ABSTRACT
Reactions initiated and proceeding under boundary and/or mixed lubrication processes concern tribochemistry, which deals with the chemical changes of both solids and lubricant molecules due to the influence of friction operating conditions. Generally, it is accepted that chemical reactions are initiated either by temperature or by a kind of irradiation [for instance, ultraviolet (UV) irradiation and nuclear irradiation], or just by mechanical treatment and/or impact. Thus, under boundary lubrication conditions, chemical reactions are also initiated by mechanical forces in solids, which support shear strains. Shear changes the symmetry of a solid and/or molecule, and is therefore more effective in stimulating reactions than in simple isotropic compression. Consequently, the mechanical action at solid surfaces tends to promote chemical reactions and produce surface chemistry that may be entirely different from those observed in static conditions. Such mechanical activity is caused by symmetry breaking, which destabilizes the electronic structure of bonding and makes the solid prone to chemical reactions.
