Oxidation studies of lubricants from Dornte to microreactors

Friction, wear and the oxidation of lubricants are concerns in most mechanical systems. Selection of the best current thermoanalytical method to evaluate the oxidative performance of a lubricant for an application is an ongoing problem. The variability and complexity of mechanical systems makes correlation with bench tests difficult. The oxidative environment in automotive applications may vary from nil in sealed-for-life components to severe oxidative conditions found in piston, ring, and liner zones. The researcher's task is to develop useful and meaningful bench tests to allow the engineer to concentrate his effort and resources on developing better lubricants for a given application. This paper reviews the evolution of oxidation test methods for the past 50 years from large complex systems to the current microanalysis methods. The mechanism of oxidation has changed very little but our understanding of additive interactions has advanced significantly. Additive depletion and the resulting oxidation process can be studied using the microthermooxidative methods. Often, a combination of methods can be used to obtain a better understanding of the thermal and oxidative processes occurring. Some comparisons of the methods and their applications are described.