The notion of anode is used in the field of physics to name a positively charged electrode. An electrode, on the other hand, is the end of a conductive material that, being linked to a medium, transfers or obtains an electric current (a flow of charges) from it.
The etymology of anode leads us to a Greek expression that can be translated as “ascending path”. British scientist Michael Faraday (1791-1867) was the first to use the concept.
An oxidation reaction is generated at the anode: its oxidation state increases from the loss of electrons. It should be remembered that, in this type of reaction, the reducing agent yields electrons to the medium and increases its oxidation state (it is oxidized), while the oxidizing agent receives these electrons and minimizes its oxidation state (it is reduced).
The anode, when oxidized, allows the passage of electric current to the negative pole, called the cathode. In batteries (also called batteries), electrical sources and electronic valves, the anode is characterized by being the electrode with the greatest potential.
Take the case of a voltaic cell. This element generates electrical energy through the oxidation-reduction reactions that take place inside it, where two metals are connected by a salt bridge or there are related semi-cells through a membrane with pores. The anode in these cells can be zinc or another material.
Lastly, the part used to provide protection against corrosion in a metal structure that is submerged or buried is called a galvanic or sacrificial anode. In the nautical field, for example, it is very important to ensure that electrolytic corrosion does not damage any of the parts that are inevitably submerged in a ship, such as the rudder blade, propeller, shaft, drift or the keel.
Electrolytic corrosion or electrolysis refers to a deterioration that the emergence of an electric current causes in submerged metals, which are grouped according to their potential: the cathodes have the greatest potential, while on the other side are the anodes, which they decompose instead of the former.
It is important to note that the action of the anode is subject to the nature of the water. Based on this factor, there are different types of anodes, such as the following:
* zinc sacrificial anode: it is used in salt water, as well as aluminum, since in this medium the resistivity is usually lower. The most common applications for this type of anode are production platforms, rudders and propellers for small vessels, the interior surface of storage tanks, ship hulls, and marine engines that are cooled by salt water;
* Magnesium Sacrificial Anode: Magnesium is a metal with an especially low, negative electrical potential, and is therefore ideal for areas where the resistivity of the electrolyte is higher. This type of anode is used in fresh water, both on boats and in water heaters. Despite being a frequent option, magnesium can cause problems if the protected metal has too negative a potential, since the mobilization of hydrogen ions at the cathode can lead to the release of the coating;
* Aluminum sacrificial anode: Aluminum, which is used in brackish water, offers a number of advantages over the aforementioned metals, such as lower weight and greater capacity. On the other hand, since its electrochemical behavior is not as stable as that of zinc, for example, it should not be used without taking certain precautions.