Zinc sacrificial anode is mostly used in soil environment with soil resistivity less than 20 ohm·m or seawater environment. The electrode potential is -1.10VCSE and the driving voltage is 0.25V. When the temperature is higher than 49℃, intergranular corrosion occurs. When it is higher than 54℃, the electrode potential of the zinc anode becomes positive, and its polarity with steel is reversed, becoming the cathode to be protected, while the steel becomes the anode to be corroded. Therefore, zinc anode is generally used in environments with a temperature below 49℃. Zinc anodes are used to fill backfill. Because zinc is more active than iron, a primary battery with zinc as the negative electrode will be formed, and it is relatively cheap. When encountering external corrosion, zinc will be corroded first to protect iron from corrosion.
The cathodic protection of zinc anode is to connect a metal or alloy that is more easily electron-carrying to the steel equipment. Some use this method. It is a relatively more active metal, such as zinc, connected to the steel gate. In this way, when electrochemical corrosion occurs, the metal that is more active than iron is corroded, and is protected by iron. Usually, a certain number of zinc blocks are installed at the stern of the ship and below the waterline of the hull to prevent corrosion of the hull, etc. This is the method used. At present, electrochemical protection is used to protect steel equipment in seawater or rivers, as well as to prevent corrosion of cables, oil pipelines, underground equipment and chemical equipment.
Zinc is a common metal in our daily life. In the periodic table, the atomic weight of zinc is 65.4, the density is 7.14g/cm, the valence is +2, and the melting point is 420 degrees Celsius. Zinc is a metal with negative potential. Its standard potential is negative 0.76v. The stable potential of high-purity zinc in seawater moves to the negative direction. The corrosion rate of zinc is different at different pH values. When the pH is less than 6 and when the pH is greater than 12, the corrosion rate of zinc is relatively large, but in the pH range of 6-12, the corrosion rate of zinc is relatively small. The impurities will also have a great impact on the zinc anode corrosion rate and anode behavior. The presence of impurities will form local corrosion power sources and local batteries. These batteries can form hydroxides on the surface of zinc, forming a solid covering layer to prevent further dissolution. This method of forming a covering layer can be used in cathodic protection systems.