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

DOI: 10.1016/j.triboint.2021.107026 DOI Help

Authors: Abdel Dorgham (University of Leeds) , Pourya Parsaeian (University of Leeds) , Abdullah Azam (University of Leeds) , Chun Wang (University of Leeds) , Konstantin Ignatyev (Diamond Light Source) , Fred Mosselmans (Diamond Light Source) , Ardian Morina (University of Leeds) , Anne Neville (University of Leeds)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Tribology International , VOL 160

State: Published (Approved)
Published: August 2021
Diamond Proposal Number(s): 18814

Abstract: Ashless dialkyldithiophosphate (DDP) antiwear additives are good candidates to replace the widely used metallic DDPs such as zinc dialkyldithiophosphate (ZDDP), which are less environmentally friendly. A newly designed in-situ tribological rig was utilised to perform in-situ synchrotron X-ray absorption spectroscopy (XAS) in order to examine the decomposition reactions of two types of DDPs; acidic and neutral. The tribological experiments showed that the two DDP additives decomposed to form protective tribofilms on the steel surface, which provided better antiwear protection than ZDDP regardless of the tribofilm thickness. The neutral DDP formed a thinner tribofilm (about 33 nm) than ZDDP (about 41 nm), whereas the tribofilm of the acidic DDP had a much lower thickness (<7 nm) but more superior antiwear protection. The two DDPs also provided lower friction coefficient (<0.1) than the 0.12 provided by ZDDP. The XAS experiments suggest that the DDPs decompose to form initially iron sulphate, which is quickly reduced to sulphide before forming the phosphate layers of the protective tribofilm. These layers consisted initially of iron phosphate of short chains but as rubbing continued organic phosphate with long chains started to form.

Journal Keywords: ZDDP; DDP; Antiwear tribofilm; In-situ tribochemistry; Synchrotron XAS

Subject Areas: Chemistry

Instruments: I18-Microfocus Spectroscopy

Added On: 21/06/2021 10:21

Discipline Tags:

Chemistry Inorganic Chemistry

Technical Tags: