A multi-edge X-ray absorption spectroscopy study of the reactivity of zinc di-alkyl-di-thiophosphates anti-wear additives: 2. In situ studies of steel/oil interfaces

✍ Scribed by E.S Ferrari; K.J Roberts; M Sansone; D Adams

• Book ID: 104266408
• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 484 KB
• Volume: 236
• Category: Article
• ISSN: 0043-1648
• DOI: 10.1016/s0043-1648(99)00286-0

✦ Synopsis

Multi-edge X-ray absorption spectroscopy, using synchrotron radiation, was used to examine changes in the structure and chemical Ž . composition of steelroil interfaces when mediated by the presence of the anti-wear additive zinc di-alkyl-di-thiophosphate ZDDP . The experiments were carried out at the Zn, Fe, O and C K-edges and the Zn and Fe L -edges. Examination of the steel substrate, prior to IIrIII reaction, revealed that the metal surface was partly oxidised, with the oxide structure mostly involving the iron atoms having a tetrahedral coordination to oxygen. Distinct changes to the oxide structure were observed following its reaction associated with the formation of its interface with ZDDP formulated in lubrication oil. Temperature programmed studies on the interfacial structure were consistent with a Ž . model involving ion exchange between Zn atoms in ZDDP and Fe II cations in the oxide in a reaction that appeared to be reversible below 758C. Grazing incidence absorption spectroscopy measurements provided evidence for the breakdown of the ZDDP molecule following its adsorption onto the steel substrate surface. At higher temperatures chemical reaction between the additive and the surface Ž . oxide layer led to the formation of an amorphous anti-wear film. The structure of this film was consistent with a Zn-O bond 1.98 A typical of partly oxidised sulphur atoms associated with the formation of a random network glass structure with corner sharing thiophosphate and sulphate anions containing network-modifying Zn cations. A reaction scheme consistent with the proposed structure is discussed.