The electrode potential of evaporated aluminum films in chloride solution

Potential measurements as negative as--1.67 EHO volts in 1N KC1 solution pH 3.2, have been measured on a freshly cut aluminum surface by a technique devised by Hagyard and co-workers (1, 2). A poly-thene-coated aluminum rod immersed in 1N KC1 solu-tion was cut by a ruby travell ing at 1000 cm/sec. Po-tential measurements were made using a high- im-pedance cathode follower coupled to an oscilloscope. From the instant the cut was made into the aluminum, its potential was recorded by photographing a single traverse of the oscilloscope trace. A typical potential measurement is shown in Fig. 1. The initial rapid potential rise to the peak was at-tributed to the dissolution of aluminum charging the double layer. After reaching the peak potential, only a small fraction of the electrode surface was thought to remain actively anodic whi le the slower hydrogen discharge process took place over most of the metal surface. The exponential fall in potential was at-tr ibuted to the polarization of the anodic and cathodic processes. The information gained using this tech-nique enabled the kinetics for aluminum dissolution and hydrogen discharge on aluminum to be studied. The object of the present work was to confirm the validity of the measurements made by the above technique. The possible alternative explanations of the potential behavior of freshly cut aluminum that were considered by the authors were (a) that in-stantaneous high temperatures were generated at the cut surface by the shearing action of the ruby cutter; the high temperatures would be rapidly reduced by heat dissipation into the bulk of the metal, (b) severe stressing and dislocation of the aluminum elec-trode surface followed by relaxation of the surface structure; the peak in this case would be a stress po-tential. Vacuum evaporated aluminum films were used in this work to obtain an uncontaminated oxide-free alu