Definition - What does Galvanic Couple mean?
A galvanic couple is a corrosive cell that is developed when two different metals are separated by electrolytes. In essence, it is the electrochemical action that is produced by the reaction of two dissimilar metals, given there is a path conducive to electrons and electrolytes. It can be identified by the existence of corrosion at a point located between the two metals.
The term is also used to refer to galvanic corrosion, since its effect results in corrosion.
A galvanic couple is also referred to as a bimetallic couple or two-metal corrosion.
Corrosionpedia explains Galvanic Couple
A galvanic couple occurs when there is a potential difference that occurs between two unlike metals. This occurs when these metals are immersed in a conductive or corrosive solution. If the metals are put in contact or electrically connected, this will result in an electron flow between them.
In a galvanic couple, the higher resistance metal turns cathodic while the less resistant one becomes anodic. Typically, the cathodic material undergoes little or no corrosion at all in a galvanic couple. Due to the unlike metals that are involved and the electric currents, the type of corrosion is referred to as two-metal or galvanic corrosion.
For example, when magnesium or aluminum alloys come in contact with stainless or carbon steel, a galvanic couple can happen, and this hastens the corrosion of magnesium or aluminum. For instance, when a helicopter blade made from aluminum is connected to a counterbalance made of steel, this will result in corrosion at the point of contact.
Another great example involves the Statue of Liberty. During regular maintenance conducted in the 1980s, galvanic corrosion was discovered between the supports made of wrought iron and the outer skin made of copper.
There are many ways to prevent or reduce this type of corrosion:
- Insulate the two different metals electrically.
- Ensure metals are dry and protected from ions.
- Coat metals with impermeable layers like plastic, paint, etc.
- Select metals with the same electro potentials.
- Electroplating as well as cathodic protection can offer substantial protection.