Evaluation of Corrosion Inhibition of Tannic Acid on Simulated Archaeological Cast Iron by EIS in Gel System

To overcome the difficulties in the practical application of electrochemical technology to the detection of metal cultural heritage, agar and sodium sulfate were used as gel electrolytes, and a three-electrode system was constructed with platinum mesh and silver/silver chloride electrodes and simulated ancient cast iron. Combined with electrochemical impedance technology, the corrosion detection of rusted cast iron could be realized, and the effect of tannic acid as a protective material could be effectively monitored. Experiments showed that tannic acid can form a corrosion-inhibiting film structure on the surface of the sample in a short period of time, which could increase the surface charge transfer resistance of thin-layered rusted cast iron by about 10 times. The rust resistance of thick-rusted iron could be increased by 3 times and the charge transfer resistance was increased by about 2 times. Besides, the inherent corrosion mechanism was not changed. However, there were micro-cracks in the corrosion-inhibiting film, which would lead to the infiltration of corrosive medium in the subsequent accelerated corrosion process, induce new corrosion and destroy the film structure, thus losing the protective effect. The experiment explored the data correlation between the electrochemical impedance in-situ detection technology based on gel electrolyte and the microscopic morphology of scanning electron microscope, which provides support for the scientific monitoring of metal cultural heritage protection.