The role of the cation in antiwear films formed from ZDDP on 52100 steel

Abstract

Phosphorus L-edge and oxygen K-edge X-ray PhotoEmission Electron Microscopy (XPEEM) have been used to characterize the chemical nature of the cation present in tribochemical films via comparison with model Fe 2+ and Zn 2+ compounds. The results are contrasted to the P L-edge, P K-edge and S K-edge XANES data. The findings suggest that antiwear pads containing long chain zinc polyphosphate glass are formed at the points of asperity contact, and a thin, short chain zinc polyphosphate film is formed where no asperity contact is made. SEM/EDX measurements helped to elucidate the distribution of the elements, and strong spatial correlations were observed between P, O, Zn and S in the pads, indicating that they are composed mostly of zinc polyphosphates, especially near the surface. The zinc polyphosphate antiwear pads are characterized by a much lower modulus than that observed on the thin film regions, the latter being characteristic of the substrate steel.

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

“…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. …”

“…The P K-edge peak does not appear to be very useful to assess the cation nature in the phosphate molecule as well as the chain length of the phosphate formed [57], useful for characterising the ZDDP tribofilm. This can be done with the P L-edge XANES analysis.…”

“…This can be done with the P L-edge XANES analysis. Analysis of P L-edge spectra can determine the phosphate chain length as well as the nature of cation in the phosphate molecule [25,27,33,57]. However, considering that the P L-edge absorption peak appears at around 135 eV, it cannot be obtained in non-vacuum conditions.…”

Chemical and mechanical analysis of tribofilms from fully formulated oils Part 1 – Films on 52100 steel

“…This edge has been useful in determining that little Fe is present in the antiwear films. 52 The Fe compounds show spectral characteristics (preedge peaks 'a' and 'a9') that are absent in the spectra of Zn compounds, which can help to differentiate between them. The origin and peak assignments of the O K-edge XANES can be found elsewhere.…”

The Effect of Steel Hardness on the Performance of ZDDP Antiwear Films: A Multi-Technique Approach

“…Experimentally, various surface analysis techniques have been used for the characterization of these tribofilms: e.g., Auger electron spectroscopy (AES) [11,12], X-ray photoelectron spectroscopy (XPS) [13][14][15] and X-ray absorption near-edge structure (XANES) spectroscopy in both area averaging and imaging modes [16][17][18][19][20][21].…”