Formation of deposits from thin films of mineral oil base stocks on cast iron

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

“…For carbonaceous material formed from low oxidation times, the normalised peak width of the TPO profile is small, indicating the homogeneity in the carbon species present in the deposit. As temperature increases, the normalised peak width also increases as the variety of carbon species increases as the film chemistry changes through loss of O and H atoms during a carbonisation‐type process . Depending on the oxidative stability of the base oil, the shape of the average peak temperature and normalised peak width curves shown in Figure varies as a function of oxidation time.…”

“…Consistent with the prior results, as the deposit undergoes visible changes over time (lacquer deposit transforming into dark carbon), the average temperature (mass‐weighted, mean oxidation temperature) monotonically increases, as described in Figure . This reflects the global (homogeneous) change in film composition . As film chemistry evolves, it becomes more complex (varied) as indicated by the increasing breadth of the TPO peak.…”

Deposit formation from lubricant degradation: a uniform layer deposition model

“…Tseregounis also described the induction time as decreasing exponentially with increasing temperature. Equation was therefore used in their study to account for the dependence of the induction time on the film thickness and the temperature …”

“…As oxidation proceeds, deposits undergo a transition, chemically, during this so‐called transitioning phase. During this period, pre‐existing polymeric deposits undergo dehydrogenation and dehydration reactions . The resulting tenacious films are polymeric in structure and carbonaceous in appearance .…”

“…Dark carbonaceous deposits resulted after 120 min of oxidation (for the PSMO conditions employed) using mineral base oil, as shown in (Figure d). Dark carbonaceous deposits are formed when polymeric deposits on hot surfaces undergo severe dehydrogenation and likely some degree of aromatisation reactions . These deposits consist mainly of elemental carbon and are indicative of the final stage of lubricant oxidation; such deposits represent the end stages of lubricant degradation.…”