making potassium (per) chlorate

[taiwanluthiers]

You almost can't ruin a MMO anode, unless of course you try to make perchlorate with it.

[TomasBrod]

Remembering something Swede said, MMO is very chemically and electrically tough, but it can be scratched. If it is scratched or physically damaged, the titanium passivates, or self-heals (part of the nature of "valve metals").

How mechanically resistant? I assuming fingernail can not scratch it. If it is scratched only the small scratch gets passivated or it spreads?

[WSM]

You almost can't ruin a MMO anode, unless of course you try to make perchlorate with it.

 

It is possible to chemically destroy MMO on titanium anodes. It's happened in industry, and it can happen in amateur systems. A few failure modes have been detailed in an article I've read and have a copy of. I'll see if I can find the reference and post it in the blog section.

 

One specific failure happens when fluoride gets into a cell. If I remember correctly, it's less damaging to the MMO than the titanium. Fluorides eat titanium and can cause a separation between the MMO coating and the titanium underneath it (causing an electrical open circuit in the anode) which is unrecoverable. There are other failures where the MMO gets covered with an interference layer which insulates the electrode and diminishes it's ability to function normally.

 

Some typical things to do to avoid destroying your anode, are:

• use pure water for your electrolyte (distilled, deionized, RO water or even filtered rainwater)
• Use pure or purified salts, or salts of known quality
• sanitize your cell between batches to minimize contaminant accumulation
• learn and practice good laboratory techniques and keep things under control
• monitor and track trends in your cell (voltage, current, temperature, length of run, concentration of liquor elements, etc.)

We need to do some "real chemistry" at certain points. Learning and practicing those skills will help ensure success.

 

WSM

Edited July 30, 2016 by WSM

[WSM]

How mechanically resistant? I assuming fingernail can not scratch it. If it is scratched only the small scratch gets passivated or it spreads?

 

Generally the small scratch will passivate. If you use tap water for making your electrolyte, all sorts of dissolved minerals can cause trouble with your electrodes (depending on what's in your water and the concentration of those contaminants).

 

If the water in your area is fluoridated, the fluorides can certainly destroy your anode. Using pure water and salts will certainly help.

 

If you have specific questions or concerns, ask them here in as much detail as you can (or by PM) and we (or I) can try to offer useful suggestions.

 

WSM

[WSM]

I found the referenced article regarding chlorate cell contamination. I've titled it "MMO Poison" but the actual title is, "Effects of Electrolyte Impurities in Chlorate Cells".

 

The site is: http://oxidizing.typhoonguitars.com/chlorate/leaddiox/mmo_poison.pdf

 

This is an excellent article explaining in 22 pages, things to avoid in running chlorate cells, and I recommend reading and understanding it.

 

WSM

[WSM]

I have two small batches of crystals drying and the already "dry" crystals from previous drying cycles are in PET jars. I've harvested crystals from all but the last jar of electrolyte (my experiment to see if they keep growing or stop at some point of equilibrium), which is going on 11 days in the fridge, so far. The crystals are getting larger and looking quite jewel-like, some are very clear. I'll show photos after I harvest them. WSM

 

The last jar of electrolyte stored in the fridge at 0^oC seems like it has reached equilibrium at two weeks. I intend to leave it for two more weeks (till I get back from the PGI Convention) and see if I'm correct.

 

One quite large crystal was taken from the jar after it fell off the sidewall so it wouldn't combine with the mass of crystals on the jar bottom. It looks nice but not as "perfect" as some smaller crystals harvested earlier. It's a twinned crystal (one running two different directions), but cracks and fissures in the crystal structure allowed the two to break apart while I was drying them off with a paper towel.

 

 

Even imperfect crystals can be nice to look at. I suppose if they were "perfect", I'd be tempted to keep them instead of dissolve them in distilled water and electrolyze them to sodium perchlorate and further processing.

 

WSM

Edited July 31, 2016 by WSM

[WSM]

I check the progress of the sodium chlorate crystal batch longevity experiment, every couple days. The crystals don't seem to be growing as quickly as at first, but the long time they're spending at 0^oC seems to encourage more perfect crystal shapes and clarity. This is possibly due to the slower growth and diminished amounts of surplus NaClO₃ at the temperature it's at.

 

When I get back from PGI, I'll harvest these last crystals from my first run and photograph them. I'll also finish the maintenance and reassembly of the experimental cell, recharge the depleted electrolyte with chlorides and start the second run without pH control. The plan is to add pH control to the third run, dial it in and note (record) the differences.

 

All of this will ultimately be written up and published, and also be posted in the blog section. Some are suggesting I combine all the articles and publish it as a book on the subject. With some polishing, it might make an interesting read. We'll see...

 

WSM

Edited August 4, 2016 by WSM

[TomasBrod]

I set up an test cell V=0.9l glass (+) mmo mesh 7x17cm (-) 2x 14x4cm iron sheet.

The current was kept low 2.5-3A with variable voltage AT-PSU, just to see how the electrodes and connections behave.

The electrodes hold in plastic lid on top and piece of plastic tube on the bottom to prevent shorts.

Current measurement was done as voltage drop on a length of cable (around 80mOhm, verified with ampere-meter).

I would like to set up voltage,temperature,current monitoring with micro-controller

PSU inside and cell outside does not work: too much cable resistance.

I need to replace my cables with lower resistance and shorter ones. A minute at 10A made one soft and hot.

Maybe bigger container and more electrolyte.

Run-time: 2 full days. Electrolyte is perfectly clear, now being re-saturated.

I decided to not use electrolyte from previous runs with (+) graphite to prevent contamination.

Thank you.

[WSM]

I set up an test cell V=0.9l glass (+) mmo mesh 7x17cm (-) 2x 14x4cm iron sheet.

The current was kept low 2.5-3A with variable voltage AT-PSU, just to see how the electrodes and connections behave.

The electrodes hold in plastic lid on top and piece of plastic tube on the bottom to prevent shorts.

Current measurement was done as voltage drop on a length of cable (around 80mOhm, verified with ampere-meter).

I would like to set up voltage,temperature,current monitoring with micro-controller

PSU inside and cell outside does not work: too much cable resistance.

I need to replace my cables with lower resistance and shorter ones. A minute at 10A made one soft and hot.

Maybe bigger container and more electrolyte.

Run-time: 2 full days. Electrolyte is perfectly clear, now being re-saturated.

I decided to not use electrolyte from previous runs with (+) graphite to prevent contamination.

Thank you.

 

Hi TomasBrod,

 

What type of salt are you using? I know that potassium and sodium cells are as different as night and day (despite the similarities).

 

What type of cable are you using (gauge)? If you can locate welding cable (large cross-section with many fine strands of copper), it should handle high current with low resistance losses. I think 4 AWG welding cable with crimped terminal lugs would probably work well.

 

MMO is vastly cleaner than graphite in chlorate cells. I believe you're seeing that now. I think you could use the electrolyte from graphite cells of you can vacuum filter it through a slow grade of laboratory filter paper (Google Buchner funnel to see what I mean). The graphite particles should stay on the filter paper and clear electrolyte should go through.

 

Can you photograph your setup?

 

I use an old-school method of data tracking, meters and regular periodic logging in a notebook. Doing it digitally is attractive, but I haven't set that up yet; maybe one day...

 

WSM

[WSM]

PGI will be unique and interesting this year. I have several family members going (six for the first time). I'm also looking forward to visiting with several APC members there (say Hi when we meet).

 

One of my old friends and fellow electrochemist will be there, too; and you can just imagine what sorts of mischief we'll conjure up . It'll be great.

 

My sodium chlorate cell experiment is on track and will resume after next weekend, so I'll report the progress then. I've talked to a friend of mine about publishing a book on amateur electrochemistry, and the thought is it likely would have to be self-published (there just aren't enough of us out there [brother, is that true!]). It's just a consideration and no solid plans at this point.

 

WSM

[WSM]

For those attending the PGI Convention, I'm bringing a hard copy of some of my notes. If you want to discuss Homegrown Oxidizers, let me know.

 

WSM

[WSM]

I got back from the PGI Convention and harvested the last container of sodium chlorate crystals. They did not keep growing continuously but they did slowly grow many more clear crystals than the short harvest cycle batches. They look like rock candy and are much more dense.

 

 

The yield of the last jar of electrolyte = 535 grams.

 

The next task is to clean up the cell, recharge the electrolyte with pure NaCl and start the next run. I'm also considering cleaning up a fresh batch of brine and then drying it for purer salt to begin with, plus use it for adding to the cell as it runs.

 

WSM

Edited August 19, 2016 by WSM

[WSM]

Oh yeah, the total crystal yield from the first batch is almost exactly 5 kilograms (about 11 pounds) !

 

I expect more in later runs.

 

WSM

Edited August 19, 2016 by WSM

[memo]

WSM that is a nice total, how many hours of run time ?

 

 

memo

[Arthur]

If you make an other gallon of saline then you can always have a cell full electrolysing and a gallon in the fridge, Then after a day or so pour the harvested liquor back with added salt and cause the next gallon to overflow to a cooling jar.

 

For the mass of crystals harvested add about half that mass of salt into solution to replenish the ingredients. So if you harvest 1kilo add about 500g of dry salt.

[WSM]

WSM that is a nice total, how many hours of run time ?

memo

Hi memo,

 

Thanks. The total run time was 1080 hours, according to the log. The volume averaged 27 liters.

 

WSM

[WSM]

If you make an other gallon of saline then you can always have a cell full electrolysing and a gallon in the fridge, Then after a day or so pour the harvested liquor back with added salt and cause the next gallon to overflow to a cooling jar.

For the mass of crystals harvested add about half that mass of salt into solution to replenish the ingredients. So if you harvest 1kilo add about 500g of dry salt.

 

That's a good suggestion.

 

I've been giving a lot of thought to purifying and drying the salt before I start. I noticed that even the pool salt is adding contaminants to the cell, though it's purer than the water softener salt. If I dissolve the salt, and then purify and dry it; I'll have a cleaner overall product and the cell should stay cleaner through the process. The main contaminants of concern are dissolved calcium and magnesium salts.

 

I imagine even a potassium salt system could benefit from purification of the starting material.

 

WSM

[WSM]

Due to a heavy work schedule, I may not get the sodium chlorate experiment running before next Monday (and possibly even later). I have some extensive maintenance to do, including disassembly and reassembly of the plumbing and thorough cleaning of the cell. Except for using re-charged electrolyte, the next phase might as well be a whole new cell (I'm leaving the setup fundamentally the same, though).

 

There's much to do.

 

WSM

Edited August 18, 2016 by WSM

[Arthur]

I've been offered some MMO mesh but it's Ir/Ta oxides on Ti mesh. do we have any wisdom on this described as MMO vs other mixed metal oxides?

[WSM]

I've been offered some MMO mesh but it's Ir/Ta oxides on Ti mesh. do we have any wisdom on this described as MMO vs other mixed metal oxides?

 

I don't know about that one, some research is called for. How much are they asking for it?

 

WSM

[TomasBrod]

What type of salt are you using? I know that potassium and sodium cells are as different as night and day (despite the similarities).

 

What type of cable are you using (gauge)? If you can locate welding cable (large cross-section with many fine strands of copper), it should handle high current with low resistance losses. I think 4 AWG welding cable with crimped terminal lugs would probably work well.

 

Can you photograph your setup?

 

I use an old-school method of data tracking, meters and regular periodic logging in a notebook. Doing it digitally is attractive, but I haven't set that up yet; maybe one day...

Sorry for delays I was away too

Using NaCl. Possible to continue to perchlorate or convert to potassium once I find it cheap local source.

I moved the PSU outside and don't experience cable heating anymore. 2x16AWG for each connection. I am using the cables as a shunt to measure current, mVmeter reads 50mV at 10A.

 

What is optimal cathode current density? I am afraid mine is too low. It's 156mA*cm^-2 for one side of one cathode and I have 2 with backsides uncovered that makes 40mA*cm^-2. Should I make them even narrower, they are already 3/7 width of anode? How do I insulate the backsides, lacquer flakes off?

And I can not go above 10A else the jar gets too hot.

 

The photos:

Edited August 20, 2016 by TomasBrod

[WSM]

Sorry for delays I was away too

Using NaCl. Possible to continue to perchlorate or convert to potassium once I find it cheap local source.

I moved the PSU outside and don't experience cable heating anymore. 2x16AWG for each connection. I am using the cables as a shunt to measure current, mV meter reads 50mV at 10A.

What is optimal cathode current density? I am afraid mine is too low. It's 156mA*cm^-2 for one side of one cathode and I have 2 with backsides uncovered that makes 40mA*cm^-2. Should I make them even narrower, they are already 3/7 width of anode? How do I insulate the backsides, lacquer flakes off?

And I can not go above 10A else the jar gets too hot.

The photos:

 

In my setups, I try to size the cathode plates to match the area of the anode. So far, it has been working well. I don't worry about the backs of the cathodes (no need to cover or protect them), since most of the work is being done by the anode (which I do want surrounded by cathode plates).

 

As for heating, A well-running cell does get hot (between 40^oC and 65^oC, typically). Even higher temperatures can be used, if the cell is set up to handle it. If you make a cell from CPVC, it could handle temperatures up to 90^oC, if I'm correct, and a cell made of PVDF or some other high-end polymer could go over 120^oC without degrading. Of course, these polymers are very expensive and take special manufacturing techniques to properly assemble the cell from them; but it is possible if the funds are available.

 

I know from personal experience that CPVC is roughly five times as expensive as PVC, and PVDF is much more expensive than that (but about 20% the cost of PTFE). I also know that PVC holds up well as a cell material, even above its rated temperature of 60^oC, if the pressure is below its rated limits (we typically run the cells at a pressure of one atmosphere).

 

The power leads can and will heat up if they're too small, due to I²R losses. Larger diameter lead wires will reduce such losses and when properly connected to the electrodes, will be more efficient. Swede and I both recommend using welding cable which is very flexible because of the many fine copper strands and the rubber sheath covering them, and solidly bolt the connections together.

 

The electrodes might be larger than the cell size can comfortably handle. You might want to consider running your cell in a 20 liter polyethylene bucket (bucket cell type of arrangement), and see if things will run better.

 

A very important note that Arthur mentioned, try adding more salt crystals as the cell runs, since the sodium chlorate is so much more soluble than the sodium chloride is, the chloride will be gone and the chlorate solution will be half as concentrated as needed to get any crystals out. Keep hunting for affordable KCl; if you want potassium salts, you'll need it at some point.

 

Keep up the good work, and good luck.

 

WSM

[WSM]

I've started the maintenance of my sodium chlorate cell. First, I've disassembled part of the plumbing and removed the cell tank. There was a fair amount of undissolved salt in the bottom of the tank, which I relocated to a PET holding jar. I believe it's a mixture of NaCl, NaClO₃ crystals and intermediate compound solutions. I think I'll dissolve them in distilled water and filter it before putting any of it back into the system (TBD).

 

Next, I washed out the cell tank and dried it. I don't know if it matters (I don't think so), but I noticed that the white PVC plastic changed color to a sort of pink color where the electrolyte was in contact with it.

 

I need to re-glue the silicone tubing lid seal, which separated toward the end of the first run, from the silicone tub caulk which was holding it to the lid backup ring. If the tub caulk doesn't work in this application, I may switch over to a seal of thin-walled Viton tubing held to the lid by PVC cement or some other (hopefully compatible) adhesive. We'll see...

 

I'm still considering purifying and drying the salt to be used in the next phase of the system, rather than recharge it with the regular, contaminated water softener or pool salt. If I keep using the recharged, original electrolyte; the contaminants can accumulate to unacceptable levels (if I don't use purified salt).

 

WSM

Edited August 25, 2016 by WSM

[WSM]

I finished the first draft of Homegrown Oxidizers Part Fifteen today and sent copies to the reviewers for critiquing. It lays out the research done with the first run and is preparatory to the second and third runs of the sodium chlorate experiment. There is much more to come...

 

I've also been busy preparing a second brine tank for use as a salt purification system, for making pure salt for the sodium chlorate process (for brine and chloride replenishment purposes). It will closely resemble the brine tank used with the chlorate cell, and in a pinch (with minor modifications), can replace it. I plan to dry the purified salt solution in a shallow layer in a black plastic cement mixing tub, using solar power. If I work out the details, I'll see if I can recover the water from the salt solution by solar distillation.

 

This idea just gets more complicated as time (and experience) goes on...

 

WSM

[WSM]

I took the several smaller clear containers of relatively dry sodium chlorate crystals and transferred them to a 2 gallon (7.57 liter) white polyethylene bucket with a lid. The crystals fill the bucket to about 4" (100 mm) height.

 

 

It seems better to keep them in one labeled container. I have more crystals but need to refine some others that have some debris from the bottom of the cell (probably due to some contamination off the cathodes [titanium hydride?] and from the pool salt used for chloride replenishment [which wasn't as pure as was expected]).

 

The NaClO₃ crystals in the bucket are ready for use in the perchlorate cells. I hope to collect a lot more before I resume my perchlorate experiments.

 

WSM

Edited August 28, 2016 by WSM