Okay, I'll just say it right now: I know it's easy to find effective cathode materials. In the case of a chloralkalai cell, I have heard that
titanium, stainless steel, and even mild steel work just fine. But while researching the construction of such cells, I found this: https://geocitieschloratesite.000webhostapp.com/chlorate/cat...
It says that "Copper is OK if you are going to use your Chlorate for bleaching! For all other uses of Chlorate it should be ruled out completely."
Clearly, this is for an undivided cell (making ClO and ClO3 salts, not hydroxide and chlorine gas) but it got me thinking. I searched on Google,
mostly found the same advice. On sciencemadness in particular, I found a post or two saying copper was bad for such a cell. One even mentioned that it
was bad to have a chlorate cell with a copper exhaust tube (or connector or something, I can't find the thread at the moment) even though it wasn't
immersed. Now, I have some questions:
Why is copper bad as a cathode? Does it reduce chlorates/hypochlorites back to chloride? Does it leave an impurity (e.g. copper salts) that is toxic
or catalyzes decomposition over time? Does it just wear out fast? (Yes, I know that corrosion can sometimes be prevented by making a piece of metal
into a cathode)
Also, is a copper cathode alright in a divided cell?
Finally, what makes Cu special in this regard? I'm by no means an experienced chemist, but I've always considered copper to be more inert than say,
mild steel.
One thing I do know is that the connecting wires of almost every power supply are made of
copper, so it has surely ended up in many cells by accident.
Again, If my end goal were just to get chlorine or sodium hydroxide, I'd buy them. If I just wanted a working cell, I'd make it with a more common
cathode material just in case, and would use steel connecting wires to reduce the chances of Copper contacting the liquid. I know that electrolysis of
salt (both divided and undivided) has already been discussed ad nauseam here (Just look at my username! Think I care?), but this specific issue of copper cathodes has yet to be described in detail. I
just like learning more about things like this.RawWork - 7-3-2018 at 07:58
Yeah, I noticed it too few years back. I don't think it's related to chlorine, hydroxide, or any oxidant being present. When I used copper wires for
both electrodes, the anode obviously converted into hydroxide, oxide and carbonate. But catode became different color, it turned from shiny red to
dark red, then to brown and finally black, and was "eaten". I think there was copper powder left below place where copper cathode was. This is more
likely to be related to hydrogen! Hydrogen dissolves in copper much more than in iron. It could be H2 or nascent H that gets generated there. Then,
when it tries to precipitate, it causes brutal damage to metal, converts it into powder, makes holes etc. Everybody everywhere recommends to use iron
cathods as they have best physical/nuclear/chemical properties. Even nuclear scientists use them for heavy water production because they have many
best parameters like isotope separation factor.
"Susceptibility to hydrogen-induced cracking ('embrittlement') is often a result of the introduction of hydrogen during forming, coating, plating,
cleaning, and finishing operations, often referred to as 'internal embrittlement'. Hydrogen also may be introduced over time (so-called 'external
embrittlement' through environmental exposure (soils and chemicals, including water), corrosion processes (especially galvanic corrosion), cathodic
protection, and/or from hydrogen generated by corrosion of a coating. To be susceptible, a combination of three factors is required: presence of (and
diffusion of) hydrogen, susceptible material, and stress." https://en.wikipedia.org/wiki/Hydrogen_embrittlementyobbo II - 7-3-2018 at 15:55
You don't want any copper ion where there is chlorate. It is generally bad news. You will get green deposits on copper cathodes and connectors which
may drop into you product or cell and cause problems.
YobVomaturge - 7-3-2018 at 19:50
Thank you both for your replies! It sounds like there are reasons not to use copper cathode period, but that there's a whole new world of problems
(like spontaneous combustion) that can happen if copper ends up in a batch of chlorate. The warning about only using copper contaminated chlorate
solution for bleaching makes sense now. In a solution, it's okay, but dried, concentrated, with a fuel, in a firework it can be dangerous.
Incidentally, I knew there was a thread about copper chlorate, but it didn't talk about the risks of making KClO3 contaminated with it. http://www.sciencemadness.org/talk/viewthread.php?tid=32221
Anyhow, I think I'll go with the steel cathode, but I won't worry about the connecting wires. Thanks.
Thank you both for your replies! It sounds like there are reasons not to use copper cathode period, but that there's a whole new world of problems
(like spontaneous combustion) that can happen if copper ends up in a batch of chlorate.
Yeah there are quite the nasty copper (per)chlorate compounds.
If you go even further you can get stuff like Tetraaminecopper-(per)chlorate compounds that are highly unstable mixtures of fuel/oxidizer.
Nothing you would want in KClO3.mysteriusbhoice - 9-9-2018 at 09:00
copper chlorate is nasty stuff!!
when its present your mixtures can ignite at less than 100 celsius because I was boiling a stupid mix! containing copper 2 acetate and chlorate along
with sugar and water and as it was boiling not even caramelizing it already lit up!!!
), but this specific issue of copper cathodes has yet to be described in detail. I
just like learning more about things like this.