Particulate erosion–corrosion of Al in aqueous conditions: some perspectives on pH effects on the erosion–corrosion map

Abstract

In the nomenclature to describe erosion–corrosion behaviour in aqueous conditions, there has been considerable confusion in relation to the terminology used to describe the various interactions. One such description has been to separate the effects into two main divisions, the effects (”synergistic”) of corrosion on the erosion rate (i.e. the change in mechanical response of the material due to corrosion) and the effects (”additive”) of erosion on the corrosion rate (the change in corrosion of the material due to mechanical action). In addition, there is confusion on why some materials exhibit high “synergistic” effects whereas others tend to lose material mainly through “additive” effects. This paper describes a programme of work carried out in an impinging jet apparatus, in which the erosion–corrosion response of Al was investigated at three pH values. The effects of applied potential and velocity were also assessed in these conditions. The results showed that the erosion–corrosion response very much depended on the pH and the potential. For Al, at pH∼13, the erosion–corrosion response was dominated by dissolution. However, at pH values of 4 and 7, the response differed due to the adherent passive film formed on Al in these conditions. Erosion–corrosion maps were constructed for Al in the various environments based on these results.