When two metals are placed in sea water, which acts as an electrolyte, they react. Some metal reacts more than the other. These reactions can lead to corrosion. For this reason, some metals are used as sacrificial anodes to protect the other metals. Basically, one metal is sacrificed for corrosion to save the lesser reactive metals. The more reactive metal is the anode and the other is the cathode. Aluminum anodes are used to protect the other metals when they are immersed in water. Aluminum anodes are the most efficient and effective compared to zinc and magnesium anodes. Aluminum anodes are good for salt water, brackish water, and fresh water. The following reasons make aluminum anodes the best option.
- Electrical potential
Aluminum anodes are mostly used in vessels sea water but they also function well in fresh water. Magnesium anodes are suitable for fresh water. Aluminum protects the propeller, bronze through-hull fittings and stainless steel propellers in sea vessels. This is because it has a more negative natural corrosion potential than zinc and its electrical potential. Even though magnesium anodes have a higher negative potential, they corrode at a higher rate than aluminum anodes in sea water. It's also immune to developing a calcareous coating. Aluminum anodes corrosion rate is much slower than most metals especially compare to zinc anodes of the same weight.
- Current capacity
Anodes produce voltage difference that flows between the anode and the protected metal through water. The more capacity the anode has, the more it will protect the other metal. Aluminum anodes last between 130-150 days depending on the manufacturer unlike magnesium anodes that last utmost 100 days.
- Quality of the anode alloy
The quality of the anode matters. There are some suppliers that sell low-quality metals that only last a short period. Low-quality anodes cause an expensive corrosion problem to the metal being protected. Ensure the anodes meet the minimum military or marine requirements. Aluminum is listed as the best followed by Zinc then magnesium.
Aluminum anodes should be replaced when they have corroded to half the original size or annually. When they are being installed clean the metal surfaces that will be in contact with the anode and remove any paint. The anodes should never be painted because they will not work. Aluminum anodes are the ultimate solution for anodes. They operate well in all kinds of water and last longer. Choose high-quality anodes for the best results.