Impurity, not more than
Open circuit potential
Corrosion products are easy to fall off, and the surface is evenly dissolved
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.
Zinc alloy sacrificial anode
is a material that protects against corrosion by cathodic protection. It is also classified as an electrochemical anode, and other sacrificial anodes include aluminum alloy sacrificial anode and magnesium alloy sacrificial anode. The protective properties of zinc anodes benefit from a strong negative reduction potential, which is more negative than the potential of the metal it protects. The oxidant that corrodes the metal will oxidize the zinc alloy sacrificial anode instead of the protected metal, preventing the structure from being corroded.
Zinc alloy sacrificial anodes are often used in saltwater, most commonly in marine applications such as hulls, tanks, rudders, and docks. They are also commonly used in underground storage tanks and pipelines.
Corrosion Lingo : Zinc Alloy Sacrificial Anode
The zinc alloy sacrificial anode uses the characteristics of potential, current capacity, and alloy mass 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 close to another metal with a greater reduction potential, it makes the other metal the cathode of the electrochemical system. When the oxidant erodes the metal surface, electrons flow through the system and are removed from the zinc alloy sacrificial anode instead of the protected metal, as shown in the formula: Zn → Zn2 ++ 2e-
Therefore, the zinc alloy sacrificial anode is oxidized and corroded instead of the protected metal surface being corroded. The greater the mass of the zinc alloy sacrificial anode, the longer it will provide protective current before it runs out on its own. An important indicator of the zinc alloy sacrificial anode is its utilization rate, which specifies how much the anode can be used before losing its protective performance. With these indicators, we can calculate the demand for the anode according to the formula. The quality of the zinc anode material is also important because impurities in the zinc metal can weaken its protective performance.
In fresh water, the zinc alloy sacrificial anode produces a thin film of zinc hydroxide on the surface to prevent current flow. Therefore, zinc anodes are ineffective in fresh water and are used in brackish water.
Like other sacrificial anodes, zinc anodes offer the following advantages:
1. No external power supply is required.
2. Easy to install.
3. Low voltage;
4. Low maintenance costs.
5. The risk of overprotection is low.
Zinc anode disadvantages include:
1. Cannot work in high-resistance environments.
2. High electrical isolation requirements from other structures.
3. The capacitance is small.
4. High density;
5. Potential interference with water flow.