Corrosion in Oxidizing Environments Without Localized Corrosion

Oxidizing environments involve cathodic reactions that occur at more positive potentials than the proton reduction reaction. Generally, these environments lead to passive dissolution in the absence of chloride or other halides that can cause localized corrosion. Thus, the presence of oxidizing species can lead to a reduction in corrosion rates of passive alloys. However, if the pH is below the depassivation pH, high corrosion rates can result. This chapter discusses corrosion of Ni-base alloys in oxidizing acids, such as nitric and chromic acid and mixtures of these with other acids. Acid mixtures containing oxidizing species, such as ferric ions, are also discussed. Some industrial acids, such as wet process phosphoric acid are described. A model-based analyses of these results is presented.