making potassium (per) chlorate

[Pyrophury]

This much of a decline in current is sucpicious for a chlorate cell and could hint towards a new case of anode passivation. In case of Pt based perchlorate electrosynthesis the decline in current towards the end of the run can be much steeper and still not indicate a major problem at the anode. Try the electrode set with a new batch of chloride solution to see if the currents rise to initial levels.

 

I tested the MMO anode in a beaker of fresh brine, even though only half submerged I was getting 5A in cold solution. So I don't think the anode has been passivated this time.

 

The cell has been running with the LD anode for 46 hours, the current dropped from 18A to 13A but after tightening the contacts it's back up to 18A. I have noticed a small amount of black sediment at the bottom of the cell and some flake like particles swirling around, which could only be from the LD anode. Temp is around 50C.

Edited February 29, 2020 by Pyrophury

[Andead]

Read the label! Some old ATX psu's had 25 to 50 amp rating on the 5volt rail modern psu's have all the power available from the 3.5v rail and maybe only 10a from the 5v rail. Either your 5v rail has broken permanently or it may recover from a possible overload.

I am using a fairly old power supply and i have found a negative 5volt lead as well as the usual positive one. Could it be that i have to connect the anode to the positive 5 volt lead and the cathodes to the usual black lead as well as the negative 5 volt ?

[Arthur]

NO! Shorting the -5 and the 0volt rails would short the psu and maybe kill it. The -5v rail is usually only very little current

[Andead]

NO! Shorting the -5 and the 0volt rails would short the psu and maybe kill it. The -5v rail is usually only very little current

Ah thanks so much , you have saved me alot of worries and troubles

[WSM]

“End of run” type calculations that are based upon guesstimated anodic efficiency and the assumption that anodic efficiency remains constant throughout the synthesis tend to just point towards the order of magnitude for required runtime. A more precise approach can be taken by performing quantitative analysis on the electrolyte samples while the process runs. E.g. by percipitation with KCl of a known small quantity of the electrolyte and weighing the resulting potassium salt yield. If one has bothered to start with a known quantity of chloride and can measure the volume contained in the cell then a rather precise set of data is obtained.

I’ve also noticed that perchlorate conversions (at least Pt based approaches) tend to perform a sort of “selfpurification” stage at the verge of full conversion. The electrolyte becomes rather caustic and percipitates most if not all of the contaminants as anodic sludge. These sink slowly to the bottom of the cell and a crystal clear translucent sodium perchlorate solution remains. After careful titration to around pH 7 using dilute hydrochloric acid a metathesis reaction can be performed to yield KClO4 without further manipulations. The yielding product is washed twice on a vaccuum filter using deionised water and dried. Purity is very satisfactory as far as can be assumed from lack of sensitivity of the mixes based on the yielded product and flame color development. This is my quick and dirty approach to involve minimum effort and manipulations in the process. But by all means one can refine the process and involve many more purification stages and methods for obtaining truly superior product

If the desired end product is not KClO4, but some other perchlorate then I would at least strongly suggest to add a chlorate destruction stage into the process for increased safety considerations. The insolubility of the potassium salt allows to skip it and use the post percipitation washings to do the job.

 

 

Your post is accurate and very much to the point.

 

I destroyed the residual chlorate before storing the sodium perchlorate solution, so I have options as to which way I may choose to use it! Typically, it works best as either potassium or ammonium perchlorate in fireworks.

 

As to purity, impure oxidizers have limitations as to their use, but pure oxidizers will work for any application.

 

WSM

Edited March 1, 2020 by WSM

[WSM]

I tested the MMO anode in a beaker of fresh brine, even though only half submerged I was getting 5A in cold solution. So I don't think the anode has been passivated this time.

The cell has been running with the LD anode for 46 hours, the current dropped from 18A to 13A but after tightening the contacts it's back up to 18A. I have noticed a small amount of black sediment at the bottom of the cell and some flake like particles swirling around, which could only be from the LD anode. Temp is around 50C.

 

 

What material is your cell made of, AND are you using pH control?

 

The answers may give a reason for what you're seeing, and it's not necessarily the destruction of the MMO.

 

Let us know. Thanks.

 

WSM

[Pyrophury]

 

 

What material is your cell made of, AND are you using pH control?

 

The answers may give a reason for what you're seeing, and it's not necessarily the destruction of the MMO.

 

Let us know. Thanks.

 

WSM

 

I'm not sure what the composition of the glass is, it's just a vase. It's not showing any obvious signs of being attacked, it's still crystal clear and smooth. The lid is PVC and the O-ring is viton.

 

I've not done any pH control at all, I've tested it periodically with test strips. It's mildly acidic, around 4-5 and has been this way throughout.

 

The electrolyte has turned quite a murky brown color now and there is a brown film on the surface. The current is about 19A and the temperature 55C.

 

 

Looks to me like the anode is wearing quickly and contaminating the electrolyte quite badly.

[WSM]

I'm not sure what the composition of the glass is, it's just a vase. It's not showing any obvious signs of being attacked, it's still crystal clear and smooth. The lid is PVC and the O-ring is viton.

I've not done any pH control at all, I've tested it periodically with test strips. It's mildly acidic, around 4-5 and has been this way throughout.

The electrolyte has turned quite a murky brown color now and there is a brown film on the surface. The current is about 19A and the temperature 55C.

Looks to me like the anode is wearing quickly and contaminating the electrolyte quite badly.

 

Okay, with what you're showing and saying, a couple thoughts come to mind;

1. Without pH control the cell will usually trend toward a high pH, maybe 10-11
2. If the pH is acid it's best to keep it above 6 or chlorine is likely to be released (not good)
3. What type and color of Viton are you using? Viton B is good to use for our cells, other types of Viton elastomer may break down (what shape is your seal in?)
4. Is your anode MMO or LD? LD can take a hit in an over driven cell and break down (causing a brown sludge). Stop running it and remove the electrodes (and rinse them) immediately if you see this. If it's high quality MMO, I doubt it's breaking down unless other causes (not yet mentioned) are the reason.
5. ALSO, I would NOT use LD for a chlorate cell, only a perchlorate cell. MMO is best for chlorate, in my humble opinion!

See if any of these points appear to be the cause of what you're seeing and let us know. Thanks and good luck.

 

WSM

[Pyrophury]

1. Without pH control the cell will usually trend toward a high pH, maybe 10-11

 

This is what I understood to be the case, but whenever I have tested with pH strips they have indicated that the electrolyte is acidic. The pH paper is good, I've tested it to make sure. Could the chlorine produced at the start of the run and which lingered in the cell formed hypochlorous acid, keeping the pH low?

 

 

2. If the pH is acid it's best to keep it above 6 or chlorine is likely to be released (not good)

 

Copious amounts of chlorine gas was released at the very start of the run, but this subsided after the first 24 hours or so. The electrolyte has always had a strong bleach smell, but this has gone completely since switching to the LD anode.

 

 

3. What type and color of Viton are you using? Viton B is good to use for our cells, other types of Viton elastomer may break down (what shape is your seal in?)

 

I'm not sure, I didn't realize there were different types. It's black and has a hardness rating of 75A. It's not showing any signs of breaking down yet though.

 

 

4. Is your anode MMO or LD? LD can take a hit in an over driven cell and break down (causing a brown sludge). Stop running it and remove the electrodes (and rinse them) immediately if you see this. If it's high quality MMO, I doubt it's breaking down unless other causes (not yet mentioned) are the reason

 

I'm currently using the LD anode, I stopped using the MMO anode when the current dropped below 5A. The electrolyte hasn't gotten any darker, certainly no sign of any significant build up of sediment at the bottom. I'm not going to stop the run just yet though, I've added water to the cooling trough, this is an effective way for me to control the temperature and reduce the current.

 

 

5. ALSO, I would NOT use LD for a chlorate cell, only a perchlorate cell. MMO is best for chlorate, in my humble opinion!

 

I think I had got as far as I could with the MMO anode as the current had dropped so low, there was definitely chlorate present as I got a strong reaction with HCl. As soon as I get some methylene blue I'll test for the presence of perchlorate (I had some but misplaced it).

[markx]

 

I'm not sure what the composition of the glass is, it's just a vase. It's not showing any obvious signs of being attacked, it's still crystal clear and smooth. The lid is PVC and the O-ring is viton.

 

I've not done any pH control at all, I've tested it periodically with test strips. It's mildly acidic, around 4-5 and has been this way throughout.

 

The electrolyte has turned quite a murky brown color now and there is a brown film on the surface. The current is about 19A and the temperature 55C.

 

 

 

Looks to me like the anode is wearing quickly and contaminating the electrolyte quite badly.

Testing for pH of the cell electrolyte with strips is useless and does always give a result that points towards a slightly acidic state. This is a result of the immensely oxidative and agressive nature of the electrolyte....the hypochlorite content simply destroys the indicator substances and bleaches them momentarily leaving a bleak colored spot that when compared to the standard scale conforms to a pH of around 4-7 depending on the type of strip used. A shortlived indication closer to truth can be obtained at the verge of the spot as the liquid creeps forward through the test strip paper and shows a fast fading coloration that to some degree is in correlation with the actual pH level of the sample. Unless regular acid addition is practiced the electrolyte always assumes an alkaline nature.

Trying to measure with ordinary pH electrodes is likewise useless and leads to a quick death of the electrode. Special electrodes do exist for the purpose, but their effective resource is also shortlived and their cost does not justify use in amateur setting.

The brown murky substance is lead dioxide dust that erodes from the anode and it is a clear indication that the poor thing shall not endure for long in the cell conditions. Perhaps you can squeeze one perchlorate conversion out of it by the looks, but anything more will be a miracle. As far as I've tried I never have been able to produce a LD coating that would be stable in chlorate bearing electrolyte. It always erodes, deforms, flakes and falls apart creating the characteristic brown sludge that collects at electrolyte surface and floats around the bulk volume.

I guess LD behaves at best like graphite which inevitably erodes and is usable only when a bulky piece of it acts as anode. Thus a thin coating will not survive for long, but in theory is able to produce perchlorate.

[Pyrophury]

Testing for pH of the cell electrolyte with strips is useless and does always give a result that points towards a slightly acidic state. This is a result of the immensely oxidative and agressive nature of the electrolyte....the hypochlorite content simply destroys the indicator substances and bleaches them momentarily leaving a bleak colored spot that when compared to the standard scale conforms to a pH of around 4-7 depending on the type of strip used.

 

This hadn't occurred to me, but makes perfect sense and seems patently obvious now.

 

The brown murky substance is lead dioxide dust that erodes from the anode and it is a clear indication that the poor thing shall not endure for long in the cell conditions. Perhaps you can squeeze one perchlorate conversion out of it by the looks, but anything more will be a miracle. As far as I've tried I never have been able to produce a LD coating that would be stable in chlorate bearing electrolyte. It always erodes, deforms, flakes and falls apart creating the characteristic brown sludge that collects at electrolyte surface and floats around the bulk volume.

I guess LD behaves at best like graphite which inevitably erodes and is usable only when a bulky piece of it acts as anode. Thus a thin coating will not survive for long, but in theory is able to produce perchlorate.

 

It's not looking good then...

[abc159201]

Maybe there is some issue at the welding point? Also, have you calculated the anode's current density? I haven't run a sodium chlorate cell. But in my experience, MMO is a very robust anode. You really shouldn't have so much problems.

[Pyrophury]

Maybe there is some issue at the welding point? Also, have you calculated the anode's current density? I haven't run a sodium chlorate cell. But in my experience, MMO is a very robust anode. You really shouldn't have so much problems.

 

The weld probably isn't very good, how could this cause excessive wear on the anode?

 

I'm using a Lead Dioxide anode at this stage, it's 10x10cm and at less than 20A the current density shouldn't be more than 100mA/cm2.

 

The temperature had gotten quite high, it probably peaked at 60C. I've cooled it down to 32C and I'm getting 14A now, the electrolyte hasn't gotten any darker so I'm going to press ahead.

[markx]

 

The weld probably isn't very good, how could this cause excessive wear on the anode?

 

I'm using a Lead Dioxide anode at this stage, it's 10x10cm and at less than 20A the current density shouldn't be more than 100mA/cm2.

 

The temperature had gotten quite high, it probably peaked at 60C. I've cooled it down to 32C and I'm getting 14A now, the electrolyte hasn't gotten any darker so I'm going to press ahead.

The weld should not be the problem, but you mentioned that you had a lead filling leak at the stem connection point. It is not entirely impossible that the exposed Pb metal is partly turning into lead dioxide under the anodic conditions and erodes into the electrolyte giving the impression that the main anode is not durable. Also it could be that only the topmost surface layer of the anode eroded away due to dendritic oxide structures that were unstable. That might have exposed a smoother more durable layer (a sort of electropolishing effect if you will). Keep going at a steady calm pace and let us know about the progress

 

About the electrode shanks/stems: I've not practiced the lead or solder filling technique to improve conductivity. Instead I've always used solid CP Ti round bar for the purpose. 10mm has been good enough to commute up to about 25A of current without catastrophic overheating issues. Sure it does get hot, but not to the point where it starts to damage the cell lid or other components.

http://www.sciencemadness.org/talk/files.php?pid=602661&aid=73879

http://www.sciencemadness.org/talk/files.php?pid=602661&aid=73881

[Pyrophury]

Nice setup! I'm partial to a cup of Earl Grey myself .

[WSM]

Testing for pH of the cell electrolyte with strips is useless and does always give a result that points towards a slightly acidic state. This is a result of the immensely oxidative and agressive nature of the electrolyte....the hypochlorite content simply destroys the indicator substances and bleaches them momentarily leaving a bleak colored spot that when compared to the standard scale conforms to a pH of around 4-7 depending on the type of strip used. A shortlived indication closer to truth can be obtained at the verge of the spot as the liquid creeps forward through the test strip paper and shows a fast fading coloration that to some degree is in correlation with the actual pH level of the sample. Unless regular acid addition is practiced the electrolyte always assumes an alkaline nature.

Trying to measure with ordinary pH electrodes is likewise useless and leads to a quick death of the electrode. Special electrodes do exist for the purpose, but their effective resource is also shortlived and their cost does not justify use in amateur setting.

The brown murky substance is lead dioxide dust that erodes from the anode and it is a clear indication that the poor thing shall not endure for long in the cell conditions. Perhaps you can squeeze one perchlorate conversion out of it by the looks, but anything more will be a miracle. As far as I've tried I never have been able to produce a LD coating that would be stable in chlorate bearing electrolyte. It always erodes, deforms, flakes and falls apart creating the characteristic brown sludge that collects at electrolyte surface and floats around the bulk volume.

I guess LD behaves at best like graphite which inevitably erodes and is usable only when a bulky piece of it acts as anode. Thus a thin coating will not survive for long, but in theory is able to produce perchlorate.

 

 

I forgot to mention, when using pH paper to measure very quickly before the indicators fade, or look at the very edge where the electrolyte is slowly soaking along into the test strip. This suggestion works best with the paper type strips, not the more expensive fancier types on a plastic tab.

 

WSM

[WSM]

The weld should not be the problem, but you mentioned that you had a lead filling leak at the stem connection point. It is not entirely impossible that the exposed Pb metal is partly turning into lead dioxide under the anodic conditions and erodes into the electrolyte giving the impression that the main anode is not durable. Also it could be that only the topmost surface layer of the anode eroded away due to dendritic oxide structures that were unstable. That might have exposed a smoother more durable layer (a sort of electropolishing effect if you will). Keep going at a steady calm pace and let us know about the progress

 

About the electrode shanks/stems: I've not practiced the lead or solder filling technique to improve conductivity. Instead I've always used solid CP Ti round bar for the purpose. 10mm has been good enough to commute up to about 25A of current without catastrophic overheating issues. Sure it does get hot, but not to the point where it starts to damage the cell lid or other components.

http://www.sciencemadness.org/talk/files.php?pid=602661&aid=73879

http://www.sciencemadness.org/talk/files.php?pid=602661&aid=73881

 

 

Nice setup!

 

A well thought out response and I agree. It appears his current density is about 0.2 A per cm² and should be fine. Certainly if this were a perchlorate cell it would be, though I saw something similar at the end of run in my perchlorate cell.

 

At the end of run of my LD perchlorate cell, I did see a brown tint in the electrolyte. I stopped the run, removed and rinsed the electrodes and let the electrolyte sit overnight. By the next day, the brown color had faded to a sort of cream color and that precipitate dropped to the bottom of the container. I never analysed the precipitate, and I'm not sure but suspect a lead compound.

 

Since my next run was with the platinized titanium anode, with no issues; PLUS having used up all my available sodium chlorate, I haven't returned to perchlorate experimenting, but switched my efforts to making high-purity sodium chlorate instead. My feeling is, if I have an abundant supply of sodium chlorate, I can continue my perchlorate research and follow it to the end-of-life of my various anodes, to know which system is best for me.

 

Of course, life always seems to interfere with such endeavors, but I'm slowly pushing on...

 

WSM

[WSM]

About the electrode shanks/stems: I've not practiced the lead or solder filling technique to improve conductivity. Instead I've always used solid CP Ti round bar for the purpose. 10mm has been good enough to commute up to about 25A of current without catastrophic overheating issues. Sure it does get hot, but not to the point where it starts to damage the cell lid or other components.

 

 

I have filled electrode leads, of course; but I normally used lead-free solder (95:5, mostly tin:antimony [sn:Sb] or tin:silver [sn:Ag]), and later used a solid, pure copper rod inside the titanium tubing instead of solder fill.

 

The copper filled titanium leads lowered the temperature quite well in those leads. I prefer using thick walled CP titanium tube for the electrode leads, when I can find it. It's important to seal the copper filling well with good contact pressure between the titanium tube and the copper rod, for the best electrical conductivity and to minimize heating that will occur when loose connections exist. It can be a tricky balance, but certainly worth the effort to accomplish.

 

WSM

Edited March 2, 2020 by WSM

[Pyrophury]

I tested a sample of electrolyte with Methylene Blue.

 

 

The sample on the left gave a strong indication for perchlorate compared to the control on the right.

[WSM]

I tested a sample of electrolyte with Methylene Blue.

The sample on the left gave a strong indication for perchlorate compared to the control on the right.

 

Congratulations!

 

It looks like you've run from chloride all the way to perchlorate. I suspect there is less chloride in the electrolyte but maybe a quantity of chlorate still in the solution.

 

It would be nice to know how much of each is in there!

 

I think a chloride test should be done first, followed by a chlorate test, to decipher what else besides perchlorate, is present in the cell liquor.

 

WSM

Edited March 2, 2020 by WSM

[markx]

Methylene blue is ridiculosly sensitive towards sodium perchlorate in solution....not so much towards potassium perchlorate. Even a minuscule sodium perchlorate concentration shall give a strong indication and it makes really difficult to determine at what stage the conversion is at: the very beginning or the very end. As an additional quick indication one can use the percipitation test with KCl sloution. With just a little bit of experience one can assess the amount of sediment formed as a quantitative indication to as far the process has progressed. Methylene blue shall give a clear and strong indication of perchlorate in the electrolyte way before it can be detected with the KCl test, so it does not suit well to determine the actual progress.

 

Potassium chlorate sedimentation from electrolyte (on the left) and potassium perchlorate (on the right) due to addition of KCl solution into either sodium chlorate or sodium perchlorate bearing electrolyte. It is useful to train the eye to distinguish between the two different sediments formed. Chlorate dominated electrolyte shall slowly form coarse dendritic cristals, whereas perchlorate dominated electrolyte shall form a fine and almost amorphous sediment instantly upon contact with KCl solution:

 

http://www.sciencemadness.org/talk/files.php?pid=605111&aid=74326

 

KCl sedimentation and methylene blue test side by side in perchlorate dominated electrolyte sample:

http://www.sciencemadness.org/talk/files.php?pid=612393&aid=75412

 

Full perchlorate conversion with the anodic sludge containing the contaminants at the bottom of cell (the electrolyte assumes a perfectly clear and vitreous appearance at that stage):

http://www.sciencemadness.org/talk/files.php?pid=613521&aid=75648

Edited March 2, 2020 by markx

[WSM]

I recall my perchlorate cell electrolyte, while using the platinized titanium anode, was mostly

clear like yours. Toward the end of the run, the electrolyte took on a very light, pale yellow tint.

 

WSM

Edited March 3, 2020 by WSM

[markx]

I recall my perchlorate cell electrolyte, while using the platinized titanium anode, was mostly

clear like yours. Toward the end of the run, the electrolyte took on a very light, pale yellow tint.

 

WSM

In my syntheses runs the electrolyte always became profoundly clear and colorless when "full" perchlorate conversion was reached and all the contaminants were captured by the anodic sludge. In fact I could tell just by looking at the cell that it was time to stop and harvest the bounty. Even a chlorate batch that was obviously and visibly contaminated by alloying elements from a grade 5 Ti anode shank that dissolved into the cell, became totally clear and colorless at the end of run. I had no great hopes for that batch and mainly decided to convert it to see if I could pull one more run out of the anode.....but it worked absolutely great in the end and yielded perfect results.

 

A slight yellowish tinge of electolyte was maintained up to very last days of coversion runs and I always took it as a sign that there was still residual chlorate left in the cell that maintained a balance with hypochlorite, thus giving the characteristic coloration. Once I got past this stage it was time to harvest and quantitative analysis has so far backed up the claim.

[Pyrophury]

Will the current drop noticeably when the chlorate level gets low enough to harvest the perchlorate?

[WSM]

In my syntheses runs the electrolyte always became profoundly clear and colorless when "full" perchlorate conversion was reached and all the contaminants were captured by the anodic sludge. In fact I could tell just by looking at the cell that it was time to stop and harvest the bounty. Even a chlorate batch that was obviously and visibly contaminated by alloying elements from a grade 5 Ti anode shank that dissolved into the cell, became totally clear and colorless at the end of run. I had no great hopes for that batch and mainly decided to convert it to see if I could pull one more run out of the anode.....but it worked absolutely great in the end and yielded perfect results.

A slight yellowish tinge of electolyte was maintained up to very last days of coversion runs and I always took it as a sign that there was still residual chlorate left in the cell that maintained a balance with hypochlorite, thus giving the characteristic coloration. Once I got past this stage it was time to harvest and quantitative analysis has so far backed up the claim.

 

Since completing the two runs (LD and Pt about four years ago), the two jars of sodium perchlorate solution are clear, and have been since 2016.

 

WSM