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Materials

As a sacrificial anode material, it must meet the following requirements:

1. Have a sufficiently negative stable potential;

2. Exhibit a low self-corrosion rate with uniform corrosion, and possess high and stable current efficiency;

3. Have a high electrochemical equivalent, meaning a large current output per unit weight;

4. Experience minimal anode polarization during operation, dissolve uniformly, and have easily detachable by-products;

5. Produce corrosion by-products that do not pollute the environment and are harmless;

6. Be widely sourced, easy to process, and low-cost.

Common types of sacrificial anodes include magnesium-based, zinc-based, and aluminum-based alloys.

Zinc is a relatively common metal in daily life. In the periodic table, zinc has an atomic weight of 65.4, a density of 7.14, a valence of 2, and a melting point of 420 degrees Celsius.

Zinc is a metal with a negative potential, with a standard potential of -0.76V. In seawater, the stable potential of high-purity zinc shifts negatively. The corrosion rate of zinc varies with pH levels: it is higher when pH is less than 6 or greater than 12, but relatively low within the pH range of 6 to 12.

Impurities also significantly affect the anode corrosion rate and anode behavior of zinc. The presence of impurities can form localized corrosion sources, creating local cells that lead to the formation of hydroxides on the zinc surface, forming a robust protective layer that prevents further dissolution. This method of forming a protective layer can be applied in cathodic protection systems.

Cathodic protection for ships includes external protection of underwater parts, covering all attachments and open areas, as well as internal protection of various cabin pipelines and bilges.

Cathodic protection for the submerged parts of ships

Implementing cathodic protection on ships without coatings is practically impossible or highly uneconomical due to the required protective current demand and current distribution. Additionally, an electrical insulation layer should be present between the ship's steel plates and anti-fouling coatings to prevent the electrochemical reduction of toxic metal compounds. Cathodic electrolysis by-products cannot prevent marine fouling. On the contrary, if cathodic protection is implemented, marine organisms may attach to inert copper materials during natural corrosion.

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