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Thoughts On Anodes

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watson.fawkes - 6-11-2008 at 18:11

Quote:

Originally posted by Swede
I'm down but not out. I'll find a way to boost efficiency. And the big question, what in the HELL hapened to my cathodes?

Here's my guess, written as a series of questions.

What the difference in resistance of the solution between the near side of a cathode plate and the far side?
Viewing these two resistances as a parallel circuit, what's the current allocation between these parallel branches?
What does the net current flow look like as a three dimensional vector field?—not just the integral curves, but the magnitude of the flow.
Assuming the current flow enters the top of the cathode uniformly, what does the current flow look like inside the body of the cathode?
What does scalar field of resistive heat generated by the current within the cathode look like?

Yep, heat warping.

tentacles - 6-11-2008 at 18:58

watson: What would you suggest to alleviate the curling? Drilling the cathode / mesh cathode? Thicker cathode (maybe plus drilling?)? I think we'd all be amenable to suggestions if you have any. Drilling might alleviate the current differential significantly (as more current would be able to pass through the back side of the cathodes, rather than almost none). And getting some current to the back side would hydride both parts at a more similar rate. There's certainly been successes using Ti cathodes, so I won't if this isn't an issue compounded by the welding stress and high temperature of the cell.. if the cell was at 90C, the cathodes may have been somewhat hotter.

Ti expanded sheet, short of buying it from ebay, and it's rarely sold, is very pricy. McMaster has it for $91/sq ft.

[Edited on 6-11-2008 by tentacles]

12AX7 - 6-11-2008 at 20:42

Are you pumping cold solution or hot solution? The better idea would be to pump hot solution so it's not supersaturated. The less preferrable alternative would be to pump cold solution, but warm it up by snaking the intake hose through the hot cell before reaching the pump. This will not prevent crystallization along the hose before the liquor inside warms up appreciably.

What does current flow have to do with anything? Water is an excellent conductor of heat and the surface of the titanium will be quite equal to the liquor's temperature. The core will be warmer, but it won't have much appreciable tangential direction to it -- assuming you're getting at some sort of front-to-back differential current flow causing this.

What does resistive heating have to do with anything? I don't see how heat alone warps it, especially so little heat. To curve that much, the material must be physically changed, which is why I suspect hydridation.

Tim

Rosco Bodine - 6-11-2008 at 21:36

Yep if anyone was wondering if it is possible to electrolytically hydridize titanium .....wonder no more.
Embrittlement is the result of deep hydriding , and disintegration to particles of what is mostly hydride is
the end result if the process goes to completion.
Since the hydride is conductive and evidently porous
and corrosive as well, it evidently forms no protective layer against further hydriding, evidently behaving as
a sort of "amalgam"- like composite which behaves as
an absorptive or kinetic conduit for free hydrogen or hydrogen ion.

This hydride formation is really more interesting for its usefulness potential as an anode substrate preparation for doping and baking processes which may exploit the hydride's thermal decomposition at about 250C to react
with dopants to form an anodically conductive interface layer with the unhydrided and unpassivated titanium of the substrate below.

Clearly it would seem better to use a different material for
the cathodes, something which is not subject to hydrogen embrittlement via electrolytic hydriding.

Maybe silver plated or even silver bearing tin solder plated "tinned" copper or iron would be better as a cathode.

[Edited on 6-11-2008 by Rosco Bodine]

watson.fawkes - 6-11-2008 at 22:14

Quote:

Originally posted by tentacles
watson: What would you suggest to alleviate the curling?

First, assume it's heat, and not some other mechanism. You can eliminate the stress by changing the current & heat distribution, or you can counteract the mechanical force generated.

As to changing the geometry, perhaps the easiest thing to do is to keep the layer structure but have mesh anodes on the ends. The mesh won't have nearly the same current inhomogeneity.

Even easier, though is to just counteract the bending force. Bond the bottom ends of the cathodes together mechanically. the very simplest way to do this with two cathodes is to form them as a loop. Alternate, run a bolt between them at the bottom. The advantage of a mechanical solution is that it addresses the symptom, regardless of what the cause is.

watson.fawkes - 6-11-2008 at 22:28

Quote:

Originally posted by 12AX7
What does current flow have to do with anything? Water is an excellent conductor of heat and the surface of the titanium will be quite equal to the liquor's temperature. The core will be warmer, but it won't have much appreciable tangential direction to it -- assuming you're getting at some sort of front-to-back differential current flow causing this.

What does resistive heating have to do with anything? I don't see how heat alone warps it, especially so little heat. To curve that much, the material must be physically changed, which is why I suspect hydridation.

Consider the magnitude of the current flowing in a cross section of the cathode from near to far side. If there's a near-to-far side disparity, there'll be differential thermal expansion. What happens at the surface isn't particularly relevant except insofar as it sets boundary conditions for the total thermal flow. You can have identical temperatures at both surfaces and still have an internal thermal asymmetry.

I'm not at all convinced that the internal heat is all that insignificant. A small force exerted over hours is completely plausible as a source of creep.

The physical change you require in this hypothesis is inelastic deformation of the cathode, which translates down into rearrangement of crystals in the bulk metal. To really get an answer I'd have to dig into some material properties (stress-strain curve for the alloy, resistance, thermal coefficients of expansion and resistance) operation parameters, dimensions, etc. and then spend a bit of time with a simulator to model the current flow within the cathode. So I'm not going to really get an answer.

Rosco Bodine - 6-11-2008 at 23:25

The idea that warp was caused by heat is a no starter
with me, kind of no way, no how do I believe that and not even maybe. Frankly it seems preposterous .
If that sort of a cross sectional expansion differential
was present , it would be indicative of a laminate like a bimetal strip kind of effect. And if that effect was purely thermally induced to such an extreme then there is no way titanium would be structurally acceptable for use
in any structural application at all, much less airframes.

[Edited on 7-11-2008 by Rosco Bodine]

Swede - 7-11-2008 at 06:41

Those cathodes were not commercially pure, if that makes a difference, they were a Ti alloy. They were also fairly heavy for sheet, being 0.062" or 1.6mm.

I had used identical cathodes in a previous cell, same spacing, same liquor, same current, with no warpage. The only difference between the setups was the temperature. The only temp I was measuring was the liquor itself, which I saw to be 90 degrees that morning. In my earlier cells, it was never more than 60. Something happened between 60 and 90 to warp those cathodes.

I have to believe it is a transformation of the material rather than simply heat warpage. I don't believe the welds had anything to do with it, either. Ti conducts heat so poorly, when those welds were made, the heat from the welding process probably never made it more than an inch or two down the cathode, yet the warping is even along the entire length, and it must be an electrochemical transformation, internally.

I'll be happy to try anything you guys want (red heat, etc) and take note of what happens.

For now, I am going to run the big vat in a stand-alone manner. I've figured out a way to use the dosing pump (I found a god timer that will work) and given the size of this thing, with careful pH control, I believe I can execute MUCH of the chlorate formation using the 6 electron, bulk formation process. This cell is fairly well insulated on its own, and I believe that I can get the temp up to 60 or 70 at least, and hold it there, due to the bulk of the liquor.

It would be nice to have mechanical stirring, rather than air-stirring, which will cool the system somewhat.

While this thing is cooking, I am going to rethink the circulation process. Hard CPVC piping, perhaps with foam wrap-around insulation, would be vastly superior to flex tubing, and the associated hose-barb choke points.

12AX7 - 7-11-2008 at 07:45

For asymmetrical current distribution to do that, it would have to be considerable indeed, I'm thinking something like a 45° angle, and there simply isn't enough current flowing out of that face, in the magnitude that it would have to be flowing (I think hundreds of amperes would be necessary to raise the core temperature that much) and at a peculiar distribution (current would have to be distributed exponentially from the bottom up). Titanium does not creep at room temperature, however it does creep at red heat, so the minimum core temperature for this possibility would be on the order of 600°C. If this were possible in water, the much thinner strap at the top would've completely vaporized quite some time ago! So that's my final word on heating.

I'm willing to bet that annealing the cathodes at up to red heat will relax them straight again.

Tim

tentacles - 7-11-2008 at 09:23

Re: Silver plated cathode... see http://www.freepatentsonline.com/4186066.html
Yep, that's right, just what we needed.... another ridiculously complicated (I didn't even read past the abstract) Titanium coating process...

I think what we're going to need is more data.. Swede, please keep us apprised of what happens to this cell run. It could be that titanium hydrides much more readily at higher temperatures. We all know Ti has been used commercially for cathodes in the past - I've come across a few references to the hydriding phenomenon taking year(s). It could simply be that the water was damn near boiling at the cathodes- Swede, was there seperate circulation air for the electrode chamber? If not(hell possibly even if so), I'm inclined to conclude it was the extreme environment of the chamber / probably very low chloride levels etc. I'll have to see it happen again during a normal run before I start looking for other cathode materials and YET MORE exotic coatings. ;P

We've seen too many successful runs with Ti cathodes for this to be much more than an unfortunate combination of circumstances... unless it happens again. Then we should probably look at the alloy.

[Edited on 7-11-2008 by tentacles]

Swede - 7-11-2008 at 12:10

Tentacles, I'm inclined to agree. I've not been at this long, but all my Ti cathodes until now have performed very well with no issues.

I never even thought of the extremely low chloride levels in the EC. I wish I had saved some of that liquor separate from the rest to test it and see what it was. Damn my shortsightedness.

That environment must have been hellish, yet the MMO held up fine, as far as I could see, so it appears to be good stuff.

@Dann2 - The reason I originally wanted to take the chloride levels very low was for two reasons... first, I wanted to see if there were any ill effects on this particular MMO mesh. Second, despite the drop in efficiency, most of the work associated with this process is in the setup, teardown, and collection of the crystals. If I can double the yield on a particular run, even if the efficiency drops a bit, then I think that's a good thing. I'm into this for the material it produces, ultimately feedstock for a bulk perchlorate setup, for pyrotechnics. The fun of the process, and the science, is a bonus. I've got a decent collection of analytical reagents to test my purification methods.

As I mentioned, I decided to do a run using just the vat. After a few hours of replumbing, it was ready to go. It's warming up now at 50 amps, and I did take what I learned and incorporated it into this iteration. I'll get some pics up. This run also will be used to test the integration of the HCl dosing pump. I like the idea of a dosing schedule that takes place every few hours, rather than a true control loop, and with a bit of effort and monitoring, I think I'll be able to get very close.

I'm going to do some serious thinking on a circulating system over the next week or two. There are some problems associated purely with the complexity. A monolithic box is hard to beat, but circulation offers so many possibilities.

One thing definitely needed; some sort of intake screen for the pump. I mentioned that my Hanna dosing pump came with a neat PVDF mesh screen, which is ideal for a chlorate cell, and they sell it separately. There's no picture on the Hanna site... it is stock number HI 721005 Foot Valve Assembly:

http://www.hannainst.com/usa/prods2.cfm?id=018001&ProdCo...

It comes as a PVDF mesh screen and a check valve, plus a PVDF fitting for 3/8" OD tubing. Something like that, shielding the pump intake, would be needed. Plenty to think about.

Rosco Bodine - 7-11-2008 at 13:14

Quote:

Originally posted by tentacles
Re: Silver plated cathode... see http://www.freepatentsonline.com/4186066.html
Yep, that's right, just what we needed.... another ridiculously complicated (I didn't even read past the abstract) Titanium coating process...

I don't recall suggesting titanium as a cathode material, plated or otherwise, because titanium is known to be vulnerable to embrittlement via hydriding. Maybe some anode coating schemes seem to be "ridiculously complicated"
but I haven't seen that for cathodes. Graphite or iron or stainless steel or just about anything could be used, and I suggested something "ridiculously simple" like tinned copper or iron.

Quote:

I think what we're going to need is more data.. Swede, please keep us apprised of what happens to this cell run. It could be that titanium hydrides much more readily at higher temperatures. We all know Ti has been used commercially for cathodes in the past - I've come across a few references to the hydriding phenomenon taking year(s). It could simply be that the water was damn near boiling at the cathodes- Swede, was there seperate circulation air for the electrode chamber? If not(hell possibly even if so), I'm inclined to conclude it was the extreme environment of the chamber / probably very low chloride levels etc. I'll have to see it happen again during a normal run before I start looking for other cathode materials and YET MORE exotic coatings. ;P

I'll do some research on that, and see if I can't get back to you with a couple of hundred schemes to select from ....
and I will of course eliminate all of them first which seem
too easy or simple

Quote:

We've seen too many successful runs with Ti cathodes for this to be much more than an unfortunate combination of circumstances... unless it happens again. Then we should probably look at the alloy.

[Edited on 7-11-2008 by tentacles]

Hydrogen embrittlement is guaranteed, it is only a matter of time . Now where did that hydrogen go that was making me think we might need a bit of supplemental hydrogen to
recombine with the chlorine for a recycle loop to hold the pH constant ???? Hmmmmm, wait don't tell me , let me think, now where did that missing hydrogen go ? I'll leave the riddle for your warped amusement.

Take a look through my sunglasses :cool:

http://www.youtube.com/watch?v=Phzn5wFgaDk
See the light ?
http://www.youtube.com/watch?v=6yWhlSd309A&feature=relat...

referencing the TiH2 thread, here are some parameters
which apply to electrolytic hydriding or avoidance of it. http://www.sciencemadness.org/talk/viewthread.php?goto=lastp...

[Edited on 7-11-2008 by Rosco Bodine]

tentacles - 7-11-2008 at 16:05

Quote:

I'll do some research on that, and see if I can't get back to you with a couple of hundred schemes to select from ....
and I will of course eliminate all of them first which seem
too easy or simple

If it doesn't require at least tin (+IV!) nitrate, then clearly it's far too simple and would never work ;P

I just posted that silver-titanium stuff because it turned up on a quick googling, and was at least somewhat similar to your silver plated copper suggestion. Would silver ions in solution potentially be hazardous? I seem to have some dim recollection of silver perchlorate being bad - assuming it might form. Silver isn't so expensive that a solid silver cathode couldn't be do-able, either.

As to embrittlement, it IS only a matter of time, but the question is how much time, at more reasonable temperatures and cell conditions?

Rosco Bodine - 7-11-2008 at 20:22

People who have money to burn or who are using electrode assemblies already made of titanium won't have trouble with it under reasonable temperatures and pH...
as it will last for a very long time. However , it is not the
best choice of material IMO, where a cathode is concerned.
Especially for a high efficiency and high temperature cell
running at high current density titanium would have a vulnerability to embrittlement.

Tin/Silver 96/4 soft solder used as tinning onto copper just seemed like a very easy and inexpensive cathode
which might be convenient, or tinned onto iron should work too. I am thinking in terms also of using plumbing parts for a coaxial electrode with a pumped flow through electrolyte ....and these materials are available. The cell temperature would be easily regulated using such an arrangement and it would solve other problems. The anode would be a solid rod form in the center axis of the cylindrical assemblyand the inside walls of the tubular housing would be the cathode.

The whole matter with regards to tin nitrate is going to be a matter of experimentation by me when I can get to it.
I documented pretty well what should be looked into there. Did you ever try using ammonium carbonate or bicarbonate for the neutralization of a stannic chloride
to precipitate the stannic acid which should be useful for obtaining the nitrate.....and that not work as reported in the literature ? Or any of the other reported methods ?
It's not some emotional deal with me what chemical reactions are reported or contemplated...this is simply science to me. But with all the literature which has described tin nitrate and its derived sols...I find it unlikely
that it is all just somehow a bunch of bullshit that has been published about this for the past couple of hundred years. It would be my guess that maybe it is sensitive
reaction and isn't workable except under a narrow range of conditions which simply are being missed by folks who are dismissing it out of hand. There are other valid reactions which I have seen that are similarly sensitive,
though not impossible to duplicate.

dann2 - 7-11-2008 at 21:01

Hello Folks,

The bent cathodes look amazing. Between cathodes bending and anodes getting eaten away by parasitic currents, I think we should throw in the towel and end this thread now (and the Chlorate/Perchlorate making too).

Swede:
Just carry on using the warped Cathodes + anode. The bend is not going to have much [none] effect on the system. A bit of uneven current distribution on the anode that is not going to have any significance at all. It's not worth bothering to try to straighten them.
I would be inclined to guess (as Tim said) that it is some sort of Hydriding effect. I have used Ti Cathodes for months without any bending. The temperatures were not any higher that 70C and it was grade one. Some of the runs went from Chloride to (almost pure) Perchlorate , ie. no or very low Chloride during a part of the run.
Would perhaps Al have leached out of the alloy on the back side of the Cathodes (Current density low, and may not have been properly cathodically protected on that side) and this caused bending. (Total guess).
Tentacles has put it well. Basically you have discovered a new way to bend Ti without at boiling water temperatures. I wonder if you had to leave the whole lot here for a day or so would the Ti have warped into a circle.
I have seen pieces of Ti strip warp when there were placed in a furnace at bright Orange heat for about 1.5 hours. The strips were only supported at each end and were about 5 inches long. Trying to make Magnetite anodes...................

I have read that Ti Cathodes 'only' last for two years (that would be 24/7) in industrial set ups. The Ti would be Grade 1, 2, 3 or 4, ie. No Al (Ullman page 30). High temps. seem to help their downfall.
Hydrogen embrittlement being their downfall. It is hard to believe that the Ti would start to fall apart in the cell but it must do just that.
If using a two compartment set up, one for electrodes and one for Chemical Chlorate formation, the electrode compartment can be at a lower temp. that CCF Chamber.

It is a pity to use any other type of Cathode in an MMO set up where one of your goals is to have spotlessly clean Chlorate coming from the cell. Ti will not reduce Chlorate which is another advantage.
Iron will corrode without Chromate, so will Nickle. You could try stainless steel of course. Don't think it will corrode as long as you cell is running (Cathodically protected). Graphite can also be used but you will get some black mess.
Most if not all other materials will corrode if you get a power outage especially if you have no Chromate present.
You could consider (since you appear to have a Hector of the stuff) using MMO for the Cathode.
If you want simplicity use Platinum! (both anode and cathode). Slab shaped pieces are good!!

Silver Perchlorate has been reported to explode on its own. Since Silver Chloride is insoluble, Silver it's not going to stay in solution. If using Na in the cell it will stay at the bottom. When using K you will be more likely to have tiny amounts of Silver Chloride in the K Chlorate.
I am inclined to keep Copper and Silver miles from Chlorate/Perchlorate that is being used for Pyro stuff.

Will the intake screen that you speak of not be inclined to plug up if crystals form?
I like the description of the reactions;
The 6 electron route (pH control).
The 9 electron route (no pH control).
Sums it up well.

There is more figures for acid need per ton Sodium Chlorate in Ullman page 27 (below).
HCl (33 %, ) 35, 30, 33 and 50 KG's per ton Na Chlorate.

Ullman (page 9) also mentions keeping CD high on cathodes to decrease hypochlorite reduction. Since you are not using Dichromate this is something you may wish to think about in rev. 3! It is a somewhat minor issue I think.

Dann2

[Edited on 8-11-2008 by dann2]

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Rosco Bodine - 7-11-2008 at 21:59

Quote:

Originally posted by dann2
Hello Folks,

The bent cathodes look amazing. Between cathodes bending and anodes getting eaten away by parasitic currents, I think we should throw in the towel and end this thread now (and the Chlorate/Perchlorate making too).

Dann2

Aw shucks Dann2 knock it off with the "negative waves"

You know when there's a light at the end of the tunnel...
it's not always just the train coming.

http://www.youtube.com/watch?v=KuStsFW4EmQ

If you are concerned about the Sn/Ag 96/4 then try instead Sn/Sb 95/5 or even Sn/Pb 60/40. Some of Sn/Bi alloys might be good also. 316 stainless would probably be good too.

[Edited on 8-11-2008 by Rosco Bodine]

Swede - 9-11-2008 at 07:21

I attempted to bring one of the cathodes to red heat without ruining the plastic, but it was difficult to achieve an even heating, even with two propane torches. I don't have an oxy-acetylene rig, so I really couldn't do a proper job of it, nor could I hold it at a high heat for any length of time.

Results: A very small but percpetible straightening. What conclusions can be drawn from that, I have no idea.

A tinned copper cathode would not be hard to do. The best way would be a pot full of molten alloy. Prep a Cu pipe section with a hydrochloric or other acid dip to flux it, then dip into the pot. I'm sure it could be done by hand as well with a handful of solder wire and a propane torch.

Question for you guys on my HCl dosing setup - the dosing pump works very well, and the concept of having a simple dosing schedule, vs. a true control setup, seems to be bearing fruit. The larger the cell, the better it works, due to the inertia of the system. Example: My 25 liter cell measures, say, 7.6 pH. I turn the pump on and count 10 pulses of the diaphragm, which equals 10 ml of acid. One hour later, the pH is 7.4. In this way, I zero'd in on 6.8, and once there, it takes many hours of running for it to begin to creep back up.

In this picture, you can see the injection nozzle on the left side of the lid. It is the one with the heavier Tygon tubing, leading to a cream-colored PVDF check valve fitting.

A schedule of 4X per day, dosing 20 to 30 ml into this 25 liter system, would keep the pH between 6.4 and 7.4 with ease. All I need now is a good timer. I am trying a consumer Intermatic timer, but I am not happy with it. I don't trust it, and the thought of it sticking ON is not a good one.

Is there such a thing as a "lab-grade" timer that you can program? Anyone have any experience with such a device? If so, I'd like to hear about it. Thanks!

Rosco Bodine - 9-11-2008 at 08:42

There are different levels of solutions as process timers depending on how pretty and fancy you need or want.
Lawn sprinkler irrigation timers should be easily adaptable.
Aquarium timers are probably the closest thing to what you need as a process controller.

http://cgi.ebay.com/3-Sockets-Digital-3680W-Programmable-Tim...

As for the alternatives...

there's fancy (and expensive) top of the line stuff
http://www.omega.com/pptst/PTC-15.html

there's improvised and cheap stuff
http://www.hackersbench.com/Projects/3bucktimer/

[Edited on 9-11-2008 by Rosco Bodine]

dann2 - 9-11-2008 at 09:12

Hello Swede,

Just wondering if you are getting a good mixing in the tank with the air pumping. (I presume you are stll stirring with air).
Is there much of a difference in temperature between the top and bottom of tank?

One safety feature you could implement is to have only approx. 50ml of acid in the dosing container so that 50 ml is the max. that could be added if a fault developes.

Dann2

dann2 - 10-11-2008 at 07:29

Hello,

Though I would post this paper here.
It seems to say that you get max. erosion for a Graphite anode when pH is around neutral!!! but the set up they use is not comparable to a Chlorate cell. They have a continous flow of salt water and do not allow any Hypochlorite (let alone Chldorate) to build up in there cell.

Dann2

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Swede - 10-11-2008 at 08:28

Rosco B, thank you for those options. I didn't even think of an irrigation sprinler. Initially I thought 1 minute ON would be too much, and most consumer timers cannot do less than 1 minute, but I've seen a one minute on will dose about 12 ml of liquid, and this is working well. For a smaller system, volume-wise, you'd need either a smaller pump, weaker acid, or less than 1 minute of dosing; otherwise, I think you risk overdose of HCl.

Dann2, I cannot measure the temperature in different parts of the tank. On an older system of mine, very tall and skinny, the air mixing worked well to achieve uniform temperature. Since this one is bulkier, I can only hope it will work as well. I do have two pumps running. Aquarium pumps are pretty weak, and it's worth buying a powerful one vs a low-end unit. I have seen the tubes get clogged with crystals before. The air flow drops the temp and there's a localized crystallization that can jam it, but a strong pump, when turned up, blows the crystals out, and then I can dial it back. I'm running these at maybe 1/3.

I measured chloride today, and it is down to 114 g/l, so there's still a way to go with this run. Samples drawn for pH, when they cool, crystallize a significant mass of chlorate crystals, so there's no doubt it's working as it should. 60 amps is too low for this system, but that is all my constant current supply can do. I want to run CC to check the efficiency. The voltmeter is hovering around 4. I've got a couple of very heavy 5V supplies that would easily do 80 to 120 amps, but I'll save those for later runs. Temperature though will be a problem. The tank is PVC, not CPVC, and I am a bit concerned when the temp gets over 60 or 70. It's a struggle between materials, and a desired process temp of 80 to 90. I wonder what commercial tanks are constructed of? Ti, maybe? That would not be economical for quantities measured in Tons. I would gladly buy a case of beer for the workers if I could get a tour of a plant.

Rosco Bodine - 10-11-2008 at 09:32

There are various digital timer and analog timer controlled
relay circuits , and counter derived hybrid sorts of circuits
which can be put together as relatively simple projects
from cheap IC's using point to point handwiring on perf board. The 555 timer IC is an example of a single chip
solution which works something like the delay windshield wiper circuit in a car .....where you can set the interval
for cycling and the duration of the "on time" between cycles as well, using a couple of potentiometers. I have thrown together a few of these little timer projects as
"process controllers" and they do the job if you can't find something already built. Years ago there wasn't so much cheap digital programmable ready to use timers, so we improvised, even before the 555 came out, using simple transistor timed relays as process cycle timers.

You might want to look at "band heaters" and some metallic sections of piping and fittings, with some thermostat controls, if you go with a pumped system,
you can then control where crystallization occurs in
a way that is parallel to what is done for the large scale industrial cells.

A thermally controlled current limiter on the cell itself would be a good idea too to prevent things from getting out of hand .

Swede - 11-11-2008 at 08:12

I've really been absorbing a lot of great info from you guys - I appreciate your expertise.

I've been wondering how they do it commercially. I understand it's an open system... the liquor flows in, get's processed in several cells, then it flows out for collection. I know they use sodium salts, and there is NO crystallization until they want it to happen. The vast bulk is retained as sodium chlorate for the bleaching of paper and wood pulp, and some of it is converted to potassium and other chlorates.

I'm picturing a giant vat of saturated sodium chlorate + byproducts... how do they extract the sodium chlorate from the liquor, and importantly, how do they clean it up?

Using potassium salts is problematic. Those crystals tenaciously form everywhere there is the slightest temperature gradient. I really, really need to think about using sodium instead, and execute a double decomp to obtain the potassium product.

I have some very basic questrions... Given say 4 liters of sodium chlorate laden cell liquor, which will be mixed with chloride, chlorite, etc ions, how does one know the correct quantity of KCl to add? If you can determine quantitatively the chlorate ion concentration, then it'd be easy, but determining chlorate concentration is not a simple thing.

After adding the KCl (hot, saturated solution, I assume) the KCl falls out. What remains in the solution is a mix of sodium, any excess potassium, and all the chlorinated ionic species, a real hash. Does this liquor then get recharged with chloride, and resused, despite the possibility of potassium in the mix?

My own lack of understanding of the metathesis process, and the ease and cleanliness, is why I use potassium chloride at the beginning, but it has huge drawbacks that I need to overcome. Frankly I do not thing a pumping/recirculating system is possible using potassium chloride... it MUST be sodium. Thoughts?

This 25 liter cell has had 50 amps through it since Saturday. Chloride levels started at 125 g/l and are now down to 95 g/l, for a yield (so far) of 30 * 25 = 750 grams of chloride converted, meaning there is 2,627 grams of potassium chlorate in there. I'll probably run it to 60 grams per liter, so another day or two at least.

watson.fawkes - 11-11-2008 at 10:34

Quote:

Originally posted by Rosco Bodine
There are various digital timer and analog timer controlled
relay circuits , and counter derived hybrid sorts of circuits
which can be put together as relatively simple projects
from cheap IC's using point to point handwiring on perf board.

These days, the single best solution to this class of problems is the Arduino microcontroller. It's got a very straighforward hardware interface and is integrated with a handy programming system (called Processing). I've done software for a long time (including embedded systems) and this is easily the best entry point I've ever seen.

More generally, any micro-scale industrial process, in the present example, chlorate manufacture, is going to need an electronic sensor and control system. I consider it just a cost of entry. Sure, it's possible to do the reactions without such control, but if you're thinking about manufacturing proper, even at a small scale, this is definitely the right way to go, for safety as well as efficiency. Arduino is an open-source hardware project. It's caught fire in the DIY crowd and lots of accessories are available for it. New and assembled, it's about 40 USD. http://www.arduino.cc/

These days when I consider a project, I start by counting sensors.

12AX7 - 11-11-2008 at 10:51

Quote:

Originally posted by Swede
I have some very basic questrions... Given say 4 liters of sodium chlorate laden cell liquor, which will be mixed with chloride, chlorite, etc ions, how does one know the correct quantity of KCl to add? If you can determine quantitatively the chlorate ion concentration, then it'd be easy, but determining chlorate concentration is not a simple thing.

Ah, but it is. Take a known volume of solution, add an excess of concentrated KCl solution and wait for it to precipitate. Filter, wash, dry and weigh the precipitate (or guess by experience). Now add enough KCl solution to drop 50 to 75% of the chlorate in solution. What remains in solution will reduce the solubility of potassium a bit. Let temperature drop to room temp (or below, if possible) and you'll have 99% or so yield based on potassium.

There's nothing wrong with sodium chlorate, either. It's really easy to handle. Doesn't even seem too hygroscopic in bulk, I've got pounds of it sitting open in the basement air and it didn't liquify at all during the summer. (The exposed sodium perchlorate, on the other hand, remained quite fluid.)

Tim

tentacles - 11-11-2008 at 16:28

I broke out the LD plating gear today.. Started with approx 300g/l Pb(NO3)2, one liter cell (tall form beaker) on a stir plate at 55C, about 3g/l Cu(NO3)2 and with residual NaF from the previous experiments. Plated at ~30ma/cm^2. Stirred, and there was still a little silica dust in solution. For cathodes, I took pieces of PCB (1/64, single sided) and ran brass threaded rod through two places at the top for the cathode assembly. Washed the MMO anode with hypochlorite/NaOH/percarbonate solution (aka diversol beer equipment cleanser).

Plating setup on my super messy bench
http://pyrobin.com/files/sdc10030.jpg

MMO compared to PbO2-MMO
http://pyrobin.com/files/sdc10033.jpg

Closeup
http://pyrobin.com/files/sdc10036.jpg

Edit: So, is pH control required with perchlorate cells? I just so happen to have almost 3lbs of commercial K chlorate and may give converting that a try with this LD anode.

Another edit:
38.5g of PbO2 deposited, 1.75mm anode thickness, 1.21mm original thickness. Coating appears adherent, a little fingernail probing indicates it's not going to flake off the MMO as easily as the Ti strap that got coated. Coating has a nice uniform texture, some pitting/bubbling but we expected that. The edges of the diamonds seem to have more pitting than the faces, not sure why on this. The bubbling is something that I believe is caused by low cell pH. I didn't add PbO at any point and it finished <1 again. Added 40g of PbO to the cell, not all of which dissolved, probably right at 25-27g, just enough to replace what plated out.

[Edited on 11-11-2008 by tentacles]

dann2 - 11-11-2008 at 17:09

Quote:

Originally posted by Swede
I'm picturing a giant vat of saturated sodium chlorate + byproducts... how do they extract the sodium chlorate from the liquor, and importantly, how do they clean it up?

After adding the KCl (hot, saturated solution, I assume) the KCl falls out. What remains in the solution is a mix of sodium, any excess potassium, and all the chlorinated ionic species, a real hash. Does this liquor then get recharged with chloride, and resused, despite the possibility of potassium in the mix?

My own lack of understanding of the metathesis process, and the ease and cleanliness, is why I use potassium chloride at the beginning, but it has huge drawbacks that I need to overcome. Frankly I do not thing a pumping/recirculating system is possible using potassium chloride... it MUST be sodium. Thoughts?

This 25 liter cell has had 50 amps through it since Saturday. Chloride levels started at 125 g/l and are now down to 95 g/l, for a yield (so far) of 30 * 25 = 750 grams of chloride converted, meaning there is 2,627 grams of potassium chlorate in there. I'll probably run it to 60 grams per liter, so another day or two at least.

If you want to use the K Chlorate for pyro stuff where colour (when burning) is important then stick with your K salts only set up. It is very difficult to get rid off all Na contamination. Just a little Na will pollute with Na orange colour.

Industry uses cyrstallizers. They are a subject in themselves.
See this board for some stuff on Ammonium Perchlorate from Sodium Perchlorate and it will give you an idea of how they do it. Ammonium Perchlorate is made in high tonnage quantities.
Don't know of any plant that makes K Chlorate directly from Na Chlorate (solution) coming directly from Na Chlorate cell.
There is some (possibly useful possibly not) info here if you like to go library digging:
_______________
R. Bauer, 'Potassium Chlorate Manufacture',
paper
presented at the Electrochemical Society Meeting,
Boston, May 1968.
________________

Ammonium Perchlorate manufacture:
http://www.sciencemadness.org/talk/viewthread.php?tid=9425&a...
see posts of 6-11-07

If you have a solution of Sodium Chlorate and you want to convert to K Chlorate. Boil off some water untill a cooled sample starts to give a ppt. (of Sodium Salts).
Stop boiling off water and add some water so that you get no ppt on cooling.
Cool the whole lot of Na solution and start adding cold KCl saturated solution untill you are getting no more ppt. You can add some, let ppt settle, add more etc so that you can see when ppt has stopped.
Filter and use the mother liquor in your cell.
Thats really the best you can do in a batch system.

If K Chlorate coming out of solution and plugging of pipes/pumps is a problem, use less saturated solutions in your cell.
You should look at the part of your system where you extract the product as seperate from the manufacturing end. If you keep the manufacturing end hot, then liquid going into a cold (crystallization stage) should give you product without any problems.
You need more chambers that two IMHO. An electrode chamber,
a Chemical Chlorate formation chamber (hot), then the crystallizer (cold). You are going to have to recharge with more KCl. I suggest another chamber or use the Electrode chamber. No Chlorate (or very little) will be formed in the elctrode chamber, all or most will form in the hot CCF chamber and hopefully stay in solution untill it reaches your crystallizer.
If you go over to Na and keep adding NaCl to the manufacturing end untill there is enough Na Chlorate in the system for it to start to crystallize when liquid is cooled (as you are going to HAVE to do if you are wanting a system operating like you desired at the very start), then pipes plugging up etc will still be a problem if you have not got enough chambers and temperatures to suit.

Most all of the diagrams of cell set ups (patents, articles etc) that you have seen have not been showing you the crystallizer. Just the Electrode chamber and large Chemical Chlorate formation chamber (or whatever you like to call it).

There is absolutely nothing wrong with the set up you have. Single chamber.
If you like you could place a cloth in it (or perhaps plastic filter material) so that all you have to do is lift it out and give it a squeeze to get close-to-usable product.
Rince once or twice by 'possing' the cloth + Chlorate in cold water.
Dissolve the solid in clean boiling water, boil some more to get rid of hypochlorites, and recrystallize for near perfect product.

EDIT:
Hello Tentacles,

It is great to see ye old Lead Dioxide coating parafanellia being wheeled out and pressed into action. New ground being broken eh!
The photO's you uploaded seem to be huge as I unable to download (slow connection).

There is a Diamond Shamrock Patent on coating MMO with LD, the only one I know off. Iit is attached.

Hope it is a success. Would suggest a much heavier coat but perhaps you are just seen how it goes.
Careful you magnetic stirres does not make a hole in the bottom of container (or is it glass).

Dann2

[Edited on 12-11-2008 by dann2]

Attachment: United States Patent 4444642.mht (74kB)
This file has been downloaded 1210 times

tentacles - 11-11-2008 at 18:57

dann: It finally got cold here, and it's rather unpleasant to be outside.. most of the time it's windy + subzero.

Mostly this coating session is just to test the process, if it works then we'll see about thicker, chunkier coatings - if needed. Your test went from chloride to perc, so the wear was understandably very high.

Have you seen Swede's blog posting on chlorate testing? He's refined the NPAA method considerably, to say the least.

Noone wants to comment on maintaining pH in a perchlorate cell? I can't imagine that no chlorine evolves, but if we add HCl, you're just bringing chloride into the solution..

[Edited on 11-11-2008 by tentacles]

dann2 - 11-11-2008 at 19:16

The once I ran a Perchlorate cell with pH monitoring (with LD Anode), the pH was inclined to go low so I added NaOH.
I think I read somewhere that Perchloric acid is used in industry if pH goes high??
(Perchloric acid not available in the hardware stores around here!)
It is not too hard to make Perchloric acid from Na Perk. + HCl.
You would only need small amounts.

I know little or nothing about chemistry of Perchlorate cells. Mixing of Anode and Cathode products is not required AFAIK.
The pH control is more to do with anode wear? or process equipment/materials of construction corrosion concerns? I don't think pH effects CE. Many articles state that CE is independent of pH.

Dann2

[Edited on 12-11-2008 by dann2]

Xenoid - 11-11-2008 at 19:26

Quote:

Originally posted by tentacles

Noone wants to comment on maintaining pH in a perchlorate cell? I can't imagine that no chlorine evolves, but if we add HCl, you're just bringing chloride into the solution..

We seem to be going around in circles again ....... !

pH is 6.6 to 6.8 in commercial operations, mainly for current efficiency reasons.

See my post on page 5 of this thread;

http://www.sciencemadness.org/talk/viewthread.php?tid=5050&a...

tentacles - 11-11-2008 at 19:47

Xenoid: I must not have caught that in your posting, that wasn't even very long ago... So then, it's ideal for us - just dump current in, maybe even add a touch of KOH to ensure a high pH. The LD plating isn't all that difficult to achieve, but the longer it lasts the better, certainly.

Xenoid - 11-11-2008 at 20:06

Quote:

Originally posted by tentacles
maybe even add a touch of KOH to ensure a high pH.

Well, no, I wouldn't do that.

Remember MMO coatings do not like high pH, if you have pinholes etc. in your LDO coating you may have problems with the MMO coating degrading beneath the LDO and possibly causing it to flake off. What I meant was that the high pH of an uncontrolled perchlorate cell shouldn't be to deleterious for the LDO. Anyway, go ahead and try it, I'm interested in seeing what happens. I might even try plating an Mn or Co oxide treated Ti anode.

Edit:
Tentacles - how did you estimate the surface area of that Ti mesh to come up with your 30mA/cm^2 plating current - or is that based on just the overall size of the electrode?

[Edited on 11-11-2008 by Xenoid]

Swede - 12-11-2008 at 06:41

Tentacles, that LD plate job looks nice! And I thought MY bench was messy!

I noticed you used cathodes to provide coverage for both sides... would a copper container acting as a cathode make a good plating cell?

The MMO that Tentacles plated is a "special" MMO. Long story, short version... I started my blog on the APC forum and was contacted by a nice gentleman in Australia, an amateur Pyro, but a career pool chlorinator cell expert. One of the problems that they were having with pool MMO was idiot end users who turn their systems on full with no salt, don't clean prefilters, essentially create an environment that is not good for an MMO mesh anode. I suspect the industry as a whole, early on, were having bad warantee and longevity issues.

From my own research on the chlorate industry, vs. pool chlorination, the anodes made for chlorate production have been perfected for many years. The users run the anodes in strictly controlled conditions. In contrast, the pool chlorinator research continued, the challenge being durability, bipolar operation, and the goal was an MMO coating that simply will not fail, under any reasonable circumstance.

The MMO in question was designed for pools. My friend in Australia has attempted to wreck this material with some extreme experiments; boiling a chloride system dry, attempting to brute-force perchlorate from chloride, etc. and the mesh has stood up. He hooked me up with his supplier, and I bought a sheet. Any failure mode we see will not be the underlying material... hopefully!

Thanks guys for the explanation of metathesis. I am getting dumb in my old age... It would make sense to use a small sample, and quantitatively determine the chlorate content by weighing the crystallized product after conversion, then simply scaling up the procedure for the remainder of the cell.

Question of the day: The "10% Rule." Traditionally, chlorate cells are halted when the chloride concentration reaches 10% by weight, 100g/l chloride ion. There are two reasons, I believe, why this should be. The first is inefficiency, the cost of the electricity, which will undoubtedly go up as chloride is depleted. The second is the wear and abuse the anode faces as chloride concentration drops.

If (and it's a big if) this MMO is as tough as I believe it to be, I am not overly concerned about wear or erosion, nor am I too concerned about the electricity. I AM interested in maximizing yield per run, within reason. Given that a potassium-salted cell starts at, best case, only 14% chloride, I'm having a tough time visualizing the cell struggling at 10%. That's only 28% of the chloride converted. I can visualize a cell beginning to gag a bit when 60 to 75% of the chloride has been converted to chlorate.

Is my logic flawed?

I've been testing chloride concentration periodically throughout this run. Since the system is at a constant 50 amps, it might be interesting to plot chloride conversion vs. time, and look at the shape of the curve. That will help visualize what is happening with regards to the rate and efficiency of the conversion.

In retrospect, I wish I had executed more chloride concentration data points, but the Hach strips are not cheap and I'm being miserly with them.

[Edited on 12-11-2008 by Swede]

tentacles - 12-11-2008 at 10:54

Xenoid: I don't have any data on the surface area ratio of this mesh, so I took the flat area of one side and multiplied by 1.5 and called it a number. It's probably in the ballpark, and if I'm a bit low or a bit high, the plating should still have been near the sweet spot for beta-LD.

Swede: I don't see any reason why you can't dissolve the KCl at closer to cell operating temperature - at 40C, you can get about 194g/l chloride ion into solution. That's not unreasonable, I think - just bring the electrolyte up to say 60C before you pour it in the cell, to warm up the container nicely. At room temp you can get about 165g/l chloride ion in there, so it's not a huge difference, but it will certainly help. I think your 14% chloride is perhaps derived from the 0C solubility? Or my math could be wrong in some significant way.

Swede - 12-11-2008 at 13:09

Tentacles, my solubility chart shows 350 grams per liter at 25 C. Chlorine is 47.5% by weight, so that would equal 166 g/l chloride, or 16.6% so I think our math is correct. The odd thing is that even when I saturate boiling water, then let it cool down, and the excess crystallizes off, it seems to measure 14 to 15% at 25C and no more.

Your point about putting the liquor in at 50 or 60, and having it carry the appropriate chloride with it, is a good one. But it can be tricky to do with 5 to 10 gallons... got to heat up the liquor, get the extra KCl dissolved, then get it to operating temp before any KCl falls out as xtals. Although I suppose if they did, they'd redissolve as the temp goes up, especially with some agitation available.

Or, execute a chloride ion replenishment rig!

Speaking of solubilities, here's a handy chart with many compounds of interest...

http://www.saskschools.ca/curr_content/chem30_05/4_solutions/solution3_1.htm

I've got a few improvements in mind for the next run, eespecially in the realm of agitation. Simply sticking in a 1/4" PTFE tube and attaching an aquarium air pump isn't hacking it. The tubes jam with crystals near the end of the run. I'm thinking a vertical, wide-bore PVC pipe, cross drilled, and open at the bottom, suspended from the lid, located close to the electrodes where the heat would be greatest. No way that thing would clog.

[Edited on 12-11-2008 by Swede]

[Edited on 12-11-2008 by Swede]

dann2 - 12-11-2008 at 15:01

Hello Folks,

The only thing I can add to the 100g per liter lower limit of Chloride in cells is:
There is a risk that Perchlorate may start to form (not a problem with MMO). This is considered a contaminant.
This amount of Chloride, together with the high conc. of Chlorate, may best suit the crystallizer end of of the process too.

You can probably go way below the '100g/l Chloride rule' with MMO if you so wish. Industry will be very concerned, as you
said, about voltage rises, etc which will not bother us.

It would be alot of work but if you were to set up a row of small opentop glass containers containing a range of
concentrations of Chloride. Into each you would place a drop of known concentration of Silver Nitrate and record
(with a photo or video) what the immediate ppt of white Silver Chloride looked like. This would give you (us all) a
permanent way to do a quick and dirty Chloride titration.

There is a useful patent below showing graphs and system for commercial K Chlorate production.
The graphs may be useful. They are not in % though which is what we would like.
Note the temperature of their cell is 75C.

@Tentacles.
The picture below shows your LD'ed MMO. The indents are caused by bubbles AFAIK. Are there as many
or any bubble indents on the top sides of the cross members of mesh (this picture is taken from the bottom
I presume).
A good shake of MMO now and again when plating would help to get rid of bubbles.
There is also a stealth bomber parked on the MMO close to the top lhs..............

For circulation, (of Chlorate cell) place a large dia. (suspend form lid or where ever) pipe over the electrodes going down to close to the bottom of the cell. The top ot the pipe needs to be below the surface of the electrolyte. The H2 will circulate the electrolyte around using this pipe.

Dann2

[Edited on 12-11-2008 by dann2]

LD_MMO_D.jpg - 34kB

dann2 - 12-11-2008 at 15:05

Patent No. 4339312

Continous process for conversion of Potassium Chloride to Chlorate

Attachment: US4339312.pdf (294kB)
This file has been downloaded 944 times

tentacles - 12-11-2008 at 15:39

dann: I think the bomber there is one of those government micro-spyplanes. Or a bit of fuzz from the paper towel I gently dried it with. Alternatively, could just be a bit of PbO trapped in the PbO2.

Swede - 12-11-2008 at 16:35

For fun, I've began plotting chloride concentration over time in a constant current setup. I'm using Hach chloride strips, diluted 50:1, using a good pipette and distilled water. The Hach strips have performed admirably for quite a while now, and I trust their accuracy.

Unfortunately, early in the run, I skipped too many opportunities to plot, mainly because it is a bit of a PITA, and the strips are about a buck apiece. I guess I'm cheap.

The starting concentration is low because I used the liquor left over from the aborted circulating run. I simply tossed it back into the monolithic vat and applied the juice.

My plots so far: Time (hours) vs chloride (g/l), 50 amps, constant current

0 124.2
64.5 114.4
103 99
119 95
126 92.5

If you plot these few points, the curve is somewhat flat, then begins to nosedive. The "nosedive" portion, where I'm at right now, is roughly linear, but it shows signs of flattening out. Something like this:

If I were to venture a guess, the upper portion of the curve is where I was refining pH control, and the correct ionic species were being created. The chloride level begins to dive in the heart of the process, where everything is close to optimum. I suspect the curve will flatten as chloride drops and inefficiency takes over a bit. The flatness of the curve, as I continue to take data, will determine when I will pull the plug on this run.

dann2 - 12-11-2008 at 16:57

Hello Swede,

Great piece of data from MMO run. The strips are definitely the biz! (price ignored).
What temperature has the cell stabilized at?
Perhaps MMO is not capable of taking the Chloride concentration low. The graph will soon be straight.

Dann2

tentacles - 12-11-2008 at 21:57

Something I meant to mention earlier, regarding the air lines clogging.. Perhaps running a length of it inside the chamber down to the bottom and back up a bit might help? This would preheat the air a tad and offer cooler places in the cell where chlorate might precipitate. Could be that the PTFE tubing won't conduct enough heat, and air doesn't have much heat capacity anyways.

Swede - 13-11-2008 at 06:57

@Dann2 - I wish I could continue with this run in particular, measuring chloride, and taking it very low, but I am having some real difficulty maintaining circulation. The PTFE tubing is clogging every 2 hours or so, and the only way to clear it is to take compressed air from a large shop compressor, and blow 20 to 30 PSI through the tube. At night, while I sleep, the tube is jammed for 6 hours at least, and I'm not comfortable running 50 amps without some circulation. I've got some ideas for the next run.

What I'd like to do is a run or two with a very small, clear cell, maybe 2 liters, 10 - 15 amps, with this particular anode material, and gather some serious data on pH, voltage, chloride concentration, etc. With a small cell, I can conclude the run quickly, get good data, which should scale well.

Timers: Looking at irrigation timers yesterday, many of them have a master relay port, designed to actuate a 24V pump relay. This means any time the timer is ON, the relay port is energized. That would be the mechanism to turn on the dosing pump, rather than one of the branch circuits.

@Tentacles: That is a good thought on the PTFE tube. One other option might be to coil the tube around a form, apply enough heat to set the tubing so that it retains the coiled shape, and that would create a lengthy path for the air to preheat a bit before it exhausts.

My sample port + valve is completely jammed as well:

I should have expected this, given how low on the cell it was placed. What I can do is create a curved standpipe that will pull liquor from the top of the cell, route it to the existing port, and hopefully that will not jam as badly as this one. The location of the jam is the threaded fitting installed in the wall of the cell; again, temperature gradients cause a premature crystallization in all the areas that are a bit cooler than the heart of the cell.

I turned the current down to 3 amps this morning. The system is cooling as I sit here, and it should be ambient in a few hours. I'll harvest the batch, and should get some interesting pics.

A plastic sieve used by the bio-diesel people, set on a 5 gallon pail, will make a handy crystal strainer:

Based upon my chloride ion measurements, I am estimating the yield at 2.5 kg. Could be better, but the starting liquor was weak.

watson.fawkes - 13-11-2008 at 09:11

Quote:

Originally posted by dann2
The picture below shows your LD'ed MMO. The indents are caused by bubbles AFAIK. Are there as many
or any bubble indents on the top sides of the cross members of mesh (this picture is taken from the bottom
I presume).
A good shake of MMO now and again when plating would help to get rid of bubbles.

A pulsed power system might help with bubble formation as well. Rather than using DC power, a pulse train is used. The simplest kind of pulse train is just some chopped duty cycle, switching the DC on and off. The reason this is effective is that it changes the ionic balance near the electrode, as well as allowing deadsorbtion of ionic species that are held only by electrostatic forces. Constant DC creates a depletion zone in the electrolyte near the electrode, depleted of the species that are plating-on. Pulsing the voltage can allow quicker regeneration of this zone; regeneration is diffusion limited. Plating rates can actually be higher at the same DC level. Fancier versions incorporate small reverse-polarity pulses to do more aggressive modifications of the depletion area.

This can get rid of bubbles by rejecting the gas forming species at the ion level before they have time to nucleate and form a bubble.

watson.fawkes - 13-11-2008 at 09:18

Quote:

Originally posted by Swede
I wish I could continue with this run in particular, measuring chloride, and taking it very low, but I am having some real difficulty maintaining circulation.

Have you consider mechanical stirring? For a cell of your size (pretty small), glass is still mechanically sound enough to be used as an axle. Melt on some paddles, pass the axle through a gasket at the top, and you're good to go. You don't need borosilicate for this application (although it's fine), because there are no large temperature gradients around. Soda-lime glass can be worked with propane/air. Glass isn't necessary, of course, anything that resists the oxidizing environment is sufficient.

Swede - 13-11-2008 at 10:34

Quote:

Originally posted by watson.fawkes
Have you consider mechanical stirring? For a cell of your size (pretty small), glass is still mechanically sound enough to be used as an axle. Melt on some paddles, pass the axle through a gasket at the top, and you're good to go. You don't need borosilicate for this application (although it's fine), because there are no large temperature gradients around. Soda-lime glass can be worked with propane/air. Glass isn't necessary, of course, anything that resists the oxidizing environment is sufficient.

watson.fawkes, I concur with your assessment. I popped the lid to T-Cell II to expedite cooling, and everything, materials-wise, looks good. There is a nice layer of fat crystals in the bottom. But the PTFE tubes were hopelessly jammed. The CPVC acid diffusion down-tube was clear, including the side-holes, so something similar would be the way to go with air, at least. Even if the side-holes jammed, I don't think it'd be physically possible to clog the bottom of the pipe.

But back to mechanical stirring - the big benefit is lack of spatter. With my acrylic tower, where I could see what was going on, the air circulation did work well, dispursing evolved electrode gases evenly, and keeping the temperature even as well, but as the bubbles broke the surface, they tossed liquor all along the seam. Even with careful attention to sealing, this creates a serious salt creep that is very difficult to halt. An additional negative - by introducing air, you are pressurizing the vessel a bit, exacerbating the problem.

A PTFE turning would make an ideal gasket for a mechanical stirrer, and a gearmotor, at perhaps 60 to 120 RPM, rotating paddles near the electrodes, would do a fine job.

The grey PVC plastic was a bit bleached but otherwise sound. The sight glass, which I was so proud of, will have to be scrapped and replaced with something having a much larger bore. I've got a ton of mental notes on improving this thing that I am going to incorporate into the next run. That's one of the nice things about (C)PVC... it solvent welds, and can be modified easily.

With the top off, the cooling should accelerate, then it's time to harvest the crop. I've got some cool pics I hope you guys will enjoy. I've also got some chems on the way, in an attempt to replicate Tentacles plate job.

[Edited on 13-11-2008 by Swede]

watson.fawkes - 13-11-2008 at 12:27

Quote:

Originally posted by Swede
A PTFE turning would make an ideal gasket for a mechanical stirrer, and a gearmotor, at perhaps 60 to 120 RPM, rotating paddles near the electrodes, would do a fine job. [...] That's one of the nice things about (C)PVC... it solvent welds, and can be modified easily.

I might suggest, for the sake of easier rework, to turn your bushing to the O.D. of a standard pipe side and thread one end with male pipe threads. Then glue in a female pipe thread fitting as the orifice. It would make reconfiguration that much faster, at the cost of slightly greater up-front fabrication time.

In that vein, you could also provide a quick mount for a stirring motor. The brass inserts that screw into wood and provide a captured machine thread can also be used in practice. Use a small-diameter, thick-walled pipe. Drill slightly undersize, heat up the insert on the end of a mandrel/bolt, and screw it right in while hot. Solvent weld the pipe section where you want it. The pipe acts as an integral stand-off. Mount your motor to a plate.

tentacles - 13-11-2008 at 15:44

One alternative to this machining time (although I know you have PTFE barstock, Swede) would be to machine a bore and use PTFE o-rings as the seal. I'm not sure what would be appropriate to lubricate with, however, but some sort of lubricant would definitely make the assembly last longer and seal better. It needs to be stiff enough, or have a second bearing surface, to keep the stirrer from flopping all over.

dann2 - 13-11-2008 at 16:31

Hello Folks,

I still think my (fantasticly simple) circulation system is all that is required, perhaps not. It would not be capable of stirring up the layer of crystals on the bottom which would sit there together with trapped fluid in their midst.
You won't beat it on price though!

A submersible pump would do the job too.
This one does 14 liter per minute and is cheap. It may not like the hot salty electrolyte.
http://cgi.ebay.co.uk/caravan-Submersible-water-pump-12-volt...

This might do:
http://cgi.ebay.com/12v-Submersible-Pump-Salt-Water-Diesel-K...

Or this outside if the salts don't plug the pipes.
http://cgi.ebay.com/IWAKI-CMD-228-PUMP-SALT-WATER-FISH-TANK-...

It's all money.

The motor + shaft + paddle +bearing/seal seems complicated and liable to wear and will generally give trouble in the medium to long term.
I guess you could have it on (another!) a timer so that it does not run 24/7.

Dann2

KISS STIRRING.GIF - 11kB

Swede - 13-11-2008 at 17:11

Dann2, I think the circulation that your thermal (and H2) forces created by the setup in your drawing might be more than adequate - it'd be well worth a try, perhaps on a small scale at first. The gasses and heat generated at 50 to 100 amps are not trivial, and if encased in a relatively narrow pipe, I suspect the flow through the pipe might be measured at several liters per hour. There's a lot to be said for KISS. I am learning that lesson well with my latest iteration.

About the only thing I'd do different from your drawing would be to seal the bottom of the pipe, and drill inlet holes in the sides of the pipe at the base, around the perimeter... this might help keep the crystals at the bottom from being drawn up into the pipe.

I harvested a giant batch (for me) from my latest rig. More details than you probably want right here....

The crystal mass at the bottom was both thick and very firm. I had to beat it into manageable chunks with a plastic rod. Oddly, it had two distinct layers:

The entire mass went into a bucket sieve for washing:

I've learned a lot from this run, and have some distinct improvements in mind for the next. I'm also more than ready to move onto perchlorate production. Thank you all again for your expertise, and great suggestions.

dann2 - 14-11-2008 at 18:01

Hello,

Going back to the 'min 100 grams per liter rule' for Chloride, I think this is from the days of Graphite (and possible Pt too), where going below this give non economic Graphite wear.
You could not run cells at higher temp. and low Cl- concentrations.
With DSA things seemed to have changed.
The attached patent is worth reading if time permits.

It states:
With the advent of DSA it has become possible to operate
cells up to boilig point and down to Chloride concs. of 30grams per liter and 700 grams per liter Chlorate.
You can then get a crop of Chlorate directly be evaporation and cooling.
With Graphite you would take a crop of Sodium Chloride out first then a small amount of Chlorate.

Two other patents showing phase diagrams for Chlorate removal are:
US3511619
US3690845

Dann2

Attachment: US3883406 Na Chlorate Phase.pdf (234kB)
This file has been downloaded 913 times

Splinky - 14-11-2008 at 18:58

Hi,
I've been getting reasonable yields with my little six amp battery charger power supply, enough for my purposes. However, I've been looking at my 55 amp welder and I can't help but wonder if it would be suited for running a cell for at least ten hours at a time.

I could set up a cooled cell and pump current into it for a day and get plenty of chlorate, I'm just concerned about letting a welder run through water for that long. Could a welder handle that kind of running time?

watson.fawkes - 14-11-2008 at 20:22

Quote:

Originally posted by Splinky
I could set up a cooled cell and pump current into it for a day and get plenty of chlorate, I'm just concerned about letting a welder run through water for that long. Could a welder handle that kind of running time?

It depends on the duty cycle rating. Most small welders are rated only 40%-50% duty cycle. Run one at full power for too long, it will fail. If you're lucky, it will only fail temporarily (resettable overload or breaker).

Note that this isn't a 50% power rating. In some modern inverter welders, internally dissipated power is roughly proportional to the number of times the internal semiconductor switches turn on and off, which isn't necessarily much less at half power than full. Your mileage will vary.

Old big-iron welders, though, exhibit primarily internal resistive loss. You can run those at lower power levels, derated by their duty cycle, and generally be just fine.

dann2 - 15-11-2008 at 03:59

Splinky:

Is there a name plate or a instruction book with the welder. It may mention duty cycle etc.
Will your anode take 50 amps?
Dann2

Splinky - 15-11-2008 at 08:36

The welder has a duty cycle of 10% at 55 amps, so I guess I'll just stick with my battery charger.

I've used a tube made from a cut up and narrowed 2 liter soda bottle for a while as a tube in a circulation system like the dann2 posted earlier, and it's worked pretty well. The usual drastic temperature gradient on the bottom of the cell disappeared when I started using it. If I were to use a smaller bottle, cut the top off, drill lots of holes in the bottom, and fill a few inches of it with crushed/whole KCl nuggets, would it provide a reasonably reliable source of constant saturation with chloride? I'm eying up a bottle I have here that would fit the bill perfectly if it works.

12AX7 - 15-11-2008 at 10:35

No, I'm sure it would clog with KClO3.

You might get away with that with NaCl, but rock salt is also too much obstruction. You want hot liquor falling on it anyway; if you make a rough inverse-U shape so that some of the convection falls over a salt bed, that might work. The key feature is hot solution.

Everything clogs with KClO3 anyway, as has been proven above. It's not a good substrate, and the hassle between negotiating KClO3 buildups versus NaClO3-KClO3 conversion is minimal. Also, NaClO3 is far better suited for perchlorate conversion.

Tim

Perchlorate from MMO Anodes

jpsmith123 - 15-11-2008 at 13:43

Well I see this thread seems to have some new life!

I recently came across this guy's page where the author claims to have made some perchlorate from a MMO anode. (Although in the comments section he says that the anode was "abused" in the process).

dann2 - 15-11-2008 at 15:56

Hello J.P.,

Welcome back.

I think the anode you are referring to is Pt coated Ti, not MMO or am I reading in the wrong place.

The new way forward for the LD anode is using the Ti + MMO substrate, as per Tentacles pioneering efforts.

One good reason for sticking to K salts as opposed to going the Na route in Chlorate/Perchlorate making is the fact that it is very difficult to eliminate all Na out of the final product where it will dilute colours that you may be creating if using stuff for Pryo displays etc. Sodium is cursed by those who are looking for very pure colours.
Some have suggested using Lithium salts as a way in. This avoids the solubility issues if going all the way to Perchlorate. The contamination by Li ion is not as strong as Na
Orange and therefor not such an issue. Li salts are very soluble. Li gives light pink colour, I think?

Dann2

tentacles - 15-11-2008 at 19:27

I honestly wouldn't believe a word of that Alan Yates' site - this is the guy who recommends using sulfur to put out Mg fires.. Anyone who has actually tried this, quickly realizes that the sulfur makes the Mg burn explosively... and it also ruins the batch of Mg-Al alloy if you put any in there..

I've heard of MMO anodes making perchlorate, but the problems are efficiency (low) and wear (high).

12AX7 - 15-11-2008 at 20:49

Odd, Fleaker has spoken of melting Mg (pure Mg) with SO2 cover gas (produced by burning S added to the crucible). Maybe it doesn't work once it's burning.

Curiously, I haven't had any problem with sodium. I've sold a number of pounds of purified KClO3 and haven't heard a complaint; my own tests show its flame color is reasonably purple. This stock was produced by metathesis (from hot liquor, then cooling), washing the crystals, then recrystallizing once more, washing and drying.

Tim

jpsmith123 - 15-11-2008 at 21:05

Hi Dann2,

Counting down from the top of the page, to me the ninth picture seems to show a mesh type MMO anode.

@Tentacles: I would guess that the efficiency and wear are at least somewhat process dependent. AFAIK he doesn't say what kind of process he was using; i.e., whether it was a one-shot chloride-to-perchlorate batch process (which I think would be the most stressful and inefficient) or whether he started with chlorate and tried to maintain a concentrated chlorate solution.

As far as efficiency goes, I wonder if the MMO anode would fare any better if instead of running continuous DC current, the supply was pulsed, running the MMO anode at a higher than "normal" current density, say two or three times higher, but adjusting the duty cycle for the same average.

Splinky - 15-11-2008 at 22:58

Well, it said one day of abuse. I'd guess from that it was a straight run, if at all. He probably meant chlorate and typed perchlorate.

It would seem to me that the pulsed current idea would end up putting more stress on the anode with no real gain of any sort.

jpsmith123 - 16-11-2008 at 06:24

Quote:

Originally posted by Splinky
Well, it said one day of abuse. I'd guess from that it was a straight run, if at all. He probably meant chlorate and typed perchlorate.

Apparently you're talking about the "caption" for the 8th picture which reads:

"Potassium Chlorate yield from 1 day of gross abuse of a computer PSU and commercial MMO electrodes. Passive cooling with a large tank of water (the bathtub) made this possible. It was especially hard on the electrodes and extremely inefficient as I was running the cell from the 12 volt rail through a nichrome rheostat that was getting plenty toasty."

With reference to the picture and the narrative, I'm quite sure I understand the sense in which he uses the phrase "gross abuse" in this instance. And I'm quite sure he says "chlorate" and that he means "chlorate".

Then, a little later, with reference to the 12th picture, he states: "[...] By abusing the MMO electrode I got a fair Perchlorate yield from this setup in future runs. [...]"

Here he said "perchlorate" and apparently he meant "perchlorate". It's not clear to me exactly what kind of "abuse" he's talking about here.

Lastly, in case there should be any doubt, in the comments section, in response to a question as to where he got the MMO electrodes, he states:

"The chap calling himself "pkhow" on the UK Pyrotechnics Society Forums was kind enough to send me some samples of commercial anode material. He worked in the Pool Chlorinator business and was talking about making a commercial Chlorate cell product.

I haven't spoken to him since I gave up Chlorate production, so I am unsure where the venture got to. I doubt the market would support it, so it likely never happened. The material he offered was excellent, producing Chlorate almost indefinitely if not abused (and I produced a small amount of Perchlorate by abusing one piece, but it pretty much wrote it off)."

So it's clear: According to him, he used a pool chlorinator MMO anode to make chlorate and *perchlorate*, but it was "abused" in the process (whatever that exactly means).

Quote:

It would seem to me that the pulsed current idea would end up putting more stress on the anode with no real gain of any sort.

Why do you think it would it "put more stress on the anode" and that there would be "no real gain of any sort"?

Nerro - 16-11-2008 at 07:34

As for the bent electrodes, could it be possible that some metals become softer if electrons are stuffed into it like they would be in high-current electro chemical cells? Perhaps inter atomic bonding weakens when when electrons are introduced into the matrix? If this is the case it could increase the effects of the heat and the opposing charge in the cathodes.

[Edited on 16-11-2008 by Nerro]

dann2 - 16-11-2008 at 08:03

Hi,

Alan has definitely made Perchlorate with MMO. I was reading in the wrong place. I also sent him a comment.
So it can be done!!

Regarding pulsing the current, I do not think it will save the Anode (but I am guessing). The anode is damaged (AFAIK) by Oxygen evolution reactions which become dominant when you try to make Perchlorate with MMO. You will still have the same amount of that going on only three times as much for one third of the time (for a three times current, 1/3 duty cycle, say, if you know what I mean).
Then again there is only one way to really find out.

Since there are so many types of MMO and it is difficult to get an answer from the sellers as to exactly what type you will have in your possession, it may be the Alan can make Perchlorate with his MMO (with abuse/erosion) and the next person that tries will fail completely under similar conditions.
MMO containing Pt Oxides may be best, I dunno.

I have also read that Iridium is capable of decomposing Chlorate and it therefor bad news in Pryo. stuff. The amounts of Ir in Chlorate would be very very small when you make Chlorate with MMO (no erosion/abuse) but when you start to make (attempt to make) Perchlorate it may be something to watch out for if using the Chlorate that came from the liquid from the Perchlorate attemt(s).

About the Orance colour from Na contamination, perhaps I am fussing too much. 'Delicate' blues, perhaps, are the only colours that get swamped with small Na contamination.

Dann2

[Edited on 16-11-2008 by dann2]

jpsmith123 - 16-11-2008 at 08:36

Hello Dann2,

Maybe you can ask him about the details of the process he used? If he used a batch process where the chlorate concentration was allowed to get low, I can see that as being a problem.

The reason I suggested pulsing (and I'm just thinking out loud) is that maybe increasing the current density will increase the oxygen evolution overpotential thereby decreasing the wear and increasing the efficiency.

Swede - 16-11-2008 at 09:04

I'm going to try it. I've got enough MMO mesh to equip a small country with saltwater pools. I made a small anode specifically for abusive testing.

I'll start with recrystallized potassium chlorate, very little or no chloride. Questions to answer - will the anode survive? And what are the efficiencies? If the efficiency is 10%, then even if the anode survives, it's not worth doing. 50%, on the other hand, yes.

jpsmith123 - 16-11-2008 at 09:23

Swede do you know the composition of your MMO anode? If you get some ClO4 forming it may be worth varying the conditions a little bit (especially current density, IMO) to see how much the efficiency can be tweaked.

[Edited on by jpsmith123]

chief - 16-11-2008 at 09:56

The amount of chlorate from the 1-day run (the cup, maybe 400 g) is right for 24 h, 50 A and 50 % efficiency.
I wonder of how good the idea is to run a single 1 electrode at this current; I usually would assume 10 A/ electrode of the shown size (the 10 l plastic-thing, with the power-supply on the same picture).

Also the temperature with this amount gets near to the boiling point at the said current, when letting evaporate and topping of maybe 3-4 liters during the time. Maybe he doesn't tell storys in this point .

About the Mg-S reaction: Powdering both, mixing them and heating them in a furnace is said to destroy the furnace from the explosion ...

Swede - 16-11-2008 at 09:59

I don't know the composition of the MMO. I do agree that IF (big if) it produces perchlorate with any meaningful efficiency, and survives unscathed, it'd be well-worth a bit of tweaking, and possibly using additives of one type or another to increase it.

I'm guessing a hobbyist would be satisfied with 40%, maybe less, but only if the MMO material does not fail. Further, if the MMO works fine initially but dies as the chlorate level drops, it'd be "no go." No one wants to make perchlorate and have to continually test chlorate levels quantitatively... that would make it nearly useless. It needs to work from, say 250 g/l chlorate right down to 20 or 30.

Slightly off-topic: One thing I encountered in a previous perchlorate run (using Pt over Ti) was the generation of ozone. I'm 95% sure that's what it was, ozone gas. The smell was potent and obvious. Am I nuts? Or has anyone else seen O3 being generated by such a rig?

tentacles - 16-11-2008 at 10:27

dann, if we can reasonably drive the chloride down to 30g/L.. the biggest problem I see is space. There won't be enough room for all the chlorate crystals! We could probably go down to maybe 70 or 75g/l before the crystals started to encroach on the electrodes.. I'm really not sure we can actually GO a whole lot lower than we are. Swede, how did the cell look, crystal-wise, when it was still hot? How much room will be reasonably have for crystals at the bottom, before they become our biggest problem?

What seems to wear out the MMO anode material is oxygen evolution - apparently the RuO2 gets converted to RuO4 and goes into solution, or at least detaches from the substrate. That thesis back a ways there mentioned the phenomenon in some detail. I'd imagine that the increased potential required for perc would involve more oxygen evolution, and thus, more wear..

Swede: but the thing is, the perc is so insoluble that it won't be long before it's all precipitating out of solution, at least in a potassium cell.

[Edited on 16-11-2008 by tentacles]

dann2 - 16-11-2008 at 12:19

Howdy,

Regarding trying to get low Chloride concentrations at the end of a Chlorate run, I had not though of not having enough room in the cell. You could always tramp down the crystals with your boot

. I guess it would be one of the problems that crop up when you are having too much success.
The main reason I wonder how low MMO can take the (Na) Chloride level is in relation to going on to make Perchlorate. The lower the Chloride the better. If you are going to extract solid Na Chlorate you can get more out (when you boil off water) before Chloride starts to come out as well when Chloride levels are low.
Also if the Na Chloride can be taken to very low levels (reasonable efficiencyl not much wear) it may be OK to go straight to making (Na) Perchlorate with the solution as it is (Using LD or Pt).
If making K Chlorate only the ability to go to low Chloride is not much of an issue IMO.
It is difficult to gauge MMO wear/damage IMHO. Looking at it with a microscope would need a trained eye, I would imagine.

As far as additives are concerned I think they are only added for to stop thing happening, which we do not want to happen, at the Cathode.
They done help stop anode wear directly.

I know Swede has made K Perchlorate from Pt and it worked OK.
When making Perchlorate using K Salts the conc. of Chlorate is nearly always going to be on the low side unless you keep cell up at 60 - 65C and add Chlorate as it gets used up. Perhaps Na salts would be a less stringent test(s) for Perchlorate making with MMO (high conc. of Chlorate).
Solid Sodium Chlorate is not too easy to comeby though!, K Chlorate is.

Lithium salts may be another way along as it is stated (Schumacher, The Perchlorates page 77 (spent a long time looking for that original (god-damm)statement))) that due to its small ionic radius, converts from the Chloride to the Perchlorate with high yield (compared to Alkali metal ions). (A patent somewhere states the same thing.) I tried it, along with Xenoid, some time ago using Tin Oxide but the stuff converted with no greater efficiency that Na as far as I could see.
It also states (same page) that Rb Chlorate cannot be converted to Perchlorate. Perhaps it is more difficult (in relation to getting MMO to make Perchlorate) to get K Perk. to form that it is to get Na Perk. to form???????
(see .gif below)
We could try Mg too.
I am just suggesting possible 'back door' methods to the (glorious) Perchlorate ion via MMO. Mind you, I'm just pontificating and doing fuck all actual work!!

I have got lots of Ozone coming from a cell using Lead Dioxide at low Na Chlorate concentrations (making Perchlorate). This is normal. Industry would not tolerate it as efficiencys would be going to hell at that stage.

The 'Perchlorates' can be had herehttp://www.archive.org/details/pwechloratesthei001740mbp:

[Edited on 16-11-2008 by dann2]

Li.gif - 105kB

Swede - 17-11-2008 at 07:21

My path to perchlorate is going to be two-step... harvest chlorate, purify (if needed) and feed potassium chlorate into a perc cell. Yes the solubilities are low, but I'm making up for it with volume. I also realize sodium-based systems are going to be more efficient in general because the concentrations are almost always going to be higher. But I really want to try and refine the process using only potassium salts.

With every single potassium chloride --> chlorate run I've done, I've pulled the plug at no lower than 7% chloride ion by weight. I don't have meaningful data, but each time, the reaction seemed to slow significantly. I simply decided "it's time."

Crystal volume issues - my old acrylic tower cell (very tall and skinny) is a pretty good indicator of volume requirements. Here it is, packed with chlorate, with the liquor at maybe 7.5% chloride ion remaining:

The camera angle is bad, but I'd put the crystal level at 30%. Chloride went from 14% to 7.5%, roughly half the chloride. Taken to zero chloride, the crystal mass would be at the 2/3 height in the cell, still leaving plenty of room for the electrodes. But remember I am starting at only 15% or so chloride, which is saturated KCl at 30 degrees C. If someone were to start with much warmer saturated stock, the mass might be an issue.

The chlorate crystal mass from a large potassium chloride-based cell is amazingly firm and compact. I use a PVC rod to beat the mass into pieces; otherwise, it would be jammed in place. Inverting that cell does nothing except drain electrolyte, and in fact that is how I decanted it.

I've got the electrodes made for the test MMO chlorate --> perchlorate mini-cell, and I'm deciding if I want to go to the trouble of recrystallizing chlorate stock to purify first, or if I want to simply stock it with raw (but washed/dried) chlorate crystals. I think I'm going to go with the latter, as a bit of a rougher test for the anode.

Earlier tests of washed/dried raw chlorate crystals from a cell showed they retained maybe 0.7% chloride... the chlorate was better than 99% pure. I'd guess residual chloride would be rapidly converted to chlorate, and then the process would (hopefully) proceed.

hissingnoise - 17-11-2008 at 07:50

Quote:

Originally posted by Swede

Slightly off-topic: One thing I encountered in a previous perchlorate run (using Pt over Ti) was the generation of ozone. I'm 95% sure that's what it was, ozone gas. The smell was potent and obvious. Am I nuts? Or has anyone else seen O3 being generated by such a rig?

You could very well be nuts, Swede; I'm no expert, and you didn't supply sufficient information for a dependable diagnosis.
Joking aside, though, ozone, if it were discharged at the anode, should oxidise chlorate to perchlorate in solution, being itself, reduced to O2. . .
The smell you noticed is more likely that of a chlorine oxide; similar oxidising odour.

jpsmith123 - 17-11-2008 at 10:10

The last post on the following linked page is by poster "pkhow", describing his use of MMO pool chlorinators for ClO3 & ClO4 production.

http://www.pyrosociety.org.uk/forum/index.php?showtopic=426&...

Xenoid - 17-11-2008 at 10:42

Quote:

Originally posted by Swede
Slightly off-topic: One thing I encountered in a previous perchlorate run (using Pt over Ti) was the generation of ozone. I'm 95% sure that's what it was, ozone gas. The smell was potent and obvious. Am I nuts? Or has anyone else seen O3 being generated by such a rig?

No you are not nuts, Swede.

Ozone is almost always produced with a Pt anode during various electrolysis situations. In fact, by using a specially designed anode and sulphuric acid electrolyte (SG = 1.075 - 1.1) it has been possible to generate oxygen containing 17-23% ozone.

I always detect the smell of ozone when using Pt or Pt/titanium anodes, especially when making perchlorate!

hissingnoise - 17-11-2008 at 10:48

Pkhow talks about K. chlorate to perchlorate; wouldn't KClO3's low solubility be a problem there.
Allowing the sol. temp to rise would dissolve more chlorate, but that would increase anode disintegration. IMO, NaClO3 would be a better starting point for perchlorates?

hissingnoise - 17-11-2008 at 11:53

Quote:

Originally posted by Xenoid

I always detect the smell of ozone when using Pt or Pt/titanium anodes, especially when making perchlorate!

Xenoid, are you sure it's ozone you smell, or simply something smelling like ozone.
Electrolytic production of ozone in H2SO4 solution is a well-known method, but I've never seen it mentioned in relation to chlorides or chlorates.
And, as I said, O3, being a potent oxidiser (highly thermally unstable) would be consumed fairly rapidly if it were produced at all.
Even nitric oxides, under certain conditions, can smell ozone-like.
Ozone is, of course, detectable in air in very small concentrations, so it's just possible a few PPM could be released over a period.
'Way too small to be of any, but academic interest.

dann2 - 17-11-2008 at 12:06

About Ozone coming from Perchlorate cell, the following is from US Patent (attached).

.....................
However, as the presence of unconverted chlorate in perchlorate imparts very serious and undesirable characteristics to the completed product, it is preferable to operate the cell to the lowest concentration of chlorate that is economically feasible. The economic limit is reached when a concentration of about 1 to 5 g/l chlorate is reached. This is due to the fact that the high current density of 450 amperes per square foot (480mA/cm^2) produces excessive quantities of ozone by reason of electrolysis of the aqueous electrolyte, thus lowering the cell efficiency to unacceptable levels.
The perchlorate cell solution at the end of the conversion is, ...........................

Dann2

Attachment: US Patent No_ 2,392,769.htm (7kB)
This file has been downloaded 1216 times

hissingnoise - 17-11-2008 at 12:49

Thanks indeed for that, dann2, I stand corrected.
It's hardly likely the patentee mistook ClO2 for O3?
It's quite interesting, actually, as ozone will oxidise NO2 to N2O5.
Perchlorates from one container---nitric acid anhydride from another (or am I losing it?).
That stated current density, though, is highly unlikely to be seen in a home set-up.

Xenoid - 17-11-2008 at 14:47

Quote:

Originally posted by hissingnoise
That stated current density, though, is highly unlikely to be seen in a home set-up.

Yes, true! But I assume on sharp edges, points, etc. one can get a "localised" high current density, much in the same way as with high voltages ionising air at needle points.

I guess it's the reason the "ozone" anode is only an edge of platinum 0.1 mm thick, exposed at a glass surface - very high current density.

Also, we're probably not talking about large quantities of ozone here, the nose is quite sensitive to this gas after all.

Swede - 17-11-2008 at 16:36

Thanks for the O3 clarification. The odd thing was, it seemed to be produced immediately, indicating "poor efficiency", yet the rig went on to make a decent batch of perchlorate.

I hope to put to rest the "MMO makes/cannot make perchlorate" question with this simple test cell:

It's 350 grams of cell chlorate dissolved in 2.5 liters of water. Because the setup is small, it's running at only 15 amps, so it'll be a while before any conclusions can be made. There are certainly trace amounts of chloride, but it is a predominantly clean chlorate solution to start with.

I've been gathering chemicals to plate one of these anodes, and I hope to give it a shot this weekend. I'm going to try a 30 RPM gearmotor to spin the anode, hopefully creating an even and bubble-free plating.

tentacles - 17-11-2008 at 19:09

Swede: How will you arrange the plating cathode(s) so that the anode will be plated evenly? Not trying to put the kybosh on your idea, but traditionally spinning is combined with round anodes.

watson.fawkes - 17-11-2008 at 21:20

Quote:

Originally posted by tentacles
Swede: How will you arrange the plating cathode(s) so that the anode will be plated evenly? Not trying to put the kybosh on your idea, but traditionally spinning is combined with round anodes.

If a flat anode and a rod cathode are sufficiently far apart, spinning a flat plate given a close-to-flat average current distribution. The worst case in terms of anisotropy is the flat plate lying in the same plane as the rod. As the distance between them increases, the current density between the close edge and the far edge equalizes.

jpsmith123 - 17-11-2008 at 22:14

Hello Swede,

One coating I've always been curious about is PdO (over MMO). Several patents imply that PdO makes for a more efficient MMO coating than RuO2 or IrO2 (for chlorine evolution at least), and one paper I seem to remember (regarding electrodes for waste-water treatment or something), found PdO to be superior.

IIRC one of the examples in one of Beer's patents uses anodic electrodeposition of PdO from a dilute PdCl2 solution. (Of course Beer's plating solution also contained TiCl3 I believe, but if you are plating over pre-existing MMO, you probably don't need to co-deposit TiO2 with the Pd).

Perchlorate as a Contaminant in Chlorate Production

jpsmith123 - 18-11-2008 at 07:11

Being that MMO anodes are used in the chlorate industry, I thought that if they are capable of making perchlorate, then there may be some patents on reducing/eliminating perchlorate from the chlorate electrosynthesis process.

IOW maybe something can be learned about which type of MMO anodes would be best for perchlorate production if we can find out how the chlorate industry minimizes perchlorate contamination.

As it turns out, I found a few patents on the subject (which implies that MMO anodes can/do make perchlorate, and that this may be a potential problem in chlorate production), but the patents unfortunately didn't go into any detail on anode design.

According to US5063041:

"A problem in chlorate processes is the formation of an undesirable amount of perchlorate which is continuously enriched in the cyclic process. The formation of perchlorate is associated with a poor function of the anodes and can be overcome partly through a careful control of the process conditions and of the selectivity of the anodes. It is possible that up to 0.5 g sodium perchlorate per kg sodium chlorate is formed, despite such control. This is equivalent to an increase in the concentration per year in the order of 5 to 10 g sodium perchlorate/l in a chlorate plant with normal power density."

Swede - 18-11-2008 at 08:22

On anode spinning - my experience with plating has been limited to decorative plating. With nickel, the spinning produced mild agitation, prevented the bubble formation that you'd find in a more stagnant plating tank, and produced a very even plating. Is there a problem with this in regards to PbO2 deposition?

With a top down view, using a single plate cathode, and an MMO-mesh target anode, it would appear that the current density over the entire surface of the anode would be a nice average - the exact middle (axis of rotation) of the anode would receive a relatively constant current, and as you progress to points away from the axis, the current density would be sinusoidal, with the amplitude increasing as you reach the edge. But wouldn't the average current each point "sees" be the same?

I am not hard-set on rotating the anode, I'm just going by what my limited experience with plating tells me works well.

jpsmith, is the PdO coating targeted at chlorate production, or perchlorate? I couldn't tell from your post if the PdO coating is designed to REPLACE, or simply COAT, an existing MMO surface?

On the MMO --> perc rig: No sign of perc yet, but it's early. No visible flecks of black MMO coating either, which is a good sign. This is just for fun, to finally put to rest the "DOES it, or DOESN'T it" question.

watson.fawkes - 18-11-2008 at 08:37

Quote:

Originally posted by Swede
With a top down view, using a single plate cathode, and an MMO-mesh target anode, it would appear that the current density over the entire surface of the anode would be a nice average - the exact middle (axis of rotation) of the anode would receive a relatively constant current, and as you progress to points away from the axis, the current density would be sinusoidal, with the amplitude increasing as you reach the edge. But wouldn't the average current each point "sees" be the same?

The current average isn't identical, as it might seem. For a first approximation, think of each point on the rotating anode as grounding through a resistor proportional to its distance to the cathode. All these paths pass current in parallel. If the anode and cathode are too close, the closest edge will hog all the current. Current density is more even when the values of those parallel paths are closer, which is what happens when they're adequate far apart.

It's even worse than this at the next level of approximation, to trace out the equipotential surfaces and to estimate the electric field within the electrolyte. The fields from the far edge enough curve out away from a straight line path significantly, causing even greater resistance. Fortunately, the same solution (move them away from each other) addresses the problem.

If they're too close, the bulk of the plating will be on the edges, leading to something of a barbell cross-section.

Swede - 18-11-2008 at 09:17

Hmm, I knew it would never be as simple as I thought! Would there be ANY advantage to rotation, or would it be an unnecessary complexity? Would stirring, then, be a superior method to create as even a coating as possible?

I finally got around to weighing the yield and calculating the efficiency from my new cell's first run. Yield was better than I thought. The dried crystals weighed in at 4,229 grams, or 34.50 moles of potassium chlorate. But the 4,229 grams is a dry yield... significant quantities of potassium chlorate, converted from chloride, remain in solution. The cell holds 25 liters. 14 of those at the start were used liquor, presaturated with chlorate, plus added chloride. 11 liters was pure KCl solution, thus, the system had to saturate those 11 liters with chlorate before even the first crystal would form. 11 liters at 20C should hold 880 grams. Thus the final quantity is closer to 5,109 grams, or 41.67 moles.

The system required 7580 amp-hours to produce this quantity.

7680 / 41.67 = 184.3 AH/mole

100% efficiency is 160.8 AH/mole; my efficiency is therefore 87.2%.

This seems a bit high. This calculation is the best I could do, and the "bonus" 880 grams is just a guess. With this sort of system, there is always chlorate produced but never crystallized. Still, my best yield in a non pH-controlled environment was 62%, and I am very happy with an efficiency in the 80's. A fairly hot cell, good pH control = mounds of oxidizers!

Sorry I keep editing this post. Being tired of having to look up all the assorted numbers for calculating efficiency, I came up with this formula for dry yield only:

For Potassium Chlorate Production:

W = Weight of yield, in grams
E = Efficiency
AH = Ampere-Hours used

E = (131.32 * W) / AH

[Edited on 18-11-2008 by Swede]

watson.fawkes - 18-11-2008 at 09:56

Quote:

Originally posted by Swede
Hmm, I knew it would never be as simple as I thought! Would there be ANY advantage to rotation, or would it be an unnecessary complexity? Would stirring, then, be a superior method to create as even a coating as possible?

Rotating seems fine to me. You'll incur greater resistive losses and maybe plate on a little heavy at the edges in order to get adequate coating in the center. All well within the imperfections of small scale.

If you want to stir instead and use fixed electrodes, you'll need to change the electrode geometry. Use a pair of plate cathodes as close as feasible to the anode and make them extend significantly past the edges of the anode, say, a cathode width three times that of the anode. That'll give you a pretty uniform electric field and even plating.

[Edit: Saying "stirring" when you mean "rotating" can be pretty confusing.]

[Edited on 18-11-2008 by watson.fawkes]

jpsmith123 - 18-11-2008 at 11:00

Swede I was thinking that the PdO would go over the existing MMO coating, just like what you apparently plan to do with the lead dioxide.

According to a patent I happened to see, supposedly Pd has the highest "selectivity for chlorine" out of all the noble metals. I suppose that suggests PdO for chlorate production...perchlorate usefulness remains to be seen.

As far as putting Lead Dioxide over MMO, I wonder, do you really need to worry about pinholes? Being that the MMO would apparently be such a robust intermediate layer, maybe it wouldn't be worth the hassle.

tentacles - 18-11-2008 at 11:12

The only problem I can see with rotation is the uneven current density - you might have alpha PbO plating at the edges and beta in the center of the anode, or some sort of mixed phase variation.

jp: The problem with noble metal oxides, is that noble metals are quite pricy.. LD has the benefit of being cheap and rather easily made.. It's nowhere near $25-50/g. Especially when you consider the cost of noble metal salts. If you're going to go to the expense (and fiduciary risk) of putting noble metal coatings over MMO, you might as well just buy a Pt plated anode and be done with it.

jpsmith123 - 18-11-2008 at 11:39

Hello Tentacles,

If MMO anodes were not such a great value, they wouldn't be used so much in industry.

MMO anodes can be bought on Ebay for something like $39.00. That's because even though the noble metals are relatively expensive, unlike PbO2, only thin coatings are required, i.e., only a few microns or so. (And, used properly, supposedly they are much more resistant to erosion than Pt).

PdCl2 can be bought on Ebay for about $20 per gram last time I looked. A few grams would be enough to make a liter of plating solution and that should be enough to coat a few anodes I would think.

Even if PdO over MMO doesn't make perchlorate, maybe it would allow a "user repairable" MMO anode without the hassle and toxicity of PbO2.

tentacles - 18-11-2008 at 11:53

jp: Why not just make RuO2 based anodes like the industry chlorate anodes (although those might not be straight TiOx/RuO2)? I mean, if you're going to make your own MMO, why not just do it? And, as you stated, MMO are cheap and readily available, so why repair? I'm not trying to stop the research here, just trying to point out that it might not be feasable or even the best course of action.. I think pool chlorinator anodes should be easy to get just about anywhere, and are innocuously shipped in more remote regions etc.

Anyone is certainly welcome to try, but my opinion is that it's probably not as easy as it would seem.. Look at 12AX7's Pt plating experiments, etc. That doctoral thesis had a MMO anode dip n bake procedure that is apparently what is used to make industrial chlorate MMO. I found it quite interesting, as well, that a thicker coat isn't necessarily longer lasting.

Again, I'm not saying that it's not possible to make a good, reliable perchlorate anode based on noble oxides over MMO (or what-have-you), I'm saying that it's probably not economically feasable, particularly compared to the ease and availability of PbO2 plating.

dann2 - 18-11-2008 at 12:51

Hello,

Spinning the MMO should definitely help to eliminate bubbles/pits. Since you have a motor (I presume) it will not be too much trouble. You will need a brush for the current (more hassle).
If you have a reasonably sensible arrangement of Cathodes the set up will be fine IMO. The edges of the MMO will come close to the Cathodes as it sweeps around and you may get heavier plating when compared to the center part of Anode.
Perhaps an arrangement like below may help to even out the average current distribution on the rotating Anode,
or perhaps spin the two Cathodes and the Anode as a single unit (two brushes now needed, more hassle).
When using Graphite as a substrate you always had to round off all sharp edges from the Graphite becasue if you did not, large amounts of LD would deposit on the corners/edges. (Ugly anodes, and you don't want one of those now, do you!!)
Tentacles did not seem to have this problem though but it will not start to show up much untill you put on a thickish coating.
If you look at the close up of the mesh you can start to see a thicker amount of LD going on at the top of each hole in the mesh. Nothing you can do about it and it does not really matter anyways.

From elsewhere:
________________________________
Another parameter that is mentioned regarding plating baths is 'throwing power'. The addition of Nitric acid is said to improve the throwing power (an advantage).
Throwing power refers to the ability of the solution to plate into nooks and crannies and around corners that are not in a direct line of sight of the cathode. To put this another way, it is the ability of the electrolyte to even-out the current distribution on all areas of the anode given a certain tank and electrode set up. There is a good explanation of throwing power in "Treatise on Electrochemistry" , G. Kortum, (Elsevier publishing Co.).
It is related to the conductivity of the solution and Nitric acid increases this. The current on the anode is more evenly distributed as a result of the greater conductivity. The current distribution is also a function of cell geometry, spacing and arrangement of the anode and cathode. The cathode should surround the anode being plated and there should not be any sharp corners (this increases the current density and increases plating on that area) or indents (less plating) on the anode.
_____________________________________

Dann2

spin.GIF - 2kB

jpsmith123 - 18-11-2008 at 12:54

Quote:

jp: Why not just make RuO2 based anodes like the industry chlorate anodes (although those might not be straight TiOx/RuO2)? I mean, if you're going to make your own MMO, why not just do it?

I'm not advocating anyone making their own "MMO" per se. Why do that? As far as making chlorate is concerned, you can buy a half-decent pool chlorinator (complete with Ti cathode and associated hardware) for $100 to $150 that will probably last a few years and take a lot of abuse.

Sorry if I wasn't clear but what I'm suggesting is using a commercial MMO coated anode as a substrate for a PdO outer layer (obviously as an *experiment* at this point), which may possibly make perchlorate at an acceptable efficiency. If it doesn't, then as a worst case (being that you already have the MMO anode and the plating solution), you may end up with a "user repairable" anode albeit only for chlorate.

Quote:

And, as you stated, MMO are cheap and readily available, so why repair?

As per the above, because you can repair.

Quote:

I'm not trying to stop the research here, just trying to point out that it might not be feasable or even the best course of action.. I think pool chlorinator anodes should be easy to get just about anywhere, and are innocuously shipped in more remote regions etc.

Anyone is certainly welcome to try, but my opinion is that it's probably not as easy as it would seem.. Look at 12AX7's Pt plating experiments, etc. That doctoral thesis had a MMO anode dip n bake procedure that is apparently what is used to make industrial chlorate MMO. I found it quite interesting, as well, that a thicker coat isn't necessarily longer lasting.

Again, I'm not saying that it's not possible to make a good, reliable perchlorate anode based on noble oxides over MMO (or what-have-you), I'm saying that it's probably not economically feasable, particularly compared to the ease and availability of PbO2 plating.

Well this is all presumptuous since neither PbO2 nor PdO over MMO have been tried yet, AFAIK, but if buying a few grams of PdCl2 at about $20 per gram is a significant economic hardship, and if you can get everything you need to do PbO2 plating for free or at a negligible cost, and you don't mind the toxicity and the mess, then go for it, I suppose.

watson.fawkes - 18-11-2008 at 13:34

Quote:

Originally posted by dann2
Another parameter that is mentioned regarding plating baths is 'throwing power'. The addition of Nitric acid is said to improve the throwing power (an advantage). [...] It is related to the conductivity of the solution and Nitric acid increases this. The current on the anode is more evenly distributed as a result of the greater conductivity.

This is another way of getting more even current densities, for essentially the same mathematical reason. The multiple current paths (properly speaking, the integral curves of the electric field) have resistances closer to each other, so current density evens out. In this case higher conductivity changes the shape of the electric field. You can use this technique in conjunction with manipulating the geometry by increasing the resistance.

tentacles - 18-11-2008 at 15:07

Quote:

Originally posted by jpsmith123
Sorry if I wasn't clear but what I'm suggesting is using a commercial MMO coated anode as a substrate for a PdO outer layer (obviously as an *experiment* at this point), which may possibly make perchlorate at an acceptable efficiency. If it doesn't, then as a worst case (being that you already have the MMO anode and the plating solution), you may end up with a "user repairable" anode albeit only for chlorate.

Well this is all presumptuous since neither PbO2 nor PdO over MMO have been tried yet, AFAIK, but if buying a few grams of PdCl2 at about $20 per gram is a significant economic hardship, and if you can get everything you need to do PbO2 plating for free or at a negligible cost, and you don't mind the toxicity and the mess, then go for it, I suppose.

Sorry, I was a bit confused there.. Pd might indeed work well, but I suspect you'll need more than a couple grams.. Probably more like saturated solution, so that you don't deplete all the Pd ion in the plating operation.

I'm assuming the PdCl plating bath would be somewhat dilute HCl? Is there some information on the process, I might be willing to give it a try. I wonder if you can add some TiCl3, if that would electroplate a mixed oxide film.

12AX7 - 18-11-2008 at 15:09

Current density follows the same pattern regardless of resistivity. There must be a surface effect in action (ligand, electric layer, etc.).

Tim

Fleaker - 18-11-2008 at 15:46

PdCl2 has quite poor solubility, so I automatically assume an acidified (therefore complexed) palladium (II) solution. Also, this solution is somewhat sensitive to oxidation.

For any who mess with platinising titanium, I suggest diamminedinitrite platinum (II) solution as it actually works. In retrospect, I wish I had sent that to Tim for he would have had success with it. This complex is easily made from K2PtCl4.

I have ruthenium metal for sale. I also have platinum, palladium, rhodium and some of their salts (halides, oxides, sulfides, etc) available to you lot here.

Of course the precious metals salts can be free of charge if you'd but share your chlorate and perchlorate with me :-)

watson.fawkes - 18-11-2008 at 16:56

Quote:

Originally posted by 12AX7
Current density follows the same pattern regardless of resistivity. There must be a surface effect in action (ligand, electric layer, etc.).

The polarization resistance (constant at low current, drops off at high) of the electrodes stays the same, but the bulk electrolyte resistance drops. Hence the total resistances along each conduction path grow closer to each other.

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