Anodic dissolution of iron in ammoniacal ammonium carbonate solution

The electrochemical behavior of iron has been characterized in aqueous ammoniacal ammonium carbonate solution. Pure iron anodically polarized in He-or O₂-saturated 2 kmol m^-3NH₃+ 1 kmol m^-3(NH4)2CO3 solutions exhibits both stable active (E =-650 to-400 mV, SHE) and passive (E =-330 to 1000 mV) regions. A cathodic loop was observed in the potential range of-380 to 100 mV. It is suggested, on the basis of cathodic polarization curves of a graphite electrode in various concentrations of ammoniacal solution, that the cathodic loop is due to oxygen discharge. The addition of CoCO₃to the ammoniacal solution has the same effect as oxygen in that it increases the cathodic current and potential range of the cathodic loop and, as such, functions as a strong oxidant.