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mrjeffy321
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Trying to figure out what happened
[Kind of a long post I now realize]
I was running an electrolytic cell in an attempt to make Sodium Chlorate from Sodium Chloride, I have done this before, and that isn’t the problem
here.
My cell is constructed using 2 carbon-graphite electrodes sticking up from the bottom of the plastic bottle containing the electrolytic solution; I
then pass a current through the electrodes to make my Sodium Chlorate.
The problem came when I left my cell unattended all night to run, sometime during the night, the anode (+) eroded away, it isn’t unexpected for it
to erode. The electrode became so thin that it just broke off at the base leaving just a little stub of electrode behind.
The next morning when I check to see why I was getting such poor performance out of the cell, I discovered what had happened and a problem with the
solution.
With all the eroded carbon particles suspended in the water it was quite black (as usual), but upon filtering, I saw that the solution had turned a
dark green. I am at a loss for why it turned green. Then I filtered it again to try to get all I could out of suspension, afterward, the solution
was left a dark yellowish (and just slightly green) color.
At this point, I figured there was nothing I could really do about what happened and I decided to just continue with the chlorate production using the
same, now discolored, solution. To readjust the pH, first I needed to boil the solution to decompose the hypochlorite so that I can use my pH paper.
Once I starting heating the solution up, it started turning dark, very dark, to a point that when it began to boil it was almost black. After I let
it cool and sit undisturbed over night, some particles settled out of it, so to get rid of these, I filtered again. This time, I took out many of the
larger particles, but now I am left with a dark green/brown solution that will not filter any more with my grade of filter paper and nothing seems to
be settling out. I am worried that all my work at making chlorate is ruined for this batch now due to some mysterious chemical reaction.
My only guess as to what happened, although probably not correct, is that perhaps the copper wires I had attached to the electrode that dissolved away
were exposed to the solution and they turned into electrodes themselves, eventually corroding away into solution. Since I was producing chlorine gas
at the anode, maybe Copper (II) Chloride was formed and then went into solution. I looked up what color a CuCl2 solution would be and it is said to
vary based on concentration from a light blue to a dark green for very high concentrations (I think about 50% or more). So maybe the coloring was due
to CuCl2 ?
But then when I boiled it what happened?
What I fear is that the CuCl2 reacted with the chlorate ions to make Copper Oxide, which would not be soluble and I could filter out. But then what
is left now in the brown/green mixture I have?
I really don’t care about the color of the solution, all I care about it preserving the Chlorate I have produced, it took me a lot of time and work
to make what I did, and now when I was near completion, I might have lost the batch.
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12AX7
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Get bigger electrodes and power supply. Make a pound per week. 
Failing that, I'd have to guess copper too. Thing is it usually ends up yellow or orange from Cu2O being produced, at least at first. My guess
is it goes into solution as Cu + 4Cl- + e- = CuCl4(-3), i.e., copper(I) tetrachloro complex (Cu2Cl2 is insoluble in water, but soluble in Cl-
solutions), which then breaks down further away from the electrode as copper hydroxide, which since Cu(I) doesn't form a hydroxide, it forms Cu2O
instead, which is orange. (If you anodize copper with sulfate, which doesn't complex, you get blue Cu(OH)2 precipitate.) As electrolysis
progressed, the Cu2O was oxidized by the chlorites and maybe became Cu(OH)2 (which should be blue, or green Cu(Cl,OH)2 given the chloride present)
which finally broke down on boiling to CuO. Now that doesn't explain how inbetween you got a solution, but possibly if you've been
adjusting pH, the acid could've dissolved it.
To answer your question, yes electrolysis of copper forms copper chloride at the anode, but it precipitates since the average pH is more or less
neutral. Plus, copper, being below hydrogen, plates out readily, even from acidic solution!
I don't know how Cu could've got there in the first place if you sealed the graphite and the copper was outside, but I'm just guessing.
Tim
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mrjeffy321
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When I boilied the solution to alloow me to adjust the pH, I ended up not messing with it any, leaving it where it was since I didnt want to interfere
with whatever was going on for fear of making it worse by adding HCl, so nothing (but some extra water to replace what boiled off) was added.
I have had problems with my electrolytic cell design from the start. The arrangement I have now had worked the best for me, but is by no means
perfect. The way I had the electrodes sticking though the bottom of the plastic bottle is I cut 2 holes the size/shape the of the electrodes,
inserted them through, then used some silicone sealant glue to fill in the space. That hold up OK for about 100 amp hours (passing a constant current
of 1 amp through the cell for 1 hour, or some combination to give me that), but then the wear and tear starts to get to it. The glue begins to leak
and let a little liquid seep down through and to my copper wires.
The copper wires I have encased in hot-glue to protect them, but that doesnt last either, so usually sometime between 90 and 130 amp hours, I need to
take eveything apart and re-make it. That is how the copper could gave gotten in, and the process would have been speeded up since my anode broke
off, basically exposing the end of the electode to the liquid.
Like I said, I dont care too much about what the stuff is in the water so much as I care about my chlorate. So does it soun like the chlorate could
have reacted with any of this stuff at any point during electrolysis, filtering or boiling?
I make my chlorate using a computer power supply an 2 carbon electrodes that when using the
+12 V output on the power supply, I can get around 8 amps.
However, recently, I have noticed that the current has severely been reduced (by a couple amps) even when the electrode was intact, due to some
increase in internal resistance of the cell. Perhaps what I am describing happened not over the course of 1 night, but rather has been happening
since my last "Clean out" of the cell, a more gradual process.
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12AX7
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Connect two cells in series at that voltage!! No wonder your graphite gave up the fight.
I never saw any point whatsoever in the bottom-electrode design. I mean if nothing else, when your anode wears out (be it in days or years), you have
to trash basically the whole thing to fix it. That's why I went for a top-electrode design.
Anyway, even if copper got in solution, copper chlorate has high solubility (at least if you'll be salting out KClO3; I never kept any NaClO3 to
test Cu(ClO3)2) so it isn't likely to cause trouble.
Tim
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mrjeffy321
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The reason I am using such an over voltage in my cell is to increase the current and reduce the amount of time it will take to make the chlorate.
Actually, the electrodes I had worked pretty good, I put somewhere between 1000 and 1500 amp hours throgh them, and I am happy with that.
The way I designed my cell with the bottom electrode design was for 1 purpose (and it wasnt for ease of fixing the electrodes). With all the gasses
generated in the electrolytic process, especially the chlorine, with my top electrode designed cell, everything would corode very fast. I said before
that I would have to fix (not replace) my electrodes about every 100 amp hours, well before using the top electrode design, I would need to replace
them about once evey 20 amp hours. For that reason alone did I redesign.
But even with the bottom electrode design, it isnt too hard to fix it up (make no misstake, I dont like doing it), but since the silicone sealant
doesnt try rock hard, all I have to do is peal it away, wash the electrodes, and then re-glue it back in.
My original plan after making the Sodium Chlorate was to then react it with KCl to make KClO3 and NaCl, which the KClO3 would then percipitate out.
I think I might still try it to see if I get any percipitate, and hopefully it will be KClO3.
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12AX7
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Well yeah, that's why you use a lot more electrode area. You can get near unlimited life (years to decades maybe) with a properly low current
density. You also don't lose any Cl2, and now your electrodes don't corrode nearly as fast. So you made problems for yourself by making
problems for yourself.
Tim
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frogfot
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I wouldn't care that much about the color of electrolyte. It depends mainly on cell materials.
I had same color change when I've used polystyrene jars as the cell containers. First the electrolyte was green and then it turned blackish on
heating, mentioned it here (http://www.sciencemadness.org/talk/viewthread.php?tid=570)
As for good material to make cells airtight, I found that black rubber (um.. dunno the composition, it's used to make gaskets somewhere in
cars..) is very chemically resistant when above the electrolyte. Don't know if resistance will be the same under the electrolyte.
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neutrino
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My suggestion: add NaOH to precipitate out the copper, filter, then add HCl to make NaCl.
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mrjeffy321
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Since I am at a point where I can redesign my cell, or atleast the electrodes, I think I will replace the anode that broke with a nuch bigger one to
lower the current density, it will probably be about twice the surface area as the old one, it will help some at least.
frogfot, it would seem that what is I am experiencing is very similar to what you encountered earlier. It isnt so much the color I am worried about,
but rather, I take the color as an indication of what chemically is happening in solution. I have produced chlorate electrolytically this was before
a couple times, and this has never happened, so I am worried something went terribly wrong.
Even though I am semi-redesigning my cell now, I feel that whatever I do to it is only a temporary solution or a half-fix to the problem of corrosion.
Some way, some how, the chlorine finds its way through just about any type of sealant I come up with (maybe it isnt the chlorine, is that a
possibility?).
What I might do is take part of the solution and try to percipitake out any KClO3 I can get, as if nothing had happened.
Then take some more of the solution and, using neutrino's idea, try to percipitate any copper, then see what happens.
and of course leave some left over for the control (which I might decide to continue electolysizing later on).
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12AX7
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FYI, I've had terrible luck with copper in solution, at least precipitating with soda bicarb. Like it makes a soluble carbonate complex or
something. I had a neutral salt solution electrolyzing a copper anode and it was plating an unusual amount of copper sponge, so I tried putzing with
it, adding acid or soda to try to precipitate it... pffbt! Copper is also soluble in strong base as cuprate (CuO2--).
Tim
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frogfot
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It's really strange that copper would get into the electrolyte when the wiers are outside..
Just remembered that green color can come from nickel (from cathodes). Some steels has up to 20% Ni. The last cell I did (without K2Cr2O7) had another
type of steel that gave strong yellow color, which most probably comes from chromium.
Whichever heavy metal there is, it will come off in 2-3 recrystallizations. Or precipitation by NaOH as noted earlier.
The color change on heating could most probably be the hypochlorite reacting with the organics dissolved from cell walls (it's most probably
chlorination and not oxidation..). Since these impurities are usually low in conc, the amount of consumed hypochlorite should be very low.
I had also some pain to make the cells airtight. It even smelled chlorine with rubber gaskets gooed into grease. But then I realised that the chlorine
escaped through the crappy impregnated anodes!!!
I impregnated already used graphite rods with linseed oil. Already present salts probably redissolved and formed small channels.. where gas could
escape.. While using them for some hours, some of the rods had formed solid salts on top of the rods.. and the smell of chlorine totally disappeared..
so the presence of these channels was confirmed.
It was actually fun to note that some of the badly impregnated rods had corroded more than others.. I have recorded the diameter of the rods before
and after a 126h run, scroll to the bottom of this page to figure 4:
http://www.frogfot.com/synthesis/chloratecell1.html
Left is before and right is after the run.
The rods where salt just started to form on top are nr 5 and 18.
So, concider that graphite is porous and impregnate it properly. One could probably do some simple test on the graphite rod to check if it's
airtight or not..
[Edited on 2-8-2005 by frogfot]
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mrjeffy321
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The color must be from copper, I cant think of anywhere else it could have came from, it is the only metal that comes anywhere near my cell
during opperation.
It had never occured to me the graphite was porous, I had always seem recomendations to soak the graphite electrodes in linseed oil to reduce
corrosion, but never bothered to do it. I think my graphite is in reality, artificial graphite that is suppose to be much harder and denser than
normal graphite, and it is based on my experience so that is why I never bothered to so anything special to them. Once I can find some linseed oil, I
will give that a try.
OK, I have quite a to do list now dont I,
-Try percipitating the copper
-Try percipitating KClO3
-Make new, bigger, electrodes
-Find linseed oil somewhere and treat electrodes
Also, since you guys seem to be such experienced experts with electrolysis, I was wondering how you measured the total charge that flowed through you
cells? To determine the running time for my chlorate cell, I know to convert X mols of NaCl to X mols ot NaClO3, it will take ___ amp hours, so then
I have to keep track of the current through the cell for a given amount of time so I have the total charge, the whole process is very frsutratingly
tedious. I had tried to build an amp hour meter my self, but sadly I am not that skilled with electronics (tiny, tiny little chips and resistors  ), and they are too expensive to buy pre-made. I had thought about using a watt hour
meter, since my computer power supply outputs a constant voltage, I could just divie the watt hours by the voltage and get amp hours, but I cant find
a suitable watt hour meter either.
Any thoughts?
EDIT:
While searching around what I now assueme to be your page, frogfot, I found instructions to treat the graphite anode with linseed oil. I plan on just
letting it soak for a couple days, bt it says to let it dry for a few weeks, is all that drying time really necesary? Cant it just be washed off and
dried?
[Edited on 2-8-2005 by mrjeffy321]
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frogfot
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Oh, sorry, you had a graphite cathode.. I forgot this..
If your powersource gives constant regulated current then sampling the current 1-2 times per day should give you a pretty accurate average value..
The drying time of the boiled linseed oil depends on the quality I guess. Some people say that it's enough to dry for 2 days.. but my takes way
longer to dry.
On package it says that drying time at 23*C is 14h.. but when I tested to paint it on a piece of plastic it took 2 weeks to dry I really don't know wtf is wrong with it..
I guess soaking the rods without a vacuum should be sufficient, but this will take more time. The capillary forces of the pores should suck up the
oil..
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mrjeffy321
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my computer power supply gives me a reasonable stable voltage, but the internal resistance changes alot and thus the current is never very stable.
Generally I see an upward or downward trend in the current depending on what stage I am in through the run. I could just pick a current to call my
average and then assume that is my constant current, but I think that is too inacurate for my cell.
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mrjeffy321
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OK, I got the linseed oil and made a new electrode (much more surfce area than the previous anode).
I am currently soaking the electrode in a sealed glass bottle filled up with a mixture of linseed oil and toluene. The mixture is about 75 to 80%
linseed oil to 20 to 25% toluene by volume.
I will give it a few days atleast, or a week at most.
[Edited on 3-8-2005 by mrjeffy321]
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mrjeffy321
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I soaked the electrode in the linseed oil solution for 5 days, then let it dry out overnight. Is there a way to tell it whatever was suppose to
happen, actually happened? I should have weighed it before I soaked it.
It is currently being glued into the cell assembly in preparation for a test.
Also, I did some experimenting with the old solution.
I tried adding NaOH to the solution, but I saw no change.
I also tried the opposite, adding lots of HCl to solution, again, no change.
Then I added a lot of KCl and boiled it for a while to make KClO3. It turned out that it did make some, although the crystals that percipitated and
dried were much smaller than what I normally get. I crushed it up and tested it by reacting it with sugar, but it seemed to work quite well, although
it isnt snow white colored, it has a slight brown tint. I might try to purify by redissolving it and then percipitating it again, it might help the
color a little and increase the purity, but I will loose some in the process.
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mrjeffy321
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I have another update for you,
After further drying of the KClO3 extracted from the green/brown solution, I crushed it up into a very fine powder (color is just off-white), and
weighed it. It comes to 58.7 grams of this semi-pure KClO3, which if you work out the math on it, since I put about 400 amp hours through the cell, I
got 40.4% efficency after all was said and done. Pretty sad, but considering all that went wrong, I guess I am happy to get what I get.
I am currently running the new cell to do a small batch, but I have noticed something already, although the anode seems to be erroding slower than
before, it is indeed eroding and leaving a sticky black residue (as opposed to just fine powder from before). Otherwise everything seems to be going
fine so far, but I am only about 50 amp hours into the batch with another 120 to go.
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frogfot
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| Quote: |
I soaked the electrode in the linseed oil solution for 5 days, then let it dry out overnight. Is there a way to tell it whatever was suppose to
happen, actually happened?
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I go by smell..
My last run gave 20% efficiency. It's so low probably due to several things combined: inaccurate current measurement, poore pH control (1
time/day in average) and lack of chromates. Gonna improve this the next run.
Any idea what is the optimal current density on graphite anodes? I for some reason hooked up on 40mA/cm2 (I think it comes from some internet page)
while a nonorg book calls for 70-100 mA/cm2.
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praseodym
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That is a big difference between the 2 numbers...
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mrjeffy321
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I ended up prurifying the discolored batch of chlorate, I originally had 58.7 grams, then after purification, I was left with about 45 grams, and then
color was still (just slightly) off white. When I tried burning it with sugar, it still burned with a yellow flame, rather than the purple one it
should have, suggesting it still had alot of Sodium in it, I dont understand it, the purification process should have gotten rid of all that.
And the batch I made in my new cell has been finsihed too.
I passed170 amp hours through the cell, and ended up making 56.2 grams, so that gives me an efficiency og about 43%, not the high number of
50% I was hoping for, but an improvement none-the-less. Maybe I will just assume an efficiency of 45% from now on.
I always seem to get really low efficiencies, even when I plan on getting 50%, I end up getting something in the 40% range. Now it could be that I
didnt even actually take a pH reading during this most recent test, I just guessed how much HCl to add based on how long it was running and how big a
fiz it made when I put a drop in. The linseed oil seemed to help with the erroding of the anode, there wasnt nearly as much Carbon dust left over at
the end as I expected, but the dust that was left was very hard to filter, it seemed to be smaller than the dust I am used to. Most of it I could
filter out, but alot I couldnt, enough to make the water a dark gray color, what I had to due was boil it a couple times and continue with the KClO3
making process until the particles grouped up together enough to be able to filter, but by then I had KClO3 crystals in the water, so I had to filter
it hot to keep then in solution.
Anyway, so the new cell seems to be a succes, the larger carbon anode really helped, and it doesnt look like it needs any matience, it still runs fine
and make acceptable quality KClO3.
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12AX7
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My electrolyte ends up pretty black too, but I just filter it anyway. I use paper towel so the colloidial particles just wash right through the paper
and the chlorate! After seperating from the mother liquor I add to a bucket of ice water and stir for a while, then filter and dry the yield.
Leftover liquor can be settled over a number of days until the graphite stays on the bottom, well until you try pouring some out so it's a real
slow process but it's not like you're sitting there the whole while.
Edit: After one such washing I get purple burn, no sodium line in sight. Maybe you didn't wash long enough/with enough water?
Tim
[Edited on 8-14-2005 by 12AX7]
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frogfot
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mrjeffy321, just wanned to ask what anode current density do you have?
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mrjeffy321
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My anode had a surface area of about 84 square centimeters and at maxiumim, my current never exceeded 7.5 amps. so,
7.5 amps / 84 cm^2 = 89 mA / cm^2.
The black goo that was made I assume is a mixture of some of the carbon particles and the linseed oil, but that was some very hard stuff to clean out
of the cell, sticks to everything. Hopefully it wont make that any more.
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12AX7
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Didja bake the electrodes?
Some paint thinner should get the goo moving.
Tim
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mrjeffy321
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No, I did not bake the electrode, Should I have? What would that do?
It took some scrubbing, but dish washing liquid worked pretty well to get rid of the black goo.
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