Chloride ion-triggered silver alginate (Alg-Ag) microcapsules for reinforcement anti-corrosion: Preparation and inhibition mechanism

The application of corrosion inhibitors provides an efficient approach for mitigating steel rebar corrosion. However, the premature failure of corrosion inhibitors in concrete remains a pending issue. The adoption of microencapsulated inhibitors shows significant promise in addressing this concern. This study proposes a novel chloride ion-triggered microcapsule designed for the anti-corrosion protection of reinforcement. The microcapsules were synthesized using calcium carbonate (CaCO 3 ) particles as a template and sodium monofluorophosphate (MFP) as the encapsulated inhibitory core. The exterior of the CaCO 3 particles was coated with a silver alginate (Alg-Ag) layer, which confers the chloride ion-triggered release mechanism. The activation of microcapsules occurs through a chemical reaction between silver ions in the Alg-Ag layer and chloride ions from the environment, resulting in the formation of silver chloride and the subsequent disintegration of the microcapsule. The MFP inhibitor is released as a consequence. The fabricated microcapsules were characterized in terms of morphology and chemical composition. The inhibitory performance of the microcapsules was analyzed by electrochemical methods. The use of the CaCO 3 template was found to be effective in producing a porous matrix suitable for the loading of MFP. The microcapsules exhibit a well-defined spherical morphology with a distinct core-shell structure. Both FTIR and TG analysis confirmed the successful entrapment of MFP within the core of microcapsules. Electrochemical corrosion tests demonstrated that the microcapsules effectively retarded the corrosion process of the reinforcement, with the corrosion inhibition efficiency increasing from 59.1 % at 24 h to 63.8 % at 72 h, indicative of a controlled and progressive release of the inhibitor from the microcapsules.