ABSTRACT
Lubricants are o§en exposed to severe environmental conditions that require the use of antioxidants to inhibit oxidation. In recent years, the eµectiveness of various antioxidants has been complicated by a number of confounding factors. ˜ese include drastic base stock changes, environmental pressures to reduce lubricant volatility and extend drain intervals, reductions in Ÿnished lubricant sulfur, ash, and phosphorus, and the exceedingly fast pace of new and more demanding oxidation and deposit control speciŸcations for lubricants. ˜is has resulted in a renewed interest in lubricant degradation mechanisms and the additives (i.e., antioxidants) used to suppress this degradation. ˜e purpose of this chapter is to review the chemistry of lubricant oxidation and antioxidant function as it pertains to the stabilization challenges encountered with today’s lubricants. ˜e mechanism of function for the most important classes of antioxidants will be discussed. In addition, the criteria for proper antioxidant selection, synergistic interactions between diµerent classes of antioxidants, and the impact hydrocracked and synthetic base stocks have on the performance of the various antioxidant classes will be presented.
