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Previous results obtained in this laboratory have shown that tricresyl phosphate vapors preferentially react with iron and its oxides in the order of the oxidation state (reaction rate of Fe3+≫Fe2+>Fe+>Fe). The reaction kinetics is attributed to a Lewis acid, FenOm, reacting with the basic phosphate ester, (ArO)3PO. The current research further investigates the role of the oxide in the reaction of the aryl phosphate lubricants, tricresyl phosphate and tertiary-butyl phenyl phosphate, with 1010 steel coupons. To measure the relative effect of iron oxides, some coupons were exposed to 400 °C air for 1 h and then sealed under vacuum in glass tubes with 25 mg of lubricant. Other samples were sealed under vacuum without the oxidation step. All of the sealed test tubes with lubricant and foil were heated to a temperature of 475 °C and held for different lengths of time. Afterwards, the coupons were analyzed with Fourier infrared microscopy, Auger electron spectroscopy, Raman spectroscopy, and scanning electron microscopy. In the case of the pre-oxidized sample, a nodular film was formed that contained organic species and iron polyphosphate. For samples that were not pre-oxidized, simple ionic iron phosphate was formed. In another work it was found that nodular structure formation is important to obtain good lubrication. This type of film forms on iron surfaces and not on surfaces passivated by inert oxide films, i.e., aluminum, nickel, and high chrome content alloys. The reaction of tricresyl phosphate with other metals and their oxides were also examined and found to correlate well with iron.