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vanBassum
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[*] posted on 18-8-2024 at 11:15
Long Chlorate Cell with Cool Bottom


Hello everyone,

I've decided to restart my chlorate cell project and could use some advice. I'm using an MMO anode with two titanium cathodes. Previously, I used a glass cylindrical container that was just slightly longer than the cells themselves, holding about a liter of electrolyte.

Now, I'm trying something different. I have a larger, long cylindrical glass container that can hold around 4 liters. The electrodes are positioned in the top third of the container, which is significantly warmer than the rest of the cell, fluctuating between 60–65°C (at a current of 20A). However, the bottom part of the container remains cold, so I suspect there's minimal movement of electrolyte between the top and bottom. For context, the cell is open-topped to allow water evaporation. My goal is for the chlorate to eventually settle at the bottom for collection. Ideally, I’d like to run the cell continuously, topping it up every day or so. When a considerable amount of chlorate has settled, I plan to collect and clean it.

I'm wondering if this setup is a good idea, or if it would be better to revert to the smaller container. The downside of the smaller container is that I have to limit the current to prevent the cell from getting too warm. Besides, it has to be collected more often due to the smaller size.

One additional detail: the cell is converting sodium chloride to sodium chlorate. I plan to stick with sodium because I intend to move on to a perchlorate cell afterward. Potassium salts are too insoluble to be practical in a perchlorate cell.

Any thoughts or suggestions?

Thanks!

[Edited on 18-8-2024 by vanBassum]
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RustyShackleford
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[*] posted on 18-8-2024 at 14:14



I have made a KClO3 cell with the type of design you're talking about, having a tall container even without evaporation makes it so the crystals grow as a nice layer from the bottom, i was able to keep track of the progress by monitoring the height of the crystal layer.
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yobbo II
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[*] posted on 18-8-2024 at 16:30


You will have to stirr the cell bottom. Its a problem with any cell that is taller than the electrodes (by more than a few inches).
Use taller thinner cathodes that go to the bottom. The bubbles keep things stirred. Its the one use that the home maker has for hydrodynamic's.
Cover the 'back sides' of the cathodes if you think the area is too big and you think you are getting too much cathodic reduction.
Use a magnetic stirrer if you have one. Put it on a timer if possible as the stirrer can bore a hole in a plastic cell bottom after some weeks. Or put a piece of glass in cell bottom.

Cat. reduction is not much of a problem if you keep cathode size sensible and dont have a large area on the side that is not facing the anode. Using a mesh (bore holes) may help.

Another solution:
Use the smaller cell and put it in a container of water to keep it cool.

You cannot run a sodium chlorate cell continously (unless at a low temperarure) and get solid out. (Alas)
You need to stop and cool (when the time is right).

Are you using pH control.
If yes you must stay hot to get the benefits.
If no, then running very cold to (hopefully) allow crystallization, will give no evaporation.
A conundrum.

Yob



[Edited on 19-8-2024 by yobbo II]
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vanBassum
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[*] posted on 18-8-2024 at 23:25


@RustyShackleford, I can see how that works out for potassium salts, but for sodium I don't know. According to this, the chlorate should precipitate out. If you have evaporation and top off the cell with fresh chloride every once in a while.
http://www.chlorates.exrockets.com/akagraph.html

@yobbo, I can see that stirring would be a solution for this. With the format of the cell, stirring is not practical, perhaps a bubble stone with an aquarium pump? What tubes would be okay, I expect that a lot of things will dissolve in this environment.

I'm not controlling the PH, I don't think the benefits outweigh the extra effort.
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vanBassum
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[*] posted on 20-8-2024 at 03:25


Also fun, I'm logging the information of the cell. See the attachment. I'm now at the point, if I take a sample and add some KCl, you see KClO3 precipitating out of solution.

Every day there is some salt at the bottom of the cell, but when I test this, it seems to be chloride. I'm not really sure why it's ppt out of solution. I would expect that things get more soluble the longer the cell runs. The first few days, I have been topping up with regular water instead of NaCl solution.

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yobbo II
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[*] posted on 20-8-2024 at 06:36



I attempted to try a continous sodium chlorate cell.

When actually trying to run a one container Chlorate cell continuously it proved impossible to obtain solid Chlorate from the cell while adding solid Chloride, without the Chloride level going too low for Anode erosion concerns. This was at 50C and above. Perhaps it may be workable at temperatures somewhere below this. There will be little point in running a pH controlled cell at these low temperature IMO.
To put it another way, the lines of the graph that you posted appear to be too far to the right or/and the knees of the curves are too high. We would like (at say 80C) for the Chlorate to be less soluble and the Chloride to be more soluble. Alas this is not so. A continuous 'one-pot' Na Chlorate cell running at 50C or above is not possible. You will have a very low (too low) Chloride concentration. A two compartment cell would probably work OK.

Someone suggested using a 'dead zone' (deep unstirred cell) at the bottom of a Chlorate cell to form a cool place where Chlorate might come out of solution and allow a continuous operation to be achieved?

Thats my take on it.

It would be interesting to see of you can get the Na chlorate to continously come out of solution if you are running the cell somewhere below 50C, how low you need to go I don't know. The sodium chlorate may not
come out of solution and nice way that K chlorate comes out (fine crystals at the bottom of the cell). It may come out like concrete sticking to everything? I don't know.
Thats what happened my cell when the power went off. The Na Chlorate was near saturation and a half inch of 'concrete type' Na chlorate came out of solution when the temperature fell and coated everything. Anode, cathode, walls, bottom, stirrer (a mess).
I had to start again.

Perhaps if you were to put a cooling pipe with cold water through the cell this cold pipe might harvest chlorate as you went along.

My cell had a lid so not much evaporation. I was able to add some concentrated NaCl solution but I also had a basket hanging in the cell which contained NaCl of various dimensions (from lumps to fine stuff) so that the NaCl stayed concentrated. The concentration kept falling and falling (monitored by titrations) and went below 50 grams per litre and no Na chlorate appearing. Thast too low a conc. of NaCl as the anode may get eroded. The CE will suffer too.

Go below 50C

You can run a continous Na perchlorate cell and harvest solid Na perchlorate. The solubilities allow this even though perchlorate is very soluble. The chlorate stays at a sensible concentration.

Yob


[Edited on 20-8-2024 by yobbo II]
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vanBassum
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[*] posted on 20-8-2024 at 11:04


So, if I get you right, the chlorate will stay in solution at 50+ degrees instead of the chloride? That would make sense, since the solids that ppt out seem to be chloride instead of chlorate. I ordered an aquarium pump, I expect that the overall cell temperature will go down, but I'm not sure if it's enough.

Previously, I got the chlorate out by boiling down the electrolyte. Then, after cooling, the chlorate comes out of solution. But this is a huge pain, especially with large volumes. I tried using ceramic pots for the boiling, and it seems to work, but it's far from perfect and still a lot of work.

Nice tip about the perchlorate, I haven't tried that yet. I just keep running the cell until almost all chlorate is consumed and destroy the rest with HCl. But this seems less wasteful. I do have to make a lot of chlorate before I can start up the perchlorate cell again.

---
Btw, this is probably basic chem knowledge, but I have a hard time figuring this out from scratch.
How do I know what salt ppt's out?

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yobbo II
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[*] posted on 20-8-2024 at 13:53


Quote: Originally posted by vanBassum  
So, if I get you right, the chlorate will stay in solution at 50+ degrees instead of the chloride? That would make sense, since the solids that ppt out seem to be chloride instead of chlorate. I ordered an aquarium pump, I expect that the overall cell temperature will go down, but I'm not sure if it's enough.

Previously, I got the chlorate out by boiling down the electrolyte. Then, after cooling, the chlorate comes out of solution. But this is a huge pain, especially with large volumes. I tried using ceramic pots for the boiling, and it seems to work, but it's far from perfect and still a lot of work.

Nice tip about the perchlorate, I haven't tried that yet. I just keep running the cell until almost all chlorate is consumed and destroy the rest with HCl. But this seems less wasteful. I do have to make a lot of chlorate before I can start up the perchlorate cell again.

---
Btw, this is probably basic chem knowledge, but I have a hard time figuring this out from scratch.
How do I know what salt ppt's out?



If you want to cool the cell more all you have to do is place the cell standing in a large plastic container of water. The large amount of water surrounding the cell will cool it. The larger the container the cooler the cell will run.

The bubbler should work ok. PVC piper will last a very long time. You may not need a actual air stone.

Figuring out what will and will not come out of solution is not a very easy thing to understand.
It's called mutual solubility and you use a mutual solubility curve to predict what should happen.
It easy when you have two possible salts like K Chloride (soluble) and K Chlorate (not very soluble). The chlorate flyes out.
With other pairs it's a bit of a nightmare.
Some links:

http://www.chlorates.exrockets.com/remove.html

http://www.chlorates.exrockets.com/mut_pdf.zip

There is a file at the bottom of this thread that attempts to explain how to use the diagrams.
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

To be honest its a PITB!

Put the cell sitting in a large container of water to get it to run at (say) 20C. Keep adding saturated NaCl solution if you can get some evaporation to occur. There will not be much at that temperature.
Hang some sort of basket or bag containing sodium chloride in such a way that the fluid in the cell moves through the sodium chloride. This is to keep the solution saturated with NaCl.
Keep running the cell and see if you get chlorate coming out of solution. Hopefully it will simply land on the cell bottom (like a K cell). It may not and instead stick to everything and everywhere that you do not want it to stick to (a mess).
If you simply put chloride into the cell (no basket or bag) it will go to the bottom and unless you are stirring (or perhaps bubbling air) it will not get taken up by the solution as you would like. It may also interfere with the chlorate that is (hopefully) going to start falling out of solution.

Yob
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vanBassum
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[*] posted on 20-8-2024 at 22:35


When I top up the cell, I use saturated NaCl, hoping it would 'salt out' the chlorate. However, based on your comments, I realize it might not be that straightforward. I’ve already ordered the bubbler, so I’ll experiment with it to see how it performs.

Previously, I had to cool the smaller cell to handle higher currents without it overheating.

My current setup is similar to the drawing in the attachment. The light blue area corresponds to the temperature from the graph, around 60°C, while the bottom part remains cool to the touch, barely warmer than the outside temperature, which is about 25°C this time of year. I was surprised to find that the zone where these temperatures mix is quite small.

The idea behind this setup was that the warmer top part would facilitate evaporation, as higher temperatures are supposed to increase efficiency. My hope was that chlorate would settle out in the cooler bottom half, since it’s less soluble at lower temperatures.

---

What if I try the following?

I place the bubbler slightly above the bottom, as indicated by the red circle. Then, I cycle the cell in two stages:

Stage 1: High current with bubbles on. The bubbles should induce circulation, ensuring the whole cell reaches a uniform temperature (except for the very bottom, where chlorate would collect). The high current will heat the cell for evaporation and production of chlorate ofc.

Stage 2: Low current with bubbles off. This stage would allow the cell to cool down. The chlorate should precipitate out of solution and settle at the bottom. The low current would help prevent electrode corrosion during this stage.

I could experiment with different configurations, such as running the bubbles continuously and only switching the current, or even adding active cooling through fans.


---
BTW, if none of this works, I’ll stick to large batches so that I only have to harvest occasionally, but in larger quantities.



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yobbo II
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[*] posted on 21-8-2024 at 05:41




Higher temperature only gives more efficiency if you are controlling pH. The 'bulk reactions' (as they are called) are favoured by high temperature.
The chemistry going on (AFAIK) with no pH control, does not benefit from high temperatures (there are no 'bulk reactions' going on).

That set up should work. You may be surprised how long you have to run the cell to get solid chlorate out. The stuff is so soluble it will be in there but in solution. It's a bit like having to fill a very wide pipe using lots of stuff before you get any stuff out the end.

Be aware that there is mist coming off the top of the cell. It will corrode all around.

"I place the bubbler slightly above the bottom, as indicated by the red circle. Then, I cycle the cell in two stages:"

Sounds good to me. If you try the cold bottom method to see if you can get chlorate in a one jar system that would be very simple.

I don't know how the chlorate will precipitate out. It may coat everyting in the cell if you cool the whole cell. It may not act like K chlorate which settles to the bottom very conveniently.

If you keep the solution saturated with Chloride that will keep the solubility of the chlorae to a minimum (still very soluble though)

Yob

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vanBassum
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[*] posted on 21-8-2024 at 07:15


Thanks for the information.

I just added the bubble stone, the temperature has gone down to 35 degrees. That's of course to be expected, since now the hot and cold parts are mixed. Over time, I know what the temperature settles at. (it's fluctuating anyway, because of outside temperature) For now, I keep bubbling and constant electrolysis. The whole cycle thing sounds interesting, but I might try this later. First, I need to get the concentration of chlorate high enough.

Oh, yes, the all killing mist of doom. I have tried to battle this, even with completely closed off cells. But it seems most practical to just place it in a corner in the middle of nowhere and let it do its thing. This is also why the cell is outside.

I hope my bubble stone and hose don't get destroyed in the cell. I have my doubts it will hold up in this environment. I have seen bubbelers completely made from glass, used for CO2 in aquariums. But that seems a bit much.
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[*] posted on 23-8-2024 at 06:34


Today, the cell reached a point where the voltage began to rise steadily.

- At 11:00, the voltage was at 4.4V, but by 13:15, it had increased to 5V, which is the limit I set. Note that this voltage is measured at the power supply terminals, not directly at the plates. By 15:15, the current had dropped from 20A to 12A. This indicates that running the cell at lower temperatures isn’t working out as expected. The lack of evaporation at lower temperatures has prevented continuous chloride addition. Additionally, crystals have formed on the electrodes, reducing their effective surface area.

For my next test, I plan to make the following adjustments:

- Smaller cell: The new container will hold about 1 liter, down from the previous 4 liters. This should help the cell reach a higher temperature. The plates will be positioned just a few centimeters above the bottom of the cell. With a warmer cell, I’m hoping for sufficient evaporation to allow topping up with saturated chloride solution.

- Cycle timing: I’ll implement a cycle of 6 hours of 'Production' followed by 30 minutes of 'Cooling'. During production, the cell will run at a maximum of 20A (with adjustments if the cell gets too warm). During cooling, the cell will run at 1A to prevent electrode corrosion.

My Hypothesis:

Production Phase:
- A high current of 20A will facilitate chlorate production and heat the cell.
- The warmer cell will promote evaporation.

Cooling Phase:
- A low current of 1A will protect the electrodes while allowing the cell to cool.
- Lower temperatures will lead to the precipitation of chlorate, which will settle at the bottom.

I will report back, when I have some results.
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yobbo II
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[*] posted on 23-8-2024 at 06:53


"Today, the cell reached a point where the voltage began to rise steadily."



You are going to have a somewhat higher cell voltage as the temperature gets lower. This in unavoidable.

" The lack of evaporation at lower temperatures has prevented continuous chloride addition. Additionally, crystals have formed on the electrodes, reducing their effective surface area."


As regards that chlorate going all over everything. That is what Sodium chlorate does.

Why does K chlorate behave itself and sodium chlorate deposites on all and sundry does any one know?



"
- Lower temperatures will lead to the precipitation of chlorate, which will settle at the bottom."

The sodium chlorate will do what it did above. Coat all and sundry including electrodes imo

Try the hot-top cold-bottom idea you suggested way above.


Yob

[Edited on 23-8-2024 by yobbo II]
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vanBassum
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[*] posted on 23-8-2024 at 08:29


The temperature was low for quite a while before the voltage began to rise, it was probably due to the lack of chloride or the buildup of chlorate on the anodes.

I have reverted to the setup with the hot-top cold-bottom. The cell seems to be running well now, makes sense since I took a rather large sample and topped it off with saturated chloride. Lets see what happens if the cell runs for a while.
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[*] posted on 23-8-2024 at 12:39


I made KClO3 my just electrolyzing 'diet salt' (2 parts KCl + 1 part NaCl) solution in a simple glass jar with an MMO anode and a stainless steel cathode. I let it run for several hours a day at 70 C and 17 A current for a few days with intermittently replenishing and filtering the hot solution.
The KClO3 cystallizes out when cooling which I filter out.
To control the pH I use a knifetip of K2Cr2O7 which turns the solution yellow like pee.
That I repeatedly rinse with ice cold water. Then I check the salt in a flame and when the color is purplish, then the Na is very scarce as even 1% Na in the salt will turn the flame yellow.
That works well for mee.
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vanBassum
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[*] posted on 23-8-2024 at 23:06


Ah yes, potassium behaves perfectly. Unfortunately, I cannot use potassium. My goal is to make perchlorate, and potassium is too insoluble for the perchlorate cell.

I know K2Cr2O7 increases efficiency, I fail to see how it controls the pH? However, I can't use dichromate, because the PbO2 anodes can't handle this. That's also why I'm using titanium for the cathodes, instead of stainless steel.
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[*] posted on 9-9-2024 at 22:25


Quick update: the cell is still running, but no chlorate has precipitated out of the solution yet. It seems like it just needs more time. I've been periodically adding chloride to maintain optimal conditions for the cell.

Every so often, I take a 8ml sample and transfer it to a test tube, where I add about 20ml of saturated KCl solution. After letting the precipitate settle at the bottom, I can see some progress based on the amount of precipitate forming.

As a side note, the voltage has been increasing over time. Right now, the voltage (at the output of the supply) is 5V. This is also the limit, current is now down to 18A from the 20A setting. I think, as the chlorate contents increase, the voltage also increases. It's a bit difficult to say, since temperature plays a large role, and chloride probably as well.

[Edited on 10-9-2024 by vanBassum]
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metalresearcher
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[*] posted on 9-9-2024 at 23:39


Maybe your solution is not concentrated enough. I have success with a concentrated solution of NaCl / KCl of 250-300g / liter water,
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[*] posted on 10-9-2024 at 01:30


Yes, when I add more chloride, the current goes up. There will probably a point where the solution becomes saturated, the big question is, what will ppt out of solution.
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[*] posted on 10-9-2024 at 12:56


Quote: Originally posted by vanBassum  
Quick update: the cell is still running, but no chlorate has precipitated out of the solution yet. It seems like it just needs more time. I've been periodically adding chloride to maintain optimal conditions for the cell.

Every so often, I take a 8ml sample and transfer it to a test tube, where I add about 20ml of saturated KCl solution. After letting the precipitate settle at the bottom, I can see some progress based on the amount of precipitate forming.

As a side note, the voltage has been increasing over time. Right now, the voltage (at the output of the supply) is 5V. This is also the limit, current is now down to 18A from the 20A setting. I think, as the chlorate contents increase, the voltage also increases. It's a bit difficult to say, since temperature plays a large role, and chloride probably as well.

[Edited on 10-9-2024 by vanBassum]


Why are you limiting the voltage to 5V? The ideal power supply for a chlorate cell is a constant current supply, just let the voltage drift to whatever it takes to maintain the set current.
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[*] posted on 10-9-2024 at 13:14


Quote: Originally posted by vanBassum  
Yes, when I add more chloride, the current goes up. There will probably a point where the solution becomes saturated, the big question is, what will ppt out of solution.


IMO you should be keeping the chloride at a max.
That's where hanging a basket (or whatever) of solid sodium chloride in the cell comes in.

What will ppt out?
Thats a question that I have always found very hard to figure out by thinking about it.

It is asking the question: What happens at the point where both NaCl and NaClO3 are at saturation in the solution (knee of mutual sol. curve) and NaCl is getting consumed and NaClO3 is being generated and the temperatature is staying constant?
I believe solid sodium chlorate comes out.
You have the added complication in this system of needing a sensible NaCl conc. If you are above 50C the saturated chloride conc. gets too low for the anode so you need to be somewhere (don't know where) below 50C.
The region M in the diagram shows where chlorate comes out.
The line between M and L is where the system travels as you run and run (and add chloride), its gets consumed and made in chlorate which falls out.
You must have the chloride in a basket/bag or the solid chlorate will mix with it.
If you have room due to evaporation (you wont at 50C IMO) you can add solution.


All above is for a single temperature cell.
The hot top / cold bottom should work.
Apologies for the repete.
Yob

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[Edited on 10-9-2024 by yobbo II]
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vanBassum
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[*] posted on 17-9-2024 at 09:38


I've been running my cell at a constant current of 20A while limiting the voltage to 5V. The reason for the voltage limit is that I've damaged MMO anodes in the past by allowing the voltage to creep up too much.

I haven't had a chance to read your reply yet, yobbo, but I’ve encountered an issue recently. I’ve noticed the anode is covered in a white substance, and I’m not entirely sure where it's coming from.

My best guesses are:

- It could be something present in the salt, possibly an anticoagulation agent.
- It might be a metal oxide, possibly from the titanium cathodes.

I suspect this buildup could also be contributing to the voltage creep.

I’ve tried cleaning it with hydrochloric acid, but that didn’t seem to help much. Has anyone else experienced this or found a solution?

Additionally, up until now, only chloride has precipitated out of the solution, which I think is due to evaporation. I ran a few tests, and there is definitely chlorate present, though I don’t know the exact concentration.

My crude testing method involves taking a 8ml sample, adding it to a test tube, and then mixing in 20ml of concentrated KCl solution. After letting the chlorate settle, I get a rough indication that I'm making progress.

Any input or suggestions would be much appreciated!

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[*] posted on 19-9-2024 at 07:05


Quote: Originally posted by vanBassum  
I’ve noticed the anode is covered in a white substance, and I’m not entirely sure where it's coming from.

My best guesses are:

- It could be something present in the salt, possibly an anticoagulation agent.
- It might be a metal oxide, possibly from the titanium cathodes.

I suspect this buildup could also be contributing to the voltage creep.





It is most likely a calcium silicate deposit emanating from the glass cell under alkaline conditions. I've ruined one MMO anode in a similar way in a non pH controlled glass cell. The electrolyte etches glass and calcium compounds in the water form a very stubborn and insoluble silicate layer on anode that passivates it for good. No amount of acid mixes or other combinations of chemicals seem to be able to remediate and dissolve this deposit off the anode.




Exact science is a figment of imagination.......
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[*] posted on 19-9-2024 at 09:16


Now that Im thinking about this, I had this problem before, perhaps a year ago or so. I left the anode in a corner somewhere and the white stuff eventually came of the anode, this is the same anode im using right now. So it seems like its recoverable, it just took about a year :S

Lesson learned, don't use glass.
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[*] posted on 1-11-2024 at 06:40


Hello RustyShackleford or any one else who can help me,

Please take a look at the attached image. It shows a titanium plate, which I believe to be nearly pure titanium rather than a titanium alloy, with dimensions of 358 mm by 245 mm. I am seeking guidance on setting up a chlorate cell. I have a long cylindrical vessel and a magnetic stirrer, allowing for electrolyte agitation if necessary. However, I am encountering challenges in determining the appropriate current to pass through the electrodes and in selecting a suitable power supply.

Could you assist me with the calculations for the required current and provide recommendations on the power supply for this setup?

Thank you very much for your help.

and the thickness of the plate is: 2mm

Titanium_Plate.jpg - 1.8MB

[Edited on 1-11-2024 by sarinox]
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