[Mark Imisides]

Even assuming that there are no other reactions but iron dissolution occuring on the anode, amount of carbon dioxide evolving will be only twice larger than the amount of hydrogen evolving. This is not as huge difference in speed as you suggest, and that's only assuming there is no oxygen evolving at the anode at all. There is oxygen evolving and anode corrosion is a slow process, so amount of carbon dioxide evelving should be much, much lower.

That's right - but the point is that being a homogenous reaction it forms much, much smaller bubbles, so while the amount that evolves is much smaller, the fact that the size of the bubbles that form is also much smaller means that you get lots and lots of bubbles - hence the effervescence that is such a widely used qualitative test for carbonates.

IU'm not suggesting that's the only reaction - just that it is a contributor.

Mark Imisides New Member -- Do you have examples of gas or liquid electrodes that are currently being used for this process?

I don't understand your question - what is a "gas or liquid electrode?"

[Borek]

I still don't feel convinced. No matter what their size is such bubbles are short lived - when they get to the surface, they pop. They don't create a stable foam.

Besides, unless the electrode is highly polished, it is much easier to start bubble creation on the surface, than inside of the solution. That's no different from using boiling chips. No idea why you think homgenous reaction gives many small bubles - quite the contrary, activation energy required to create a bubble is very high in the bulk, so once the bubble is created its grow is favored over new bubble creation. That leads to small number of large bubbles, not large number of small ones. On the rough surface of electrode situation is opposite, nucleation being a key word.

[DrCMS]

Is the foam a solid stabilised foam caused by bubbles of hydrogen, oxygen or carbon dioxide stabilised by the insoluble carbonates

[Borek]

stabilised by the insoluble carbonates

Honestly, you were faster by several hours. Few hours ago I have seen some precipitate on the surface of water I am using to water my plants and something clicked... but I forgot to look for this thread and add a comment.

If that's the case, just using distilled (DI, RO) water should stop foam creation.

[Mark Imisides]

I still don't feel convinced. No matter what their size is such bubbles are short lived - when they get to the surface, they pop. They don't create a stable foam.

Besides, unless the electrode is highly polished, it is much easier to start bubble creation on the surface, than inside of the solution.

Correct - but the size of a bubble is determined by when it stops growing, not how easily it starts growing.