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Author: Subject: Electrodes for potassium chlorate electrolysis
arsonist
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[*] posted on 24-2-2014 at 10:45
Electrodes for potassium chlorate electrolysis


Hi all! I have recently bought titanium MMO anode for my chlorate cell. In the recipes I have read on Internet was recommended to use stainless steal for cathode. When I turned on my cell at the beginning everything was fine, but after a while my solution became yellow color and some particles of what appears to be rust started to floating around. After two days of work some amount of KClO3 was produced but it was heavily contaminated with iron chlorides and oxides and my SS cathode had black and orange spots on it. After my research I found that there are many types of stainless steal, so my question is what type of SS is best to use, and if possible where I can find it as household items. For my experiment for cathode I used stainless steal spoon(Don't laugh ;P ) I also tried to use graphite but it produces fine dust which mixes with the product and is hard to separate. Thank you!
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Zyklon-A
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[*] posted on 24-2-2014 at 11:02


Well, yes there are different quality's of Stainless Steel (Note spelling), the more chromium in the alloy, the better it will be. I would think that a spoon would be decent quality, but maybe not. I have used a SS knife for a cathode, and it worked fine. If you have any other, better SS, you should try it.



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arsonist
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[*] posted on 24-2-2014 at 11:22


Quote: Originally posted by Zyklonb  
Well, yes there are different quality's of Stainless Steel (Note spelling), the more chromium in the alloy, the better it will be. I would think that a spoon would be decent quality, but maybe not. I have used a SS knife for a cathode, and it worked fine. If you have any other, better SS, you should try it.

Thanks for the suggestion... I have couple high quality knives from German SS :D ... I'll give it a try :). And sorry for my English

[Edited on 24-2-2014 by arsonist]

[Edited on 24-2-2014 by arsonist]
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papaya
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[*] posted on 24-2-2014 at 12:28


You can try copper sheet for the cathode, I've used it in small scale (200ml) cells and as long as it was connected to power it stood well (both above the liquid and below). To the question will cathode material affect the efficiency I have no answer.
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Metacelsus
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[*] posted on 24-2-2014 at 12:47


I use titanium.



As below, so above.
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hyfalcon
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[*] posted on 24-2-2014 at 18:47


Yep, titanium is the way to go. Be sure to get grades 1 thru 4 though or CP (chemically pure).
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macckone
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[*] posted on 24-2-2014 at 21:51


http://www.metalliferous.com/22-ga-0025-Titanium-Sheet-6-x-3...

Great source for common metals in small quantities and a few not so common ones.
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testimento
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[*] posted on 25-2-2014 at 10:05


Titanium is good. Copper should work also when active. Stainless steel you're gonna head for AISI 316L grade, which is used in many cookware and mostly every plumbing piping because of it's high resistivity against chlorides.

For small applications you dont have to worry, but on any larger scale, keep in mind that stainless steels have very low conductivity, even as low as 1-2% of copper, so you're gonna do some math to make sure the cross surface area won't bottleneck your cell.

If you've got graphite or metallic lead electrodes and you get goo into your electrolyte, bring it to boil and filter it when hot. Potassium chlorate has a lot higher solubility when hot, and it'll crystallise out nicely when you cool down the liquor.

[Edited on 25-2-2014 by testimento]
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arsonist
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[*] posted on 25-2-2014 at 10:56


Thanks for the answers! Will it be good idea to cut in half my mmo anode and use the half as cathode ?
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Zyklon-A
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[*] posted on 25-2-2014 at 11:22


NO!, Do not do that! You'll waist you anode, it won't work, and even if it does (which it won't) SS or Ti is much cheaper.
Watch this and read the comments, a lot of your questions are answered there.;)




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Mailinmypocket
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[*] posted on 25-2-2014 at 11:52


For lack of titanium mesh or sheet I have a chlorate cell that has an MMO anode and cathode. It's produced probably around 12 batches and there is no degradation at all. It might be a waste in terms of using MMO where it isn't needed but so far so good.
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Zyklon-A
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[*] posted on 25-2-2014 at 12:04


Really? I'm trying to remember where it is, that I heard that MMO, corrodes rapidly if used as a cathode. Either way, I do not suggest it, find something else.
Best case scenario, it works fine as a cathode, but now your anode is half the size, which means you can only use half the normal current. Also, if you cut the anode, wouldn't that expose some of the Ti? Once the protective layer is gone, your anode is useless. Or does the Ti passivate well enough?
Pt corrodes as a cathode.




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testimento
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[*] posted on 25-2-2014 at 12:25


Titanium passivates within seconds by forming thick oxide layer, so don't worry about that, Ti take care of itself. :P But the current limitation is of concern, if you mind it in the first place. A sheet of 100mm titanium with 1mm thickness has 100mm2 CSA which will conduct about 20-25 amps. It must have surface area of at least 200cm2, or 10cm long, to conduct about 100mA/cm2. You should also have copper or aluminium liner that is 100mm wide to cover the entire electrode, because if you just tap it with connector, you'll have very poor surface area and limited current.

[Edited on 25-2-2014 by testimento]
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Mailinmypocket
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[*] posted on 25-2-2014 at 13:44


Quote: Originally posted by Zyklonb  
Really? I'm trying to remember where it is, that I heard that MMO, corrodes rapidly if used as a cathode. Either way, I do not suggest it, find something else.
Best case scenario, it works fine as a cathode, but now your anode is half the size, which means you can only use half the normal current. Also, if you cut the anode, wouldn't that expose some of the Ti? Once the protective layer is gone, your anode is useless. Or does the Ti passivate well enough?
Pt corrodes as a cathode.


Well I am not an expert in chlorate cells but I know these electrodes have worked like a charm without degradation. Now... If you turn the cell off and leave the electrodes in the solution this is where damage occurs, also switching the polarity can cause damage IIRC. Perhaps somebody can elaborate more on this.
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hyfalcon
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[*] posted on 25-2-2014 at 18:51


They switch polarity on pool chlorinators all the time with twin MMO electrodes. It keeps the hard water buildup down to a minimum when used in that application.

Reminds me, spring is coming up. I need to hit the local pool shops and remind them to call me if they scrap any pool chlorinators this spring.

[Edited on 26-2-2014 by hyfalcon]
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