Dear Felix Lampert,

As is well known, corrosion of metals occurs when favorable conditions are created. In the field, the temperature has a strong influence on the occurrence and acceleration of corrosion processes. In addition, acids change their properties of aggression at low and high temperatures. At high temperatures, due to the expansion of the interatomic distance, the corrosive accelerates. Corrosion occurs at the boundaries of the young deer, increasing to pitting corrosion. At low temperatures, a process of shrinkage of metals begins. Pressure stresses occur between different grain sizes. Nano cracks appear conducive to corrosion. This can be accelerated by lowering the temperature. Hydrogen (H +) as a chemical element causes brittleness of destruction of the surface of steels. Low temperatures accelerate and favor this adverse effect.

Hi Emil,

Thanks for the interesting answer. This does not answer my question, however. I do not want to estimate the corrosion rate, but rather find out why corrosion occurs at all in glacial acetic acid. I doubt that we can describe glacial acetic acid as electrolyte, so I'd generally rule out an electrochemical mechanism behind the phenomenon. From what I've seen it appears at low as well as high temperature (again, I am not trying to describe the corrosion rate) as a more general/uniform type of material wastage. I am specifically looking for the reaction that causes corrosion in glacial acetic acid and I would like to know if this reaction produces atomic hydrogen that could potentially cause HE.

Best regards, Felix

Even the anhydrous acetic acid has some water (Wikipedia says 1%) and if the acid can further absorb water from the air, electrochemical reactions may become possible again (and then probably H effects). But I´m not sure how many water is necessary for EC reactions.

Yes dear Felix Lampert, you are right in that the corrosion mechanism of steels in aqueous acetic acid solutions is based on electrochemical concept with H+ reduction as cathodic reaction , while this concept is not work in case of glacial acetic acid . Since the interaction that occurred between steel and glacial acetic acid is primarily a physical in nature rather than chemical effect. In this respect, such physical interaction going on in two main corrosion forms:

(1) Uniform dissolution, selective and intergranular dissolution of the structural steel,

(2) Diffusion of the glacial acetic acid melts into the steel structure by means of uniform and intergranular diffusion.

This means that the weight loss of steel comes from physical dripping of steel into the glacial acetic acid melt without any hydrogen uptake into steel structure.

Best regards

Dear Mohammed Hussein j. H. Al'Atia , thank you for the very interesting explanation of the phenomenon! Since I am not familiar with this type of materials degradation - do you have or can you recommend a written source that explains this interaction in detail? Kind regards, Felix

Thank you dear Felix Lampert for your feedback.

Yes, my explanation was based on my finding long time ago where such interaction between steel and glacial acetic acid melt was found as a corrosion process that going on by the concept of the liquid metal corrosion or what known by low temperature hot corrosion process. The acid above its melting point (say 16.7oC) poses as non-conductive electrolyte and reveal very high voltage (IR) drop during steel corrosion test by the electrochemical impedance analysis where the total overpotential is solely due to resistance polarization where the activation and concentration polarization being non-existent and there is no Tafel region on the current potential curve. The same results was reported later by S K Singh and et tal., but the addition of diluted forming acid to the glacial acetic acid enhanced the cathodic reaction rate due to increase in conductivity of the electrolyte and thus in this case considered to represent hydrogen evolution electrochemical reaction.

Best regards, Mohammed Hussein j. H.

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I think it might be due to the formation of a coordination complex [Fe3O(CH3CO2−)6(H2O)3]+ , which is a brown precipitate, from the direct reaction of glacial acetic acid with iron/iron oxyhydrates . Since the reaction between iron and glacial acetic acid results in a non-protective precipitate, it will continue. Glacial acetic acid in this case won't behave as an acid, but as a complexing agent