Study on the affinity sequence between inhibitor ions and chloride ions in Mg-Al layer double hydroxides and their effects on corrosion protection for carbon steel

A simple method was proposed to investigate the affinity sequence between inhibitor ions and chloride ions based on the pH values of filtrate after reconstruction of calcined layered double hydroxides (CLDH) in the corresponding salt solution with the following results: CrO42- > C6H5COO- > Cl- > NO2- > NO3-. The relationship between pH values and affinity sequence was further discussed by a conceptual model. Another common method was also performed for comparison and the same results verified the feasibility and accuracy of the above method. Electrochemical tests revealed the LDH loaded with inhibitors could provide effective corrosion protection for carbon steel in the simulated concrete pore (SCP) solution with following inhibition efficiency sequence: NO2-LDH > NO3-LDH > C6H5COO-LDH > CrO4-LDH. Long-term immersion experiment showed the NO2-LDH had the best anticorrosion effect in a long period. Therefore, NO2- can be an excellent candidate for inserting into LDH interlayer to exert LDH's dual effects of releasing inhibitor anions and immobilizing chloride ions.