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Anodic protection (AP) otherwise referred to as Anodic Control is a technique to control the corrosion of a metal surface by making it the anode of an electrochemical cell and controlling the electrode potential in a zone where the metal is passive.
Sacrificial metals are widely used to prevent other metals from corroding: for example in galvanised steel. [3] Many steel objects are coated with a layer of zinc, which is more electronegative than iron, and thus oxidises in preference to the iron, preventing the iron from rusting. [4]
A galvanic anode, or sacrificial anode, is the main component of a galvanic cathodic protection system used to protect buried or submerged metal structures from corrosion. They are made from a metal alloy with a more "active" voltage (more negative reduction potential / more positive oxidation potential ) than the metal of the structure.
Aluminum sacrificial anodes (light colored rectangular bars) mounted on a steel jacket structure. Zinc sacrificial anode (rounded object) screwed to the underside of the hull of a small boat. Cathodic protection (CP; / k æ ˈ θ ɒ d ɪ k / ⓘ) is a technique used to control the corrosion of a metal surface by making it the cathode of an ...
The difference can be measured as a difference in voltage potential: the less noble metal is the one with a lower (that is, more negative) electrode potential than the nobler one, and will function as the anode (electron or anion attractor) within the electrolyte device functioning as described above (a galvanic cell).
Certain metals, such as zinc, may become embrittled from the hydrogen gas which is evolved at the cathode. The anodic process avoids this effect since oxygen is being generated at the anode. The major advantages that are normally touted for the cathodic processes are: Higher levels of corrosion protection are possible.
Corrosion prevention measures, including Cathodic protection, designing to prevent corrosion and coating of structures fall within the regime of corrosion engineering. However, corrosion science and engineering go hand-in-hand and they cannot be separated: it is a permanent marriage to produce new and better methods of protection from time to time.
The anodes can be either simple copper slabs or titanium or steel baskets filled with copper nuggets or balls. [6] The anodes may be placed in anode bags, which are typically made of polypropylene or another fabric and are used to contain insoluble particles that flake off the anode and prevent them from contaminating the plating bath. [2] [7]