Flade potential defined

Among the parameters that are particularly affected by sensitization are ip and ice, as defined in Fig. 12.1. In this example, the ability to sustain passivity increases as the current density to maintain passivity Up) decreases and as the total film resistance increases, as indicated from measurements obtained with different metals exposed to 67% sulfuric acid (Table 12.3). The lower or more reducing the potential at which a passive metal becomes active, the greater the stability of passivity. The depassivation potential corresponding to the passive-active transition, called the Flade potential, can differ appreciably from Epp measured by going through the active-passive process of the same system. This technical distinction is important for the control aspect of anodic protection where Epp is the potential to traverse to obtain passivation, and the Flade potential is the potential to avoid traversing back into active corrosion. 

The passivation potential and the Flade potential are defined in slightly different ways by various authors. 

---