Erosion-corrosion mapping of Fe in aqueous slurries: some views on a new rationale for defining the erosion-corrosion interaction

In studies of erosion-corrosion of materials in aqueous conditions, there have been various attempts to define regimes of interaction. Such regimes indicate whether erosion or corrosion may dominate the wastage mechanism. However, intermediate regimes in which corrosion and erosion interact with each other may lead to situations where the wastage is far greater than the sum of the processes acting separately. A common method of defining erosion-corrosion interactions has been to distinguish between the regime in which erosion enhances the corrosion rate (the so called "additive effect" because the corrosion contribution can be measured electrochemically and thus added to the erosion contribution to assess the overall wastage rate) and the regime where corrosion enhances erosion (the so-called "synergistic" effect). However, regimes of erosion-corrosion, where corrosion impedes the erosion are also of great importance mechanistically, and usually these are termed as exhibiting "negative synergism". Defining the conditions in which a transition from "positive" to "negative synergism" occurs, is useful in order to optimize the parameters to minimize the wastage rate. This paper reviews the rationale that has been used to define erosion-corrosion regimes in aqueous conditions as part of a study of the erosion-corrosion of Fe at various pHs. The mathematical definitions are discussed in relation to practical erosion-corrosion problems. In addition, a new "antagonistic" erosion-corrosion regime is proposed to properly define the concept of "negative synergism"