An analytical study of tribofilms generated by the interaction of ashless antiwear additives with ZDDP using XANES and nano-indentation

Abstract

Mixtures of zinc dialkyl dithiophosphates (ZDDP) and ashless fluorothiophosphates and thiophosphates were examined under tribological conditions. The tribofilms were studied using nanoindentation, electron microscopy and XANES spectroscopy. With the addition of ashless fluorothiophosphates and thiophosphates there is significant reductions in wear at identical phosphorous levels. Tribofilms formed with mixtures of ZDDP and ashless antiwear additives had stable pad like structures while those from ZDDP alone were more heterogeneous. When ZDDP alone is used P L-edge indicates a preponderance of sulfates at the surface of the tribofilms while in the presence of a mixture of anti-wear additives a mixture of sulfates and sulfides was observed. In all cases the phosphates formed were short chain polyphosphates of Zn.

Quantitative comparison of tribological performance of chromium- and zinc-phosphate-coated piston rings in tribotest rig

“…The differences in friction coefficients were small and lower friction coefficient of PCR can be attributed to zincphosphate coating, including Zn and P elements in the composition where they reacted with iron surfaces and formed iron phosphates antiwear pads. It also reacted as a friction modifier like phosphorus containing lubricating oil additive, during the tests as explained by Davis 28 and Sharma et al 29 in their study. Observed abrasive wear scars were parallel to the sliding direction and in different angle with honing marks.…”

Friction-condition-dependent sulfide and sulfate evolution on dialkylpentasulfide tribofilm studied by XANES

“…Chemical composition measurements were conducted by FY and TEY mode XANES to detect the valence states of the sulfur element on different depths of tribofilm. Compared with the methods reported in previous studies [22][23][24], the experimental data were obtained at different detection modes of the same beam line station, and the data of different depth surfaces could be compared and analyzed with the K-edge of the sulfur element [25]. An X-ray beam was monochromatized by a fixed-exit double-crystal Si(111) monochromator, and it covered the photon region of 2,460-2,490 eV with 0.30 eV resolution.…”

Chemical and physical properties of tribofilms formed by the interaction of ashless dithiophosphate anti‐wear additives

“…[25][26][27][28][29] ZDDP is a widely used anti-wear additive that offers secondary benefits such as antioxidant, corrosion inhibition and extreme pressure protection. [30][31][32][33][34] ZDDP is outstanding at forming stable hard glassy protective tribofilms on the surfaces. 33,35 Large-scale production of ZDDP since its development in the early 1940s has made it significantly cheaper in comparison to other additives.…”

“…18,41 Several studies investigating ashless additives have been shown to have comparable or better anti-wear, antioxidant and extreme pressure properties as compared to ZDDP, however understanding the mechanisms for wear protection with these additives remains a challenge. 36,[42][43][44] X-ray absorption near edge structure (XANES) spectroscopy has been effectively used by Najman et al, 21,23,45,46 Sharma et al, 30,47,48 and Kim et al, 22,36,49 for characterising spatial distribution of chemical species in tribofilms derived from ashless antiwear additives. They concluded that the tribofilms contained short or long chain polyphosphates and iron sulfates.…”