Anodic Dissolution of Iron in Ammoniacal Ammonium Carbonate Solution

Abstract

The electrochemical behavior of iron has been characterized in aqueous ammoniacal ammonium carbonate solution. Pure iron anodically polarized in He- or O=,-saturated 2 kmol m -'~ NH:~ + 1 kmol m -'~ (NH4)2CO:3 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 CoCO:~ to 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.