Application of sealed capsule differential scanning calorimetry - Part II:Assessing the performance of antioxidants and base oils (c)

For many years antioxidants have been added to lubricating oils to suppleme nt antioxidants naturally occurring in the oil. These artificial antioxidan ts added alone or in synergistic combinations extend the operating life of the oil by improving its "oxidation stability." In this study, the relative oxidation stability of a range of antioxidants was successfully evaluated by a sealed capsule differential scanning calorimetry (SCDSC) technique. If was found that under the test conditions employed, an aromatic amine, diph enylamine (DPA), was the most effective antioxidant followed by a group of hindered monophenols and finally a hydroperoxide decomposing ZDDP. The SCDS C technique was also used to evaluate the oxidation performance of a number of base oils which are used to blend formulated oils. It was found that th e aromatic content has an important role in resisting base oil oxidation. F inally, the technique employed successfully evaluated the performance of a known synergistic antioxidant mixture, 2,6-di-tert-butyl-4-methylphenol and DPA. Overall, the SCDSC technique is capable of screening different antiox idants and mineral base oils for product development work. The technique is precise, uses only microliter quantities of sample and is not dependent on operator interpretation.