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Author: Subject: Thoughts On Anodes
Splinky
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[*] posted on 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?
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watson.fawkes
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[*] posted on 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.
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dann2
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[*] posted on 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
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Splinky
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[*] posted on 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.
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[*] posted on 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.

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jpsmith123
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[*] posted on 15-11-2008 at 13:43
Perchlorate from MMO Anodes


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).
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dann2
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[*] posted on 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
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[*] posted on 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).
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[*] posted on 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.

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jpsmith123
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[*] posted on 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.
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Splinky
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[*] posted on 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.
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[*] posted on 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"?
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[*] posted on 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]




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[*] posted on 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]
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[*] posted on 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.
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[*] posted on 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.
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jpsmith123
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[*] posted on 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]
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[*] posted on 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 ...
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[*] posted on 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?
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[*] posted on 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]
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[*] posted on 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 :D. 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
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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&...
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[*] posted on 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!
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