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Author: Subject: Thoughts On Anodes
12AX7
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I don't think so. I have a suspicion that my horribly low current efficiency (~15% even at the best estimate) is due to the horribly large cathode, being the cell itself.

Tim

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Rosco Bodine
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Some of the most efficient cells are coaxial cylinder form
cells with 2mm interelectrode gaps having a pumped
electrolyte. The pump rates are so high on some of these
that they actually have to consider flow erosion from
the friction of the moving electrolyte, as much as any chemical wear.

I think to get acceptable cell performance efficencies
along with pH control the working gap is going to have
to be in the 6-10 mm range max.

[Edited on 28-10-2008 by Rosco Bodine]
12AX7
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For relatively large pipes, bigger than the gap, that would be reasonably effective, because the areas are then similar.

A continuous pumped cell would pwn. Brine in one end, chlorate out the other; oh, but considerable hydrogen must come out, too. You could pump from the bottom and let the hydrogen rise, although I'm not sure how you prevent it from sticking (passivation). That much flow rate would do it, but inevitably you will produce far more gas than liquid volume if you don't let it go, so I guess it will proceed as any other cell does, the liquor always being well mixed and circulated from a tank, say. Oh well. Just another approach to the process, then, nothing so remarkable as a one-step continuous process.

Tim

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Swede
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Those that have read my blog know that I am going for a circulating system, not in the sense that chloride goes in at one end, and chlorate is extracted at the other; rather, it is a closed loop using two cells, one small (containing the electrodes) the other large (being a cooled collection chamber). A variable pump powers the flow. The goal is to create a system that forces crystals to form (and be collected from) the cooler cell.

One of the benefits of this is that the volume is variable. Additional containers can be daisy-chained into the system. The other benefit is that it may be possible to recharge the hot effluent from the small electrode cell with additional chloride ion. I have been putting a bit of thought into how to do this.

One thing that came to mind... the typical 40 lb sack of KCl has large, heavy crystals. I was thinking about a PVC water filter cannister from a typical home improvement store, highly modified. The cannister is charged with large KCl nuggets, and the hot effluent from the small cell (probably at 60 to 80 degrees) is flowed through these crystals, proceeds up and out, and is routed back to the large, cooler collection chamber.

I am using potassium salts, not sodium. Two problems come to mind. Dissolving KCl appears to be slightly endothermic. As the hot, chlorate-laden electrolyte contacts the KCl nuggets, it cools quickly, and chlorate is dumped in the chloride cannister. The second potential problem: assuming it works, you now have recharged electrolyte carrying extra chloride and chlorate flowing to the collection chamber, whereupon it cools even more, and KCl falls out, contaminating the already-crystallized potassium chlorate. With the salts intermingled there, it would be likely that the KCl would NOT redissolve, and your product would be heavily contaminated.

What do you guys think? Chloride cannister = waste of time and resources?
tentacles
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I think putting the chloride "recharger" after the collection phase would work best, but with a several degrees preheat to keep more chlorate from dropping out. I wonder what the equilibrium of K chloride to chlorate is in this situation. Will more Cl dissolve and precipitate out the chlorate until there is none, or some percentage, left?

There's probably a chart somewhere that's very hard to decipher.
Xenoid
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 Quote: Originally posted by tentacles There's probably a chart somewhere that's very hard to decipher.

The KCl - KClO3 mutual solubility data is available on Dann2's site here;

http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...

I think I plotted this up by hand, on graph paper, at some stage but I can't find it now!

 Quote: Originally posted by 12AX7 I don't think so. I have a suspicion that my horribly low current efficiency (~15% even at the best estimate) is due to the horribly large cathode, being the cell itself.

Or perhaps by your horrible, corroded, twisted wire connections, Tim -
12AX7
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No. Kirchoff's node law. Bad connections produce a voltage drop, and the voltage drop across connections pales in comparison to the ballast resistor I used. Voltage drop costs power efficiency but not current efficiency. Besides, even if I made that accounting mistake, assuming current efficiency were a typical 50%, the measured voltage drop of 2V would only be 60% loss, dropping power efficiency down to 30%, still more than a factor of two away from the 13% or whatever it was I observed. And the error bars on that 13% are much smaller than a factor of two (and have the statistical support of two measured runs!).

So all that remains in proving this hypothesis is to build a cell with evenly proportioned anodes and cathodes. Maybe next summer I'll pick up some more graphite bars (or some chloronitrosylplatinate or whatever the good stuff is and slap that on titanium) and cook up a five gallon bucket of black-stained goo.

As for process, I'm convinced the best method is a batch/continuous sodium process. Potassium chlorate is low solubility and will crystallize everywhere you don't want it. So don't use it. Sodium chlorate is high solubility, but sodium chloride has no change in solubility vs. temperature, so there is no endothermic dissolution to worry about and it forces sodium chlorate to precipitate on cooling.

To use a two tank method, I think the best approach would be a circulating pump in the electrolysis cell, drawing or forcing liquor through a basket loaded with rock salt. A small faction of the outgoing liquor is diverted to the crystallizing tank. It must be a small fraction, because if the cell's contents are constantly changing, there will be an extremely small deltaT and crystals will be forced to form everywhere. Imagine it this way: you only want to crystallize as much solution as there has been chlorate added to it. It's okay to have a somewhat higher rate, in which case you're just pumping a little more solution than crystallizes, fine, but not too much that it lowers the cell temperature / raises the crystallizing tank's temperature and not too little that the cell's concentration becomes supersaturated and crystals form in both anyway. So there's an ideal middle range which is good.

I think a small circulating pump in the cell will suffice for mixing, while natural convection into the crystallizing tank will suffice for its flow. Use a relatively low aspect ratio for the tank, so it is able to cool effectively. A narrow rectangular box shape would be excellent.

Tim

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dann2
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Hello Folks,

 Quote: Originally posted by tentacles I think putting the chloride "recharger" after the collection phase would work best, but with a several degrees preheat to keep more chlorate from dropping out. I wonder what the equilibrium of K chloride to chlorate is in this situation. Will more Cl dissolve and precipitate out the chlorate until there is none, or some percentage, left? There's probably a chart somewhere that's very hard to decipher.

Would agree with Tentacles. If you were to (loosly) thermally attach the recharging chamber (which comes after ppt chamber) to the anode/cathode chamber this would keep it warmer than settling chamber. What you want IMHO.
A very small pump is required for the circulation, you may be better to have the pump set up on a timer that pumps every half hour for a few seconds (say).
What about a reaction chamber?? You are going to control pH I presume? If so it will be advantageous to have a large chamber (after anode chamber) that is warm/very warm to allow the chemical formation of Chlorate. You will add acid into this chamber. The anode/cathode chamber will be OK for a reaction chamber IMHO if you do not want to add (yet another chamber).

You could get rid of KCl addition chamber by adding finely powdered KCl to anode/cathode chamber and stirring gently.(magnetic stirrer) every day or so. The amount of KCl will be found out when you have discovered you current efficiency (how much KCl you are destroying) per day.
I presume there will be no evaporation from the system. If there is (say you have a reaction chamber (will be warm 60, 70C) with a fairly large surface area open to the air), then you can easly add KCl via a concentrated solution of the stuff to the anode/cathode chamber.

What will come out/stay/dissolve in the solution is depicted by ye old mutual solubility diagram.
Thanks to Watson.Fawks, who turned up an explanation of how to use (bloody) mutual solubility diagrams, you can educateyourself on how to interpret them here:
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...
See the first few pages of 'How to disign fractional crystalization processes'.
There is a mutual solubility diagram for KCl and KClO3 here:
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...
Unfortunately it is in mass ration, you want mass percent in order to figure out what will/will not stay in solution as per the Watson.Fawks article.
Does anyone know how to convert the graph? The axis are easy but it is difficlult to know where to draw the lines. Would need to sit down and study the thing. The table that Xenoid showed you has the data in mass % (and you could draw a (lovely ) graph).
There will be no problem getting the KClO3 out as it is less soluble and also has a large slope in it's solubility graph.
Me thinks that if you just set the system up and let it belt away for a day or two it will work as you require. It will take it a day or two to reach its 'working point' where K Chlorate comes out nicely and KCl goes in nicely. You may have to insulate the whole thing (or keep shed reasonably at the same temp.) as wildly varying outside temperatures may upset it.

Regarding efficiencys: The anode to cathode spacing debate has more to do with voltage drop accross cell which is related to power efficiency (very very important to the industrial Chlorate makers). Not very important to you.
The largest increase in current efficency (time efficiency) for the amateur can be got by pH control and (since pH control is being implemented) using a seperate chemical chlorate formation chamber which is hot or use a fairly large anode/cathode chamber (ie. the anode/cathode chamber is also the chemical chlorate formation chamber).

The next biggest step up for to get high CE is to keep the Chlorde level high.

From then on you will just be tweeking at the edges for little CE return.

My two cents worth on Cell chem. is here:
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...

Regarding reduction at the cathode:
From what I can figure out from all my bedtime reading adventures (read: sad fuck) Iron cathode are good at reducing Chlorate and hypochlorite back to Chloride. (What we don't want). Ti is not as good at converting Chlorate and Hypochloride back to Chloride. (that's good for us).
Therefor area of Cathode (large area gives low current density and this increases reduction, read this somewhere, can't remember where I'm afraid) is even less important to us when you use Ti. (I am not trying to say that area of Cathode is a really big deal anyways). Chromates are added to cell to stop reduction in industry. Perhaps you will get away with adding no Chromates if Ti cathode is used?????????
Perhaps if you use a very small Ti Cathode it would really reduce reduction without having to add Chromate etc.
Industry would NEVER use a very small cathode as it would raise voltage accross the cell a bit (they would'nt tolerate that at all).
The less additives the better. Then again Chromate also buffers the solution which is an advantage.

Well, I'm glad I got all that off my chest!!!!!!!!!!

Cheers,
Dann2

[Edited on 29-10-2008 by dann2]
Rosco Bodine
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cutting through the fog

Here's some test data on a large coaxial cell .

US3385779

Attachment: US3385779 High Efficency Coaxial Chlorate Cell.pdf (127kB)

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pH control is important... pH controllers are common and easily available. I picked ip a 1/4 DIN industrial unit off eBay that will hopefully work (He said "Tested and working"). Unfortunately, I don't have a probe yet, and the probe selection has me a bit stumped. Even a "cheap" probe, isn't. I'd rather spend $150 or$200 now than have to buy 4 or 5 \$50 probes.

I sent an email to Hanna tech support. In the email, I asked them what they would recommend based upon the species and the environment these electrodes are forced to operate in, continuously.

This is the list of assumptions I've been working with:

- Double junction
- need NOT be fast response
- need NOT be extremely accurate, +/- 0.2 is more than adequate
- PTFE diaphragm? I am not sure if this is needed
- Either glass, CPVC, or PVDF (Kynar) bodied; anything else will suffer
- A threaded body is best, but I can adapt almost anything
- ATC NOT required
- Highly salted electrolyte but few if any solids; flow low or zero
- Temperature from 25 to 80 degrees C.
- Primary range 4.0 to 11.0

I have a few process electrodes in mind, but I'm curious to see what they come up with, if anything. The easiest to adapt would be one with a 1/2" or 3/4" tapered pipe thread, or the metric equivalent.
Swede
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Hanna emailed right back. They didn't comment on anything, simply pointed me to their HI1000 series of electrodes, which is pretty much what I presumed. Double-junction, PTFE diaphragm, gel-filled, PVDF body. I really hate the thought of coughing up so much money. But I am really concerned that anything less than a high-quality industrial electrode is going to be poisoned quickly or physically die after only a few runs. We're talking DAYS immersed in that stuff.
dann2
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Hello,

It is amazing the near absence of Graphite erosion that industry can achieve.
4kg Graphite per ton Chlorate produced, @30C. That's 4 grams per KG , and not all of the four grams will appear as black gunk. Some will have gone off as CO2.
We are doing something(s) very wrong when using Graphite. No pH control I guess is by far the biggest issue.

@Swede
Would you not need to mention the more aggressive species that the pH probe will be in contact with + the fact that the temperature will be up at 60C. These factors will be a pH probe killer, perhaps not?
It can be hard to extract the info. you need from people selling stuff.
While my suggestion will not be in line with your (to put it mildly) exacting standards, you could set up the system and just have a constant feed of acid into cell and check pH twice per day (or more at the start).
I did this with a cell before and the pH stayed in the wanted region remarkably well.
The rate of acid addition was 0.35ml per amp each hour. Acid was 12% hardware store (used for cleaning cement) HCl. pH stayed in the region of 6.7 to 7.
You would need 17.5ml per houre if your cell was running at 50 amps. Of course you cell might need more/less. 17.5ml per hour sounds alot. 0.42 liters per day.
You still need to get a pH probe and may neet to take a sample out of the cell both to let it cool and to stop voltage gradients in the cell from putting the pH reading haywire.

Which reminds me of another point for your pH probe in the actual tank. Will it operate with the voltage gradient that is in the tank?
Mine would not. Samples had to be removed. If you had a seperate 'chemical chlorate making vessle' (hot), there would be no voltage problem is this vessel and a permanently installed pH probe shoud work OK there.
You may also be able to shield the probel with a metal shield to keep voltage field from probe in anode/cathode chamber.

Dann2

[Edited on 29-10-2008 by dann2]
Swede
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Dann2, I love your contributions to this discussion, thank you.

I did mention "heavy concentrations of chlorites, hypochlorites, and chlorates, as well as aqueous chlorine." Hopefully that registered with him. Materials-wise, a PTFE diaphragm and PVDF body would be ideal.

One of my goals for my current project was automation, not because it's needed, but mainly because I enjoy the gadgetry, and the challenge of putting it all together. I agree that periodic check of the pH with a standard (cheaper) system would be much easier, but eventually, I would like to let the controller do its thing. I was going to place the probe in a separate tank from the electrodes, so there should be little or no problem with interference. Placement of the acid injection relative to the probe will be an interesting problem. Too close, and you'll have very rapid cycling of the valve or pump that administers acid. Too far away, and you might overdose with acid. This will depend also upon turbulence in the tank, with higher probably being better. I plan on using aquarium air pumps for stirring.

I am a bit concerned about the volume of acid you mentioned. 1/2 liter a day seems like quite a bit. I'm hoping to use upwards of 75 amps with this thing, and I don't know that I am going to evaporate 1/2 liter per day. Maybe concentrated HCl, to keep the volume low, might help.

Also, for an acid "pump", I was considering an airtight vat, and letting a powerful aquarium air pump pressurize the vat, which would force the acid out a line and into the system. When the controller turns off the air pump, the acid flow should cease. Sort of a poor man's dosing pump.

[Edited on 29-10-2008 by Swede]
dann2
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Hello,

Thank You Swede, it's a pleasure!
<table border=3>
<tr><th colspan=4> pH control on current efficiency and acid consumption</th></tr>

<tr><td align=center>Quality of <BR> pH control</td><td align=center>pH drift</td>
<td align=center>Current efficiency, %</td><td align=center>35% HCl consumed<br>kg/ton - NaClO<SMALL>3</SMALL></td></tr>

<tr><td align=center> Medium </td><td align=center>6.0 to 7.8</td><td align=center>74.4</td><td align=center>87.5</td></tr>

<tr><td align=center> Good </td><td align=center>6.7 to 6.8</td><td align=center>84.5</td><td align=center>62.5</td></tr>
</table><small>From: Electrochemical Technology. 6 (1968) 402. </small>
</center>

Data on acid consumption in Chlorate cells has always been hard to find.
Figures from Encylcopedia of Chemical Processing and design gives a figure of 0.996 kg HCl per 185.553 kg Sodium Chlorate produced. (They dont say if they mean 'pure' acid (35% HCl or what)

From the article below:
http://www.geocities.com/lllwolly/further/perkform.zip
acid consumption is given as pounds of HCl per ton Na Chlorate . It has wild variation from 5 to 35 (average about 25 lbs) in a 9 amp cell.
In a 144 amp cell they give a figure from 98 to 19 lbs HCl per ton Na Chlorate (100% basis used as Hydrochloric acid in calculations) Electrodes were Pt.

My own cell that I controlled the pH in was an extremly simple jam jar type. Anode was Magnetite. Perhaps I could have added less acid, I am not too sure. If you add too much acid the cell will start to emit more and more Chlorine. I could not detect a smell of Cl. I quoted the figure in ml per amp per time. I achieved a CE of 60%. Magnetite is not a great anode! 3% CE with no pH control. I dont have a figure for the total amount of Chlorate I produces and the total amount of acid I added to get that amount of Chlorate.

Anyhow, the above will give you some guidelines, very very wide one's by the looks of it!!

I attach an artical about adding acid to cells. It's in Japanese. Can anyone decipher.

Dann2

[Edited on 29-10-2008 by dann2]

Attachment: denki.pdf (395kB)

tentacles
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Keep in mind that it isn't just evaporation, but also we're cracking the water for it's delightful oxygen, so there will be water lost there as well.

dann: Your hardware store has 12% HCl rather than regular muriatic (28-31 or whatever %)? Or do you mean you diluted muriatic to 12%?

I'm still waiting on the mail to deliver the anodes Swede made for me to start testing.. Also have to come up with somewhere to *put* a cell. I just recently filled my outside storage area with 2/3 cord of firewood.
Rosco Bodine
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 Quote: Originally posted by dann2 Hello, It is amazing the near absence of Graphite erosion that industry can achieve. 4kg Graphite per ton Chlorate produced, @30C. That's 4 grams per KG , and not all of the four grams will appear as black gunk. Some will have gone off as CO2. We are doing something(s) very wrong when using Graphite. No pH control I guess is by far the biggest issue. Dann2

In the thread "treating gouging rods" is some information that is probably one added factor. Such preparations for
toughening graphite is probably also useful for anodes of the GSLD type which should be workable for perchlorate.
I have always though that a coaxial electrode is the best way to go, as it offers several advantages physically and electrically. It can simplify cell construction also.
dann2
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Hello,

@tentacles
My hardware store has 12% HCl acid only. Cannot obtain any higher except lab supply stuff.

I often wondered if we changed the solvent that we put our Chloride into what would happen. We would still need some water for the O2 so it would have to be miscible with water but would something weird and wonderful happen that might suit our purposes.

Dann2
12AX7
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What solvent? Most will be oxidized by the hypochlorite and radicals, and the rest aren't even miscible.

Tim

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Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
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I managed to get my first batch of chlorate dry today, I was able to make a red comp yesterday out of some wet chlorate crystals, SrCO3, and powdered sugar, so it seems pretty pure.

It still has a hint of bleach smell, is this normal or should I have washed it more? I just washed it once in a large amount of cold water and kept whatever didn't dissolve.

Swede- Maybe you could have a large tube with the KCl nuggets in it and a smaller tube containing the chlorate solution running through the larger one, so the KCl dissolving would cool down the chlorate and let it fall out, like a condenser. Then push the solution back through the larger tube to restock the KCl and continue the cycle.
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Hi Splinky - how did you harvest the chlorate? Did you start with potassium salts, or sodium? Either way, once you had your potassium salts, remember that they are VERY insoluble in cold water. If you used some sort of filter rig, once the potassium chlorate is sitting there in the filter basket, you can pour (wash) significant amounts of ice cold water on them, which will remove much clinging contaminants, and also residual chloride, while dissolving very little of the chlorate. I wash first with ice water, then with an alcohol/water mixture (also cold) as a final wash. The alcohol helps in the wetting of the crystals and also speeds drying. They should not smell like hypochlorites when dry.

It might have been your washing technique. Did you get the ice water to all of the crystals with a bit of mixing/stirring of the mass? If you simply pour cold water over the surface of the crystals, the water will follow a path of easiest flow, and may not access clumps of crystals in some parts of your rig.

I tested some potassium chlorate crystals washed in this manner, and they had a low chloride residual; they were 99.3% pure. Recrystallizing KClO3 is easy and will produce a quality product.

I like your thought of using the KCl crystal mass as some sort of heat sink! Interesting. Along those lines, I picked up what is called an "offline chlorinator" at a pool store today. Thes are cannisters designed to accept 3" chlorine tablets, and have water trickled through them to leach the chlorine, which is then injected back into the pool. This is what it looks like:

This sort of gadget can find all sorts of uses in (per)chlorate electrolysis. The plastic is designed to withstand wicked oxidizers. It is also engineered to be completely sealed. I can see something like this being a stand-alone cell (the volume is impressive, about 4 liters), an electrode cell, or a chloride replenishment cannister; any of these with just a bit of work. They can be had on eBay relatively cheaply. I'll take a look at it today and snap some pics.

@Tentacles: That sucks that the anodes have not arrived yet. Hopefully customs will release them soon. I'll bet they will be opened and inspected. Hopefully they'll repack them properly.

I am going to take my small test anode of this material and set up a perchlorate cell, starting with recrystallized chlorate, and rip some serious amperage/voltage through it to see how it stands up. Another one will do duty as a chlorate-only anode.

[Edited on 30-10-2008 by Swede]
dann2
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 Quote: Originally posted by 12AX7 What solvent? Most will be oxidized by the hypochlorite and radicals, and the rest aren't even miscible. Tim

I guess that's the end of that whacky idea, if solvents that may be suitable would get attacked by Hypochlorite.

@Spinky
Cleanlyness is next to godlyness in the Pyro. (or indeed chemistry business in general) business. It would be no harm to to recyrstallize. Be careful.

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When a little over an inch of chlorate had accumulated on the bottom of the cell (I started with KCl), I shut it off overnight to cool and let more precipitate out. Once it had accumulated on the bottom I poured the water out into another container and filled the cell with cold water and let it sit with occasional stirring for a while. I disposed of that water and did it again with a little less water and agitation, then let it dry by a fan overnight. I should go with more filtering definitely, I think I'll go with your process and run cold water over it for a while.

I would use the offline chlorinator as a cell, that looks to be perfectly suited for it. A three foot or so section of two inch pvc with a section of thin (cpvc maybe) half or three quarter inch running through it would probably work well as the condenser/restocker thingy.
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Hmm, that would be one way to wash crystals, and it should have done so thoroughly, Make sure you save the was water for your next run... it'll carry chlorate with it. Replenish that water with chloride, and it'll give you a head start.

"Used" chlorate cell electrolyte is loaded with intermediate species, and significant quantities of chlorine as well. I have about 5 gallons in a poly jug over KCl crystals to replenish for the next run, and with the lid removed, it becomes unbearable in the vicinity of the jug. This is mainly due to the chlorine, but also the bleach.

Anyway, maybe someone else has some thoughts on washing. I used to use coffee filters, but when the batches approached a kilo, that was too slow, so I made a plastic filter/funnel rig. The entire batch gets dumped into this, then the cold water is applied with stirring; the holes allow the water to drain. I have never had a dried chlorate batch smell like anything at all.

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I reused the original liquid from the cell, the immediate production of chlorate is more satisfying.

I found a much larger jar that looks promising for a cell, will most plastics containing chlorine hold up well to cell conditions?
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Good plastics: PVC, CPVC, PTFE, PVDF (Kynar), PET (Coke bottle plastic)

Acrylic seems to do OK, but there is definitely some fogging and crazing. HDPE lasts a few batches, but eventually dies. It is economical, though, and it is what most people use. Polypropylene for me has not done well. Nylon is about the worst, and unfortunately that's what most hardware-store hose barbs and fittings are made of. They rot/crack pretty quickly.

PET (polyethylene terepthalate) would be an awesome plastic, except most containers made of PET are really thin and flimsy, like a 1 liter coke bottle.

I made my own PVC/CPVC system, but it wasn't easy. A better bet would be one of these PVC tanks + lid:

http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&category%5Fname=29&product%5Fid=1888

They are not cheap but will do some serious production, at about 1 kilo per 6 liters, starting with saturated KCl. The lid will need to be modified to create a seal, and you might have to glue some bolt hold-down strips on the upper rim, but if I ever need to do another tank, I'll buy one of these rather than make one.

Another option is a short section of large-bore PVC pipe. You get a lot of volume per inch when you're talking about 12" dia PVC pipe. Remember PVC is not good above 40 to 50 C, so if you want to run hot, consider CPVC.

All of this you can ignore if you just want to make 400g now and then... use an HDPE food container, slotted for the anode and cathode.
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