Molecular Modeling of Corrosive Environments in Cracks

Presented are concepts and results of molecular modeling of the chemistry of the environment - crack interactions. Water, salt and acid solutions, hydrogen, and hydrogen sulfide were evaluated on magnetite and hematite covered open surface and crack tip. Interactions of these environments with the oxides are expressed as relative interaction energies. Individual molecules and ions of the environment equilibrate in their preferred positions within the crack and other surfaces. When different crystallographic planes are present, the chemical species often separate, forming groups of cations, anions, and neutral molecules. The results indicate relative aggressivity of the environments, types of chemical/corrosion reactions, and the rate of mass transport to the crack tip. They may lead to models of the mechanisms of stress corrosion and corrosion fatigue.