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1¡¢ Principle of cathodic protection
Cathodic protection is called cathodic protection, in which the negative current is applied to the protected metal and the electrode potential is moved to the stable potential of the metal by cathodic polarization. Cathodic protection is a method to control the electrochemical corrosion of metals. In the battery composed of cathodic protection system, the oxidation reaction mainly occurs on the anode, thus inhibiting the corrosion of the protected metal as the cathode. Cathodic protection is an electrochemical protection technology based on the principle of electrochemical corrosion. The principle of cathodic protection can be understood from electrode reaction, polarization curve, polarization diagram and potential pH diagram.
2¡¢ Electrode reaction
The combination of any two metals / alloys can form an electrochemical cell; the anode of the battery with low potential is the main oxidation reaction; the cathode with high potential is the main reduction reaction. Due to the potential difference between the anode and cathode, there will be current flowing through the battery between the anode and cathode, which accelerates the corrosion of the anode and inhibits the corrosion of the cathode, so that the cathode metal can obtain cathodic protection.
3¡¢ Polarization curve and polarization diagram
According to the mixed potential theory, the local anode and local cathode on the metal surface converge to a common mixed potential through their respective polarization, that is, the metal self corrosion potential Ecorr; at this time, the oxidation reaction rate of the local anode is equal to the reduction reaction rate of the local cathode, which is equal to the metal self corrosion current icorr. The real polarization curves of local anode (EE, afpsa ') and local cathode (EE, csmbd) of iron in neutral aqueous solution, as well as the experimental anodic polarization curves (ecorra) and cathodic polarization curves (ecorrgobb') of iron in neutral aqueous solution.
When the cathode is polarized to any potential, the applied negative current is equal to the difference between the local cathodic reduction current IC and the local anodic oxidation reaction current IA. When the cathodic polarization makes the metal electrode potential move negative to the stable potential EE, a of the local anodic reaction, the external polarization current is almost equal to the local cathodic current, because the local anode current can be ignored. Of course, the corrosion on iron is completely inhibited, that is, complete cathodic protection is obtained.
4¡¢ Potential pH diagram
Potential pH diagram is the theoretical basis for explaining cathodic protection from thermodynamics. In neutral water with pH = 6 ~ 7, the iron is in active corrosion state, and the electrode potential of iron can enter the corrosion free zone from the corrosion zone by the cathodic polarization of external negative current. For iron, this is a thermodynamic stable region, and the metal corrosion stops, that is, the iron has obtained cathodic protection.
5¡¢ Description of cathodic protection for metal interface reaction
The electrochemical corrosion reaction of iron at the metal interface in NaCl solution (or soil) and the effect of external negative current generated by cathodic protection system through magnesium anode or external power supply on these reaction processes indicate the existence and transmission of various reaction particles and reaction products. Because the cathodic protection system can provide enough electrons to the metal through sacrificial anode or external power supply (applying the required negative current), the metal interface becomes negative and reaches enough negative electrode potential, thus inhibiting the oxidation reaction (Fe ¡ú Fe2 + + 2e); at this time, the electrons required for the reduction reaction are completely obtained from the sacrificial anode or external power supply. Thus, the cathodic protection is realized and the corrosion process of metal is stopped.
Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing cathodic protection technology, engineering design, installation and technical services.