CHANGES IN THE SURFACE POTENTIAL OF SOME METALS ON OXIDATION IN AIR.

The method of contact difference in potential was used to investigate the changes in surface potential of Al, Zn, Mg, and Ti after mechanical dressing in air. Experiment confirms that the increase in surface potential of metals, in the early stages of oxidation, is attributable to the tunneling of electrons from the metal through the thin film of oxide. They then combined with adsorbed oxygen to give a negative surface charge. On further oxidation the surface potential gradually approaches the value for the massive oxide.