Comparison of four antitarnishing self-assembled monolayers on silver coin

Abstract

By accelerated tests and electrochemical measurements, the characteristic of four self-assembled monolayer (SAM) covered silver, which were octadecanethiol monolayer from aqueous solution (OSA), octadecanethiol monolayer from organic solvent (OSO), phytic acid monolayer (IP₆) and silicon tungstemic acid monolayer (STA), was studied. The results indicated that the OSA, STA, IP₆ and OSO on the silver provided a practical method to prevent silver from tarnishing. All SAMs acted as cathodic inhibitors. The protection effect of OSA was similar to that of OSO, both of which were more effective than IP₆ and STA. The charge transfer resistance increased from 76 Ω cm² for bare silver up to 1456, 474 , 1050 and 1212 Ω cm² for OSA, STA, IP₆ and OSO covered silver respectively. The 48 h accelerated tarnishing tests proved the protection efficient of SAMs, in the order OSA≈OSO>IP6>STA, which indicated that STA and IP₆ were not the completely compact film.