1. Introduction

Oxidation is an unwanted process which results in degradation of lubricants (containing hydrocarbons C20-C70) and generation of degradation products. Oxidation can start with the presence of oxidative agents such as oxygen to form a wide range of oxidation products with higher or lower molecular weight relative to the original oil depending on the progress of the process. Generation of lacquer and varnish, viscosity increase, sludge and deposit formation, and corrosion are some important consequences of oxidation. Copper and iron in metal parts, and harsh conditions such high pressure, high temperature, high friction and high metal concentration are factors that accelerate lubricant oxidation. In combustion engines, the generated heat from combustion process would be high enough to oxidize the lubricating oil unless antioxidants present in the formulation inhibit the progress of oxidation and the formation of degradation products.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

distribution, and eproduction in any medium, provided the original work is properly cited.

Antioxidants are a group of additives that have the potential of prohibiting oxidation of base oil in the lubricants and the inhibition of oil breakdown and thickening [1, 2].
