Last week I posted a question on the relationship between the chloride concentration and CO2 hydration in water. I was thinking that increasing the chloride concentration restricts CO2 hydration in a way that decreases the concentrations of the corrosive H2CO3 and HCO3- species -- and accordingly, the corrosion rates become lower. I am still searching for a way by which I can link experimentally, not thermodynamically, between chloride concentration and CO2 hydration. I would like to indicate that a group of researchers came up with very interesting and important points on the last week's question: https://www.researchgate.net/post/How_can_we_link_together_CO2_hydration_and_chloride_concentration_in_water
Now, could you please check out this trend between the corrosion rates and chloride concentration. The corrosion rates (or corrosion current densities) were calculated from 0.5 mV/s potentiodynamic scans. They increased with chloride concentration up to certain maximum value beyond which they decreased.
What do you think? Any suggested reasons behind this trend?
Dear Faysal,
One of my recent publications explored an issue related to this, i.e., the pitting corrosion risk of steel as a function of pH, chloride concentrations, and DO.
It may or may not be useful for your scenario:
Shi, X., Nguyen, T.A., Kumar, P., and Liu, Y. A Phenomenological Model for the Chloride Threshold of Pitting Corrosion of Steel in Simulated Concrete Pore Solutions. Anti-Corrosion Methods and Materials 2011, 58(4), 179-189. DOI:10.1108/00035591111148894
One other possibility is that the rust become a corrosion inhibitor. I remember that 3.5% NaCl (or similar number) is most corrosive concentration to steel; likely for the same reason(s). In your case, there is also the dynamics between free and bound chlorides...
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