Abstract
Cathodic protection of metals has long been known and widely applied in many varied situations, but the technique of anodic protection has only recently been used for corrosion control. Anodic protection cannot be expected to fill the entire niche of cathodic protection but anodic currents can prevent corrosion of some metals and alloys on the acid side of the pH range for which they are normally considered suitable.
The Pourbaix diagram calculated for iron has very nearly the same shape as the curves obtained by anodic polarization. Both curves show the same areas which are either passive, trans-passive or active. A complete theoretical explanation for anodic protection or passivity is difficult. Several theories exist with some agreement between the proponents of each theory.
The classical potentiostat of Prazak is a manually-operated instrument. It has been modified by Hickling to include a variable speed drive for scanning the potential range and an automatic control system which replaces the manual reversing switch of Prazak's design.
Use of the potentiostat to record anodic polarization curves and application of anodic passivity theory present a new and useful approach to evaluation of inhibitors. These methods, if applied correctly, can give more accurate analysis of corrosion rates and understanding of inhibition mechanisms and effectiveness.
