Removal of copper corrosion using in-situ and ex-situ film formed from hydrogels

Eco-friendly and non-harmful hydrogels were developed with the aim of corrosion removal from copper. The target for cleaning was prepared through electrochemical corrosion of copper sheets. X-ray diffraction analysis was performed to determine the corrosion products. Using the hydrogel, of which the composition was optimized, specifically one containing 15 wt% poly(vinyl alcohol) (PVA) with 10 wt% glycerol as well as one with 15 wt% sodium carboxymethyl cellulose, corrosion removal of the aforementioned target was carried out. For cleaning with in-situ films, the gels to which 7 wt% citric acid was added were applied and dried directly on the corroded copper, while ex-situ films were prepared by casting gel in a petri dish, drying, and immersing in 7 wt% citric acid solution and placed on the corroded copper. By peeling the films from the copper, corrosion removal was done. Deeper corrosion removal with a better area selectivity was achieved with in-situ films. In the case of PVA-based in-situ films, although the treatment influenced the deeper corrosion layer, the cuprite layer adjacent to the metallic copper was preserved. Infrared spectra of the in-situ PVA film formed on clean copper and corroded copper were compared to discuss the mechanisms of corrosion removal. Strategies for the corrosion removal with a high area selectivity using hydrogels are therefore proposed.