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An Investigation of the Effects of Oxygen and Water Vapor on the Compressive Strength of Boundary Films on Iron Substrates.

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Final annual rept.,

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The purpose of this program is to determine the effects of O2 and H2O on boundary film formation by studing a model system consisting of 2-ethylhexyl sebecate and tricresyl phosphate TCP on ARMCO iron surfaces. This report deals with the first year, wherein, film compressive strength measurements, supported by ellipsometry, were used to study the behavior of these reactants as a function of time and temperature in a laboratory atmosphere. For films formed out of the pure ester, two transitions in compressive strength and film thickness were observed at 93 C and 180 C. The rate of change of film compressive strength of TCP-ester solutions decreases with temperature of 100-120 C after which the rate increases. For the pure ester, the rate of formation of a mechanically significant film is low until temperatures 120 C are reached. Under all conditions of temperature, mechanically significant films form relatively slow -- of the order of minutes -- from the TCP solution. Water, adsorbed or dissolved, appears to play a significant role in the formation and degradation of these films. A working hypothesis in terms of the hydrolysis of the ester to form sebacic acid at temperatures around 100 C is presented. Ellipsometric data suggest that the high temperature loss of compressive strength in those films is due to the onset of rapid substrate oxidation, perhaps accompanied by decomposition of the surface-bound organic species. Author

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  • Physical Chemistry
  • Lubricants and Hydraulic Fluids

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