Thermal decomposition of lubricant oil adsorbed on gold and oxidized iron foils

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Abstract
The thermal decomposition of poly-α-olefin base lubricant oil (tridecene oligomer) adsorbed on clean gold and oxidized iron foils has been studied by x-ray photoelectron spectroscopy (XPS) and thermal desorption (TDS) in order to elucidate the chemical reactions associated with lubrication and wear. Thermal treatments were performed both in vacuum where the progress of reaction was monitored by XPS and TDS and in air with periodic examination of the surface by XPS. The coverage of oil was many monolayers on both surfaces at room temperature in vacuum. The intact poly-α-olefin desorbs at 130 °C with an activation energy of 70 kJ/mol which is equal to ΔH of vaporization. Thermal decomposition of the remaining adsorbed hydrocarbon occurs above 150 °C as indicated by the appearance of volatile hydrocarbon fragments and by shifts in the C(1s) binding energy. The temperature dependence of decomposition is identical on both substrates suggesting that it is not catalyzed by the surface. Under vacuum conditions the iron is reduced by surface reaction intermediates to produce carbon monoxide and metallic iron. This suggests that iron on the surface of bearings may cycle between oxidized and reduced states.

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