Nanocrystalline Ag–C Composites Containing a Hexagonal Diamond Structure to Inhibit Tarnishing of Sterling Silver

Abstract

Three-dimensional nanocrystalline Ag–C composites containing a hexagonal diamond structure were produced by electrochemical reduction of acetic acid and electrodeposition of Ag­(NO3) (0.01 M) at −1.1 V vs Ag/AgCl at ambient conditions. After applying the negative potential, an ultrathin layer of Ag (<0.1 μm) was first deposited, and subsequently, competitive electrodeposition of Ag and electroreduction of acetic acid resulted in the formation of nanocrystalline Ag–C products on the electrodes. A combination of microscopic, structural, and spectroscopic characterization results reveals that the nanocrystalline Ag–C contains a hexagonal diamond structure with an average crystallite size of 26 nm. The nanodiamond phase remained unchanged throughout 15–140 min reaction time. However, increasing the reaction time, the thickness of nanocrystalline Ag–C films increased to ∼2 μm with some large polyhedra carbon structures. The nanocrystalline Ag–C composites were utilized in the casting process of sterling silver to enhance its antitarnish properties. The antitarnishing of sterling silver upon exposure to a H2S environment was significantly improved by 50% with 0.005 wt % loading of the Ag–C composite.