I want to know the basic difference between chemical corrosion and electrochemcial corrosion of the metals. Can chemical corrosion happens without electron transformation and presence of electrolyte. Someone was relating it with bacterial corrosion (I don't know how). Please explain in details with examples.
Thanks in advance.
Dear Dr. Sunil Sinhmar ,
I try to summarize the answer, in a few words and, at the same time ,to be sufficiently clear.
Chemical corrosion is caused by the metal reacting directly with an aggressive solution, gas at high temperatures, etc. Chemical corrosion is the redox process in which the electrons of the metal are passed directly to the material in the environment.
Electrochemical corrosion is a redox process in which the metal is corroded by the action of an electrolyte solution that generates electrons that move from the anode (having a not noble potential in the galvanic series = more negative potential) to the cathode (having a noble potential in the galvanic series = more positive potential).
Conditions for electrochemical corrosion:
1) The electrodes must be different. For example Cu and Zn. In this case, if it is present also condition 2), Zn is the anode and is eroded whereas Cu is the cathode, and on its surface, for example in a solution contained oxygen, the oxygen reduction reaction occurs.
2) The electrodes must be in contact with each other (either directly or indirectly via conductor) and in contact with an electrolyte that contains a reduction element (e.g. dissolved oxygen).
3) The corrosive effect is given by the electrochemical balancing of the two reactions that take place at the cathode and at the anode.
Best regards, Pierluigi Traverso
Dear Pierluigi Traverso,
Thanks for your effort to explain the question. One more doubt created after reading the explanation - Does chemical corrosion not require existence of anode and cathode (like electrochemical corrosion)?
Dear D. Sunil Sinhmar,
chemical corrosion refers to the gradual degradation of a metal surface due to the reaction of the surface with substances in its external environment. It is often characterized by the oxidation of a metal with an acid to form oxides.
Sometimes the anode and the cathode are different areas of the same material....
For more details, you could take a look at:
https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Electrochemistry/Exemplars/Corrosion/Corrosion_Basics
and
https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_Chem1_(Lower)/16%3A_Electrochemistry/24.08%3A_Electrochemical_Corrosion
Best regards, Pierluigi Traverso
The corrosion is chemical if Ox and REd meet and change electron directly.
The corrosion is electrochemical if Ox and Red don't meet and the electron change is mediated via an external (electron) conducting circuit; the places where the electrons are released/accepted are called electrodes and are in fact interfaces between the solution (ionic conductor) and the external circuit (electronic/metallic conductor).
Chemical corrosion is happening by itself as it happens naturally with most of the metals. It can be more aggravated by adding more chemicals to the surface of that metal. For example, adding Al to Mg above some limit, aggravate the corrosion, so it's a natural process. However, electrochemical corrosion is a term used to cause corrosion by applying voltage and forcefully making the metal lose electrons. In this way, it can be quantified, how many electrons are lost (A) with respect to the applied voltage. Such a process gives us the opportunity to quantify the corrosion and specify the metals according to their corrosion status in a short time (30 min). Otherwise, we have to wait for 30 days to do weight loss test or use a very complex process of salt spray test to quantify corrosion.
Dear researcher;
A good reference to read about the different types of corrosion could be found below:
https://publicapps.caa.co.uk/modalapplication.aspx?catid=1&pagetype=65&appid=11&mode=detail&id=7979
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