A mathematical model is developed to describe the processes by which transient appearance of salt films occurs during initial stages of corrosion of oxide-free metal surfaces. The model describes transport-controlled processes which lead to supersaturation by anodic dissolution, to precipitation of a salt film, and eventually to dissolution of the salt film after oxide passivation of the substrate material. Experimental observations on iron repassivation in 6AT H2SO4 were used to test predictions of the model. Measurements of the lifetime of the salt film on the iron surface were in agreement with the model predictions; measurements of the extent of supersaturation prior to precipitation and of the moment of precipitation were in agreement with previous studies. In applying the model to predict the behavior of titanium in 3N HC1, calculations indicated that salt films of 20-100Å would be expected to form and then disappear within the time period of 10-5-10-3 sec after generation of the oxide-free surface; during this period of time, the anodic dissolution rate of titanium would be expected to exceed 150 A/cm2 if the salt film hypothesis is valid. The model presented here should be useful in guiding future experimental work into critical regions of parameter space.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry