Dissolution properties of cerium dibutylphosphate corrosion inhibitors

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 similar to 1 mM solubility limit between pH 2 and 9, whereas at pH 1, we found similar to 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.