Any vessel docked or sailing in fresh, salty or brackish water is subject to corrosion and to its effects generate serious consequences causing high costs for its owners.
When metals are steeped in an electrolyte, e.g., sea water, they have distinct electrochemical capacity when they are in touch with each other and form a galvanic cell. The metal with the lowest potential in the galvanic less noble cell is then corroded, and the one with the highest nobler potential is protected. Let us take as a practical example the bronze propeller and the stainless steel shaft dipped in seawater, such as bronze of the propeller is less noble, it will be corroded, and the stainless steel shaft will be protected.
The most influential metal like zinc anodes is now the anode for others and is sacrificed by corrosion to safeguard the cathode propeller and stainless steel shaft, so we have the sacrificial anode.
Other variables boost corrosion, such as:
- The higher the salinity of seawater, the higher the corrosion percentage.
- The higher the water temperature, the higher the water conductivity, the higher the corrosion level. To give you an idea, the corrosion rate doubles every 10°C.
The Efficiency of Zinc Anodes
Zinc is a metal, sometimes classified as transition metal even though it is strictly not, it bears similarities to magnesium and beryllium in addition to the metals in its group. This element is not abundant in the earth’s crust but can be easily obtained.
It is a bluish-white metal that burns in the air with blue-green flame. Dry air doesn’t attack it, but in the presence of moisture, it forms a surface layer of basic oxide or carbonate which isolates the metal and protects it from corrosion.
Practically the only oxidation state it has is 2+. Reacts with non- oxidizing acids to the 2+ oxidation state and releasing hydrogen, and can dissolve in bases and acetic acid.
The metal has a high resistance to cold plastic deformation which decreases with heating, forcing the blade it above 100 ° C.
Zinc is used basically in the manufacturing of metal alloys such as brass and bronze, in addition to being used in the production of tiles and residential gutters. Zinc is also used as a sacrificial metal to preserve iron from corrosion in some structures, in the production of dry batteries and as a pigment in white paint.