Tribochemical reactions at and in the vicinity of a sliding contact

Tribochemical reactions, which are involved in both friction and wear processes, are crucially important to solve tribological problems. The origins of chemical reactions in mechanical contacts are threefold depending on the reaction regions: inside the contact area (ICA), near or in the vicinity of the contact area (NCA) (especially in the gap between a sphere and a plan), and far outside the operating contact area (OCA). Each of the three region reactions has significant role depending on the tribosystem, the friction conditions and the time. Two or all three of the reaction regions can operate simultaneously or consecutively to cause chemical reactions, leading to effective or poor lubrication of the tribosystem. We discuss here tribochemical reactions both inside (ICA) and at the vicinity (NCA) of the contact area presenting some representative examples.