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The same kind of metal immersed in the same electrolyte solution can form a concentration difference or temperature difference battery due to the different concentration, temperature or relative velocity between the medium and the electrode surface.
(1) Salt concentration cell
If one end of a long copper rod is in contact with dilute copper sulfate solution and the other end is in contact with concentrated copper sulfate solution, the anode of the battery will be corroded due to its negative electrode potential. At the other end of the concentrated solution, Cu2 + ions will precipitate on the copper surface at this end as the cathode of the battery due to its positive electrode potential. The reduced copper is deposited on the electrode surface.
(2) Oxygen concentration cell
This is due to the contact between metals and solutions with different ancient oxygen contents. The metal in the high oxygen concentration area is the cathode, and the metal in the low concentration area is the anode. The anode metal will be corroded by the solution. For example, engineering parts are often connected by riveting, welding and thread. If the connection is not handled properly, cracks will be formed. Because it is difficult to replenish oxygen in the crevice, the concentration difference battery will be formed, which leads to serious corrosion at the gap. Metal pipes and equipment buried in soil with different density or depth also form oxygen concentration cell corrosion due to uneven aeration of oxygen in soil. The water line corrosion of ships also belongs to oxygen concentration cell corrosion.
(3) Thermoelectric cell
This kind of battery is often formed when the metal immersed in electrolyte solution is at different temperature. It often occurs in heat exchanger, digester, immersion heater and other similar equipment. In sulfate aqueous solution, the high temperature end is the cathode and the low temperature end is the anode. The anode end of the low temperature end is dissolved and the high temperature end is protected. However, in salt solution, the hot end is anode, the cold end is cathode, and the hot end is corroded. For example, when repairing the stainless steel heat exchanger, it can be found that the corrosion at the high temperature end is more serious than that at the low temperature end, which is caused by the temperature difference battery.
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.