Ca and O (Gosvami et al , 2015; Kaleli, 2002; Stratmann et al , 2017; Hsu et al , 2020). The general structure is well-described in literature (Gosvami et al , 2015; Brizmer et al , 2017; Spikes, 2004; Gellman and Spencer, 2002).…”