General Overview: Atomistics of Surface Reactions

The adsorption of a molecule is the first step in the modification of the mechanical properties of a metal by the environment. Once adsorbed, the molecule can play a number of different roles that are relevant to the phenomena of fracture. It can react with the surface to form a coherent and stable layer that protects the solid from further influence from the environment; it can react with the solid to corrode it. This reaction can be activated by mechanical energy stored in locally enhanced stresses and lead to stress corrosion cracking. Hydrogen can dissociate and penetrate the metal and lead to hydrogen embrittlement. The molecule can displace from the surface, or react with, a potentially harmful adsorbate and stop the environmental degradation of the solid. Thus, the study of the physical and chemical interaction of fluids with solid surfaces is of importance to the understanding of environment effects on the fracture of a material under stress.