The effects of added impurities upon the electrochemical behaviour of iron in liquid ammonia solutions

Polarization data are presented for an iron electrode in liquid ammonia solutions containing ammonium salts and small amounts of the impurities: water, oxygen, nitrogen, ammonium carbamate, urea and boron trifluoride at 40°C. Additions of water up to a limiting concentration increase the iron dissolution currents in the active region. Additions of oxygen have a similar effect. The presence of either oxygen or water assists the onset of passivation and gives the phenomenon a more irreversible character.In ammonia, one mole of oxygen with two moles of Fe(II) forms a complex which can be cathodically reduced on vitreous carbon (1.0F per mol of Fe(II) or on iron (2.0F per mol of Fe(II)). On an iron cathode molecular oxygen is reduced at a rate determined by the mass transfer of oxygen, except at values of electrode potential more positive than the iron passivation potential.Nitrogen and urea do not affect the polarization behaviour of iron. Ammonium carbamate increases the iron dissolution currents obtained with nitrate or fluoroborate electrolytes but considerably inhibits the process in chloride electrolytes. Boron trifluoride profoundly increases the activity of iron towards dissolution.