A metal or alloy with a more negative potential is attached to the protected metal tube line and buried in the soil. This metal or alloy with a more negative potential is called a sacrificial anode. Sacrificial anodes get their name because they can be consumed while providing protection.
Which material can be used as a sacrificial anode? It should have the following characteristics: (1) the electrode potential should be negative, and the driving voltage of the protected structure should be large; (2) its current output is stable and its current efficiency is high; ③ the capacitance of the material should be large; (4) Self-corrosion should be small and dissolve evenly, and corrosion products are easy to fall off; ⑤ The material is cheap, widely sourced and easy to process.
Commonly used sacrificial anode materials are: magnesium, aluminum, zinc.
Magnesium anode has a large effective voltage and a large current per unit area, so it can be used in soil or fresh water with high resistivity. But the price is slightly higher than other materials, and its own corrosion is large, current efficiency is low, when the anode output current is small, because of its corrosion is large, the actual capacitance will be lower.
Aluminum anodes are alloy anodes with high effective power and are the most economical sacrificial anodes at present. However, contaminated seawater and high electrical resistivity can affect its function.
Zinc anode itself corrosion is small, the anode life is long, in addition to high temperature fresh water, can play a role in many environments, can also be used inside the tank. The disadvantage is that the effective voltage is low and less electricity is generated.