This is called applying a polarization overpotential. When it is small, the polarization overpotential has a linear relationship with polarization current, similar to Ohm s Law. Hence, the relationship (potential divided by current) is called polarization resistance. The corrosion rate is inversely proportional to the polarization resistance. [Pg.790]

Linear polarization measurements are executed rapidly. The currents in linear polarization measurements are measured in the potential range between 10 and 20 mV from the equilibrium potential. The E-I dependence in this potential range follows a linear relationship. The slope of the plot, dE/ di, represents the polarization resistance. The corrosion current is calculated using the Stem-Geary equation for known values of the anodic and cathodic Tafel slopes. The ratio of the overpotential to the current represents the resistance in Ohm s law and is often termed the charge transfer resistance or the polarization resistance, Rp. [Pg.24]

The other main electrochemical method for determination of corrosion rates is the (linear) polarization resistance method (the LPR method). In a limited potential range around the corrosion potential (up to 20 mV) a linear relationship exists betw een the potential increment AE and the increment in external current Ale, as shown in Figure 9.2. It can be shown mathematically that the slope of the curve in this potential range is given by Stem-Geary s equation [Pg.224]

This is perhaps the singly most important technique it arises from the Stern-Geary equation which describes a linear overpotential - current relationship in the vicinity (typically + 20 mV) of the corrosion potential where the linear polarization resistance is [Pg.539]

A further barrier to corrosion reactions is provided by electrical resistance. When the anodic and cathodic reactions at the metal surface take place with locally different current densities, resistance in the current circuits can cause a measurable drop in potential (resistance polarization). This resistance polarization is a linear function of the current. Resistance polarization frequently arises through the formation of passive films. The resulting relationship between the change in potential and the current usually no longer follows Ohm s law, but instead is subject to a logarithmic relationship. [Pg.540]

Indirect methods of corrosion rate measurement involve aspects of the electrochemical process other than metal dissolution. These measurements involve cathodic reactions, such as the evolution of hydrogen, or consider current-potential relationships, such as polarization curves or polarization resistance values. [Pg.276]

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