Electromotive Force Series (EMF Series)

Published: | Updated: May 29, 2020

Definition - What does Electromotive Force Series (EMF Series) mean?

An electromotive force series (EMF series) is a metal's ranking in respect to inherent reactivity. The metals located at the top of the series are considered the most noble, with the highest level of positive electrochemical potential. The metal that can be found at the bottom is the most active and contains the highest amount of negative electrochemical potential.

This series is helpful in determining the tendency of a metal to release energy and corrode.

Corrosionpedia explains Electromotive Force Series (EMF Series)

The material ranking in accordance to potential can be seen in the EMF or galvanic series. For instance, those that have higher EMF values include gold, copper and platinum. Materials that have low EMF include zinc and magnesium. These EMF values have been computed suited for standard cases, but the order may differ according to the environment. Metals like aluminum and titanium can build highly protective oxide layers at room temperatures.

There can be different potentials in situations where two metals are utilized within a single environment. If these metals are connected electrically or come in contact with each other, an adequate amount of potential difference might result in electron flow between the metals. The more noble a metal is, the less resistant it is to corrosion. This leads to heightened levels of corrosion of material that is anodic and less attack in cathodic material. Knowledge of the electromagnetic force series helps in understanding corrosion and how it can be reduced or prevented.

The EMF series can be most useful in evaluating the possible occurrence of galvanic corrosion. It is essential that accurate values are utilized or identified for the right temperature and solution. Essentially, the anode’s relative area in comparison to the cathode highly influences the rate of corrosion. The bigger the cathode portion in relation to the anodic area, the faster the rate of corrosion will be. For instance, bolts made of steel placed through a copper sheet which is nobler will corrode faster than the copper sheet in an identical environment. So, the principle is that galvanic corrosion can take place when two alloys or metals come in contact with each other within an electrolyte. Between the two, the less noble metal will undergo corrosion.

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