Aluminium in alkaline solution non-uniform and rough films

Aluminium in alkaline solution non-uniform and rough films 

By dropping the potential to a value where the oxide stops forming, the dissolution process can be watched in its entirety (Fig. 14). The A-t// curve now follows a trajectory that lies within the original figure until almost all the oxide has been dissolved. This effect, too, has been modeled in a similar way, taking account that, as soon as the formation process stops, dissolution occurs throughout the depth of the oxide, including the denser layer in contact with the metal. 

The surprising feature of the dissolution curves is the large and very reproducible excursion or loop as the starting-point is approached. This traverses a region of the A—ift surface that is inaccessible by an combination of transparent layers and therefore has to be due to the development, and the subsequent disappearance by a remarkable self-healing process, of a rough layer or pitted aluminium surface. 

The modeling technique applied to the transparent oxide layers also works in this case provided a suitable depth profile for the roughened surface can be found. Trial-and-error procedures were used and a profile consisting of triangular-section furrows was found to give good agreement with experiment. 

---