Electrochemical studies on single-crystal aluminium surfaces

The electrochemical behaviour of single-crystal aluminium oriented in the (111), (110) and (100) directions in chloride- and indium-containing solutions was studied. It was found that the susceptibility of the single crystals to the onset of pitting attack in the chloride solution varied in the order (111)>(110)>(100). This was evident from pitting potential and induction time data, where the most noble pitting potential values and the longest induction periods were recorded for the (100) surface. This was explained in terms of differences in the surface energy of (111), (110) and (100) planes. It was also found that cathodic reduction reactions (hydrogen evolution and oxygen reduction reactions) proceeded at a greater rate on the (100) surface. In addition, the time delay between the addition of indium ions to solution and the onset of activation of the immersed electrode by the indium species was shorter for the (100) surface. This was attributed to the more efficient incorporation of indium into the (100) lattice.