163 / 2022-04-30 09:35:22

Application of zeolitic imidazolate framework (ZIF-8) as high-efficient corrosion inhibitor for the reinforcement in cement extract

Metal-organic frameworks; Corrosion inhibitor; Adsorption; Steel reinforcement; Cement extract

The deterioration of reinforced concrete structure caused by corrosion damage of the reinforcement is severe engineering problem, significantly shortening the service life of reinforced concrete. Admixing organic corrosion inhibitor is regarded as an efficient way to prevent the corrosion damage of the reinforcing steel. Metal-organic frameworks (MOFs) can be potentially applied as corrosion inhibitors for reinforced concrete due to their supramolecular structure.



In this study, the inhibition effect of the prepared zeolitic imidazolate framework (ZIF-8) corrosion inhibitor on the reinforcement in cement extract was extensively investigated by electrochemical measurements and surface analysis. It was found that the well-defined ZIF-8 with representative rhombic crystalline structure and uniform size distribution was successfully synthesized by solvent method (Fig. 1). ZIF-8 prepared in this study exhibited good chemical stability in alkaline and neutral solution; as a result, the concentration of the released 2-MeIm from ZIFG-8 was very low in alkaline and neutral solution, while ZIF-8 decomposed in acid solution (Fig. 2), leading to possible “self-repairing” effect after during pitting corrosion propagation of the reinforcement in cement extract.



In chloride-containing cement extract, ZIF-8 corrosion inhibitor was efficiently adsorbed on the reinforcement surface and mainly reduced the anodic reaction rate by halting the dissolution of the reinforcement, thus significantly increasing the charge transfer resistance of the reinforcement (Fig. 3) and exhibiting high inhibition efficiency during the initial 24 h. Meanwhile, the inhibition efficiency was still maintained at 87.8 % after 168 h with ZIF-8 concentration of 0.04 wt. % (Fig. 4) due to the pH drop caused by pitting propagation at the local corrosion sites resulted in the decomposition of ZIF-8 and Fe-N coordination bond formed between the released 2-MeIm ligands and reinforcement.



Based on SECM (Scanning Electrochemical Microscopy) mapping, no obvious current peaks occurred but relative homogeneous current distribution presented with a flat surface on the reinforcement surface in cement extract with ZIF-8 (Fig. 5), implying pitting corrosion was dramatically halted and uniform corrosion was aroused on the reinforcement surface in the presence of ZIF-8. The excellent corrosion inhibition performance of ZIF-8 was ascribed to the strong adsorption behaviors of ZIF-8 on steel surface. The adsorption of ZIF-8 on the reinforcement surface was finished during a very short period of 40 min in cement extract, including fast chemisorption stage within 20 s and film thickness increase stage resulting from the rearrangement process of ZIF-8 (Fig. 6). Therefore, ZIF-8 corrosion inhibitor proposed in this present study provides a promising way for the effective corrosion protection of reinforced concrete under chloride-contaminated environment.