An anode is an electrode that has a positive charge.
The notion of anode is used in the field of physics to name an electrode with a positive charge . An electrode, for its part, is the end of a conductive material that, when linked to a medium, transfers or obtains from it an electric current (a flow of charges).
The etymology of anode leads us to a Greek expression that can be translated as "ascending path." The British scientist Michael Faraday (1791-1867) was the one who first used the concept .
Generation of an anode
An oxidation reaction is generated at the anode: its oxidation state increases due to the loss of electrons. It should be remembered that, in this type of reaction, the reducing agent gives up electrons to the medium and increases its oxidation state (it is oxidized), while the oxidizing agent receives said electrons and minimizes its oxidation state (it is reduced).
The anode, when oxidized, allows the passage of electric current towards the negative pole, called the cathode . In cells (also called batteries ), electrical sources and electronic valves , the anode is characterized by being the electrode with the highest potential.
Let's take the case of a voltaic cell . This element generates electrical energy through the oxidation-reduction reactions that occur inside, where two metals are connected by a salt bridge or there are semi-cells related through a membrane with pores. The anode in these cells can be zinc or another material.
A sacrificial anode protects a metal structure that is buried or submerged against corrosion.
Corrosion protection
The piece used to provide protection against corrosion in a metal structure that is submerged or buried is called a galvanic or sacrificial anode. In the field of nautical, for example, it is very important to ensure that electrolytic corrosion does not damage any of the parts of a ship that are inevitably submerged, such as the rudder blade, propeller, shaft, drift. or the keel.
Electrolytic corrosion or electrolysis is the 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 first.
Types of sacrificial anodes
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 : 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 of small vessels, the inner surface of storage tanks, ship hulls, and marine engines that are cooled with salt water ;
* magnesium sacrificial anode : magnesium is a metal with an especially low, negative electrical potential, and that is why it is ideal for areas in which the resistivity of the electrolyte is greater. This type of anode is used in fresh water, both on boats and in water heaters. Despite being a common choice, magnesium can cause problems if the protected metal has too much negative potential , since the mobilization of hydrogen ions at the cathode can lead to the coating coming off;
* aluminum sacrificial anode : aluminum , which is used in brackish water, offers a good number of advantages over the aforementioned metals, such as lower weight and greater capacity. On the other hand, given that its electrochemical behavior is not as stable as that of zinc, for example, it should not be used without taking certain precautions.