What is a sacrificial anode?
Sacrificial anodes are made of highly active metal materials and are used to prevent corrosion on less active metal surfaces, such as steel. Its natural potential is more negative than that of the metal being protected, thus replacing the corrosion of the metal it protects, which is why it is called a "sacrificial" anode.
What is cathodic protection?
When a metal surface comes into contact with an electrolyte, an electrochemical reaction called corrosion occurs. Corrosion is the process of reducing a metal to this natural state of ore, in which the metal reacts and weakens its structure. The most common is rust, which can be seen everywhere in our life. From pipes to buildings to ships, corrosion is ubiquitous and unavoidable. Although corrosion cannot be completely eliminated, measures should be taken to slow it down and ensure that these metals last longer, a common method is so-called cathodic protection technology.
Sacrificial anode cathodic protection is one of the two forms of cathodic protection, the other form of cathodic protection is impressed current cathodic protection.
Metal corrosion in seawater can explain the principle of cathodic protection of sacrificial anodes. The iron metal is in contact with the electrolyte, and under normal circumstances, the iron metal will react with the electrolyte, begin to corrode, and the structure becomes weak. Zinc acts as a sacrificial anode to prevent the "corrosion" of iron. According to the standard reduction potential meter, the standard reduction potential for zinc is about -0.76V, and the standard reduction potential for iron is about -0.44V. This difference in reduction potential means that zinc oxidizes much faster than iron. In fact, zinc is completely oxidized before the iron begins to react.
Explain the principle of sacrificial anode and cathode protection
What material is the sacrificial anode made of?
The materials used for sacrificial anodes are either relatively pure active metals such as zinc or magnesium, or magnesium or aluminum alloys specially developed for sacrificial anodes. If the sacrificial anode is buried in the ground, a special backfill material needs to be wrapped around the anode to ensure that the anode can generate the required current.
A sacrificial anode works by introducing another metal that has a more negative potential and is more anodic, current will flow out of the newly introduced anode, and the protected metal will become the cathode, forming a galvanic cell. Oxidation reaction occurred on the anode surface and reduction reaction occurred on the cathode surface.
How is the sacrificial anode installed?
Sacrificial anodes are usually equipped with leads or flat steel to facilitate their connection to the protected structure. Leads may be welded or mechanically connected to structures that should have low resistance and should be insulated to prevent increased resistance or damage due to corrosion.
In the process of providing electrons to the less active metals for cathodic protection, the more active metals will corrode. The sacrificial anode is more active, so the sacrificial anode will first corrode the more active metal (anode) to protect the less active metal (cathode). The degree of corrosion depends on the metal used as the anode, but is proportional to the current provided.
Sacrificial anode application
Sacrificial anodes are used to protect hulls, water heaters, pipelines, power distribution systems, above-ground storage tanks, underground storage tanks and oil refineries, and anodes in sacrificial cathodic protection systems must be inspected regularly and replaced before they are exhausted.
1. What is the purpose of using sacrificial anodes?
Sacrificial anodes are used to protect metal structures from corrosion.
2. How does the sacrificial anode work?
The sacrificial anode works by oxidizing faster than the metal it protects, and is completely consumed before any other metal can react with the electrolyte.
3. What different metals can be used as sacrificial anodes?
The three metals that can be used as sacrificial anodes are zinc, aluminum, and magnesium.