Anodic protection is a method used to prevent corrosion. This method is most often used in highly corrosive environments to protect metal immersed in a solution with uncommonly acidic or basic qualities. Anodic protection is different from cathodic protection, another technique used to prevent corrosion in metal devices and structures. In anodic protection, electric current is used to create a protective oxidized layer on the base protected material, often known as the substrate. This process is most frequently employed in industrial production.
Usually, anodic protection is used to protect metal in environments too corrosive for other methods of protection like cathodic protection to be effective. Cathodic protection differs from anodic techniques because cathodic protection uses a metal rod called a sacrificial cathode to corrode in place of the protected metal. This technique is usually used in water, while anodic methods of protection are used in more corrosive environments.
Commonly used to protect metal in solutions with unusually high or low potential hydrogen (pH) levels, which indicate the acidic or basic nature of a solution, anodic protection is most frequently used for steel. This technique can usually be found in factories that work with high or low pH solutions, particularly sulfuric acid, phosphoric acid, or chromic acid. Other lesser-used substrate materials that can benefit from anodic protection include magnesium, titanium, and zinc.
Anodic protection works by forming a protective layer called an anodic film on the base metal. An anodic film is a controlled oxidized layer formed on the metal using controlled electric current that can be used to increase and decrease the thickness of the anodic film. This film acts as a barrier against the corrosive nature of its environment. In industrial applications involving highly corrosive materials, a constantly maintained balance of current keeps metal containers from corroding. Sensors monitor the level of current in the solution and in the protected metal, which functions as the anode, and if the monitor senses that levels of current have fallen below safe levels, the system alerts a technician.
When anodization is not being used for anodic protection, a similar process is used to add color to metals like those seen on body jewelry and personal media players. When dyeing metal with anodization, instead of oxidizing the surface metal on the protected substrate, the anodization process sticks a colored metal that was dissolved into the solution to the substrate metal. The result is a colorful coating all over the metal object.