Corrosion-Induced Performance Degradation of Phosphorus-Containing Scale Inhibitors at Carbon Steel–Water Interface

Phosphorus-containing scale inhibitors have been widely used to mitigate CaCO 3 scaling on the surface of metal device. In this work, the antiscale performances of two typical additives, sodium salts of hexametaphosphate (SHMP) and ethylenediaminetetramethylene phosphonate (EDTMPS), were evaluated on carbon steel through comparing scaling behavior under self-corrosion and cathodic polarization conditions, respectively. Results reveal that anodically released Fe 2+ ions exert important influences on their antiscale behavior at carbon steel–water interface. During cathodic polarization processes, fewer or no Fe 2+ ions are produced at the interface, and the two inhibitors effectively retard scale formation by their chelating role. However, once electrochemical corrosion occurs, more Fe 2+ ions released from anode tend to diffuse toward cathodic regions, strongly interfering in their antiscale performances by preferentially replacing interfacial chelated Ca 2+ ions. Then, these liberated Ca 2+ ions are forced to react with cathodically formed CO 3 2– ions, resulting in the scaling of CaCO 3 at carbon steel–water interface.