making potassium (per) chlorate

[PTFE]

I have one of those Alibaba anodes too and would not recommend to cut them, WSM got the point. (can't remember if I was the one who brought qixinti in discussion here on topic, but i got the same 100x100 sample-anode and posted it here in 2016..good company for our purpose)

 

 

The salt building upon the Cathode will not electrically short your supply since its not conductive when dry.

It could lead to a larger current draw since it's wet but it will dry out inside due to heating of the saltbridge and build up even more. Take a look at it and maybe top up the solution until everything has dissolved and remove some electrolyte afterwards if you desire to. (it will dissolve if its no kclo3)

[PTFE]

hello,

i'm ne new one from Germany.

I have a bunch of questions, so please help me.

 

At first, I see videos on youtube, where a PbO2 anode is making with electrolysis out of a pb rod.

 

What is the disadvantage of this anodes? They write, they will be soft, but I need no mechanical strength during electrolysis

 

 

best regards

Hey, im also from the same country maybe i could help you even further.

 

Also if you are highly interessted in the Chlorate/Perchlorate topic, you should take the hard route and read through all this 253 pages. ( i've done it 2 or 3 times now.. always an open tab on my mobile)

If not found yet, take a look here.

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

this is probably one of the best sites for information.

[abc159201]

I remember the salt build up on my titanium leads in the past.

 

I can't remember if it was due to extreme heating of the leads (before I filled the titanium tubing with solid copper rods), but the salt comes from the hydrogen bubbles popping and spraying the electrode leads above the electrolyte with brine mist.

 

If you don't want to cover the leads, you could put a plate of PVC between the electrode leads (suspended from the cell lid) and see if that helps.

 

Vinyl tubing might work but could be readily damaged by the electrolyte. PTFE shrink tube would probably work better. Possibly wrapping The leads with plumber's Teflon tape would be a field-expedient test for such a system?!!

 

Let us know what you end up trying.

 

WSM

 

 

Yes, I think this is cause by the heat of the electrodes. I also suffer from this too,and I choose not to do anything. That would not cause shorting(because that is solid salt not salt solution anymore).But removing those salts is just pain in the ass. Those salts are mixture of KCl and KClO3 so you need to use hot water to dissolve them.

[Pyrophury]

I remember the salt build up on my titanium leads in the past.

 

I can't remember if it was due to extreme heating of the leads (before I filled the titanium tubing with solid copper rods), but the salt comes from the hydrogen bubbles popping and spraying the electrode leads above the electrolyte with brine mist.

 

If you don't want to cover the leads, you could put a plate of PVC between the electrode leads (suspended from the cell lid) and see if that helps.

 

Vinyl tubing might work but could be readily damaged by the electrolyte. PTFE shrink tube would probably work better. Possibly wrapping The leads with plumber's Teflon tape would be a field-expedient test for such a system?!!

 

Let us know what you end up trying.

 

WSM

 

I bent a glass rod and was able to nudge the salt crust off of the leads, it wasn't adhered very well so not a problem really.

 

Seriously, I wouldn't consider trying to cut a lead dioxide electrode in half. You'll likely have a massive amount of the coating flake off if you do!

 

Consider scaling up your cell to accommodate the larger electrodes without modifying them. I would only ever cut MMO material, but not lead dioxide (which is brittle, somewhat like glass).

 

 

I have a couple LD on titanium electrodes, virtually identical to yours, and my plan is to spot-weld thick walled titanium tubes to the short lead straps, and fill the tubing with solid, pure copper rods, to lower the resistance of the titanium leads.

 

Surrounding the anode with titanium sheet metal cathodes should nearly double the production rate of perchlorate formed in such a setup.

 

WSM

 

 

I have one of those Alibaba anodes too and would not recommend to cut them, WSM got the point. (can't remember if I was the one who brought qixinti in discussion here on topic, but i got the same 100x100 sample-anode and posted it here in 2016..good company for our purpose)

 

 

The salt building upon the Cathode will not electrically short your supply since its not conductive when dry.

It could lead to a larger current draw since it's wet but it will dry out inside due to heating of the saltbridge and build up even more. Take a look at it and maybe top up the solution until everything has dissolved and remove some electrolyte afterwards if you desire to. (it will dissolve if its no kclo3)

 

Thank you both for cautioning me against trying to cut the LD anode, I'm not going to even attempt it now. I'll leave it as is and perhaps just use a single ti plate for the cathode instead of surrounding it.

 

The current dropped from 30 to 20 Amps over night, I've turned up the voltage up to 5.40V and its now holding at 30A again at about 40C now.

Edited February 12, 2020 by Pyrophury

[markx]

 

I bent a glass rod and was able to nudge the salt crust off of the leads, it wasn't adhered very well so not a problem really.

 

 

 

 

Thank you both for cautioning me against trying to cut the LD anode, I'm not going to even attempt it now. I'll leave it as is and perhaps just use a single ti plate for the cathode instead of surrounding it.

 

The current dropped from 30 to 20 Amps over night, I've turned up the voltage up to 5.40V and its now holding at 30A again at about 40C now.

You can use opposing Ti cahtode plates with anode in the middle. I've acustomed to such configuration and it works very well. This way you will utilize the anode surface more efficiently and evenly from both sides. Trying to cut LD is in not a good idea as was already mentioned before and I do agree totally. The coatings are very fragile and can crack or peel off when the anode is bent, dropped, scratched or severly heat shocked. MMO is pretty much indestructibe for that matter and survives cutting and even spot welding with ease.

[Pyrophury]

The current in my cell is still dropping. I've increased the voltage to the power supply's max (6.05V) and emptied the cooling trough, so the temperature is now 60C, but I'm only putting 15A into the cell now. At this rate I've now calculated it will take an additional 12 days to completion (assuming the current doesn't drop again). I didn't expect such a sudden drop in current until the very end of the run?

 

Edit - Still dropping. 1 hour since last reading, now: 10A / 50C.

Edited February 12, 2020 by Pyrophury

[WSM]

The current in my cell is still dropping. I've increased the voltage to the power supply's max (6.05V) and emptied the cooling trough, so the temperature is now 60C, but I'm only putting 15A into the cell now. At this rate I've now calculated it will take an additional 12 days to completion (assuming the current doesn't drop again). I didn't expect such a sudden drop in current until the very end of the run?

 

 

When running a KClO₃ cell, I track the current level. When the current draw of the cell drops to about half its starting point, I stop the run.

 

The next step is to harvest the chlorate, recharge the used electrolyte with chloride and prepare to run the cell again.

 

If extra care is taken to ensure the purity of the raw materials used, the accumulation of contaminants can be kept to a minimum and the final product will be higher purity.

 

WSM

[WSM]

The current in my cell is still dropping. I've increased the voltage to the power supply's max (6.05V) and emptied the cooling trough, so the temperature is now 60C, but I'm only putting 15A into the cell now. At this rate I've now calculated it will take an additional 12 days to completion (assuming the current doesn't drop again). I didn't expect such a sudden drop in current until the very end of the run?

Edit - Still dropping. 1 hour since last reading, now: 10A / 50C.

 

 

If there isn't something wrong with the electrical properties of the power supply circuit, or the electrical properties within the cell itself; then maybe the run is completed sooner than you expected.

 

Under normal circumstances, when the chloride level drops, the reaction slows and the current draw changes to reflect this change.

 

As an experiment, you may want to drain your cell and save the electrolyte; then fill the cell with fresh chloride electrolyte and see if there's a difference.

If the is a difference, you may want to re-evaluate your estimate of when the run is complete. If there is no difference, then I suspect an electrical problem.

 

Good luck.

 

WSM

[Pyrophury]

 

 

If there isn't something wrong with the electrical properties of the power supply circuit, or the electrical properties within the cell itself; then maybe the run is completed sooner than you expected.

 

Under normal circumstances, when the chloride level drops, the reaction slows and the current draw changes to reflect this change.

 

As an experiment, you may want to drain your cell and save the electrolyte; then fill the cell with fresh chloride electrolyte and see if there's a difference.

If the is a difference, you may want to re-evaluate your estimate of when the run is complete. If there is no difference, then I suspect an electrical problem.

 

Good luck.

 

WSM

 

Assuming I've come to the end of the run and the chloride level has dropped to around 100g/l, would I have to boil off half of the water before I can get a sensible crop of chlorate to precipitate at 0°C? Thanks.

[PTFE]

Could you give a total run time in days in a order like followed?

-days----current-

-time out due to overheating-

-days---current-


It seems the run could come to an end but im not sure.

With the time out it 's a bit harder to say as always through the screen.

 

Do you use PH-control?

 

When im not sure with my cell behavior at the end of a run, I dump in another 50-100g of salt to see, if the current goes back up.

Also there is something like a feedback of temperature and current.
-As higher the temperature is the higher the current will be.

 

 

with the calculator from alan i estimate your run to take 11,5days@50%CE and 33Amps

with a CE of 70% it's around 8 days.

Edited February 12, 2020 by PTFE

[Pyrophury]

START

6Hrs - 20 -> 54A

STOP

84Hrs - 33A

18Hrs - 20 -> 10A

 

Total ~108Hrs

 

No PH control.

 

I'll try adding 100g of Salt and see what affect this had on the current. Thanks.

[PTFE]

mh, that could not be the end of the run in my opinion.
Since you do not use no PH control and only one cathode i assume a CE of 50-60%.

 

90h,CE50% @ 33A will convert ~540g of NaCl and you should have 1110g Nacl left which is 67% of your starting material.
Maybe you got into a negative feedback loop due to the cooling and the current drop lead to a colder electrolyte which results in an even lower current and so on.

 

But the long and steady runtime at 33Amps still confuses me.

Could any conection of the cables get loose contact or maybe the connection of one of the electrodes?

 

WSM had a nice idea of changing electrolyte. This could also be a good test.

 

Maybe you should add dilute HCL via a tube to the bottom of the cell and start control the ph a little.
I remember that pages ago there where problems with some type of glassware in an uncontrolled cell getting attacked and maybe damaging the elecrodes.

[Arthur]

The current has likely subsided because of the loss of available chloride to react. As WSM said add say 100g of chloride and watch for changes if the current is partly restored then add half of the original amount of chloride, then the chlorate formed should more readily ppt out when this addition is reacted and the liquor cooled.

 

Then weigh the dry product, calculate the actual amount of chloride needed to make that much and add that much again and repeat for ever!

[abc159201]

In my setup, I do not estimate CE and run-time.Because every setup won't be the same. I choose constantly add KCl everyday to make sure my electrolyte is saturated, so the current will not change(if the current changes,then it means there is something wrong).And I stop the batch until there is too much KClO3 crystal in the cell. However, this method has an obvious drawback --- those KClO3 will heavily contaminate with KCl. But there is nothing we can't solve by washing it with ice cold water and one recrystallization.

Edited February 13, 2020 by abc159201

[WSM]

Please be aware:

 

If the power to your cell is off, be sure to remove the electrodes from the electrolyte.

 

If you leave the electrodes in the electrolyte with the power off, the electrodes can be damaged (no cathodic protection!).

 

WSM

Edited February 13, 2020 by WSM

[Pyrophury]

Thanks for the reminder, yes I siphoned out the electrolyte before I shut off the power to avoid any damage that way.

 

The cathode plates have a white film on them now, which won't wash off with hot water.

 

 

I'm wondering if the silicone grease I used on the gasket has contaminated the electrolyte and coated the electrodes in an insulating layer of silicone. I suppose I'll find out when I refill with fresh chloride solution and turn on the power...

Edited February 13, 2020 by Pyrophury

[markx]

The white deposit seems to be composed of alkali earth metal hydroxides/carbonates of low solutbility that form on cathode if the electrolyte is prepared from tap water containing salts of Ca and Mg. They are quite firmly adhered, but can readily be removed with a soak in acidic solutions (vinegar, dilute HCl, dilute HNO3). These deposits do not seem to block cathode surface or hinder the operation of the cell, so I mostly leave them as is.

[Pyrophury]

The white deposit seems to be composed of alkali earth metal hydroxides/carbonates of low solutbility that form on cathode if the electrolyte is prepared from tap water containing salts of Ca and Mg. They are quite firmly adhered, but can readily be removed with a soak in acidic solutions (vinegar, dilute HCl, dilute HNO3). These deposits do not seem to block cathode surface or hinder the operation of the cell, so I mostly leave them as is.

 

Yes, I thought it's probably just scale. My water is slightly hard.

[Arthur]

If you are going to reuse the cell liquor then starting with de-ionised or RO water is a good plan.

[PTFE]

could you try to make a photo of the anode surface? From the picture it looks good though but one could just see that the coating is still on.

 

I would soak the electrodes in ~20%HCL, over some hours before you readd them to the cell.
This will dissolve the hydroxides formed as that white adheasions. I have that problem too, but did not had any problems of current drop whilst a run.

 

for silicone as sealant I had no problems in the past other than the silicone get crumbly after a while.

[markx]

Just a generic sidenote.....it may not be the best idea to raise the cell voltage above 5,5V with Ti substrate anodes ( or any other "valve metal" substrate anodes) in the attempt to force the current to wanted level. My observation has been that above that voltage level the risk of passivating the titianium surface rises quite considerably. Keeping the cell voltage low ( thus also anode polarisation is lower) is always a safer approach that is oriented towards a longer life of the anode. Increasing the electrode areas, using heavier cables and keeping the connections clean is a way healthier approach for raising the current when needed.

It is quite normal that the current fluctuates downwards as the electrosynthesis proceeds towards completion in a chlorate cell. Also temperature shall go over some "humps" during the run....starting low....then raising quite considerably on the first 30% of the run....then starting to fall towards the end of the run. I make no attempts to keep the current constant as this shall force the anode under higher polarisation in the end portion of the cycle, which in turn makes the sidereaction of passivation more probable.

[Pyrophury]

I've replaced the electrolyte with fresh chloride solution, but the current is still very low (less than 2A). I suspect therefore that the problem lies with the electrodes and that they have been passivated like you suggest, the current did drop more rapidly after I raised the voltage.

 

I will try soaking the electrodes in dilute hydrochloric acid for a few hours and see what affect this has.

[Andead]

With great sadness I think that Feanor Forges has stopped selling electrodes. From my experience, they are worth their price and he offered both manganese dioxide as well as lead dioxide electrodes. This is a dark day for amateurs who can not make their electrodes....

[PTFE]

With great sadness I think that Feanor Forges has stopped selling electrodes. From my experience, they are worth their price and he offered both manganese dioxide as well as lead dioxide electrodes. This is a dark day for amateurs who can not make their electrodes....

no it isnt all that bad. you can get MMO from china or india (Tiaano/india was the company of choise for me. you can chat with them via facebook and they will weld you a complete set of electrodes toghether if you desire toThey manufacture MMO,PbO2 and i think also platinated mesh.)

 

I've replaced the electrolyte with fresh chloride solution, but the current is still very low (less than 2A). I suspect therefore that the problem lies with the electrodes and that they have been passivated like you suggest, the current did drop more rapidly after I raised the voltage.

 

I will try soaking the electrodes in dilute hydrochloric acid for a few hours and see what affect this has.

thats not a good sign

I never had problems with any anode-failure so im hoping the problem occurs on another spot of the circuit but not the anode coating.

 

I've abused my MMO several times with temperatures from 90-100°C for ~2weeks.

I Had ph controll failure and several hours of 100°C elektrolyte at ph 12 and higher. One run was long enough to start perc. production (Methylene blue test turned purple with strong precipitant and after adding kcl a immediate precipitate of really fine perc crystals have formed...)MMO still okay.

 

I also use tap water without deionizing.

 

One thing i never did was using suspicious materials. I always and only use PTFE, Borosilicate Glass and Titanium for elektrolyte touching parts. I also never had risen the voltage higher than 6V but had current densitys of over 0.3A/cm² on that anode. (its 23cm long and 8,5cm wide on 1mm substrate)

Around 10Kg or more where produced with this anode and the coating is quite thinn now. One can scratch it off with a light stroke of sandpaper as you can see on the picture. Some scratches from handling have also appeared over time but this anode still draws 120Amps in a simple configuration with 2 cathodes.

 

 

Edited February 14, 2020 by PTFE

[PTFE]

Here is a side by side comparison of the old anode with an new one, never used before.

Those are the anodes for the next cell.

 

Edited February 14, 2020 by PTFE