Voltage-driven growth of phosphorus tribofilms
File(s)
Published version
Author(s)
Zhao, Yun
Zhang, Jie
Spikes, Hugh
Wong, Janet
Type
Journal Article
Abstract
Ashless phosphorus-based lubricant additives, which are increasingly deployed in next-generation formulations, often suffer from slow tribofilm formation and poor film stability, limiting their effectiveness under demanding operating conditions. As mechanical systems become increasingly electrified, understanding how lubricants respond to electrical stimuli and developing strategies that exploit such stimuli have become critical for ensuring reliable operation. Here, we investigate the tribological performance of bis(2-ethylhexyl) phosphite (BEPite) in polyalphaolefin (PAO2) lubricated, electrified steel/steel contacts. Current is kept low to limit current-induced effects. Compared to an unbiased surface, BEPite produces thicker and denser tribofilms on anodic rubbing surfaces as voltage increases. This enhancement, however, is only observed when sliding is present. Chemical analysis reveals the presence of oxidised PO32−-related species and abundant iron in the tribofilm. Static electrochemical cell experiments show surface oxidation is enhanced on anodic surfaces. This suggests voltage-driven triboelectrochemical oxidation and reaction promote tribofilm formation. Either iron oxides or released Fe ions may alter the tribofilm structure. These phenomena appear general for phosphorus-based ashless additives, as both phosphites and phosphates with different structures have seen increased tribofilm growth at anodic rubbing surface. This work demonstrates that an applied voltage, coupled with sliding, can intensify triboelectrochemical reactions, providing new insights for the design of next-generation lubricants.
Date Issued
2026-07-08
Date Acceptance
2026-06-28
Citation
Tribology Letters, 2026, 74
ISSN
1023-8883
Publisher
Springer
Journal / Book Title
Tribology Letters
Volume
74
Copyright Statement
© The Author(s) 2026 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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Publication Status
Published
Article Number
79
Date Publish Online
2026-07-08