What Does Zinc Anode Mean?
A zinc anode is a type of sacrificial anode used to prevent corrosion through cathodic protection. It is also classified as a galvanic anode, with the other galvanic anodes being made from aluminum or magnesium. A zinc anode's protective properties result from a strongly negative reduction potential, which is more negative than the metal it is protecting. Oxidants, which corrode metals, will oxidize the zinc anode rather than the protected metal structure, thus preventing the structure from being corroded.
These type of materials are known as sacrificial anodes because they release electrons, causing the slow corrosion of the anode in place of the actual metal in use, which is less negatively charged.
Zinc make a great choice for a sacrificial anode because it's a highly active metal that is capable of being sacrificed. Zinc anodes are recommended for salt water applications. They are most commonly used in marine applications, such as on boat hulls, tanks, rudders and piers. They are also commonly used for underground tanks and piping.
Corrosionpedia Explains Zinc Anode
Zinc anodes protect metal surfaces from corrosion by using properties of electrical potential, current capacity and alloy quality. When immersed in water, a zinc anode will have a reduction potential of -1.05 volts compared to a reference electrode. When the zinc anode is placed in close proximity to another metal with a greater reduction potential, it makes the other metal the cathode of the electrochemical system. When an oxidant attacks the metal surface, electrons flow through the system and are removed from the zinc anode, rather than from the protected metal, as described by the equation:
Zn -> Zn2+ + 2e-
Thus, the zinc anode is oxidized, or corroded, rather than the metal surface requiring protection. The greater the mass of the zinc anode, the longer it can provide protective current before it is itself depleted. An important metric of a zinc anode is its utilization factor, which specifies how much of the anode can be used before it loses its protective properties. With these metrics, the mass of a zinc anode needed for a particular protective application can be calculated. 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 anodes produce a film of zinc hydroxide on the anode's surface, which blocks current flow. Because of that, zinc anodes are not effective in freshwater and are used in saltwater applications instead.
Like the other galvanic anodes, zinc anodes have the following advantages:
- Require no external power source
- Easy to install
- Low voltage
- Low maintenance
- Low risk for over-protection
- They don't work in highly resistive environments
- Requirements for electrical isolation from other structures
- Current capacity limitations
- High weight
- Potential interference with water flow