What is the principle of cathodic protection?

Cathodic protection is a kind of used to prevent the metal dielectric (such as sea water, fresh water and soil medium), the electrochemical corrosion protection technology in the basic principle of this technology is to make the metal components as cathode, exert a certain amount of dc current, make its produce cathodic polarization, the potential of occurring when the metal was a potential value, the electrochemical inhomogeneity on the surface of the metal be eliminated, The cathodic dissolution process of corrosion is effectively suppressed and the purpose of protection is achieved. The polarization curve is used to illustrate the principle of cathodic protection. To illustrate the problem, the cathodic and anodic polarization curves are simplified into straight lines, as shown in Figure (1) below.

In order to achieve complete cathodic protection, the potential of the entire metal must be reduced to the equilibrium potential at the most active point. Let the anode potential and cathode potential of the metal surface be Ea and Ec respectively. Due to the effect of polarization in the metal corrosion process, the potential of the anode and cathode are close to Ecorr(natural corrosion potential) corresponding to the intersection point S, and the corrosion current at this time is Icorr.

Figure (1)

If on cathodic polarization, will from the more negative potential direction, anodic reaction curve EcS from S extend in the direction of C point, when the potential polarization to E1, the polarization current I1, equivalent to the AC line, including the BC segment this part is a plus, this part AB line current is provided by the anodic reaction of current, metal corrosion has not at this time. If the metal cathode is polarized to a more negative potential, such as Ea, then the potential of all areas of the metal surface is equal to Ea, the corrosion current is zero, and the metal is fully protected. At this time, the impressed current Iapp1 is the current required for full protection.

According to different ways of providing cathodic polarization current, cathodic protection can be divided into sacrificial anode cathodic protection and impressed current cathodic protection. According to different ways of providing cathodic polarization current, cathodic protection can be divided into sacrificial anode cathodic protection and impressed current cathodic protection.

What is the principle of corrosion cathodic protection