Zinc alloy sacrificial anodes are materials that are protected from corrosion by cathodic protection. It is also classified as an electrochemical anode, other sacrificial anodes include aluminum alloy sacrificial anodes and magnesium alloy sacrificial anodes. The protective properties of zinc anodes benefit from a strong negative reduction potential, which is more negative than the metal it protects. The oxidizing agent that corrodes the metal will sacrifice the anode of the zinc oxide alloy instead of the metal being protected, thus preventing the structure from corroding.
Zinc alloy sacrificial anodes are commonly used in saltwater and are most commonly used in Marine applications such as hull, tank, rudder and dock. They are also commonly used in underground storage tanks and pipes.
Chemical Composition
Chemical Element | Al | Cd | Impurity, not more than |
Fe | Cu | Pb | Si | Zn |
content% | 0.3-0.6 | 0.05-0.12 | 0.005 | 0.005 | 0.006 | 0.125 |
|
Electrochemical Performance
Performance | Open circuit potential
-V(SCE) | Working potential
-V(SCE) | Actual capacitanceA·h/kg | Current efficiency
% | Solution condition |
In seawater | -1.09~-1.05 | -1.05~-1.00 | ≥780 | ≥95 | Corrosion products are easy to fall off, and the surface is evenly dissolved |
In soil | ≤-1.05 | ≤-1.03 | ≥530 | ≥65 |
Note 1: Reference electrode - saturated calomel electrode Note 2: Medium - seawater medium adopts artificial seawater; The soil medium is wet soil, and the filling material is added around the anode. |
Corrosion Encyclopedia: Zinc alloy sacrificial anodes
Zinc alloy sacrificial anodes use the characteristics of potential, current capacity and alloy quality to protect the metal surface from corrosion. When immersed in water, the zinc alloy sacrificial anode has a reduction potential of -1.05V compared to the reference electrode. When the zinc alloy sacrificial anode is in close proximity to another metal with a greater reduction potential, it makes the other metal the cathode of the electrochemical system. As the oxidizer erodes the metal surface, electrons flow through the system and are removed from the zinc alloy sacrificial anode rather than from the protected metal, as shown in the formula:
Zn→Zn2++2e-
Therefore, the sacrificial anode of the zinc alloy is corroded by oxidation rather than by the protective metal surface. The more massive the zinc alloy sacrificial anode, the longer it can provide a protective current before it exhausts itself. An important indicator of a zinc alloy sacrificial anode is its utilization rate, which specifies how much the anode can be used before losing its protective properties. With these indicators, we can calculate the anode demand according to the formula. The quality of the zinc anode material is also important because impurities in the zinc metal can weaken its protective properties.
In fresh water, zinc alloy sacrificial anodes create a thin film of zinc hydroxide on the surface, preventing the flow of current. Because of this, zinc anodes are ineffective in fresh water and are used in salt water.
Like other sacrificial anodes, zinc anodes have the following advantages:
1. No external power supply is required;
2, easy to install;
3, low voltage;
4, low maintenance costs;
5. Low risk of overprotection.
Disadvantages of zinc anodes include:
1, can not work in high resistance environment;
2, high electrical isolation requirements with other structures;
3, small electrical capacity;
4, high density;
5. Potential interference with water flow.
