Definition - What does Corrosion Microcell mean?
A corrosion microcell is a microscopic cell formed on a continuous piece of metal consisting of an anode and cathode immediately next to each other. This creates the electrochemical conditions that make corrosion possible. Corrosion microcells are formed due to impurities, environmental conditions, and other factors.
Corrosion microcells are usually present in many corrosion processes and the corrosion of most metals. Microcell formation - and therefore corrosion - can be minimized by the use of corrosion-inhibiting compounds and coatings.
Corrosionpedia explains Corrosion Microcell
By considering the steel bar as made up of several elements, a corrosion microcell is formed when both the anode and cathode exist within one element, while a macrocell is when the two are formed at different elements.
A corrosion microcell may be formed on a continuous metallic element or bar due to different environmental conditions between two areas close to each other on the same surface. This could be due to the composition of the metal, differences in the electrolyte concentrations, aeration, or differences in stress levels in the metal bar.
An example is steel which, being an alloy of carbon and other metals and therefore heterogeneous, allows the formation and existence of the several corrosion cells possessing different electrochemical potential levels.
Corrosion microcells are common in concrete reinforcement steel and are usually caused by concrete carbonation or high chloride concentrations in the area surrounding the steel. The different environmental conditions on materials such concrete reinforcement steel can be attributed to variations in surface condition, chloride concentrations, availability of oxygen, moisture, or the different pH levels.
Corrosion types are classified based on the spatial locations of the anodic electrode and the cathode electrode. When corrosion microcells are formed on the reinforcement steel, any presence of an electrolyte will lead to anodic and cathodic reactions taking place at a microscopic scale, leading to microcell corrosion.