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Application of temperature‐programmed oxidation (TPO) in studying the mechanism of deposits formation from the degradation of lubricants on metal surfaces

Temperature‐programmed oxidation (TPO) was used to investigate the mechanism of lubricant‐derived deposit formation on metal surfaces. The relationship between the crystalline structures of different carbonaceous specimens, along with their chemical reactivity, was used to distinguish between more reactive and less reactive lubricant deposits. Multiple CO2 peaks obtained were attributed to differences in the oxidation reactivity of the deposits with respect to their structural characteristics. Findings from this work suggest that as deposits evolve, they become more complex (varied) due to loss of O and H atoms during a carbonisation‐type process. As these deposits undergo visible changes over time (lacquer deposit transforming into dark carbon), the average peak temperature (weighted average oxidation temperature) monotonically increases. Characterisations of lubricant deposits by TPO indicate that the global change in carbonaceous structure proceeds across the deposits in a uniform layer deposition model. Copyright © 2013 John Wiley & Sons, Ltd.