During the corrosion of aluminum, we have the oxidation of aluminum to its ionic form and this reaction is balanced by a reduction of ions in solution.

So basically it is the reduction of $\ce{H+}$ protons and oxygen ($\ce{O2}$). But we generally presume the overall reaction is the oxidation of aluminum and the reduction of hydrogen protons and we neglect the oxygen reduction.

Why do we only talk about hydrogen evolution for most metals?

Thank you for your answer but actually my question was why when writing the corrosion reaction of Aluminum or other metals , we generally just write the one representing the hydrogen evolution and the oxidation of Oxygen and we do not mention the other reaction which the reduction of oxygen. So basically the two reactions considered are the oxidation of Aluminum and the hydrogen evolution.

  • $\begingroup$ Please use the "Contact Us" link at the bottom of the page to merge your two accounts. Then you'll be able to edit the question and comment anywhere on the question or answers. $\endgroup$ – jonsca Sep 22 '16 at 22:51

Hydrogen evolution is an output that is relatively easy to measure because it can be detected by changes in pressure or displacement (volume), or by mass spectrometry. The oxidation of metals (or reduction of oxygen) conversely is much harder to measure in real time. Where a corrosion rate of a metal is to be determined then it is much easier to study the hydrogen evolved and then convert those numbers back to mg/m^2/y. It is also particularly useful for passive metals, such as aluminium or zirconium, as a small evolution of hydrogen will generate a pressure change that is quite significant compared with its mass, so even a very slow reaction can be measured over a sensible timescale.

Hope this helps

  • $\begingroup$ Hi, @Chris. This is a mathjax-enabled site. so, please use it. For quick reference, check this meta Math.SE post. $\endgroup$ – user5764 Sep 21 '16 at 8:45

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