Characterization of fully and partially additized lubricant deposits by Temperature Programmed Oxidation

Temperature Programmed Oxidation (TPO) was used to analyze carbonaceous deposits derived from the thermal decomposition of a Group 1 base oil and a fully-formulated lubricant. Deposits generated from thermal decomposition of concentrated blends of detergents, dispersants, viscosity modifiers, and antioxidants additives were also analyzed. Results obtained from each of the deposit specimens featured “unique” oxidation profiles. For fully-formulated lubricants and base oil-derived deposits, two characteristic peaks with an overlapping tendency were observed. The first evolved at a relatively lower oxidation temperature and the second at a higher oxidation temperature. Similarities between formulated lubricant and base oil TPO profiles were attributed to the common base oil found in both samples. However, higher thermal stability of the fully-formulated lubricant led to minimal deposition and less intense TPO peaks compared to the base oil-derived deposit profiles. For concentrated additive-derived deposits, deposits showed distinct oxidation profiles, unique to each category of additive and not comparable to any other deposit type.