making potassium (per) chlorate

[WSM]

One other thought; if I remember correctly, a (vertically mounted) long narrow anode encourages hydrogen lift better than short wide anodes do.

 

This will stir things up better by promoting convection-like currents in the cell.

 

WSM

Edited February 3, 2020 by WSM

[PTFE]

 

It'd be a shame to cut them down, but I'm really surprised at the current draw for what I'd considered already quite modest sized electrodes (35 x 150mm).

 

 

Those seems like the simplest solutions. Although I do have a hotplate/stirrer, it's a bit precarious balanced on there.

 

 

That's re-assuring. Thanks all.

 

I would not cut the anode down and instead try to get the cell stabilized at a temperature which you deserve.

When you have a mag.stirrer, put something around it to give your cell a good stand (wood or some bricks maybe).

You could also put the cell in a bucket with water. The stirrer should be strong enough to couple through.

 

But i first would look, if a fan+stirrer is enough to cool the cell down.

 

Another good way is, if you could get some 60A silicium diodes. Over one diode you should get a voltage drop of ~0.7V but you must have a look at the datasheets. Some diodes have a voltage drop lower than that.

 

 

[abc159201]

 

Moving the electrodes further apart is not really an option I even want to consider, it would be a last resort.

 

The voltage pot is already as low as it will go. I like the suggestion regarding the PWM, I'm inexperienced when it comes to electronics though so unless it's something that I can buy off the shelf I've got no hope. Thanks.

 

If you have some soldering skill plus some electronics background. 4.5V won't be the lower limit of this psu. You can try take it apart, change the potentiometer(in order to adjust voltage more easily and more precisely ), and than change the voltage dividing resistors(to change adjustable range). After those changes,my psu can adjust from 3.75V to 6V.

 

I can't tell you the exact way how to do it since every psu model have different design. MW brand and rip-off brand also won't be the same. But the procedure won't have any different. You can pick the resistor value by trial and error(or you can analyze the whole circuit to determine the value ).

Edited February 4, 2020 by abc159201

[markx]

 

Moving the electrodes further apart is not really an option I even want to consider, it would be a last resort.

 

The voltage pot is already as low as it will go. I like the suggestion regarding the PWM, I'm inexperienced when it comes to electronics though so unless it's something that I can buy off the shelf I've got no hope. Thanks.

There are rather "beefy" PWM and voltage conversion modules available that can handle several kW worth of power, but they usually tend to operate at higher input voltages than the 5V supply that is used in our case. Theoretically you could use a higher voltage power supply (say 12-24V DC) coupled with a strong PWM or voltage converter module that brings down the final output voltage to a reasonable level.

If you can find a converter module that is rated to operate at 5V input and can handle an excess of 50A then you could get away with it off the shelf running the cell at about 20A load, but otherwise some tinkering is required

 

I did construct a universal lab dc power supply that operates on this principle: a 12V dc SMPS coupled with a SEPIC voltage converter forms a universal dc supply that can have output voltages from 1V-50V dc at the turn of a pot knob. I've used this supply successfully for small scale perchlorate synthesis, so the concept does work.

 

E.g. the following converter module (or a similar one) could be of use in current situation:

https://www.ebay.com/itm/DC-DC-20A-300W-Abwartswandler-Step-Down-Buck-Konverter-Spannung-Charger-Modul/333125493922?hash=item4d8fd3a4a2:g:3fMAAOSwL-9ckzL-

 

It can be adjusted as constant current module or as constant voltage module....and supposedly works off a 5V supply. I would suggest to turn up the power supply voltage to the maximum level that is possible from the pot on the SMPS. I guess it goes to about 5,5-6V if you are lucky, that should ensure the converter operates normally. These types of converters can usually be parallelled for handling greater currents. I would not run them more than 50% (10A) load in continuous use as they tend to overheat and fail unless forced cooling is applied.

[WSM]

It seems most folks get an anode and build a cell around it.

 

I propose the better course is to first get a decent power supply (with as high a current capacity as you can afford) and design a cell system around that.

 

I sympathize with those who make the leads too short, resulting in a cell that's too hot on top and cool on the lower portion (I've done that, too), but unless you can mount such electrodes through the bottom of the cell, the best approach is to use longer leads from the top of the cell (to reach deeper down, and promote more circulation through "hydrogen lift").

 

I'm offering the benefit of my own experience in this situation.

 

WSM

[Pyrophury]

Thanks for all the input, I've found an example of someone modifying a similar 12v model of the power supply I have here: https://www.youtube.com/watch?v=JL4FS4QOd0M (mine is the S-300-5) It doesn't look too complicated but I don't know if I'd be able to use exactly the same components in my 5v PS? If I can find a PWM that can handle it, that might be the safer option.

 

In the meantime I think I'll just try longer cables and rig up a platform I can fit my magnetic stirrer under, if it's still too hot I'll place it in a tub of water.

[Pyrophury]

It seems most folks get an anode and build a cell around it.

 

I propose the better course is to first get a decent power supply (with as high a current capacity as you can afford) and design a cell system around that.

 

I sympathize with those who make the leads too short, resulting in a cell that's too hot on top and cool on the lower portion (I've done that, too), but unless you can mount such electrodes through the bottom of the cell, the best approach is to use longer leads from the top of the cell (to reach deeper down, and promote more circulation through "hydrogen lift").

 

I'm offering the benefit of my own experience in this situation.

 

WSM

 

It's valuable experience, as are your blog updates, without which I doubt I'd have gotten this far!

[Arthur]

Fat speaker cable is easy to find as is car hi-fi power cable. both are suited to the voltage that the cell runs at. Use a terminal block if necessary to insert a little more cable.

[abc159201]

Thanks for all the input, I've found an example of someone modifying a similar 12v model of the power supply I have here: https://www.youtube.com/watch?v=JL4FS4QOd0M (mine is the S-300-5) It doesn't look too complicated but I don't know if I'd be able to use exactly the same components in my 5v PS? If I can find a PWM that can handle it, that might be the safer option.

 

In the meantime I think I'll just try longer cables and rig up a platform I can fit my magnetic stirrer under, if it's still too hot I'll place it in a tub of water.

 

IMO, using PWM devices to control current is not a good idea. Your PSU might not be able to follow the fast switching speed thus causing higher ripple&noise. Also, I don't think it is a good way to use a psu. if you really don't have the skill to mod it. Why not just buy a 4.2V version instead

Edited February 5, 2020 by abc159201

[Arthur]

Ripple is bad in electroplating, especially so with a platinum electrode. Industrially three phase rectifiers are used to reduce ripple, I've read of motor generator sets being used to produce a low voltage six phase so that the ripple can be even lower.

 

The very simple answer is to use slightly longer leads to add a milli ohm or ten to reduce the current resistively. It's probably also the cheapest answer.

[WSM]

Ripple is bad in electroplating, especially so with a platinum electrode. Industrially three phase rectifiers are used to reduce ripple, I've read of motor generator sets being used to produce a low voltage six phase so that the ripple can be even lower.

The very simple answer is to use slightly longer leads to add a milli ohm or ten to reduce the current resistively. It's probably also the cheapest answer.

 

I agree, and will add that one common and effective method used to smooth out ripple is to use a Pi filter after the rectifier in the DC power supply circuit.

 

WSM

[markx]

I agree, and will add that one common and effective method used to smooth out ripple is to use a Pi filter after the rectifier in the DC power supply circuit.

 

WSM

Capacitive filters are by far the most effective way to smooth out the switching ripples. The output and input stages of dc supplies as well as pwm and voltage converter modules are all capacitively snubbed to get rid of the ripples that arise from switching the power through inductive devices (transformers and coils). The trick is to use electrolytic caps in combination with ceramic or other nonelectrolytic types. The electrolytics, although able to store a great deal of charge, are slow to react because of the charge having to travel through the actual electrolyte inside the cap. The nonelectrolytic types are fast acting and able to smooth out the high frequency switch noise that may partly bypass the electrolytic banks. Also ripple tends to be dependent upon load: the higher the current passing the supply the more likely the capacitor filters tend to fluctuate the voltage in tact with the switching.

[abc159201]

Capacitive filters are by far the most effective way to smooth out the switching ripples. The output and input stages of dc supplies as well as pwm and voltage converter modules are all capacitively snubbed to get rid of the ripples that arise from switching the power through inductive devices (transformers and coils). The trick is to use electrolytic caps in combination with ceramic or other nonelectrolytic types. The electrolytics, although able to store a great deal of charge, are slow to react because of the charge having to travel through the actual electrolyte inside the cap. The nonelectrolytic types are fast acting and able to smooth out the high frequency switch noise that may partly bypass the electrolytic banks. Also ripple tends to be dependent upon load: the higher the current passing the supply the more likely the capacitor filters tend to fluctuate the voltage in tact with the switching.

 

What you said is absolutely right. However,the higher your current runs the greater the capacitor you will need. At 20A or higher, we might need mF level (or even F level).

I totally agree with Arthur and WSM. Using a longer lead is a good & cheap way. But if you want to run your cell at specific ampere,you might need to try a couple times.That's why I suggest buying a 4.2V version instead. Take LRS-350-4.2 for example. This model can adjust the voltage between 3.6 to 4.4V.

[markx]

 

What you said is absolutely right. However,the higher your current runs the greater the capacitor you will need. At 20A or higher, we might need mF level (or even F level).

I totally agree with Arthur and WSM. Using a longer lead is a good & cheap way. But if you want to run your cell at specific ampere,you might need to try a couple times.That's why I suggest buying a 4.2V version instead. Take LRS-350-4.2 for example. This model can adjust the voltage between 3.6 to 4.4V.

Definitely, if one has no desire to plunge into the world of high amperage power electronics manipulation, then it makes total sense to look for off the shelf solutions. In the end the cost of "tinkering" on half baked solutions and letting the magic smoke out of a few ones tends to amount to a far greater loss than just buying a ready made device. Not to mention the time spent....although if one enjoys working on electronics then it might make a fun hobby project

 

For example Meanwell offers a 60A 4,2V power supply (also a 3,3V version if needed) and their quality is quite fair. So this might be the simplest and quickest solution to get the system running on desired amperage levels without having to disturb the cell or any other components of the setup.

[WSM]

Well, I just found a large and thick enough piece of PVDF sheet on Ebay and ordered it, so I'll make the high temperature cell's lid of PVDF instead of PVC. As a cell lid, it aught to work very well. We'll see...

In a recent study of the characteristics of PVDF, I learned that it won't tolerate high alkalinity, so if in contact with chlor-alkali electrolyte, pH control is HIGHLY recommended. This is good to keep in mind if designing a system incorporating PVDF in direct contact with the mother liquor in an operating cell.

 

Rather than use PVC or PVDF for a lid, I obtained through a lucky eBay purchase, a heavy duty piece of Teflon (PTFE) to use for a lid in this cell. It measures 1" thick by 8" by 11.5".

 

After proper measurement and determining an excellent method of solid attachment to the cell, this lid should work admirably.

 

I'll post more as this develops...

 

WSM

[WSM]

Definitely, if one has no desire to plunge into the world of high amperage power electronics manipulation, then it makes total sense to look for off the shelf solutions. In the end the cost of "tinkering" on half baked solutions and letting the magic smoke out of a few ones tends to amount to a far greater loss than just buying a ready made device. Not to mention the time spent....although if one enjoys working on electronics then it might make a fun hobby project

For example Meanwell offers a 60A 4,2V power supply (also a 3,3V version if needed) and their quality is quite fair. So this might be the simplest and quickest solution to get the system running on desired amperage levels without having to disturb the cell or any other components of the setup.

 

Excellent suggestions.

 

I've always bought my power supplies and devote more time to the electrochemical efforts. If you love the electronic challenges, more power to you! There's enough room for everyone in this field.

 

Working together, we can come up with some amazing configurations.

 

WSM

Edited February 8, 2020 by WSM

[Pyrophury]

I replaced the 30cm 16mm2 cables with ones 100cm and 10mm2, placed the cell in a container topped up with approx 5l of water on a platform above the magnetic stirrer.

 

 

The voltage across the cell hasn't changed though, it's actually slightly higher - it was 4.61V, now it's 4.67V. Perhaps I needed to use much thinner cables to see a significant voltage drop?

 

The current has settled at around 33A now though and the cell temperature is about 50-55C. I feel more at ease running the cell at these parameters.

 

Using the run time calculator assuming 50% current efficiency, I estimate the run to take 8 days.

 

I have some sodium persulphate at my disposal to improve the current efficiency, but I decided not to use it this time. Instead I'll try to establish the current efficiency without it at the end of this run, then add it to the next run and compare it.

[WSM]

Looks good.

 

Let us know how it goes with this run.

 

WSM

[Pyrophury]

Things appear to be progressing smoothly, it's been almost 3 days and the temperature and current is still stable at ~50C/30A.

 

I've only had to top up with 100ml of salt solution each day to keep volume in the cell at the 5L mark.

 

I am getting quite a lot of salt building up on the cathode strap, not enough to concern me yet, but if it touches the anode strap I assume it will cause a short and severely affect production?

 

 

If it does become a problem I'll need to figure out a way to remove it, if possible without taking off the lid, as this is a bit dicey even when the cell is empty.

 

Next time I'll sheath the electrode straps in PVC hose to prevent this from happening.

Edited February 11, 2020 by Pyrophury

[germaniser]

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

[Arthur]

Lead dioxide exists in two forms one is soft and one is hard almost like glass, the hard form is best by far. The difference is the conditions of the electroplating solution in which the lead dioxide is plated onto the substrate. Swede's blog tells a lot of the amateur research so far, Swede no longer posts or reads the forum.

 

The current state of the hobbyist art is to use a MMO electrode for the chlorate stage and a platinum electrode for the perchlorate stage.

[Pyrophury]

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

 

If you're looking for a PbO2 anode you might try alibaba, I sourced my 100x100mm anode from here: https://qixinti.en.alibaba.com/ . I cant remember how much it cost in the end (delivery and import duties included), but it was still quite reasonable.

 

 

I've not tried it yet though, I plan to cut it in half and attach a long electrode strap so I can use it in my closed cell.

Edited February 11, 2020 by Pyrophury

[markx]

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

Metallic lead does form a lead dioxide coating under anodic potential in e.g. sulfuric acid solution. But that coating is not durable (at least according to my experiences) and shall disintegrate in chloride bearing electrolyte within seconds. It might serve as an intermediate substrate coating for further deposition of lead dioxide from a bath containing soluble lead salts (nitrate, plumbate). Doing that in amateur setting is unsafe and tricky because of lead contamination that tends to escape the cells. Also it tends mostly to be unfruitful as the formed coatings are not stable and will usually disintegrate, crack and fail quite quickly once put into use in chlorate or perchlorate cell conditions. Although the diy coatings seem stable enough to work in acidic cells for different purposes like electro oxidation of organic wastes, dyes etc. But chlorate/perchlorate application more often than not shall remain elusive with the homemade PbO2 anodes.

For a long period of time I tried to devise a reasonable method for producing PbO2 anodes that would be stable in perchlorate cell conditions, but my efforts remained in vain. I just gave up and moved forward (or rather back) to manipulations with very thin Pt layers. This proved to be a much more fruitful approach that has granted me with the ability to conjure perhlorate at will for a very reasonable cost and effort

[WSM]

Things appear to be progressing smoothly, it's been almost 3 days and the temperature and current is still stable at ~50C/30A.

I've only had to top up with 100ml of salt solution each day to keep volume in the cell at the 5L mark.

I am getting quite a lot of salt building up on the cathode strap, not enough to concern me yet, but if it touches the anode strap I assume it will cause a short and severely affect production?

If it does become a problem I'll need to figure out a way to remove it, if possible without taking off the lid, as this is a bit dicey even when the cell is empty.

Next time I'll sheath the electrode straps in PVC hose to prevent this from happening.

 

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

[WSM]

If you're looking for a PbO2 anode you might try alibaba, I sourced my 100x100mm anode from here: https://qixinti.en.alibaba.com/ . I cant remember how much it cost in the end (delivery and import duties included), but it was still quite reasonable.

I've not tried it yet though, I plan to cut it in half and attach a long electrode strap so I can use it in my closed cell.

 

 

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