papaya
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Chlorate cell with base metal anode?
Not having MMO or Pt anode as well as from curiosity I'm doing now my most desperate experiments ever 
You might already know that electrodes made of nickel are successfully used for generation of H2/O2 in water electrolysis, so when the medium is
alkaline Ni anodes stand up well and are really inert. So an idea came into my mind, that if I try to electrolyze NaCL solution where enough NaOH is
added then probably I can avoid degradation of Ni anode while at the same time the cell might generate chlorate. I wanted to try to experiment on this
desperate idea so I assembled a 200ml cell for that. To prepare the electrolyte I dissolved as much as possible NaCl in water and then added a lot of
NaOH flakes, I roughly estimate that concentration of NaOH is not below 15-20% now, and there's a deposition of salt now - I guess NaCL is not very
soluble in the presence of NaOH. For cathode I use a copper (strip of PCB) and not having pure Ni for anode I decided to go with a thick nichrome
wire. All assembled and connected to variable voltage power supply I started with 3V potential for first. A gas generation started at both electrodes
(approx 1A current) and waiting for few hours I really confirmed that anode stands well with no at all degradation. I must note that at 3-3.5V the
current was much lower compared to the same cell when only NaOH solution is electrolyzed. Anyway, to speed up the process I started to increase the
voltage stepwies and found that nichrome anode starts to degrade (pitting corrosion) above 4 volts, while the current is not sufficiently high, what a
pity.
Next and the most interesting thing happened when I decided to replace NiCrome anode with a regular thick iron nail! Guess what ? At a voltage of 5.2V
and current 8A it doesn't even think to corrode for the last 5 hours of run! The solution only changed to a light pink color, which I think is some
manganese from the nail entered into solution and oxidized to permanganate. No rust, at all!
Of course you will now throw stone towards me saying that no cloride is going to be oxidized at all and all I do is generationg oxygen at the anode
and may be you are right, especially that the cell doesn't smell of chlorine. For this to try I took some ml from that solution to test for chlorine
species after some hours of run, part of that I dropped into conc. HCL solution - well it fizzled a bit, HCL turned greenish color, but no distinct
strong odour of chlorine is observed. I also dropped it into ammonia solution and then acidified it - I can really smell the unbearable chloramine (so
I guess some hypochlorite is present).
This was just the first crude test with even no concentrations measured, because I thought it'll be a total failure, which it seems isn't!
Now, yout thoughts please, can chlorate be generated on Fe (or other base metal) anode in strongly alkaline solutions (+ NaCL) even with little
current efficiency ? Am I ONLY wasting current to generate oxygen and no chloride turns into higher oxidation states? What if take less NaOH (but
which still defends the anode some way) and try to fine tune the process?
[Edited on 14-1-2014 by papaya]
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Zyklon-A
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I don't think you're 'only waisting current', but it wont be effective, either. It might work I'm sure you're making some -CLO3.
When I've done it the cell hardly smelled like chlorine at all, which is good.
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papaya
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What you have done?
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papaya
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What some easy qualitative tests for the presence of chlorate in solution are known that I can do?
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elementcollector1
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Add KCl, chill.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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subsecret
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Fe does not hold up well to NaOH in the presence of an electric charge. I made an electrolysis cell with stainless steel bolts, washers, and nuts
(staggered: Nut, washer, nut, washer), and an NaOH electrolyte. The chromium in the stainless steel oxidized to chromate, so sodium chromate was
formed. A little bit of iron oxides precipitated on the bottom of the cell, after it was on for a total of several minutes. Electrolysis with iron
electrodes is one way to prepare iron oxides, but is not very efficient.
Fear is what you get when caution wasn't enough.
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papaya
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Maybe, but in my case it runs 3rd day already, at first I put too high voltage and Fe nail started to degrade slowly, I decreased voltage a bit (it's
now in between 4 to 5volts max) and it stopped to give oxides. The nail is about 5mm diameter, about 4A current is running now through it (it was 8A
previously), and 3 days isn't a joke, that's why I'm amazed (keep in mind it's not just NaOH, it's NaOH + NaCL, I add sometimes more NaCL to keep it
saturated). Even if it doesn't live forever I don't care, I'm only interested if under these conditions chlorate can form. I guess in highly alkaline
medium only possible mode of generation of chlorate is direct oxidation of hypochlorite anion on anode and not the reaction in bulk, but the question
is if it in fact happens in my cell.
Sometimes I take few drops from solution and add to test tube with HCL - now it fizzles considerably at contact, I really can smell chlorine like
smell, HCL becomes yellow colored, but I don't know if it's the effect of hypochlorite or chlorate, any ideas how I can test even for LOW
concentrations of chlorate?
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phlogiston
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from http://www.vk2zay.net/article/80:
| Quote: | - Prepare a boiling solution of 5 parts strong HCl and 1 part aqueous 0.1 % Indigo Carmine. Add 5-6 parts of the dissolved composition to the boiling
reagent, a sharp de-colourisation is indicative of Chlorate. This test is very sensitive.
- Place a small quantity of composition in a white well plate and cover with several drops of Aniline Hydrogen Chloride. A blue or green colouration
forming within half an hour is indicative of Chlorate. This test has reasonable sensitivity.
- Place a small quantity of composition on a tile outside and cautiously touch a stirring rod dampened with concentrated Sulfuric Acid to it. Ignition
indicates Chlorate. This test is not considered reliable or safe. |
I have used a test based on N-phenylanthranilic acid in the past which worked well. I am sure you can find it with google.
edit: also read http://www.oocities.org/capecanaveral/campus/5361/chlorate/t...
[Edited on 16-1-2014 by phlogiston]
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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