Markovfff
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Orange stuff
Hi,
Chlorate cells use chromates/dichromates or other additives to prevent reduction of chlorate at the cathodes. They are Used together with ss, graphite
cathodes, that is what I know.
I searched a lot of forums and tutorials to find anything about using dichromate with titanium cathode. Found nothing. I heard that titanium does not
reduce chlorates but then i saw people adding it to the cell... Im confused.
So adding it to the electrolyte will do someting, or its just a waste of resources? Also whats the dichromate influence on mixed metal anodes? I
encountered (maybe 2,3 times) people saying that it can even damage the anode, they talked about covering the anode with a layer of something... How?
I don't know.
[Edited on 3-12-2017 by Markovfff]
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symboom
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Chromates /dichromates are to prevent chlorates from being reduced by the cathode it is to improve yield not necessary required another thing people
do to improve yield is adjusting the pH in the optimal range.
[Edited on 3-12-2017 by symboom]
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yobbo II
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There are vast amuonts of nonsence out there on the web when it comes to chlorate making. All starter chemists/hobbyists have a go at chlorate. There
are alot of cases of what monkey sees, monkey does. You neeb to add chromate becauce I read it somewhere etc.
Don't add any. What are the problems associated with removing it from the final product and possible problems if not removed properly?
Just use a small cathode that is well distributed around the anode.
See the bottom of this link
https://geocitieschloratesite.000webhostapp.com/chlorate/rea...
Yob
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Markovfff
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I still didn't get answers for my questions. My curiosity still isnt satisfied :V
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yobbo II
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https://geocitieschloratesite.000webhostapp.com/chlorate/cat...
Some more info
The chromates form a layer on cathodes which effectively lowers there surface area without the disadvaantage of raising cell voltage.
Just use a small (sensible size) cathod to keep current density high on cathode. Dont have areas of cathode with low cd like for example the
"back"sides. Use perforated cathodes.
Chromates are used by manufacturers to obtain small very important gains in current efficency. Not worth bothering about in amateur cells because of
extra hassle of removal from product.
Smaller cats will raise v a small amount but it will hardly be noticable. The serious manufacturer could not tolerate this small rise.
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Markovfff
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Thank you, this is what I was searching for.
[Edited on 7-12-2017 by Markovfff]
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yobbo II
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http://www.sciencemadness.org/talk/viewthread.php?tid=62495
This thread is useful.
Yob
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woelen
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I do not agree with yobbo II. Some years ago I made a few batches of KClO3 from KCl, using a small MMO anode and a titanium cathode. Adding some
dichromate makes a BIG difference. It is remarkable how little dichromate is needed for good results, but adding no dichromate at all makes production
very inefficient. Separating dichromate (or chromate) from the potassium chlorate is not difficult at all, due to the excellent crystallization
properties of KClO3.
See this webpage, I made a fairly extensive write-up of what I did:
http://woelen.homescience.net/science/chem/exps/miniature_ch...
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yobbo II
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The cathode being used in the write-up is a classic example of the type of "layout" that is going to maximize hypochlorite reduction at the cathode
in a cell without chromate. The cathode is somewhat large (not excessively) and is going to have low current density on the side of the cathode away
from the anode (the dark side shall we say). This promotes hypochlorite reduction as I understand it.
It would be interesting to use a cathode that is quarter the area, drilled like the anode and placed both sides of the anode. Or perhaps use the
same arrangement with a plastic cover on the cathode "dark side" or just use a piece of wire for the cathode and run without chromate.
My bottom line is that cathodic reduction can be controlled or eliminated by physical means (electrode geometry and position) as opposed to chemical
means (chromates).
There must be some advantage in doing it the chemical way or the big manufacturers would not be doing it. In a proper industrial cell the anode and
cathode are very close together (mm's) and using small cathodes would lead to current distribution problems on the electrodes? Not a problem when
electrodes are an inch apart or so. There is also other advantages of using chromates like corrosion reduction in plant equipment, though this may be
more historical nowadays.
Copied below from the net....
Helps prevent corrosion of Fe Cathodes.
Helps to buffer the electrolyte in the pH range 5 to 7 (pH control used).
Inhibits Oxygen evolution at the Anode.
Suppresses ClO- and ClO3- reduction reactions by forming a Cr3O4 film on the Cathode. It effectively raises the cd on the Cathode.
Supresses Perchlorate formation at high Chlorate concentrations in the Chlorate cell. (according to JAE 1 (1971) 207-212)
I have not measured current effeciency in a cell with small cathodes versus a chromate cell with the same or comparable cathodes so I could be wrong.
It would be a great experiment to set up the cell as Woelen has done, run some time untill bubble production stabalized, then add a plastic cover to
the back of the cathode and see of bubble production increases and temperature of cell decreases (less hypochlorite reduction).
Chromate can be removed with barium chloride as barium chromate is insoluble if doing a sodium chlorate cell.
Get with the times. Go Green!
Yob
[Edited on 11-12-2017 by yobbo II]
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Markovfff
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What would be the optimal grams per liter dichromate level? I remember making electrolyte for my 2nd cell, and had read to use about 2-5g/L of
solution, I think thats definietely to much. I even had trouble with dissolving it( potasium dichromate) and ended up on filtrating the solution to
get the remaining dichromate out.
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woelen
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In my cell I used a few tens of mg, for 100 ml of liquid. I would say, try with 300 mg. Your solution will have a bright yellow (not orange) color.
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Markovfff
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Thanks, currently runing a 6L cell, adding dichromate made a huge difference. Even if looking only on the temperature: went down from 63C ( and If I
would let it go, it would get probably to 70-75C) to stable ~55C.
[Edited on 19-12-2017 by Markovfff]
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yobbo II
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Document attached on additives and alternatives for Na dichromate for chlorate cells.
Attachment: afa_sd-0038-01-aa_en.pdf (1.9MB)
This file has been downloaded 729 times
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