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Substituent Effect on the Reactivity of Alkylated Triphenyl Phosphorothionates in Oil Solution in the Presence of Iron Particles

Mangolini, Filippo ; Rossi, Antonella ; Spencer, Nicholas

In: Tribology Letters, 2010, vol. 40, no. 3, p. 375-394

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    Titre
    • Substituent Effect on the Reactivity of Alkylated Triphenyl Phosphorothionates in Oil Solution in the Presence of Iron Particles
    Auteur
    • Mangolini, Filippo. Department of Materials, ETH Zurich, Laboratory for Surface Science and Technology, Wolfgang-Pauli-Strasse 10, 8093, Zurich, Switzerland
    • Rossi, Antonella. Department of Materials, ETH Zurich, Laboratory for Surface Science and Technology, Wolfgang-Pauli-Strasse 10, 8093, Zurich, Switzerland
    • Spencer, Nicholas. Department of Materials, ETH Zurich, Laboratory for Surface Science and Technology, Wolfgang-Pauli-Strasse 10, 8093, Zurich, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Tribology Letters, 2010, vol. 40, no. 3, p. 375-394. Springer US; http://www.springer-ny.com
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:321088
    Summary
    The effect of the substituent attached to the phenyl rings on the reactivity of alkylated triphenyl phosphorothionates (t-butyl TPPT (b-TPPT) and p-nonyl TPPT (n-TPPT)) in oil solution at high temperature (423 and 473K) was investigated by means of Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The FT-IR and NMR results show that the alkylated TPPTs were highly thermally stable and did not completely decompose in oil, even upon heating at 423K for 168h and at 473K for 72h, with and without steel filings and iron particles (both metallic iron and iron oxide particles). The reaction of alkylated TPPTs was found to start with the scission of the P=S bond to yield alkylated triphenyl phosphate. The kinetics of the thermo-oxidative reaction was slower when steel filings and iron particles were added to the oil solutions during the heating experiments. The reactivity of the unsubstituted molecule (TPPT) was higher than that of alkylated TPPTs at 423K, while at 473K TPPT and n-TPPT were more reactive than b-TPPT. In the case of the experiments performed at 473K in the presence of steel filings or metallic iron or iron oxide particles, the reactivity of the alkylated TPPT molecules decreased with the length of the alkyl chain bound to the phenyl rings. The XPS results show that a reaction layer consisting of carbon, oxygen, phosphorus and iron was formed on the 100Cr6 steel filings immersed for 72h in oil solutions containing alkylated TPPTs and heated at 473K. Sulphur was neither detected on the surface nor in the composition vs depth profile. During the heating experiments, the base oil (PAO) was oxidized. At 423K, the alkylated TPPTs had a strong antioxidant effect, which was found to be more pronounced upon increasing the length of the alkyl chain bound to the phenyl rings. At 473K, the TPPTs did not inhibit the oxidation of the base oil as effectively as at 423K