Dissolution properties of cerium dibutylphosphate corrosion inhibitors

Abstract

The corrosion inhibitor cerium dibutylphosphate, Ce(dbp)₃, prevents corrosion by cerium and dbp deposition at the alkaline cathode and acidic anode respectively. The pH dependent Ce(dbp)₃ solubility seems to play an essential role in the inhibition degree. We found that Ce(dbp)₃ scarcely dissolves in water with a ̃1 mM solubility limit between pH 2 and 9, whereas at pH 1, we found ̃3 mM due to protonation of dbp, and for pH >9, the cerium precipitated as Ce(OH)₃. We believe that the Ce(dbp)₃ dissolution process is an important aspect for understanding its release from coatings and thus the corrosion inhibition. In case of a pressed Ce(dbp)₃ tablet, its dissolution is dominated by transport of dissolved Ce(dbp)₃ across a stagnant diffusion layer. The chemical bond strength between cerium and dbp is a major factor in their transport. The infrared spectrum of Ce(dbp)₃ powder revealed a covalent-like bond, while the molar conductivity showed complete dissociation, so Ce(dbp)₃ transports in water as separate ions.