What Does Cyclic Polarization Mean?
Cyclic polarization refers to both anodic and cathodic polarization techniques which are performed in a cyclic manner. These techniques measure the pitting tendencies of a specimen in a given metal-solution system.
Cyclic polarization is a short-term exposure test. It provides information on both corrosion characteristics and corrosion mechanisms.
Cyclic polarization measurements are typically used to characterize metals and alloys that derive their corrosion resistance from the formation of a thin passive film. They are also useful for characterizing noble metal electrodes such as platinum and gold, and in particular for assessing the likely severity of galvanic corrosion between noble and non-noble metals in implantable devices.
Corrosionpedia Explains Cyclic Polarization
Cyclic polarization is a type of polarization which is performed in a cyclic manner. It is susceptible to pitting corrosion described by pitting potential. The potential is swept in a single cycle (or slightly less than one cycle), and the size of the hysteresis is examined along with the differences between the values of the starting open circuit corrosion potential and the return passivation potential. The existence of the hysteresis is usually indicative of pitting, while the size of the loop is often related to the amount of pitting.
Materials exhibiting higher values of pitting potential (EP) and repassivation potential (ER) are more resistant to pitting corrosion, and cyclic polarization experiments are commonly used for this purpose. In an oxidizing environment, or for a material that is very susceptible to pitting, the open circuit potential, which is determined by the intersection of the polarization curves associated with the anodic and cathodic partial reactions, will be above EP, and the material will spontaneously pit at open circuit.
A final measure of pitting susceptibility is the difference between EP and ER, which is related to the extent of hysteresis in a cyclic potentiodynamic polarization curve. Generally, alloys that are susceptible to pitting corrosion exhibit a large hysteresis.
It is noted that at low densities, corresponding to larger pore sizes, the detrimental effect of pores is small and gradual. At higher densities, it becomes very pronounced, producing very low corrosion resistance or very large hysteresis.
ASTM G-61 test methods are used for conducting cyclic potentiodynamic polarization measurements for localized corrosion susceptibility of iron, nickel or cobalt-based alloys.