K. Osseo-Asare, M. Deelo, K. Weil
Apr 28, 2006
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Abstract
The role of the ammonium ion during iron deposition in a ferrous sulfate bath was investigated. When cathodic polarizations were performed in a solution of 0.02 M FeSO 4 at pH 3, quartz crystal microbalance measurements showed that the presence of ammonium sulfate led to increased mass growth of Fe metal on the cathode surface. The surface pH was measured by placing a flat-bottom electrode behind a stainless steel cathode mesh. Potentiodynamic sweeps generated pH versus potential curves which revealed that in the presence of ammonium sulfate surface pH rose to alkaline levels. These two sets of findings (i.e., mass growth rate of Fe metal and surface pH results) suggest that the ammonium ion enables formation of ferrous ammine species (e.g., Fe(NH 3 ) 2 2+ and Fe(NH 3 ) 4 2+ ). This inhibits Fe(OH) 2 precipitation on the electrode, a process that can lead to surface passivation, and therefore, limited Fe metal deposition.