The reduction of copper sulfide and copper oxides originated during artificial tarnishing of copper was studied using potentiodynamic potential/current density experiments. Six copper surface treatments were considered: mechanical polishing; indoor exposure for 7 days; chemical etching in 1.6 M nitric acid; chemical etching and heating at 160 deg C; and chemical etching and dipping in a 9 X 10~(-4) M or 0.9 M potassium sulfide (K_2S) solution at 70 deg C. Cuprite (Cu_2O) and chalcocite (Cu_2S) were the main compounds formed. A linear relationship with the square root of the scan rate (v) was obtained by plotting the potentiodynamic potential/current density for the tarnish dissolution processes. A relationship between potential and current density cathodic peaks was not obtained, according to Muller's model, showing a proportionality factor with the dimensions of a resistance.
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