ABSTRACT
Perhaps the most misleading comment in the mechanics of tribology relating to the instant of contact is, "and there is adhesion," apparently implying bonding of uniformly high strength over the entire contact area. It is not that simple in the vast majority of contacting events. Ever-present but ill-defined adsorbed gases and contaminants, as well as the directional properties of atomic bonds, limit attachment strength to modest values. The bond angles are very specific in covalent solids. There are four atomic bonding systems in nature: the metallic bond, the ionic bond, the covalent bond, and the Van Der Waals bond systems. These are often referred to as cohesive bonding systems. Actually, chemisorption involves two steps — physical adsorption followed by the combining of the adsorbate with substrate atoms to form a new compound. However, when two different ceramic materials are rubbed together, there is an increased probability that some fortuitous and adequate alignment of lattices occurs to form strong bonds.
