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When two or more different metals are placed in electrolyte solution, they will establish their own corrosion potential. If there is an obvious potential difference between them, and if they are in direct contact with the electrolyte solution or through the external metal to form an electrical connection, thus forming a galvanic pair, this is a macroscopic electrochemical cell. In this galvanic cell, the metal with relatively positive self corrosion potential will become the cathode of the galvanic cell, while the metal with relatively negative self corrosion potential will become the anode of the galvanic cell. A measurable current will flow between the anode and the cathode. The corrosion rate of anode metal is significantly increased due to anodic polarization, while the corrosion rate of cathode metal is significantly reduced or even equal to zero due to cathodic polarization.
In the galvanic cell, the phenomenon that the anode metal is coupled with the cathode metal corrected by self corrosion potential in the electrolyte is called galvanic corrosion, also known as contact corrosion and bimetallic corrosion. The phenomenon that the cathode metal in the galvanic battery is coupled with the anode metal with more negative self corrosion potential in the electrolyte will significantly reduce its corrosion rate or even completely inhibit its corrosion, which is called cathodic protection.
Because this kind of cathodic protection is realized by coupling with the lower potential anode metal in the galvanic cell to accelerate the corrosion and dissolution consumption of the anode metal, it is called sacrificial anode cathodic protection, also referred to as sacrificial anode cathodic protection. The anode in the galvanic cell is called sacrificial anode.