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Many people may be unfamiliar with sacrificial anodes, as they are rarely used in daily life. Their performance and effectiveness are even less well-known. However, sacrificial anodes are highly corrosion-resistant, especially in the aquatic industry. So, how much do you know about their role? Let's take a look at the following introduction.
Among the many chemical elements, sacrificial anodes are commonly used in electrochemical cathodic protection projects. These materials are highly chemically active. Their electrode potential is relatively negative, resulting in a high driving voltage. Another characteristic of sacrificial anodes is that they are difficult to form a protective film on. Sacrificial anodes are also highly corrosive.
Although sacrificial anodes are inherently highly corrosive, they do serve to slow the corrosion rate of steel, thereby protecting the cathode. However, sacrificial anodes cannot protect all steel; their protection is conditional. The fundamental prerequisite for sacrificial anode protection is that the cathode is protected without any interference from the cathode. This type of corrosion is electrochemical, meaning that an electric current is generated during the corrosion process.
The first requirement is that the corrosive medium of the sacrificial anode must be conductive, allowing for a continuous electrical circuit. The medium contained in the material the sacrificial anode is intended to protect must be easily polarized; otherwise, the sacrificial anode will not be able to protect it. It's important to note that sacrificial anodes should not be used for reactions conducted in tanks. Due to the varying uses of magnesium anodes, their shapes and sizes vary, and the type of sacrificial anode is generally determined by the object they are intended to protect.
Chloride penetration into concrete depassivates the rebar surface locally, releasing free electrons. The remaining passivated rebar surface then becomes the cathode, forming a corrosion couple with the anode. The principle of cathodic protection using sacrificial anodes is to use an aluminum alloy, zinc alloy, or magnesium alloy, which is electrochemically more active than steel (i.e., has a more negative potential), as the anode. This anode is electrically connected to the steel being protected, sacrificing its own corrosion to provide free electrons, thus providing cathodic protection for the steel. To implement cathodic protection so that any angle on a large area of steel mesh can evenly receive sufficient free electrons, it is impossible to rely on a small number of sacrificial anodes or impressed current cathodic protection anodes placed on the surface of the structure at large intervals. At the same time, cathodic protection can only be successfully implemented by using an anode system that is evenly distributed over the entire protected surface. Therefore, the design of the anode system becomes the key to cathodic protection technology for salt-contaminated reinforced concrete structures exposed to the atmosphere.
