What does it mean to 'model' a corrosion process? If you read a typical corrosion journal you will probably come to the conclusion that it can mean many different things, depending on the circumstances. In a very simple case, a 'model' might simply be a written explanation of the underlying reasons for experimental results; for example, the high dissolution rate within pits in stainless steel is due to the maintenance within the pit of an aggressive local chemistry, with a lower pH and higher chloride concentration than in the bulk solution outside the pit. At another level, the same 'model' might be described using a series of chemical and/or mathematical equations; for example, chemical equations can easily be written out for the hydrolysis of dissolved metal ions to produce local acidity within a pit, and thermodynamic calculations can be used to show the existence of potential-pH conditions in which the passive film is not stable and active corrosion would be expected. To such a 'model' it is then possible to add some kinetic equations (e.g. Tafel's Law) and use finite-element methods to run computer simulations of the growth of corrosion pits.
展开▼
