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Do i have to have certain metals to synthesize potassium perchlorate using electrolysis? Answered

I know how to make potassium chlorate using electrolysis but I've seen on YouTube that you can use NaCl (table salt) in a mixture with water and that i can electrolyze it with platinum and titanium (or steel) electrodes. i need to get around shipping stuff to myself (because my parents) so i wanted to know if i should just make KClO3 or if  i can use two stainless steel electrodes or if there are other easy accessible metals i can use

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Jack A Lopez (author)2013-02-19
I have read a lot about electrolysis cells used to produce chlorate ion, and it seems to me there are a number of problems to overcome to make a cell that actually works.

Starting this story from the beginning:  There are four different kinds of chlorine-oxygen ions, all consisting of 1 chlorine atom and n oxygen atoms.  In order of increasing n (and also increasing valence on the chlorine atom), these are:
  • hypochlorite ClO-
  • chlorite ClO2-
  • chlorate ClO3-
  • perchlorate ClO4-
This page,
http://en.wikipedia.org/wiki/Chlorite#Oxidation_states
has a little table with some nice pictures and data for those different ions.


Of course, the ion you want is chlorate, ClO3-,  and the usual recipe for making it is to bubble chlorine gas through warm water containing OH- ions, i.e. through a basic solution.  How warm, at what temperature? Well, the Wikipedia article on Chlorate ion, says 50 to 70 C, here:

http://en.wikipedia.org/wiki/Chlorate

Interestingly the same reactants, Cl2 gas and OH- ions,  in cold water, will make hypochlorite ion, ClO-
http://en.wikipedia.org/wiki/Hypochlorite

So I think getting the temperature right is the first challenging part. 

The next challenging part is what you were saying about the electrodes:  chlorine gas in warm water is corrosive to most metals. 

The first thing I would try is using carbon electrodes, like those harvested from a carbon-zinc battery, or from an old electrolysis type humidifier.  To  me that seems like the easiest thing to try.

The second thing I would try would be putting a regulator on the current supply, so that you can actually control the current density at the electrodes.  BTW current density (has units of ampere*cm^-2) is just the current in the circuit (in amperes) divided by the area of the electrode.

Also on the subject of control, it would be nice to have a thermostat on the whole cell, so you can actually keep it at the temperature at which the reaction is supposed to happen.

I mean you kinda have to know that's what the pros are doing. I mean the chemical engineering wizards that  actually make, and sell, chlorate on a large scale.  The parameters of their cells, current, temperature, pH, concentrations, etc, are all under tight control, so the reaction happens consistently, and optimally.

But the naive garage-based chemist would prefer to just stick some electrodes in a glass jar, and hook it up to a car battery, and just hope for the best:  Hope it warms up to the right temperature.  Hope the current density is not destroying the electrodes.

Anyway... I think your main question was about electrodes, and the choice of metal, or material, for this.  I have read lots of chatter on this subject.  The corrosion is worst at the anode, where the Cl2 gas appears, and I think the pros use titanium coated with other the oxides of other metals, like oxides of manganese, cobalt, iron, etc.

The reason for making an electrode with a special metal oxides layer was that naked titanium passivates when used as an anode; ie. it builds up a layer of TiO2, and that layer is an electrical insulator, and that stops the current.  In contrast, those other metal oxides are electrically conductive, at least in very thin layers.

I have also read rumor of lead, or lead-alloy electrodes. Guessing that those naturally develop a layer of conductive lead oxide on them, when used as an anode.

I seem to recall that NurdRage
https://www.instructables.com/member/NurdRage/
http://www.youtube.com/user/NurdRage?feature=watch
did some work, and videos, on the subject of making a mixed metal oxide (MMO) coated titanium electrode. 

Make Manganese Dioxide Electrodes (for chlorate or HHO cells)
http://www.youtube.com/watch?v=BjKYiu8eKa8

Make Manganese Dioxide Electrodes - Revisited
http://www.youtube.com/watch?v=nvMVlhBmv7M


To me that looked like a lot of work, but if that's the electrode you want, I guess that's the way to do it.  I'm not sure what it costs to actually buy such an electrode. I'm not sure if I want to know. ;-)

Anyway, like I was saying before, there are other things to try.  I suspect that cheap carbon electrodes will hold up, if you just go easy on the current density, and the way you do that is by making, or buying, a power supply that can supply constant current.  So you've got a knob you can turn to control current. 

A thermostat (via a heater or cooler) to make the cell temperature be just what you want it to be, that would be nice too. 

Another approach might be using a  cell with a separator, so that you could make Cl2 gas, and then pipe it to a separate reactor where it bubbles through base (OH- ions) to make your chlorate.

However, I think the regulator for electric current is the most important improvement you could make, and you should focus on that first.  I mean if you want to do it that way. 

Like I was saying before, I think most amateurs just build a cell, and plug it in, and then pray that it works, with no attempt at actually controlling the reaction parameters.
 





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user

well i definitely thank you for the extremely in depth answer you gave me but you answered actually other things about my question that i was absolutely oblivious to such as the temp. and the certain current needed. i have seen the project done with even two steel knives and 2 9volt batteries so i guess i will have to be that naive garage-based chemist that really doesn't know exactly what he is doing and i might just go ahead and do it with my computer power source and some knives in plastic jug and i might just defy the professionalism that is neccissary (and no i don't mean that as an insult to you or other smart or smarter chemists)

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mpilchfamily (author)2013-02-19

If your having to sneak this around your parents then maybe you shouldn't be doing it.

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user

well now that i see the be nice statement under my comment that ruined my chances a totally disowning you. but the thing is is that i've put so much work into my home science projects that my parents would only be the slightest of skeptical if i purchased even a full lab set that contained the most eye-opening equipment so i just really don't care as to what you say about me and my ways around pyrotechnics and chemicals.

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