Radical Scavenging Mechanism and Antioxidant Effect of Fullerenes in Lubricating Oils (Part 3)

―Antioxidant Performance of Fullerenes Compared to Conventional Lubricant Antioxidants―

Abstract

Zinc dithiophosphate (ZnDTP) is used in lubricating oils as an antioxidant. However, its use has been discouraged because it contains phosphorus, which has a high environmental burden. Thus, a new multifunctional additive is required, and fullerenes are attracting attention for this purpose. Although it is known that fullerenes prevent oxidation, their antioxidant performance compared to conventional lubricant antioxidants has not been evaluated, nor has their antioxidant mechanism been elucidated. In this study, we evaluated the oxidation stability of fullerenes and conventional lubricant antioxidants. In addition, model radicals were reacted with fullerenes and conventional lubricant antioxidants in oil to determine the number of radicals captured per molecule. It was shown that fullerenes can capture about five radicals per molecule in oil, which is more than can conventional lubricant antioxidants. Furthermore, it was found that the radical scavenging effect of fullerenes is correlated with the number of dissolved fullerenes.